Proceedings of the fifth annual Florida Highway Conference, May 14 and 15, 1951


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Proceedings of the fifth annual Florida Highway Conference, May 14 and 15, 1951
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Table of Contents
    Front Cover
        Front Cover
    Title Page
        Page 1
        Page 2
        Page 3
    Table of Contents
        Page 4
    Highway construction for war or peace
        Page 5
        Page 6
        Page 7
    Highway contractors study the big job ahead
        Page 8
        Page 9
        Page 10
        Page 11
    State-city relationships in traffic problems
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
    Observations on urban highway design
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
    A comparison of present methods for the thickness design of flexible pavements
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
    The California bearing ratio (CBR) test for flexible pavements
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
        Page 39
    The design of flexible pavements by the modified CBR method
        Page 40
        Page 41
        Page 42
        Page 43
        Page 44
        Page 45
        Page 46
    Building Florida highways
        Page 47
        Page 48
    New equipment for compaction of subgrades and bases
        Page 49
        Page 50
    Highway research at the University of Florida
        Page 51
        Page 52
    Preparation of county engineering soil maps
        Page 53
        Page 54
        Page 55
        Page 56
    Studies of corrosion resistant finishes for iron and steel structures in Florida coastal areas
        Page 57
        Page 58
        Page 59
        Page 60
    A report on truck traffic test project in Maryland
        Page 61
        Page 62
        Page 63
        Page 64
        Page 65
        Page 66
    ARBA on-the-job training program for civil engineering students
        Page 67
        Page 68
    Back Matter
        Page 69
        Page 70
        Page 71
Full Text
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May 14 and 15, 1951
Sponsored by the
Civil Engineering Department
University of Florida
with the cooperation of the
State Road Department of Florida

Bulletin Series No. 50
January, 1952

Published monthly by the
College of Engineering University of Florida e Gainesville
Entered as second-class matter at the Post Office tit Gainesrille, Florida

The papers in this Bulletin were presented by various
speakers at the Fifth Annual Florida Highway Con-
ference, sponsored by the Civil Engineering Depart-
ment, College of Engineering. as a public service
function of the Engineering and Industrial Experiment
Station. University of Florida. The opinions of the
speakers are their own. They do not necessarily reflect
the opinions of staff members or the policies of the
University of Florida.

The Fifth Annual Florida Highway Conference was held in Gainesville on May 14 and 15,
1951, under the sponsorship of Elie Civil Engineering Department as a public service function
of the Engineering and Industrial Eaperiment Station.
The continuing objective of this series of annual meetings is to promote closer relationships
among all the groups concerned with highway and street problems in Florida. This objective is
being accomplished through the personal association and discussions of mutual problems which
occur before, during and after the conference sessions.
Approximately 300 persons, interested in the highway field in Florida, attended this year's
conference. Those in attendance enjoyed an excellent program; the papers were very interesting
and well presented. The policy of splitting the conference into two specialized groups for one
afternoon session was repeated this year. Separate sessions were held concurrently, one being
devoted to "Problems Accompanying Highway Improvements in Urban Areas" and the other to
"Structural Design of Flexible Pavements."
Again, the success of the conference was in a large measure due to the concerted and indivi-
dual efforts of the steering committee, which this year included:
C. H. Baker, Jr., Asphalt Paving Company. Jacksonville
R. C. Bannerman, Jr., State Road Department, Tallahassee
J. M. Boyd, County Engineer, West Palm Beach
Bill Bryanto City of Jacksonville
R. T. Cunningham, City Manager, Gainesville
G. D. Curtis, Portland Cement Association, Tallahassee
Bill Day, ltlhway Equipment & Supply Company, Orlando
Don Hipskind. Gibbs Corporation, Ocala
W. A. Krattart, State Road Department, Ta llahassee
J. A. Long, Tallahassee
Hugh MaoCotter, Director of Public Works, Jack sonville Beach
W. T. Mcllwain, City Manager, Coral Gables
W. H. Mills, The Asphalt Institute, Atlanta
Show Pearsall, Marion Construction Company, Ocala
Julius Perkins, Construction Equipment & Supply Co., Gainesville
J. R. Phillips, Macaspholt Corporation, Lakeland
E. J. Reeder, Rader, Knappen Tippeuts Engineering Co., Miami
L. J. Ritter, Department of Civil Engineering, University of Florida
L. B. Thrasher, Limerock Sales Corporation, Ocala
Millet Walston, City of Tallahassee
H. C. Weathers, State Road Department, Gainesville
The wholehearted cooperation and support of the officers and members of the Florida Road
Builders' Association and the Associated Equipment Dealers of Florida were again a large factor
in the success of the conference. Our thanks also go to the State Road Department of Florida
as a group for their usual substantial support of the conference.
Finally credit is due the adminisuarive staff and faculty of the University of Florida for
their support of the meetings.
We at the University of Florida feel that these conferences are continuing to grow in scope
and influence. It is hoped that this trend will continue and that these meetings will be widely
recognized for their contribution to the solution of problems relating to highways and streets
in Florida.
L. 1. Riter
Associate Professor of Civil Engineering


Highway Construction for War or Peace, Lt. Gen. Eugene Reybold ....5
Highway Contractors Study the Big Job Ahead, Arch Carter .. .. .. .. .. .. 8
State-City Relationships in Traffic Problems, W. M. Parker .. .. .. .. .. .. 12
Observations on Urban Highway Design, llarry E. Stark ....... 77
A Comparison of Present Methods for the Thickness Design of Flexible
Pavements, A. C. Benkelman .. .. .. .. .. .. .. .. .. .. .. .. .. .. 22
The California Bearing Ratio (CBR) Test for Flexible Pavements,
W. J. Turnbull .. .. . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 32
The Design d Flexible Pavements by the Modified CBR Method,
John 11. Swanberg .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 40
Building Florida Highways, Alfred A. McKethan .. .. .. .. .. .. .. .. .. 47
Now Equipment for Compaction of $ubgrades and Bases, Paul D. Moon .. .. 49
Highway Research at the University of Florida, L. R- itter .....51
Preparation of County Engineering Soil Maps, W. t1. Zimpfer ........53
Studies of Corrosion Resistant Finishes for Iron and Steel Structures in
Florida Coastal Areas, A. L. Kimmel ... . . ..57
A Report on Truck Traffic Test Project in Maryland, Fred Burggraf .. .. .. 61
ARBA On-the-Job Training Program for Civil Engineering Students,
E. N. Rodgers .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 67

Lt. Gen. Eugene keybold
Executive Vice President
American Road Builders' Association
1 ashingwn, D. C.

The American Road Builders' Association is the
oldest national good roads organization in the country,
having been founded in 1902. Its membership consists
of engineers, contractors, manufacturers, educatorsand
students-, state, county and municipal officials: local
good roads groups, and other individuals representing
a cross section of the entire highway industry and
profession. We are not a trade association. We arc a
nonprofit federation of all groups and individuals
interested in the promotion of an adequate national
highway system.
The question before us at this time is what effect
will the present emergency have upon our highway
program. To come up with any kind of bulletproof
answer to that question would require a great deal
of crystal-gazing. Frankly speaking, business as usual
is definitely out and FedeW control of supplies and
materials is upon us. tar, or even the threat of war,
disrupts all business to some extent. Even before the
formal proclamation of a National Emergency by the
President, it had become clear that the present un-
stable conditions were going to dominate our lives for
many years to come. In adjusting ourselves-our personal
lives; and our businesses-it is important that we bear
in mind our current endeavors are by no means confined
to the speedy mobilization of an adequate fighting
That, of course, is out short-range objective-the
thing we must do speedily in order to be ready for a
full-scale war. At the same time, we must not over-
look the long-pull problem of maintaining a strong
economy. Our civilian demand for goods must be kept
as nearly satisfied as possible under the unusual cir-
cumstances. That, to me, is fundamental.
Even more than it depends on our armed forces,
the world today counts on an economically strong
America. In World War 11 our production superiority sur
prised the world and overwhelmed the enemy. Our
country is, in fact, the arsenal for all free liberty-
loving nations. And as to out highways, they are inter-

woven with the ever-expanding national economy-an
economy which has characterized our growth as a nation
and our assumption of world leadership. Always-in
peace or in war-our highways have been a vital part
of our country's assembly lines. Durin" the past two
decades, construction anj rehab i licationo of these lines
of communication have not kept pace with our industrial
expansion. As compared with the rest of the world,
we have the best network of roads and streets ever
known. But that very fact-rhe relative superiority of
our highways-has blinded US EO the more important
fact that they are still not good enough. Frankly, for
20 years or more, we have committed the shortsighted
blunder of sweeping under the rug a serious national
problem. The plain simple fact is that our production
of, and the varied uses of, motor vehicles has far out-
stripped highway construction. Present progress is
such that we are not even holding out own, let alone
catching up with the backlog.
And this is true despite the fact that highway trans-
portation is and always has been a vital part of our
economy. You know the situation and I shall not bur-
den you with a mass of statistics and reasons why we
should do better. We in ARBA are very much alert to
the situation and you may depend upon us to assert
ourselves to the responsible authorities whenever and
wherever the need is apparent. We are not asleep at
the switch.
Nevertheless, no matter what lines of action we
pursue in keeping the highway situation alive, I am
sure you realize it is impossible to predict what the
immediate future holds in store. A great deal naturally
depends upon the military situation and that is some-
thing that changes from day to day. As a result, the
things we might predict as of today could well change
as of tomorrow. History, on the other hand, never
changes. So let's look back for a moment.
A critical review of World War 11 procedures brings
into sharp focus the undeniable fact that highways
were not given proper recognition in the over-all plan-


ning of that period. The program was reduced to a
level that barely provided necessary maintenance.
While it is true that certain access roads of prime
military importance were given a high priority rating,
nevertheless the over-all system of major routes was
sadly neglected. The effects of this neglect and the
close margin by which highway transportation was
able to meet war requirements is now obvious. Due to
a maze of red tape and a lack of clear understanding
as to the essentiality of highways, it became impos-
sible to obtain necessary materials and equipment to
prosecute essential work. Also, the taking of personnel
from the 48 highway departments by the armed forces
so depleted their ranks that had material and equip-
ment been available there remained insufficient profes-
sional and skilled manpower to meet even the minimum
requirements, and by this I mean requirements that
were essential to the war effort and to the civilian
economy. Those statements are historical facts.
As to the present emergency, a note of encourage-
ment is found in current national policy dealing with
highways. In contrast with World War H procedures,
we are today fortunate in having our problems reviewed
and passedupon by the best qualified agency in the
entire Federal setup, viz. -the Bureau of Public Roads.
This Bureau has been designated as the official claim-
ant agency for the highway industry. This is what
should have been done in World War H. In its simplest
terms this means that Commissioner MacDonald and
his splendid organization of experts will represent
and be the spokesmen for the highway industry. Under
such a setup there is a sense of security in the knowl-
edge that our highways will be given full, sympathetic
and intelligent consideration. This, I am sure, will
result in highway problems during this emergency
being met to the fullest possible extent consistent
with military requirements.
Under present emergency conditions we can only
justify highway work by establishing its essentiality
in relation to the defense effort and the expanding
civilian economy generated by that effort. Ibis, in the
final analysis, will be the determining factor in decid-
ing when and where and to what extent highway work
will be undertaken for the duration of the emergency.
During the last war, as I have previously indicated,
we managed to get through by a close shave. We cannot
hazard such a risk again. As a matter of fact, it is now
clearly established that our highways cannot withstand
another such beating without continuous and extensive
rehabilitation. Essential highway work must go on un-

interrupted. By this I don't mean to impart any thought
that I am advocating the wholesale construction of
highways without regard to the over-all requirements
of the national emergency. Obviously there are plans
on the drawing boards today which, although highly
desirable and economically justified, will have to be
It is our duty in the highway field to spearhead
a vigorous and continuing movement for recognition of
the essentiality of highway communications and of
the relationship between highways and expanded
production. To do this job the highway and transporta-
tion fields must display a unity of effort. We face the
task of impressing upon our nation's leaders the in-
escapable and important relationship between highways
and the national welfare.
We cannot pursue the businesslike procedure of
expanding our production without simultaneously pro-
viding for the speedy and orderly movement of our in-
creased output. Failure in this respect would be to
invite disaster in the form of an economic breakdown.
And such a breakdown would be precisely the kind our
Red aggressors would delight to see in this country.
which now is the stronghold and the hope of the entire
free world.
In the American Road Builders' Association, we
feel that now, as the second half of the Century of the
Motor Vehicle gets under way, there is a greater-than-
ever need for a bigger-than-ever job on our part. We are
stepping up our efforts in the public interest to pro-
mulgate a continuing highway program on a scale justi-
fied by sound engineering and economic investigations;
and on a scale commensurate with the requirements of
traffic, safety and the national defense. Together with
all our affiliated groups and individual members, we,
as a National organization, provide a practical medium
for the interchange of information and a broadening of
relationships withinthe highway industryand profession,
all to the end of obtaining unity of action and solidity
of purpose. Specifically:
We advocate the encouragement and development of
sound highway planning.
We are in full support of the principles of Federal-
aid as a fundamental expedient toward the economic
and expeditious development of an integrated national
highway system. This includes Federal-aid for the
development of primary routes, for connecting our urban
arterial highways, for the National System of Interstate
Highways, and for secondary roads.

We are for the dedication and application of highway
revenues to highway purposes. In other words we are
unalterably opposed to diversion of highway revenues
to nonhighway purposes; and we stand in full support
of clarifying and strengthening of existing Federal
laws curtailing this vicious practice. We favor the
adoption of constitutional provisions outlawing diver-
sions by all states.
We are for the- free enterprise system and insistence
upon maximum utilization of the economic contract
method for highway construction.
We advocate advancement of highway safety through
the applications educationaland enforcement measures;
and through the utilization of proven engineering tech-
niques in the design, construction and reconstruction
of highways.
We advocate improvement of inter-industry and pro-
fessional relationships swell as relationships between
the various governmental agencies at all levels charged
with the responsibility of highway administration.

We are for the advancement and improvement of
highway engineer training forstudents.
We promote the practical application of research
findings and other technical data in highway design,
and construction.
We maintain a sound and continuing public relations
program directed toward a broad public understanding
of the need for and the value of adequate highways;
and the close relationship that exists between highways
and the general welfare.
To these policies the ARBA is rededicating itself.
We solicit your cooperation and the cooperation of other
groups throughout the Nation in the carrying out of our
program. Without such cooperation our efforts will fall
There's a big job to be done. Let's coordinate all
our efforts and do that job.

Archie N. Carter
Manager, Highway Ditision
Associated General Contractors of America, Inc.
lashington, D. C.

Because the role of the highway contractor will be
a major one in the huge roadbuilding job that lies
ahead, it is a real pleasure to participate in the Fifth
Annual Florida Highway Conference as a representa-
tive of the nation's highway contractors.
Membership in t1he Associated General Contractors
of America, Inc., totals nearly 6,000 general contractors
and of these firms between 2,500 and 3,000 do highway
construction. Here in Florida, the A.G.C. has 130
members, including numerous firms that do highway
construction. For all of its members the A.G.C. wishes
to thank you for the opportunity to make known to this
important conference the highway contractor's views
on rhe big road construction job the United States now
As everyone here is aware, the nation has failed to
keep its highway construction in pace with the growth
of automobile ownership and travel. in nearly every
section of the country traffic problems today are worse
than they were 10 years ago-some areas are extremely
critical and are cause of extreme losses in life and
property and travel time. In order to bring the Nation's
highways up to the standard desired, a tremendous
planning and construction program will be required.
This program will be a challenge to the construction
industry and must be forcibly pursued and carried out.
To improve America's highways to the desired
standard would cost $41 billion, a joint Committee of
Congress reported a few months ago, following inten-
sive study of the problem. Other groups estimate the
road construction needs of the U. S. at between $40
and $50 billion, or an average of around $1 billion per
st at e.
The Bureau of Public Roads in 1949, after a study
completed as part of our national defense program,
placed the cost of bringing the 37,800-mile strategic
Interstate System up to the desired standard at $11.3
billion. This is only the 37,800 miles of highway con-
necting our major cities. Some 1,141 miles Of the Inter-

state System are located in Florida, and improvement
of this mileage is estimated to cost over $115,000,000.
'Me tremendous U. S. highway problem is further
revealed by the huge motor vehicle registration at the
end of 1950 of over 48,000,000, which is an all-time
high and a major increase over the total registration
at the end of 1949. If all of the cars and trucks produced
in the United States last year were placed bumper to
bumper, they would total nearly 20,000 rriles in length.
Truck registration now totals 8,500,000 units or 70 per
cent higher than 10 years ago, and motor buses total
220,000. In the January 1951 issue of Automobile Facts
it is pointed out that U. S. trucks last year transported
8.3 billion tons of freight over America's highways, or
three times as much tonnage as was hauled in the U. S.
by railroad, water, and air combined.
In 1948, 32,259 people were killed on America's
highways. In 1949 the slaughter was reduced to 31,500.
But in 1950 the highway traffic loss jumped to 35,500
deaths and 1,799,800 additional persons injured. Total
gasoline consumption and total miles of travel hit new
records in 1949 and again in 1950. Delays to highway
traffic and highway accidents last year cost the U. S.
about $2.8 billion, it is estimated by the National
Safety Council.
Other staggering' figures could be cited to illustrate
the large road construction task we face, but today we
want to discuss how we can make the highway construc-
tion of the next few years most effective. In other words,
we want to consider how we can bring up to date our
rpost basic form of tran sportation -that of highway trans-
portation, which today is a huge $30 billion industry
that accounts for employment of 9,000,000 people and
one-eighth of the National income.
Ten-Year Program is Recommended
At the annual convention of the American Associa-
tion of State Highway Officials last December in Miami,
Commissioner Thomas If. NfacDonald of the Bureau of

Public Roads recommended a ten-year highway improve-
ment program with the average annual volume of new
construction exceeding that of 1950, which was a fairly
good year. Commissioner MacDonald's recommendation
has received wide approval. Working through its joint
Cooperative Committee with the AASIIO, which was
formed in 1921 and which has served as an excellent
sounding board, the A.G.C. is making every effort to
see that a Program of this size is accomplished. Today,
then, let us consider how we can secure maximum bene-
fit from each dollar spent for highway construction.
The first step is the preparation of good plans. In
this work the state highway departments must make
long-range plans outlining programs of several years.
The most capable highway engineers in the country
must be employed by the State Hlighway Departments.
To secure such men in adequate number the states must
pay better salaries.
For the past several years, the joint Cooperative
Committees of the AASIIO and the A.G.C. have been
working on this problem. But each person here, plus
all segments of the contracting industry, niust fight
for better salaries for our highway engineers if the
huge construction task ahead is to he planned properly.
I am glad to report that the joint Cooperative Com-
mittee of the American Society of Civil Engineers and
the A.G.C., which was organized in 1948, is at work
attempting to provide better trained civil engineers
for construction. This committee is striving hard to
improve the ASCE student chapters in the U. S. engi-
neering colleges. All A.G.C. chapters are assisting
at every opportunity in this program.
This joint Committee also plans to help in every-
way possiblec in providing summer employment for student
engineers and to attempt to get more engineer graduates
to enter highway construction. Such activity should
aid greatly in overcoming the severe shortage of engi-
neers for highway work.
To return to the Preparation of plans, on both long-
range studies and detailed engineering planning, out-
side consultants tthat are specialists in the highway
field may need in be employed by many states, county
and municipal highway departments. These consultants
can design many special structures outside the high-
way departments, thereby reducing the peak load on
the engineers of the state.
Numerous states, including Illinois, California,

Oregon, Washington, Idaho, Iowa, Michigan, Minnesota,
.Mississippi, Nebraska, Kansas, Maine, Ohio, Vermont,
and others, have already completed long-range plans.
Other states have long-range studies in progress. This
is excellent progress.
Advantages of long-range planning:
1. Needs will be mote fully understood and appre-
ciated by the state highway departments
2. The long-range plan is required to sell the
public on financing the big job to be done.
3. Required land can be secured on schedule
and at lower cost.
4. More contractors will take an interest and
better bids will result.
5. Better engineers can be employed, for they
will know they can expect employment with
the state highway department for several years.
6. Producers of construction materials will be
more apt to have the necessary capacity to
produce adequate supplies, as they can make
more logical investments to meet the large
needs to be filled.
7. A big financial saving to the entire constrric-
tion program will result.
Diversion of Funds Mwt End
The second big step in meeting the nation's highway
construction needs is financing the P~rogram. This
work requires termination of the diversion of gasoline
taxes and other highway-user taxes to nonhighway
During the years 1924 to 1949 inclusive, this diver-
sion totaled over 52.8 billion, and in 1949, the last
year for which detailed figures are available, eight
states diverted more than 10 ner cent of their highway
revenues. Last year about $1.5 billion of new road con-
struction xas awarded by the state highway departments,
which indicates forcefully the great scope of diversion
to date. Described in another way, the diverted high-
way taxes in recent years were sufficient to have im-
proved nearly 100,000 miles of highways, the llighway
User's Conference repo~rts.
Diversion can be stopped effectively only by the
states passing antidiversion amendments. At least 21
states have already taken such action, and this year
twelve or more states are to consider such amendments.
But the support of the general public must be placed
behind the drive for similar laws in the retraining states

if diversion is to be prevented.

The 1950 Federal-aid Highway Bill provides $594
million for each of two years for highway construction.
Of this amount $94 millions for work in national forests,
national parks, and other federal areas; the remaining
$500 million is for Federal-aid to the various states
and is to be matched on a 50-50 basis.
When Congress was holding hearings on the 1950
law, representatives of the A.G.C. testified and stressed:
(1) Long-range financing programs of several
years permit better planning and thereby
move economical construction.
(2) Highway construction costs are in line with
the prices of other services and commodities,
so that full value is assured for the invest-
ment in highways.
(3) Intense competition prevailing and expected
to prevail in highway construction is assur-
ance to the public that the construction will
be executed as efficiently as possible.
(4) The highway contracting industry has the
capacity to carry out an expanding highway
construction program, and to do the work
(5)Highway contractors, through their local and
national associations, are cooperating with
highway departments in practical means of
increasing the efficiency of construction
Actual Construction a Challenge
After comprehensive planning and financing have
been completed, the actual construction is the third
big step in meeting the country's highway needs. This
part of the program is where the highway engineers
must write clear specifications and prepare good plans.
This work must be accomplished in a manner chat tells
the contractor what is to be done, but leaves him free
to choose the construction equipment and methods he
considers the most satisfactory. In other words, highway
engineers should specify results, but not methods.
It is assumed, of course, that construction will be
by the contract method. This view is taken for the
following reasons.
1. Cost of the project is guaranteed before con-
struction starts.
2. Quality is guaranteed in accordance with
plans and specifications.
3. The general contractor haste financial incen-
tive to complete the project on schedule.
4. Lowest possible cost is secured through free

At present the following 21 states have constitutional
gunendments to conserve highway revenue for highway


Kentucity Missouri
Maine N evada
Massachusetts New Hampshire
Michigan North Dakota
Minnesota Ohio
West Virginia

South Dakota

It is to be noted that Florida is without the protec-
tion of such an amendment.
In 1949 increases in motor fuel taxes were passed in
15 states, in 1950 several states approved increases,
and in 1951 still more states passed increases. In all
the financing work good long-range plans will be needed
and will be invaluable if the financing job is to be
accomplished at the required rate.
Those attempting to finance large highway construc-
tion programs received a valuable aid in July, 1949,
when the Brookings Institution released a comprehen-
sive report on our highway problem.* This study con-
cluded that investing less for highway construction
and improvements means greater payment for highway
The Brookings Institution found that if the per-mile
cost of automotive transportation is to be brought to
the lowest possible level, a greater portion of the
automotive transportation dollar must be devoted to
improving America's over-burdened highways. Today
only 5 to 10 cents of every dollar spent for automotive
transportation is applied to the provision of highways,
the remaining 90 to 95 per cent being absorbed by ve-
hicle maintenance, gasoline purchase and other operat-
ing costs. This investment in highways is considered
much too small and illogical.
"The logic of this division of the highway trans-
portation dollar appears highly questionable wherever
the highway system is inadequate, since the excessive
cost of the vehicle may in large part result from this
inadequacy. Paying less for highways may mean paying
more for highway transportation. What we save in high-
way expenditures we may lose in higher operating costs,
with lower standards of service the net result," the
report concludes.
*Automotive Transportation Trends and Problems, by Vilfred

and open competition between competent
general contractors.
5. The detailed planning required by skilled engi-
neers before bids can be taken assures a prop-
erty planned project.
6. The contract method centralizes responsibility
for maximum efficiency of construction in the
general contractor.
7. Experience has demonstrated repeatedly that
the construction industry through its normal
channels can fulfill public needs more econom-
ically and move rapidly than is possible by
any other means.
Numerous contractors report chat their state high-
way departments could make a big improvement if they
would retain but 10 per cent on partial estirrares until
50 per cent of the work is complete, and then retain
only 5 per cent of partial payments until the job is
Completed. Some contractors report that their states
long ago saw the value of this procedure and are already
following such a policy. '.Still other contractors reported
their highway departments have made even greater
Prompt payment to the contractor must be made as
the work proceeds. The highway contractor's invest-
ment is huge and his financial responsibilities severe.
'Me contractors stress that prompt payment is only
good business and that major benefits will result to all
concerned. Contractors also consider it highly desirable
that much less be retained by the state highway depart-
ments on partial payments. A net contract In use by the
Rural Electrification Administration contains a provision
that calls for payment of interest to the contractor if he
is not paid promptly for work completed. Such a plan
might be beneficial on highway construction.
Other ways to speed up highway construction viewed
by the contracting industry include:
L. Permit the contractor free use of new types of
2. Be sure land is available and the job is ready
for the contractor to move in and start work
when bids are opened.
3. Use local construction materials to a maximum,
which will also reduce costs*
4. Cut hand labor to a minimum.
5. Award programs in contracts of various sizes.
6. Work for greater standardization of design to
permit, for example, those savings possible
where the contractors can use the same type
of bridge forms in neighboring states.

7. To make each year's construction season as
long as possible, have some contract lettings
as early as possible each year to permit max-
imum use of the contractor's equipment and
personnel, and thereby get better prices.
8. Seek a balanced construction program each year-
Because of the uncertain picture today regarding the
future supply of some types of building supplies, such
as steel, the A.G.C. favors the use of a clause in high-
way contracts to permit their termination if the contrac-
tors find that new government regulations or other de-
velopments prevent the delivery of critical materials,
and require that the projects be shut down. Rather than
require the contractor to complete work that has been
suspended for perhaps two or three years, such as hap-
pened on numerous jobs in World War 11, with much
higher prices to be paid for both labor and materials
than was originally planned, highway contractors prefer
the use of a termintition clause that will permit the
owner to Cancel the contract and pay the contractor
for completed work. Use of such a clause can be ex-
pected to aid in securing lower bids.
The wisdom of using a termination provision in the
contract is borne out the fact that such a provision is
being used by the following stares: Arkansas, Califor-
nia, Colorado, Kansas, Kentucky, Indiana, Iowa, Loui-
siana, Michigan, Nfinnesota, Missouri, New Hampshire,
New York, North Dakota, Ohio, Oklahoma, Wisconsin,
Wyoming, and Utah plus the Territory of Hawaii.
Public Relations Must Be Improved
For any program to be successful, the general pub-
lic must be kept fully informed of the extensive know-
how required for highway construction projects. In a
nutshell, this means the public must be better informed
than ever before regarding what is being done and the
great effort being made to improve America's highways.
To do this, highway officials and contractors alike
must improve greatly their public relations programs.
Finally, each of us must remember that almost each
half hour at least one person dies in the U. S. from
traffic accidents, and each few seconds a major accident
occurs on America's highways, I repeat that 35,500
people were killed on America's highways last year.
This slaughter must stop. We must all work hard to
accomplish this aim. In so doing, highway officials and
the contracting industry must not only build and improve
our highways, but they must sell the general public on
the great value of what is being done and on the great
importance of highway transportation to our economy
and to national defense.

Change in scenery and environment is the spice of
American life. This inherent restlessness in our people
does much toward creating the traffic congestion prob.
lems with which we are faced today. The city dweller
drives into the country in search of pleasure or for
business. The rural residents converge upon the towns
and cities seeking the same things.
An integrated state-wide system of highways con-
tinuing through the cities requires a high degree of
cooperation and close relationship between state and
city authorities. City streets serving as connecting
links of state highways are essential links in that
system. Cooperative effort on the part of state and
city officials is essential to fulfill this responsibility
and provide the public with a safe, economical, and
efficient system of highway transportation. Motorvehicle
traffic on our highways and streets recognizes no juris-
dictional boundaries.
While it is true that highway traffic recognizes no
jurisdictional boundaries so far as its right to free
movement is concerned, it is immediately aware of the
restrictions and controls to which it is subjected when
:-assing from rural areas into congested urban areas.
Many of the controls on traffic are justified in urban
areas because of the multitudinous activities char-
acteristic of such areas and the high premium placed
on space in which all functions must be conducted. On
the other hand, many of the controls and restrictions
on urban traffic are not necessary. They are the result
of existing and generally accepted practices which
have forced the passenger vehicle drivers to share the
roadway with packers, service and delivery trucks,
uncontrolled pedestrians and unwarranted traffic lights.
In rural areas the entire roadway is devoted to mov-
ing traffic. Parked vehicles are seldom encountered on
the traveled way. Stop signs or traffic lights are far
apart. In cities, however, the downtown streets are
normally available for curb parking. Parallel curb park-
ing greatly reduces a street's traffic carrying capacity.
Angle parking causes even a greater reduction in street
capacity. Where parking is allowed a street can oper-

ace at only a portion of its des;gaed efficiency.
When traffic on an important street is periodically
stopped by traffic lights, a further reduction in oper-
ating efficiency up to 50 per cent occurs. If the traffic
lights are warranted the resultant congestion is unfor-
tunate but necessary. If the lights are unwarranted
the congestion is almost tragic since it is created with-
out benefiting anyone. Street capacity therefore is
limited as well to a considerable degree by the inter-
section capacity.
Pedestrians in downtown areas add to the confusion.
The degree of this unnecessary congestion varies with
thi amount of control exerted on pedestrians. Proper
control of pedestrian traffic alone can help materially
in reducing traffic congestion.
Urban extensions of stare highways must not only
carry the rural traffic entering the urban area, but in
addition, must carry large volumes of traffic that has
both its origin and destination within the city. Thus
urban sections are required to carry several times the
number of vehicles usually found on rural sections of
the same state highway. It is evident that the urban
traffic problem is complicated mainly by certain factors
that normally do not greatly influence the rural traffic
problem. These are restrictions in speeds, curb parking,
closely spaced traffic lights. and conflicting pedestrian
movements. In addition to this, city streets must carry
the combined urban and rural traffic.
Having established the principal underlying causes
of urban traffic congestion, it would appear logical
that we seek the proper remedial measures to eliminate
or materially reduce the effects of these factors. Unfor-
tunately, in most instances there is only. one real cure.
This involves building new highway facilities of modern
design through the urban areas. In many localities with-
in the state, expressway or limited access type designs
would be required. The expense involved in constructing
suitable urban highways is so great that such a program
of improvement could not be financed for many years
without greatly increasing our highway revenue. Even

W. M. Parker
Engineer of Traffic and Planning
State Road Department
Tallahassee, Flodda

that the improvements submitted do in general me-t
with the anproval of the interested city officials.
This association is the beginning of a state-city
relationship in traffic affairs that can grow as fast as
different cities atreciate the need for cooperative
effort. iBoth the cities and the state have the responsi-
bility of moving traffic into and through urban areas
with a ninionum of delayy and inconvenience. Ylihat better
plan could be devi,;ed under cordial state-city relation-
shirs than that the state develop an ir-artial program
of traffic control within a city and that that city, through
its legislative body and its police force, -lace the
program into effect. In this way both governmental
agencies will be perforin4g the function, for which
they are best suited.
Those of you who live inl cities kn0ow that the traffic
problem is critical. Let me cite one angle that, perhaps,
many of you have given but little thought. The central
business districts, which are the backbone of a city's
tax revenue, are losing ground. It is no lon er a rleawire
to shop there because of congestion. helpingg to accel-
erate the decline of downtown business is the growing
trend toward neighborhood shopping centers. Often they
are located beyond the city limits and therefore '-eyond
its taxing jurisdiction.
Examples of the effect traffic congestion and the
lack of adequate parking facilities have produced on
assessed valuations in the central business districts
of certain cities of varying population grops are
shown in Table I.*
Ttaffic engineering can do much to arrest these
trends if its principles are properly applied. It is easy
to see why city officials and police officers, regardless
of their abilities in their chosen fields, cannot always
hope to cope with this problem. Suggestions are usually
advanced by local experts (I use the word advisedly)
and as often as not, their suggestions are put int.
operation, oftentimes with unhappy results. This should
not be. There is as much logic to these procedures as
there would be if one suffering with a toothache went to
the village barber rather than a dentist.
The President's Highway Safety Conference Com-
mittee on Engineering has recommended that all cities
over 50,000 population employ a traffic engineer on a
full-time basis. Actually few cities in Florida have
traffic engineers. They can be counted on the fingers
*From AAA Parking Vanual, 1946. Appendix 11, p. 169.

assuming the money to be available it would take some
time before engineering studies and detailed plans
could be prepared for every city in Florida.
What then, is the answer to growing traffic conges-
tion in our cities? The answer must be that we get the
greatest possible efficiency out of our existing streets.
In order to do this, appropriate traffic engineering in-
v.stigations should bc conducted in each Florida city.
lIecornmemations should be made which are predicated
upon facts. Only in this manner can urban areas hope to
cope with the paralyzing effects of traffic congestion.
Fit the cloth to the pattern. More often however it
will be found that the pattern must be lttted to the
cloth. The existing facility may in some instances be
*videned! but usually this is not practical mid we find
we must atternt to make better use of what is presently
Where traffic congestion exists first study the ex-
isting parking situation. It may be that elimination of
parking on one side may solve the problem, and for cer-
tain sections it may be deemed expedient to remove
parking entirely. Should this not provide the necessary
relief for traffic the next step wnuld be to a system of
one-way streets, provided adjacent parallel streets are
available. Then on these one-way streets study the
parking situation and correct as needed. Quite often
these approaches will satisfy traffic requirements, at
least for some time to come. Removal of parking should
always be accompanied by a compensating off-street
program where parking needs are critical.
Most Florida cities are not prepared to make the
traffic investigations so necessary to formulate sound
traffic control regulations. They have no employees on
their staffs who are qualified to carry out this special-
ized work nor would it be economically feasible to
employ such personnel in the smaller cities.
The State Road Department has a number of qualified
traffic engineers who, as a part of their duties, conduct
urban traffic studies and make impartial recommenda-
tions. In the spirit of state-city cooperation, the Depart-
ment has already made more than two dozen investiga-
tions for cities.
It is a requirement of the Bureau of Public Roads
that, before any Federal Urban Funds are allocated to
a city of 5,000 or more population, a traffic study first
be made to determine the need as well as the scope
and type of improvements to be constructed. Further,

Table I

Over 500.000 Population
Decline Decline
Valuation Yewr Valuation vest Dollars %

Baltimore, Md.
Boston, Mass.
Cleveland, Ohio*
Detroit, Mich.
Milwaukee, Wis.
New York City
Philadelphia, Pa.
Pittsburgh, Pa.
Toronto, Ontario, Can.
Atlanta, Ga.
Birmingham, Al.
Columbus, Ohio
Louisville, Ky,
Minneapolis, Minn.*
Portland Oregon
Rochester, N. Y.
Seattl e, Wash.
St. Paul, Minn.**
Chattanooga, Tenn.*
Erie, P.
Fort Worth, Ter-
Hartford, Conn.
Lowell, Mass.*
New Bedford, Mass.*
Springfield, Mass.*
Trenton, N. J.
Yonkers, N. Y.
Worcester, Mass.
Altoona, Pa.*
Binghamton, N. Y.
Harrisburg, Pa.
New Rochelle, N. Y.
Schenectady, N. Y.
St. Petersburg, Fla.

$ 175,000,000
511,8 93,706
168,277,9 22

S 60,000,0
88,625,8 t0
2,158.3D 3, 559
36,910, 061
$ 48,480,152
158,000, 0(0
30,778, 230
$ 10,962Z,377
8, 352630
3, 591,7 18
26, 139,017

1 93

$ 115,000,000
156, 339,40 2

1 945


250,000 500.000 Population

$ 308,325,052
713,656, COo
151,69 5,018
37, 100, COO


S 259,842,490
20 3.7 25,657
23,490, 350
2D,700,0 00
100,007,00 0

100,000 250.000 Population

S97,195, 350
133, 255,000
28 2j 99,910


S 84,23Z,973
229, 30 7,255
123,312, 97 5
10, 228, 550
247, OO0,0 00


20. 3%
29. 27*

50.000 100.000 Population

$ 86,000,000
16, 210,130
89, 585,870


$ 71,000,000
31,778, 36 0

Under 25,000 Population

Anaheim, Calif.



*Represents entire city, including central business district.
"'Land only.

of one hand and still have a few fingers left. There
are at least two reasons why smaller cities cannot hope
to employ engineers. First, the cost would be too high
for, after the initial studies were made, there would be
insufficient workrokeep such an employee busy. Second,
the available supply of qualified personnel is at present
too small to supply the existing demand of the larger
cities. The State Road Department is in a position to
employ a reasonable number of such personnel on a
permanent basis.
Still another factor enters into the need for a closer
relationship bemeen city and state on traffic control
matters. Under the Federal Aid Highway Act of 1944
and subsequent amendments, cities whose urban area
population is 5,000 or more according to the latest cen-
sus are eligible for Federal highway funds. These funds
may be spent on arterial streets within the urban area
where the need for improvement is established by ade-
quate traffic engineering investigations. These Studies
must be conducted by the Road Department and the
approval of specific urban projects must be approved
by the State and Federal Governments, as well as by
the city officials in accordance with the facts obtained.
'Mere are those who feel that it is false to claim
that the cities of Florida would receive only benefits
through a program where the State would establish
traffic controls on urban arterial streets and the city
would enforce them. They insist that some disadvan-
tages exist and should be considered.
For example, such a program allows the State to
usurp local control of a local problem. according to some
city officials. There is no question but that state con-
trol of traffic on its maintained connecting links through
cities would usurp the control of local authorities. There
is, however, some question as to whether the problem
is purely local in scope. If a city fails to incorporate
modern traffic engineering practices into its traffic
control program, all people who drive upon the State's
connecting links through that city must suffer delay
and inconvenience. Many of these people do not reside
within the city, yet in following the marked routes of
our State highways they are usually forced to traverse
the more congested areas. The State has an obligation
to these people.
The State also has an obligation to all residents of
the State, particularly those whose economic security
is dependent on good highways, to see that all traffic
"bottlenecks" on our State Highway System are reduced
to a minimum. Cities that fail to improve their traffic

operations constitute such "bottlenecks- and have a
general depressing effect on our efforts to expand our
tourist and resort business. Since our tourist trade is
the largest source of income to the people of the State,
this is a serious consideration. There are no less than
112 cities having a population of 2000 and over.
There are also those who would claim that a coop
erative program such as is under discussion here today
is merely an effort on the part of the State to grab
more authority, which is unwarranted. Was this same
argument presented when the State Department of Edu-
cation assumed supervisory control of the city schools,
or the State Board of Ilealr established minimum stand-
ards of sanitation and disease control? Frankly, I do
not know but I do know that cities as well as rural
areas have benefited immeasurably from the work of
these EWO State agencies. There was a time when high-
way and street traffic was a local problem, but today
it has grown to the point where it is a major factor in
the State's economy. The need for centralizing the
authority to cope with this problem is becoming more
obvious every day.
On the other hand, the advantages inherent in such
a program are numerous. Probably the more important
1. Specially trained technical personnel can be
employed by the State on a permanent basis
and made available as conditions permit.
2. Traffic control regulations will be free from
local bias and pressures.
3. Uniform practices will tend confidence to
the motor vehicle driver.
4. In many cities the State Road Department is
required to make traffic studies to satisfy
Federal requirements. Traffic studies to aid
the cities could be performed at the same time
at little additional cost.
5. Both the City and Statecan profit from working
together because before the State Administra-
tors and Engineers at all times will be the
plight of the cities and their need for adequate
arterial streets.
Of the advantages just mentioned, at least one
deserves further discussion. I stated that under the
proposed program, traffic control regulations will be
free from local bias and pressures. In those cities of
Florida where we have made traffic surveys and arrived
at sound recommendations for improvement of traffic
conditionsmany have failed to put the recommendations

into effect or only Partly so. We have discussed this
situation informally with several officials in these
cities and find that while the officials for the most
part want to make the necessary changes in traffic
operations, they are unable to do so because small
groups of influential individuals with personal interests
exert undue blocking pressure. These individuals are
unable to see that better traffic operations will mean
a better city and, in the long run, a better city will pro-
duce better business conditions. Thus the rights of
thousands of individuals who drive over the streets of a
city each day can be abrogated by the organized pres-
sure of these few persons.
There are 49 cities in Florida with a population of
5,000 or more persons according to the 1950 census. As
has been already mentioned, in recent years the State
Road Department through its Division of Traffic and
Planning has conducted, or is now conducting, ade-
quate traffic engineering studies in 25 of these cities.
Studies in the remaining 24 cities in this population
range will be undertaken as rapidly asfunds and person-
nel permit.
V e are particularly proud of the Jacksonville Traffic
Survey which established the need for $50 million
worth of expressways and bridges now under construc-
tion. We believe that we will be able to point with
even greater pride to our traffic and parking surveys
in Miami which have been in operation for the past
year. We believe that these studies will justify a con-

struction program that will solve many of Miami's traffic
problems for many years to come.
just to give you an idea of the size of the Miami
problem on which we are now working as the State's
contribution to the relief of traffic, the field survey
started June of 1950 and will last slightly longer than
one year. For a goodly portion of the time as many as
110 persons were employed on work relating to the
survey. 'Me cost to the Road Department will be around
$250,000. The survey covered such necessary informa-
rion as an analysis of daily and rush-bour travelvol-
umes; the effect of the various recreational movements,
such as to the race tracks and the beaches; facts on
origin and destination and the cause and extent of
congestion. Local records of land use, land values and
land development are now being studied. Survey and
aerial photographic maps will give essential information
on topography and physical barriers. These facts and
many others are necessary before a real analysis of
the situation can be made.
I would like to repeat that I am convinced that
city-state cooperation in traffic control is highly desira-
ble. The problem is big and the solution will require
the cooperative efforts of both city and state agencies
to achieve success. So long as we have the same goal -
that of moving our traffic safely and expeditiously on
our present streets and highways, our differences will
be honest ones. They can be resolved by the clear
light of facts, and our mutual success assured.

Harry FE. Stark
Bureau of Public Roads
Athnta, Georgia

urban projects. I will not attempt to add ao~thing on
that phase of the work other tian in emphasize rhe
importance of a highway and transportation plan for
every' urban area. In order to select the location and
type of facility a good preliminary engineering report
is a "must". The scope of this report will depend
upon the size of the city and the complexity of the
problem. It might include a study for a complete system
of highways in a city, several projects or one specific
project, or a single intersection problem. These prelim-
inary engineering reports will always be important in
bringing various groups to agreement, in introducing
projects to the public, and in furnishing information
to the designer.
In any discussion of urban design problems it might
be wise to hesitate long enough to summarize the major
differences between rural and urban design. Essentially
rhe difference is one of complexity and cost. Items
that are of minor concern on rural projects can and do
assume major proportions on urban jobs. One of these
is the handling of traffic during constrnirion. Usually
a simple matter to be handled by the contractor on rural
work, this feature must be considered at all stages of
urban design. The shifting of several. thousand cars a
day to other existing streets might be a practical im-
possibility, in which case it might become necessary
to make, extensive improvements on other routes in
advance of the construction of the arterial improvement.
Another item is stage construction. In the deter-
intation of early urban projects it must be recognized
that stage construction is inevitable, due to nonavail-
ability of funds, maintenance of traffic during construc-
tion, etc. On rural roads stage construction usually
means grading first and providing a light surface, with
the idea of building up the surface at a later date until
it is suitable for heavy traffic. However, in urban areas,
the point is that stage construction must be planned
so that projects or portions thereof that can immediately
carry large volumes, and heavy load must be consider-
ed first. This might take the form of completing a short
section of highway that can be opened to traffic; con-

flirou~ghout the years of highway development the
attention of hi ;hway officials was focused on the con-
struction of an adequate q~stcm of rural roads. Intercity
transportation anti '"getting people out of the mud"
%,Vrv- (if ptim *i qtlya~
As this program of rural construction progressed
and traffic volumes increased, a situation developed
which found most cities being approached by many
good roads of adequate capacity in the rural and sub-
urban areas, while in the cities themselves, where
traffic volumes were hi,iie-t, very little was done to
provide adequate facilities. The result in cities has
been traffic congestion, frequent stops at street inter-
sections, decreased average travel speeds, delays,
inconvenience, accidents, and increased Costs Of motor
vehicle operation. This condition was doubtless quite
obvious to highway officials and the traveling public
alike. Bnr very little was done to relieve this increas-
ingly bad situation.
Prior to the passage of the 1944 Federal-aid Hligh-
way Act only a few cities had taken any real steps to-
ward putting into action an urban highway program
that would relieve the traffic congestion that was and
still is throttling our cities. But since the passage of
that Act, earmarking Federal funds for projects in urban
areas, a more realistic approach has been adopted in
most of our cities. The movement has now gained such
momentum that it is of primary importance in the minds
of officials of cities, states, and the Federal government.
Due to the great number of governmental agencies
involved in any urban program, a maximum of coopera-
tion between these agencies is an absolute necessity.
Numerouis conferences between representatives of all
agencies should be held in order to work out solutions
satisfactory to all concerned. City planning commis-
sions can give invaluable assistance, for any urban
project must of necessity fit the over-all plan peculiar
to the individual city.
Mr. Parker has covered the subject of planning of


destruction along the whole length of a highway, deferring
portions such as grade separations; or, in the case of
expressways, constructing frontage roads as the initial
highway and adding the main pavements later as funds
are made available. There are two especially dangerous
possible developments that must be avoided on urban
stage construction:
(1) Right-of-way development that renders future
stages impossible.
(2) development of traffic that is impossible to
re-route after being put on the stage improve-
Everyone connected with the urban highway field
is fast realizing the problems posed by adjustments to
utilities. On rural work this item is usually a minor
one, consisting of moving simple pole lines and such.
But on urban work these adjustments must be made
on everything from simple electric lines to all kinds of
complicated steam, gas, electric, and water lines, etc.
These adjustments are not only costly from the stand-
Point of construction, but making the adjustment with.
out interruption of service may present a complicated
problem. Close cooperation with the engineers ofthe
utilities involved is necessary in order to obtain a
practical and economical solution. Utilities can very
wel I affect the location and design of an urban project.
Drainage on urban projects is not a matter of just
taking the water from one side of the facility to the
other, as is usually the case in rural areas. It can be-
come the determining factor as to location or general
type of design. In flat areas drainage structures may
have to be carried for miles along the arterial route.
This has been the case on a nu ber of urban projects
in Florida, and in some instances the cost of drainage
structures has amounted to half the total construction
cost. On the West Side Expressway in Chicago a longi-
tudinal storm, drain has to be carried several miles to
the lake, since the city facilities are wholly inadequate.
In addition, boosters with pump-houses are required at
intervals. For seven or eight miles of this expressway
the drainage will cost several million dollars. In the
matter of drainage there should exist reasonable re-
lations between the state and the city, and problems
should be worked out jointly. Cities should certainly
accept their responsibility for the drainage of urban
projects and should make reasonable contributions
toward the cost of drainage facilities.
Another difference between rural and urban facilities
is in the use of control devices and traffic signals.
A well-designed signal set-up is a necessary part of

urban projects.
The matter of appearance, while important on rural
highways, applies even more to urban facilities, be.
cause there are more people around. For a small addi-
tional expenditure we can obtain structures that are
pleasing to the eye and roadsides that are properly
planted and landscaped. These facilities are built for
the public, and public reaction to a good-looking job
certainly warrants the extra effort expended.
Urban projects must be "tailor-made" according to
conditions peculiar to the area involved. The type of
improvement may be one of the following, depending
upon the service to be rendered:
(1) Major street
(2) Expressway at grade
(3) Expressway
(4) Freeway
In the design of arterial highways, standards of
alignment and grade as high as those in rural areas
cannot be expected, but they should be consistent with
design speeds, topography, etc. Design speeds will
not be higher than 60 miles per hour: on major streets,
30 to 50; expressways at grade, 30 to 50, or Possibly
60 in outlying areas; on higher types (expressways and
freeways), 40 to 60 miles per hour. Winding alignment
maybe necessary in urban areas on account of expensive
development. However, all possibilities to maintain
high standards should be explored.
Grades will vary from those of existing streets to
the desirable 3 per cent maximum. Flat grades are
desirable but should be held to a proper minimum to
provide drainage. Ramp grades can be as high as 6
per cent for up-ramps and up to 7 per cent or even
8 per cent where necessary on down-ramps.
An important feature in the design of urban highways
is the control of access. This is developed to varying
degrees by the following steps:
(1) The control of turns at intersections, primari-
ly left turns during rush hours;
(2) The elimination of mid-block turns by use of
a median;
(3) The elimination of crossing and left-turning
movements at entering streets by extension
of the median through the intersection;
(4) The elimination of some street connections
by use of cul-de-sacs;

(5) The elimination of major crossings by grade
(6) The elimination of allcrossings at grade.
All design features should be correlated with the
design speed; this, together with the control of access,
determines the type of facility.
Design speed, degree of control of access, type of
traffic, and cross section (number of lanes) are the
primary features that determine highway capacity. Lane
capacities on major streets are governed by capacities
at intersecting streets. These are affected principally
by the time of green interval for through flow, extent
of turning movements and pedestrians, and parking.
Lane capacities vary from 300 to 500 vehicles per
lane per hour. On controlled access facilities, lane
capacities range from about 1500 per hour without
commercial vehicles to approximately goo per hour
with 20 per cent commercial vehicles in rolling terrain.
Capacities on expressways at grade fall between those
of through streets and fully controlled acci ss highways.
Lane capacities vary from 600 to 1,000 per hour. Much
information on highway capacities is now available to
the designerfor application to thedesign of any specific
For free-flowing facilities of the expressway and
free-way type, traffic lanes 12 ft. wide arenow accepted
as standard. On major streets 11-ft. and 12-ft. lane
widths are called for. There is a real need for 10-ft.
parking lanes where provision must be made for parking.
Both traffic lanes and parking lanes should be provided
in multiples of two. Three-lane pavements are not
desirable in sections within urban areas. A curb-to-curb
width of 48-50 ft. is especially undesirable. This is
the range in which we should not build.
Opposing traffic on major streets should be sepa-
rated, either by center striping, flush median, or some
form of raised median. Medians may be paved separators
4 to 6 in. high-, may be crowned and/or corrugated type,
or may be jiggle bars. There are conflicting opinions
as to the type of curb to be used on narrow raised
medians. Some engineers prefer a 6 in. barrier curb,
while others favor low mountable curbs. There is a
wide variety of designs in use today, and much can be
said in favor of each design. However, it seems that a
low mountable curb, with its advantages of not rending
to reduce the effective width of pavement and not tend-
ing to throw a car out of control when contact is made
with it, is preferable to the higher barrier type.

There are numerous major street facilities that have
been completed and placed under traffic in the South-
eastern States. Some of the designs are as follows:
(1) Tennessee on 92 ft. right of way
4-12 ft. traffic lanes
2-10 ft. parking lanes
4 ft. crowned and corrugated concrete median
2-10 ft. sidewalk and utility areas
A similar section is now being used in Georgia.
(2) Florida on 100 ft. right of way
4-11 ft. traffic lanes
2-10 ft. service lanes
2-8 ft. parking lanes
4 ft. flush median with raised pedestrian
2-8 ft. sidewalk and utility areas
This is a special design, applicable only
in areas with high volumes of in-and-out
park ing.
(3) Florida on 100 ft. tight of way
4-12 ft. traffic lanes
2-8 ft- parking lanes
14 ft. curbed and grassed median
2-11 ft. sidewalk and utility areas
All these sections appear to be functioning satis-
facEorily under traffic. However, by combining the more
desirable features of each section and by increasing
the righr-of-way width to 106 ft. the following section
is obtained:
4-12 ft. traffic lanes
2-10 ft. parking lanes
18 ft. grassed median
2-10 ft- sidewalk and utility areas
The 18 ft. median allows the incorporation
of a full 12 ft. median lane at intersections
where left turns are allowed.
On urban facilities a wide range of median widths
is in use today. Some widths for certain advantages are
as follows:
4 ft. -minimum that should be used: this
width is necessary for erection of
signs and refuges for pedestrians.
8 ft. may be grassed.

12 ft- minimum to allow for Center Pier-
16 ft. provides median lane for storage, maneu-
vering, and speed change of left turning
20 ft. note positive separation, no curbs required,
may be depressed to collect drainage, may
be planted to screen headlight glate.
25 ft. minimum width to obtain all advantages of
a median.
30-50 ft. desirable for all multiple lane highways;
permits addition of traffic lanes in the future.
The lengths of openings in a median should be
designed to fit the paths of turning vehicles. A 50-ft.
inside turning radius plus a clearance of 2 ft. should
be provided.
Experience has shown that shoulders are a necessi-
ty on all urban arterials to avoid complete stoppage, a
pile-up of traffic, and annoying delays when there is a
breakdown or rear-end collision. The frequency of
breakdowns is much higher than is commonly supposed.
Latest figures show that a breakdown can be expected
for every 8,000 vehicle-miles of travel. Even an ele-
vated structures of appreciable length at least a partial
shoulder might well be considered. On major streets
parking lanes may function as shoulder areas during
peak flows, or disabled vehicles may be removed to
cross streets. On higher type facilities shoulders at
least 8 ft. and preferably loft. wide should be provided.
They should be of a color and texture in contrast with
the through pavement and should be designed to en-
courage use for emergency stopping but to discourage
use by through traffic. They may be paved, turf, or a
combination of 3-5 ft. of surface treatment with the
remainder rurf. I
On a great number of urban arterial highways, frontage
roads will be required. These may be of local service
or major street character. Two-way frontage roads
should be avoided, for they complicate operation at
intersections and ramp junctions, add many conflicts,
and decrease capacity.
The area between the through pavement and the
frontage road or some other service area, called the
outer separation, separates physically the through
traffic from local traffic and has the function of accom-
modating a shoulder, speed change lanes at intersec-
tions, and bus turnouts. Outer separations should be
wide enough to accommodate all features to be included
in them, provide for necessary turning movements,
and keep retaining wall construction to a minimum.

One of the most important items in urban arterial
design is access connections, their spacing and treat-
ment. In the design of expressways every effort is made
to eliminate as many intersecting streets as possible.
On major streets, where all or nearly all cross streets
must remain as grade intersections, the capacity is
determined more by the capacity of its intersections
than by any other factor. le, therefore, must direct
out attention toward any layout changes and traffic
control devices that will minimize any likely conflicts
and will increase capacities through the intersections.
The major means of accomplishing this are:
I. Posting of stop signs at cross streets.
2. Elimination of U-turns and restriction of left
3. Use of traffic signal control.
4. Pedestrian control.
5- Use of adequutc pavement marking.
6, Provision of ample radii at curb returns.
7. Installation of median lanes.
a. Channelization of cross and turning move-
ments, especially where streets intersect at
angles other than nearly 90 degrees and where
five or move streets meet in a common area.
The design of intersections demands the most in-
tense study and investigation if we are to build facil-
ities that will function safely and efficiently. In chan-
nelizing an intersection at grade, all possible move-
ments cannot always be provided for, and some minor
movements very often are better omitted to simplify
operation and to improve efficiency and capacity.
Ileavy movements should be favored, and added lanes
for storage and deceleration of left turning traffic
should be considered.
The design of a major interchange is a rather com-
plex operation and can rarely be accomplished directly
upon first trial. Before any final design can be prepared,
preliminary plans, estimates, and economic analyses
should be worked up for all logical alternates. These
must be based on complete physical data for the site,
analysis of traffic data, and a determination of the
future location and type of all highways in the area.
On urban projects it is highly important that ade-
quate lighting be installed, particularly on facilities
with grade crossings such as major streets. Basically
this means getting enough light and in the right places.
The amount of light needed varies widely with the
type of facility, the presence or absence of pedestrians.
Manufacturers of lighting equipment and technicians of

curb the tremendous losses in highway investments
which we are now suffering. It may be that the provision
of frontage roads can adequately provide access con-
trol in the absence of special legislation.
My remarks thus far have been confined to features
of design of new facilities. A logical question would
be, "What can be done to improve traffic conditions
in our urban areas besides the improvement of arterial
streets and the construction of expressways and free-
ways?" Many things can be done. Much benefit can be
derived in a short time with little expenditure of funds
by making spot improvements. The need for these im-
provements may have been evident for years without
any action being taken. It is a safe bet that their in-
clusion in a preliminary engineering report will go far
toward bringing the desired action. Sorne examples of
such improvements are:
1. Re-routing of traffic over adjacent streets
that are less congested.
2. Establishing one-way streets to speed up
operation by minimizing effects of left turns
and to divide traffic loads.
3. Construction of islands to channelize and
control traffic.
4. Construction of grade separations at intersec-
tions of important routes.
5. Removal of unnecessary jogs on important
6. Extension of important dead-end streets to
form part of a connected system.
7. Modernization of the traffic signal system.
8. Regulation of curb parking and provision of
off-street parking.
All over the country today the increasing number
of motor vehicles and their greater usage is resulting
in increasing congestion, particularly in urban areas.
The use of trucks, busses, and passenger cars is such
an important part of the industrial, commercial and
social life of the community that inability to move
freely in motor vehicles results in great economic loss,
sluggishness in community life, and great distress due
to accidents. The development of measures for the
relief of congestion in urban areas truly is an effort
of high priority.

most power companies have been furnishing excellent
technical assistance in the design of lighting systems
for some of the facilities constructed in the last few
A very important part of any urban arterial is proper
signing and marking. The AASHO Manual on Uniform
Traffic Control novices should be followed in the de-
sign of intersections with traffic signals and other
traffic control devices. Adequate signing must be kept
in mind during the geometric phases of design, for signs
may influence size, shape, and position of islands and
possibly points of access. Signs should be planned on
paper, but allowance should be made for adjustment
and expansion after the facility is built.
Thus far I have not attempted to cover the subject
of right of way. That is a field within itself, one about
which much has been and will be written. It is equally
as important as any other phase of urban highway work.
The urban right-of-way problem is relatively new and
in it lies some of the most difficult phases of the urban
program. On many projects the right-of-way cost is as
much as or greater than the construction cost. The
location can very well be dictated by right-of-way
considerations. It is therefore imperative that the right-
of-way engineer be brought into the picture in the very
early stages when an urban project is being planned.
Any mention of right of way automatically brings
to mind the term control of access, which is "the con-
dition where the right of owners or occupants of abutting
land or other persons to access, light, air, or view in
connection with a highway isfully or partially controlled
by public authority." Every day it is becoming more
obvious that control of access on major arterials by
legal and physical means is a necessity, as well as a
long-range economy. With the completion of each new
facility not so protected we see development of road-
side businesses, the attendant decrease in traffic
capacity and increase in accident hazard, and the re-
sultant loss of our highway investment. In most of the
Southeastern States there is no legal authority for
establishing controlled access facilities. The highway
engineers in those states without such legal authority
must act and act soon to bring about the passage of
adequate controlled access legislation, if we are to

A. C. denkelman
Bureau of PubAc Roads
tashington, U C.

Not so many years ago the design of pavements of
the flexible type was based almost entirely upon the
experience and judgment of the engineer. Those were
the days before we realized that a balanced or efficient
design of pavement depended to such a great extent
upon the proper engineering evaluation of the sub.
grade soil.
In 1929 the group system of soil classification of
the Bureau of Public Roads was developed and shortly
afterwards a number of the state highway departments
adopted the practice of varying the thickness of the
pavement structure in accordance with the character
of the soil, as determined by this system of classifica-
tion. This meant that for the first time the design of
flexible pavements was being placed upon a rational
basis, to the extent that recognition was being accorded
the fact that the thickness of the structure should be
related to the type of soil on which it is built.
In 1935 the idea of evaluating the soil by means
of small-scale strength tests was advanced. It was
about this time that the Florida Bearing Test was
conceived and a few years later the now well-known
CBR test was developed Previously it had been the
thought that if the strength of the soil was to be evalu-
ated as an aid in determining pavement thickness re-
quirements, it would have to be done by the use of
large-scale plate load tests. However, because of the
time and expense involved in making such tests, their
use as a routine procedure never became a reality.
Research on the design of flexible pavements con-
ducted during World War U in connection with the con-
struction of airport runways served to further empha-
size the feasibility of small-scale strength tests as a
means for evaluating the subgrade soil. "Ibe method of
design developed by the Corps of Engineers, Depart-
meni of the Amy, utilized the CBR test for this pur-
pose. The program of investigational work of this
Government agency conducted during and since the war
is a matter of record and will not be discussed in this
report, except to state that the method of design as

originally developed, with minor modifications, is still
in use.
It has become evident during recent years that a
large part of our mileage of flexible pavements was
not designed to accommodate the increase in traffic
that has occurred. In many sections of road general
structural deterioration of a serious nature has devel-
oped. In others, the trouble is more localized in char-
acter, indicating that the original design did not prop-
erly take into account the physical and environmental
characteristics of the existing soil types. This situa-
tion, one of considerable concern to highway authori-
ties, has been largely responsible for the development
of improved procedures for flexible pavement design
that are being used by the State highway departments.
The Flexible Pavement Structure
A flexible pavement is a structure consisting of
selected or processed materials superimposed upon
the supporting subgrade soil. In its simplest form it
may consist of a course of local granular material only
or of a course of processed gravel or crushed rock
stabilized by the addition of soil binder or stone screen-
ings. In the higher types of flexible pavements the
major structural element is the base course, strength-
ened as well as protected by a bituminous wearing
surface and, in some cases, supplemented by under
lying subbase courses.
The principal function of a flexible pavement is
to distribute concentrated loads to the supporting sub-
grade so that the transmitted pressures will be so re-
duced as to not exceed the safe bearing capacity of
the material. The distinguishing feature of such a
pavement is that the reduction of transmitted pressure
is accomplished through lateral distribution of the
concentrated load with depth rather than by beam
it follows, therefore, that a flexible pavement will
fail or undergo structural deterioration if its over-all

thickness is inadequate to protect the subgrade from
movement of an excessive or of a progressive perma-
nent nature. A pavement of this type can fail also if
the materials composing it do not possess sufficient
inherent stability to resist distortion within themselves
under the action of traffic. As a general rule, lack of
adequate thickness cannot be compensated for by the
use of ultra-high quality materials nor can the defi-
ciencies ot poor-quality paving materials be compen-
sated for by increasing the thickness of the structure.
Wearing Course
Bituminous surfaces are placed upon nonrigid bases
EO perform the following functions;
1. Provide a smooth riding surface and protect
the base or foundation course from the abra-
sive action of traffic.
2. Waterproof the underlying base and subgrade
against the penetration of surface water which
might adversely affect the load-supporting
capacity of these components.
3. Increase the load-supporting ability of the
entire structure.
Bituminous wearing courses may consist of the
1. Surface Treatments. --These are effective for
waterproofing, but require careful maintenance
to preserve the load-supporting ability of the
base. They are used generally where the
traffic is composed principally of light loads
or as a temporary CapCtlicat as toads carrying
heavy traffic.
2. Road Mix, Cold-Laid Plant Mix. Penetration
Macadam-These surfaces are usually much
more resistant to the abrasive effect of traffic
and are, therefore, more durable than surface
treatments. However, they require frequent
applications of a seal coat to reader them
3. Dense-graded Hot-Mix Surfaces. --These fur-
nish maximum protection for nonrigid bases.
When well designed and compacted, they are
practically impervious and possess a high
degree of structural strength. They are, there-
fore, well adapted to all types of traffic.

element of nonrigid pavements. Their function is to
distribute loads to the underlying subbase or subgrade
so that the ensuing deformation of these materials is
not destructive in magnitude. They should possess
sufficient inherent stability to resist distortion within
themselves and sufficient compaction to prevent ex-
cessive consolidation. They should also be adequately
resistant to volume change or softening due to moisture
Many materials have been found to be suitable for
base courses, such as crushed stone, gravel, slag,
sand-clay, and sand-clay gravel, caliche, limerick,
stabilized soil and others. Natural soils when stabilized
by adding cement, lime, bitumen or other materials, in
many cases, make acceptable base courses. Two of
the most important considerations are (1) avoidance of
softening due to adverse moisture conditions by using
materials (fraction passing the No. 40 sieve) having a
low degree of plasticity (plasticity index not exceeding
6) and (2) avoidance of frost damage by using relatively
free draining materials.
Subbases are often used on fine-grained subgrade
soils to:
1. Provide proper drainage;
2. Prevent damaging frost action;
3- Minimize the effectofaubgrade volume change;
4. Prevent intrusion of the subgrade into the
base course;
5. Increase structural support of the overlying
The subgrade is the natural soil on which the pave-
ment is to be built as it exists at the site of the work.
A survey is generally made to determine the char-
acteristics of the subgrade soil and to classify the
material. The subject of soil classification is covered
in detail in other articles and will not be discussed
here. However, it is pertinent to state that the soil
survey and the classification of the soil material is a
necessary prerequisite in the problem of design of
flexible pavements.

Empirical Procedures of Design

Base Course

Base courses serve as the principal structural

The most important factor entering into the problem

of thickness of nonrigid pavements is that of the sup.
porting capacity of the subgrade soil. Some soils as
they are found in nature, when compacted, possess
the ability to support concentrated loads with little
ensuing deformation. Others possess very little ability
in this regard. A high-type pavement on soils of the
first class may consist of a wearing course only, where-
as on soils of the second class it should, of necessity,
be a structure of appreciable over-all thickness. There
are, of course, other factors to be considered in the
design of nonrigid pavements such as the amount and
character of the traffic, the prevailing climatic condi-
tions and the type and quality of the pavement mate-
rials. They will be discussed in more detail lam on in
this paper.
At the start of World War H the problem d thickness
design of flexible pavements was substantially as
1. The great majority of the State highway de-
partments were using the experience-judgment
method which, as implied before, in many
cases was not conducive to the best results.
2. About ten of the state highway departments
were making use of the Bureau of Public
Roads' group system of soil classification as
a means for taking into account the character
of the subgrade soil, in the design of the
3. Several of the departments were employing
small-scale tests as a means of evaluating
the strength of the materials, particularly the
subgrade soil.
In 1946 the Committee on Flexible Pavement Design
of the Highway Research Board learned that a number
of the states, including Minnesota, Colorado, Kansas,
North Carolina, Wyoming, Texas, Michigan and New
Mexico, were using new or empirical procedures for
thickness design. Subsequently this Committee was
instrumental in having the details of these procedures
reported at successive meetings of the Highway Re-
search Board and 1 blushed in the annual proceedings
2. 3. 4. 5. 6, 7. 8. Considerable interest was mani-
fested in these methods of design and it was not long
before many of the other state highway departments
undertook to revise their currently-used methods or to
develop new ones. That considerable progress has been
made is evident from the results of a nationwide survey
of design practices being conducted by the Committee.
ne survey was begun in 1949 and is still in pro-

gress. Initially the states were requested by letter to
furnish the Committee with a descriptive statement of
the details of their procedure. From the information
obtained a tabulation of the essential features of the
methods was prepared and subsequently copies of the
tabulation were returned to the states for checking and
amplification. The process was repeated, a second
more complete tabulation of the data was prepared and
copies were again returned to the states for clarification
of information reported for one of the items and for
final clearance pending formal publication.
At the annual meeting of the Highway Research
Board in January 1951 the status of the information
assembled was discussed as a part of the report of the
Committee on Flexible Pavement Design. This report,
in summary form, was printed in the February, 1951
issue of Highumsy Research Abstracts: It contains a
copy of the most recent tabulation of the design data
which was appended thereto as a matter of preliminary
information pending publication of the comprehensive
report of all the material that the Committee anticipates
will be assembled. The fact that the tabulation of data
has been published makes it possible for the writer to
summarize in detail the status of the information in this
The information in the tabulation is listed under
three headings -General, Method of Evaluation, and
Miscellaneous. Under the first is included information
dealing with the subgrade soil: (a)method of classifica-
tion, (b) soil constants tests and (c) soil strength
tests; under the second: (a) traffic, (b) climate, (c)
subgrade and (d) pavement (wearing surface, base and
subbase); under the third: (a) years method used, (b)
load restrictions in spring (primary roads, secondary
roads) and (c) remarks.
A general summary of the information follows:
1. Forry-seven of the State Highway departments
classify their soils, 31 utilize the P.R.A. or
B.P.R. soil group system, 12 the H.R.B.
system, 10 the Pedological method, 3 on a
basis of texture and 6 utilize special or mis-
cellaneous methods.
2. Thirty-three states perform the soil constant
tests as a routine procedure.
3. Thirty-eight consider the factor of traffic in
their design procedure, 13 in terms of the
total volume of traffic, 17 in terms of the vol-
ume of commercial vehicles, and 8 in terms of

the magnitude of the legal wheel load.
4. Twenty-nine states consider the factor of
climate in their design method.
5. Forty-seven states report that they utilize
some method for evaluating the soil. Of the
20 states evaluating the material by means
of strength tests, 15 employ the C.B.R. test,
3 the triaxial test and 2 the Hveem Stabilo-
meter; 22 vary the design of the pavement in
accordance with the character of the soil, 9
according to the P.R.A. soil groups and 3 ac-
cording to the H.R.B, soil groups, 10 utilize
values of the group index; 6 the results of de-
tailed field soil surveys. Several use methods
of a :.peciAl or miscellaneous characer and a
total of 13 states utilize more than one method.
The information furnished the Committee on methods
being used for evaluating the pavement components
(wearing, base and subbase course) is incomplete at
this date and no attempt will be made to present a
summary of it. This is one item that has been referred
back to the states for clarification. In some cases the
information relates to methods that are employed for
evaluating the quality of the components, in others to
methods for evaluating the thickness of the components.
It is anticipated that complete information will be ob-
tained as to methods used to accomplish both purposes,
and this material will be included in the comprehensive
report that is to be prepared.
It has been emphasized before that the thickness of
flexible pavements should be related to the character
of the soil on which they are built. For this reason the
information presented in the summary of the material
on design procedures that concerns the methods of
evaluating the subgrade soil is of particular interest
and significance. The methods were divided into three
categories (a) strength tests, (b) character of the soil
material and (c) detailed field surveys.
It is not possible, of course, in this report to de-
scribe even in brief detail all Of the currently used
methods of design. However, three methods, one for
each of the above categories, will be described.
Strength Tests, Kansas Method
This method utilized the results of triaxial compres-
sion tests conducted on each component of the road
structure4. Samples of subgrade in either undisturbed
or disturbed conditions are tested in triaxial compres-
sion after being saturated. Undisturbed samples of

subgrade are preferable although disturbed samples
may be used for estimating purposes. Each project is
sampled frequently enough to evaluate all conditions
which exist, usually an average of about three samples
per mile. The frequency of sampling depends upon the
topography. Preliminary investigation is made to deter-
mine the locations to he sampled. Tests of the other
components such as subbase, base and surface courses
are made as required. An average of one test per hour
may be completed in the laboratory with one full set of
equipment. Test data provide information for stress-
strain curves, from which moduli of deformation are
computed. Coefficients based on volume of traffic and
rainfall are used in correlating traffic with all of the
materials involved. Ch artN we prepared from the follow-
ing formula for determining the thickness of surface
course required on any subgrade.
'%her e:
T = Required thickness of pavement, in inches,
Cp -- modulus of deformation of pavement or sur-
face course, psi,
C=modulus of deformation of subgrade or sub-
base, psi,
P = base wheel load, in pounds,
in =-traffic coefficient based on volume of traffic,
n -- saturation coefficient based on rainfall,
a = radius of area of tire contact corresponding
to Pmo, in inches, and
S = permitted deflection of surface, in inches.
This formula is directly applicable to single wheel
loads. When the load is applied by dual wheels, the
effective radius of tire contact area is not easily deter-
mined. This difficulty is overcome by computing the
stress imposed by each tire separately and deriving
charts to account for the combined effect.
Kansas and many other states have a stautory
18,000-1b. axle load limit, or a 9,000-lb. wheel load,
a load which usually is carried on dual tires. Ordinarily
in this State rigid pavements are employed on highways
with a great volume of heavy traffic.
Flexible type pavements are used on highways with
less heavy traffic. The percentage of vehicles carrying
maximum loads as related to the total number of vehi-
cles is fairly constant over most of the State's high-
ways. The variation affecting design occurs mostly in

the total volume of traffic. Coefficients have been
determined according to the volume of traffic, but wre
varied for exceptional conditions of heavy or light
traf fic.
The Kansas method requires that all samples be
tested in a saturated condition. Saturation is deemed
desirable in order to obtain a direct comparison for
all types of materials and at the same time obtain a
measure of the strength when the material is in its
most critical condition. Materials such as soils and
stable mixtures seldom fail when dry. Undisturbed
samples of subgrade are obtained and completely sat-
urated in the laboratory by means of a vacuum. This
procedure makes possible a uniform condition through-
out the specimen. For many areas of low rainfall, sat-
uration provides a considerable factor of safety. It
proves to be more of a factor of safety than economical
construction might dictate in areas where field moisture
conditions are not as severe as in the saturated con-
dition imposed on the samples tested. This situation
is conveniently dealt with, however, by using a sat-
uration coefficient based on the average annual rain-
fall for the specific location being considered. This
coefficient is not to be construed as being the percent-
age of saturation. The test conditions and methods
remain constant, hence the test values remain compara-
tive and an economical design is possible. Such proce-
duredoes not differ materially from that used by design-
ers of other types of structures.
The assumed permissible deflection of the surface
is 0.1 inch for design purposes. This value was deter-
mined from measurements of flexible pavements in var-
ious conditions and correlated with other values in the
When a combination of two types of flexible course
is desirable the following formula may be used:
tt W(ts tp x ^j -- --
tt=- thickness of base course or subbase, in
ts = thickness of flexible pavement required
directly on the subgrade, in inches,
tp = thickness of flexible pavement desired in the
combination, in inches,
Cp modulus of deformation of flexible pavement,
psi, and

Ct =modulus of deformation of have course or
subbase, psi.
Considerable research has been conducted to corre-
late test results with service conditions, using the
coefficients for traffic and rainfall. The flexibility of
this method of design makes it adaptable to conditions
found in many places.
Chatractear of the Soil, Group Index Method
The group index method of design utilizes soil
test data. Values of the index are computed by means
of the formula:
Group Index = 0. 2a + 0.00 5 ac + 0. 01 bd
In which:
a = that portion of percentage passing No. 200
sieve greater than 35 and not exceeding
75, expressed as a positive whole number
(I to 40),
b = that portion of percentage passing No. 200
sieve greater than 15 per cent and not ex-
ceeding 55 per cent, expressed as a positive
whole number (I to 40),
c = that portion of the numerical liquid limit
greater than 40 and not exceeding 60, ex-
ptessedas a positive whole number (I to 20),
d = that portion of the numerical plasticity index
greater than 10 and not exceeding 30, ex-
pressed as a positive whole number (to 20).
The formula gives values ranging from a fraction of
I to 20 and is so weighted that the maximum influence
of each of the three variables is in the ratio of 8 for per
cent passing the No. 200 sieve, 4 for liquid limit, and
8 for plasticity index.
Under average conditions of good drainage and
thorough compaction the supporting value of a mate-
rial as subgrade may be assumed as an inverse ratio
to its group index, that is, a group index of 0 indicates
" "good" subgrade and a group index of 20 indicates
" very poor" subgrade material.
The application of the group index in estimating
desirable subbase and total pavement thicknesses has
been described by D. J. Steele (Proceedings, Htighway
Research Board, Vol. 25, 1945). He indicates that for
good subgrades (0-1 G.I.) no subbase is necessary, for

fair subgrades (2-4 G.I.) 4 in., for poor subgrades (5-c,
G.I.) 8 in., and for very poor subgrades (10-2D G.I.)
12 in. These thicknesses of subbase are additive to
those of the surface and base course considered to be
necessary for light, medium and heavy commercial
Detailed Field Surveys, Michigan Method
This method of arriving at the thickness of pave-
ment required for different conditions is based upon
the combined judgment and experience of a staff of
engineer-soil specialists. Field studies rather than
laboratory studies and testing are emphasized in this
design procedure. Detailed soil surveys awe made,
utilizing the pedological profile system of classifica-
tion. Soils engineering data have been compiled for
each of the soil groups, data which provide information
relative to the grade line, elevation of the water table,
ditches, cross section, and required thickness of the
subbase, base, and surface portions of the pavement.
The majority of the methods of design, such as that
of Michigan, considers the environment or condition of
the subgrade soil as well as its character. This is
significant since a true value of the strength of a sub-
grade can be obtained only when the material is its
the condition that will obtain after the paverrent is
laid. Many of the methods that employ strength tests
recognize this fact. For example, while the Colorado
and Wyoming methods strength- eval uate the subgrade
in a soaked condition, the manner in which they con-
sider rainfall, frost and drainage conditions serves in
a sense to adjust the soaked condition to that actually
prevailing. The Kansas method likewise requ 'ires allI
soils to be tested in a saturated condition. However,
the use of a rainfall coefficient in their thickness
formula tends to give proper consideration to the con-
dition of the material as it may obtain after the pave-
ment is built.
One criticism of the group index method of thick-
ness design is that it normally provides for a consider-
ation of the character of the soil only. In other words,
it does not compensate for changes in the conditions
of the soil due to its environment. However, by taking
into account the prevailing climatic conditions, the
thickness of pavement indicated to be necessary by
this method can be adjusted in much the same manner
as in the case of the Colorado, Wyoming or Kansas
methods that make use of soil strength tests.
The information presented in the summary of the

data on design procedures points to the fact that an
ever-increasing appreciation of the importance of
volume of traffic has developed during recent years-
At one time, in designing pavements, little considerii-
tion was paid to the volume and character of the antici-
pated traffic. The principal consideration was the per-
missible wheel load.
The point was made previously that the procedures
of design of the states, particularly those of recent
origin, employing strength tests are empirical in nature.
Thicknesses of pavement determined from their use
for a given set of conditions are in agreement generally
with those found from experience to be adequate. In
fact, many of the methods were developed by studies
and sampling of roads in service at locations where
they had given both good and por performance and the
correlation of test values of the subgrade with the
existing thicknesses of pavement. Such studies resulted
in the development of thickness criteria for various
amounts of traffic and for subgrades having different
bearing strengths or physical properties.
Correlation of Design Methods
The title of this paper "A Comparison of Present
Methods for the Thickness Design of Flexible Pave-
ments" contains the implication that the author will
present data that might serve to compare thicknesses
of pavement arrived at by the use of the many current
methods of design. Very little data of this nature exist.
However, in this connection, the Committee on Flexible
Pavement Design of the Hlighway Research Board re-
cently initiated a new activity which merits mention.
The following is, in part, a reproduction of the
project outline of this study:
Correlation of Flexible Pavement Design Methods
Objective.--To develop information relative
to the thickness of pavement indicated to be nec-
essary by various methods of design for a given
subgrade soil, base course material, and for
different specified patterns of traffic.
Procedure. -Samples of the subgrade soil
and base course material of the [lybln Valley,
Virginia, test pavement, U. S. Bureau of Public
Roads, will be distributed to a number of labora-
tories for design evaluation. Based on these
evaluation data, each laboratory will develop a
design of pavement for three specified patterns
of traffic.

Sobgrade soft*
Cndition (a Condiilon (tb)

Density ...
per cubic foot 100 94 138
Moisture content
per cent of
dry weight 25 305
.Uniform condition to depth of 5 ft.

Traffic Pattern

IType optional
2 Use and type optional

Factual Data -
(A) Condition of materials (after placement of pave-

( Number of axles 12,000 lbe .
( Number of axles 14,000 lb ....
( Number of axles 16,000 Ib, * .
( Number of axles 18,000 lb ....
Pattern (b)
(Passenger cars:
( Number of vehicles .. .. .. .
(Commercial vehicles:
( Number of axles 10,000 lb.
Of o less ,. . .
( Number of axles 12.000 lb...
( Number of axles 14,000 lb .. .
( Number of axles 16,000 lb .. .
( Number of axles 18,000 lb .. .

Base course


(B) Traffic.

Patter (c)

Pattern (a)

Passenger cats:
Number of vehicles ...... 3200
Commercial vehicles:
Number of axles 10,000 lb...
or less ........ .... ... 400
Number of axles 12,000 lb... 160
Number of axles 14,000 lb.... 120
Number of axles 16,000 lb. ... 80
Number of axles 18,000 bo ... 40

Per Lane
Per dayv


Passenger cars:
Number of vehicles .......
Commercial vehicles:
Number of axles 10,000 lb.
or less . a # # e * a *...

LIGHT .. .

(C) Pavement Components.

Per sample submitted
Selected material
Per sample submitted

Surface course
Base course
Subbase course 2

Per sample submitted
Selected material
Per sample submitted

Per sample submitted
Selected material
Per sample submitted

The study has not progressed to the point where
definite conclusions can be drawn, although it is pos-
sible to present a few very broad generalizations.
Is The over-all thicknesses of pavement of
seven of the 12 laboratories that have sub-
mitted their evaluation data vary approximate-
ly within 2 inches of the average. in general,
this is true for the two soil conditions and for
the three patterns of traffic specified in the
project outline.

Participating Laboratories -
State Highway Departments: California, Col-
orado, Kansas, Kentucky, Michigan, Minne-
sota, Missouri, Montana, Ohio, Oregon, Texas,
Virginia, Washington, Wyoming
U. S. Navy Department (Washington, D. C.)
U. S. Engineers (Vicksburg, Mississippi)
Road Research Laboratory (Great Britain)

or evaluation. Some of the methods now in use are not
applicable to the entire range of usable materials,
others do not give dependable test values.
Another phase of the problem in need of systematic
study is that dealing with the effect of highly concen-
trated traffic upon bituminous pavements. The fact
that a low-traffic or low-cost road is apt to be sub-
jected to the same maximum wheel loads as the highest
type of pavement necessitates the development of data
on traffic effects to aid in determining how the thick-
ness of pavement should be varied to accommodate
different traffic intensities. Controlled tests with vari-
ous weights and intensities of moving loads should be
conducted upon experimental pavement sections as well
as upon selected sections of pavement now in service.
Nfore factual information is needed also regarding
the moisture content and density that the subgrade
soil attains after placement of the pavement. It is not
sufficient to design a pavement for some assumed con-
dition of the subgrade because, in many cases, this
factor is equal in importance to that of the proper
evaluation of the character of the material.
Current R*search
A considerable amount of research is currently in
progress in this field. The work of the state highway
departments to develop and improve the design proce-
dures in use is an important type of research. The
systematic observations and records of the performance
of roads built according to specific design procedures
that are now being maintained will add considerably
to our store of knowledge.
There are at least four outstanding researches
currently in progress:
1. Cooperative Project on Structural Design of
Nonrigid Pavements; Highway Research Board,
The Asphalt Institute, and the U. S. Bureau
of Public Roads to,
2. Load Transmission Test for Flexible Paving
and Base Courses; Airport Development
Division, Civil Aeronautics Administration,
Indian apoli a. Indiana 11,
3. Stress Distribution in Soils and Flexible
P avem eat M at eri at a; Flexible Pavement
Branch, Waterways Experiment Station, U. S.
Corps of Engineers, Vicksburg, Mississippi 12.
4. Research in Sweden in the Field of Flexible
Pavements; Swedish State Road Research
Institute, Stockholm, Swedeu13.

2. The over-all average thickness of pavement
reported for traffic pattern (b) (moderate traf-
fic) is 29 per cent greater while that fos pat-
tern (c) (heavy traffic) is 49 per cent greater
than that for traffic pattern (a) (light traffic).
This means that a pavement 8 inches in thick-
ess, designed for light traffic, would be in-
teased to 12 in. for heavy traffic.
3-Six of the 12 laboratories specify the use of
subbase for pavements for all classes of traf-
fic while 8 specify its use for medium and
heavy traffic pavements only.
4. In general, surface treatments or road-mix
surfaces are specifiedfor light traffic, bitu-
minous plant mixes for medium, and bituminous
concrete for heavy traffic. This is much in
accord with accepted practice.
5. The laboratories using the C.B.R., the triaxial,
stabilometer and the group index methods of
flexible pavement design provide for an ad-
justment of pavement thickness in accordance
with traffic and soil conditions. It appears
that the group index method may require further
modification to compensate adequately for
environmental changes in the strength of sub-
grade soils otter the pavement has been placed.
6. The use of standard soil and base course
samples in the correlation of flexible pave-
ment design methods is the reasonable and
logical approach because it minimizes both
the work and cost of testing that any one or-
ganization must do to relate their method of
design or other design methods currently used,
After a more complete analysis of the data obtained
from the work done to date on this study is made, a
final report will be released by the Committee on Flex-
ible Pavement Design. It is anticipated that the study
will be continued and extended to include other types
of subgrade soils and paving materials.
Needed Research
Many phases of the problem of thickness design of
nonrigid pavements are in need of further investigation.
One of the more urgent is the need for the development
of data of a quantitative nature with respect to the
relative ability of various materials, soils, soil aggre-
gate mixtures, graded aggregate mixtures and bitumi-
nous mixtures of all types to support load. Until such
data are available, it will not be possible to use to the
best advantage processed materials or local materials
in the construction of nonrigid pavements. 'What is
needed is the development of improved methods of test

The first of the four researches involves the load
testing in a variety of v6ays of experimental sections
of pavement forming an oval track. The results of this
study should yield definite information on many ,4iases
of the problem. For the particular materials used the
tests should result in the development of quantitative
load-pavement-thickncss data. Also considerable infor.
nation should be obtained relative to the effect of
moving versus standing loads and of the effect of vari.
ous types of traffic upon different thicknesses of pave-
The second of the four investigations is unique in
that it employs a mechanical type of subgrade for study-
ing the ability of typical Paving materials for supporting
and distributing load. Tbis study should throw consid-
erable additional light upon that phase of the probleir.
having to do specifically with the merits of the many
different materials now used in the construction of non-
rigid pavements.
The third research should also add considerably to
our knowledge of the mechanics of load support of
snils and other paving materials. The tests are exe-
cuted in such a manner that it is possible to relate the
results to values computed on a basis of the elastic
The fourth study is also fundamental in character.
The manner of execution of the experiments makes it
possible to compare the results of the load tests with
theoretically computed values. Particular attention is
being paid to the radius of curvature of load deflected
pavement surfaces and use is being made of these data

in the development of design criteria.
The U. S. Department of the Navy, the Department
of Transport, Canada, and a number of the engineering
schools and colleges are also studying various phases
of the problem. The attention being accorded the prob-
lem is a clear indication of the importance now attached
to it.
Of all the factors entering into the problem of thick-
ness design, that of subgrade support is the most im-
portant. Ibis is evident from the fact that certain soils,
as they are found in nature, require only a surfacing
course to form a high-type pavement whereas others
require structures having thicknesses ranging up to
214 ft.
A growing appreciation of the importance of con-
sidering traffic in terms of its volume has developed
during recent years and the majority of the procedures
of design of the state highway departments recognize
this fact. In the United States the design of pavements
is largely the responsibility of the state highway de-
partments even though, on Federal-aid projects, the
methods of design and the recommended designs are
subject to review and approval by the Bureau of Public
Roads. These procedures of the state highway depart-
ments, for the most part, do provide for a logical and
systematic consideration of the factors important in
design. That pavements being built utilizing the de-
scribed procedures are more balanced in diau
formerly is already apparent.


1. Report of Committee on Classification of Materials
for Subgrades and Granular Type Roads, and Dis-
cussion by D. J. Steele, Applications of the Classi-
fication and Group Index in Estimating Desirable
Subbase and Total Pavement Thickness. Proceed-
ings, Highway Research Board. Vol. 25, 1945.
2. Development of a Procedure for the Design of
Flexible Bases, by 1. H. Swanberg and C. C. Han sen.
Proceedings, Highway Research Board, Vol. 26,
3. Design of Flexible Bases, by R. E. Livingston.
Proceedings, Highway Research Board, Vol. 27,
4. Design of Flexible Pavements Using the Triaxial
Compression test, By Kansas State Highway Com-
mission. Highway Research Board, Bulletin No. 8.
19 47.
5. Current Base Design Practices in North Carotina,
by L. D. Hicks, Proceedings, Highway Research
Board, Vol. 26, 1946.
6. Wyoming's Method of Design of Flexible Pavements,
by 1. E. Russell and D. L. Olinger. Proceedings,
Highway Research Board, Vol. 27, 1947.

7. Texas State Highway Soils Laboratory Method of
Designing Flexible Pavements. Highway Research
Board, Bulletin No. 8-R, Nov. 1949.
8. Design of Flexible Surfaces in Michigan, by W. W.
McLaughlin and 0. L. Stokstad. Proceedings, High-
way Research Board, Vol. 26, 1946.
9. Design of Flexible Bases. by E. B. Bail, Proceed-
ings, Highway Research Board, Vol. 27, 1947.
10. A Cooperative Study of Structural Design of Non-
rigid Pavements, by A. C. Benkelman and F. R.
Olmstead. Public Roads, Vol. 25. No. 2, December,
11. Load Transmission Test for Flexible Paving and
Base Courses, by R. C. Herner and W. M. Aldous.
Highway Research Abs-tracts, Highway Research
Board, January, 1950,
12. Stress Distribution In Sells and Flexible Pavement
Materials, by C. R. Foster an$ S. M. Fergus. Re-
search Report 12-F, Highway Research Board, 1951.
13. Research in Sweden in the Field of Flexible Pave-
ments, by Nils Odemark. Highway Research Board,
Highway Research Abstracts, January, 1950.

W. J. Tumrbull
!.. S. tatemays Experiment Station
Vicksburg, Mississippi

The responsibility for the design and construction of
military airfields was assigned to the Corps of Engi-
neers in the latter part of 1940. The urgency for the
construction of these airfields was very great. The
Westergaard method of design for rigid (concrete) pave-
ments seerred to be quite universally used and appear-
ed to have a good background of experience. It was
immediately adopted by the Corps of Engineers for
design of concrete pavements. Preliminary studies
soon indicated to the Corps' engineers that there was
no quick and easy theoretical method to design flexible
pavements. Several empirical methods of design for
flexible pavements were studied, together with theoreti-
cal conceptions. It was readily apparent that the prob-
lem was too complicated for a solution by theoretical
formulas. This left an empirical solution as the only
alternative. After some months of study, the method
of design utilized by the California State Highway
Department for highway pavements was tentatively
The controlling reasons for the adoption of this
method of design were many. Among these reasons
were: (1) the California Bearing Ratio test, commonly
denoted by the letters CBR, had been correlated with
the service behavior of flexible pavements and con-
struction methods and used successfully by the State
of California for a number of years; (2) it could be more
quickly adapted to airfield pavement design for imme-
diate use than any other method; (3) it was thought to
be as reasonable and sound as any of the other methods
investigated; (4) two other states were known to have
methods of a similar nature that had been successful;
(5) the subgrade modulus could be tested with simple
portable equipment either in the laboratory or in the
field; and (6) testing could be done on samples of
soil in the condition representative of the foundation-
moistuure state under most pavements.
Figure 1 shows the CBR relationship. Briefly, the
CBR test is a penetration-type test and in effect fur-
nishes an indication of the shearing strength of a soil
material. As developed it is a useful tool in the design,

evaluation, and construction control of airfield flexible
pavements. The CBR test compares the strength of a
given material when penetrated 0.1 in. (0.2 in. if value
is greater) with a piston, having an end area of 3 sq.
in., with the strength of a standard high-grade crushed-
stone material when penetrated by the same piston to
the same depth. An original series of tests on crushed
stone by the California Highway engineers had shown
that the unit penetration resistance of such material
was 1000 psi at O.1-in. penetration. Therefore, if a
material shows a penetration resistance of 100 psi,
its CBR is 10.
It was early apparent that the original California
procedure needed modification to it the problems faced
by the Corps of Engineers. A comprehensive laboratory
study of the CB3R test and procedure was carried out
at the Waterways Experiment Station from 1942 to 1944.
General studies also were carried out in the field, in-
cluding close observation and study of experience in
acual construction. The principal development of these
studies with respect to the CBR test and design proce-
dures were: ( 1) modification of the Standard Proctor Com-
paction procedure to what is currently known as Modified
Proctor Compaction; (2) substitution of dynamic com-
paction for static compaction; (3) all control compaction
for the CBR test to be accomplished in the 6-in.-dia-
meter mold; (4) if necessary as indicated by the stress-
strain curve, all CBR values should be corrected by
adjusting the zero point of the curve; (5) CBR test
results on samples of soil with large gravel tend to
be erratic, with the only apparent solution being the
performance of a greater number of tests to get a rep-
resentative average; (6) the development of two lab-
oratory test procedures for determining design values;
and (7) the development of the field in-place CBR test
and its use in verifying the design curves.
It will not be possible to present and discuss de-
tails of the CBR test equipment, sample preparation,
or test procedures. There details can be found in (1)
A.S.C.E. Paper No. 2406, a symposium of eleven papers
entitled "Development of CBR Flexible Pavement




PbaR -5 Qor !CV431 f
VERY PoR -5v).5R-AD!

A-16119[E /

Fig. 1: Relationships Determined by California Bearing Ratio Test.


Fig. 2: CBR Laboratory Equipment Used for Penetration and Expansion Tests.

Fig. 3: Field Equipment for CBR Soil Tests


Design Method for Airfields,"' and (2) Waterways Experi-
ment Station Technical Memorandum No. 213-1 entitled
"T7he California Bearing Ratio Test as Applied to the
Design of Flexible Pavements for Airports," July, 1945.
Figure 2 illustrates the CBR laboratory equipment in
position for the penetration and expansion tests. Figure
3 demonstrates the field equipment for testing the CBR
of the soil in place.
It is desired to describe briefly the two laboratory
rest procedures or methods for determining design
CBR values.
Figure 4 demonstrates the minimum, or method 1,
CBR test procedure. The compaction curve is fully

developed for the modified effort, and samples are
prepared for two lesser compactive efforts at modified
optimum moisture. CBR values on three soaked speci-
mens molded at optimum water content for the three
compactive efforts are obtained. Thus, at optimum
moisture the range in CBR values with density is
shown. The variation of the CBR with moisture is not
obtained; consequently, unless very close control of
the moisture in field construction is maintained, con-
siderable variation in strength would result.
Figure 4 also demonstrates the longer CBR test
procedure, or method Z, which consists in developing
compaction curves for the modified compactive effort,
and for two lesser efforts, and determining the CBR

cc 50


a 10







thickness, it is desired to discuss them at least in a
general manner. The original design curves for airplane
loadings were extrapolations of the basic highway
loading curves developed by the California State High-
way Department. These curves have been correlated
with field behavior by measuring the CBR, in place, of
test sections and existing pavements and by observing
the effect of traffic. The curves have been adjusted to
the point where it is considered that, if in-place CBIR
values for a specified base and subgrade are available,
the curves will reflect their behavior under traffic. In
other words, when the field in-place test indicates
underdesign, overdesign, or correct design, by the
present curves, the actual results of pavement behavior
under traffic have generally substantiated the curves.

of each compacted specimen. The data developed by
method 2 will furnish design engineers and field engi-
neers with a visual picture of the possible spread of
CBR rest values with-i both the water content and the
density of the soil. The design engineer thus has a
better means for choosing the design CBR value, and
the field engineer has a better tool for the control of
construction. By building up a background of experience
and familiarity with the soils in a given area, the
design engineer can evaluate the results of the CBR
tests and select a value that he can expect to obtain
in the prototype--one which he can use with confi-
dence. One must be impressed by the implication that
field compaction and moisture control can be very
critical in determining the final strength of the sub-
grade and base course.
Since the design curves (Figure 5) are the end
product of the CBR test in determining base course

This is partculaly true for fine-grained cohesive
soils. Some scattering of data has been experienced
for cohesionless materials, especially for clean sands,
and the design curves are generally considered conserv-
ative for these materials. Extreme accuracy should not
be read into the curves; generally, they could be shift-
ed an amount equvalent to I in. or 2 in. of pavement
thickness and would still agree reasonably welt with
the data.
One criticism of the California method is that the
base thicknesses obtained by this method are too great.
As previously stated, the thicknesses indicated by the
design curves are not excessively conservative. Also,
it is noted that no safety factor of additional thickniess
has been included in the design curves. The criticism
is partly the result of a lack in understanding the
basic design premise with respect to permanent con-
struction as used by the Corps of Engineers. Permanent
construction may be defined as resulting in stable
pavements for continuous use by the designated wheel
load for a long period with only minor maintenance.
Permanent construction is obtained by using a conserv-
ative design which (1) assumes maximum field moisture
in the base and the subgrade, and (2) requires high-
quality upper base and wearing courses. In general,
permanent construction as defined is considerably
more conservative than either highway or airport design
in the years preceding World War IL Ibis is not a criti-
cism of flexible pavements designed by agencies other
than the Corps of Engineers but does indicate a prob-
able difference in the definition or interpretation of
anticipated life. It is realized that many arguments
can be advanced against a pavement design meeting
the requirements for permanent construction as defined
by the Corps of Engineers; however, it has been and
still is, considered feasible to design permanent mili-
tary airports within the continental limits of the United
States by this criterion.
The two most important phases of the CBR test
itself will be discussed briefly. The penetration part
of the CBR test is relatively simple with little chance
for the personal element to affect the results. Experi-
mentation on the mechanics and the procedures in mak-
ing the penetration test, both in the laboratory and in
the field, has indicated that it is reliable and results
can be reproduced reasonably well in the hands of
ordinarily good technicians. In testing clean sands,
it is necessary to surcharge the surrounding area during
the test to obtain CBR values that are indicative of
the behavior of the sands. Difficulties are experienced
in reproducing results on materials such as clay-gravels

0 ...... 2 0...........

60 80

W 30-
Z tj
!C >



which contain large-size particles, because large parti-
cles directly under the piston affect the results. A
large number of tests on these materials and an average
of the results will assist materially in obtaining good
test values. Soil is always a variable material and few
uniform deposits exist. In using the CBR test, it is
necessary, as with any other test, to conduct a suffi-
cient number of tests to obtain good average results.
Admittedly, the penetration test has the weaknesses
of all empirical-type tests. However, it has the follow-
ing advantages:
a. It is supported by a background of practical
b. It is applicable to a wide range of materials;
c. The equipment used in the rest is light and
mobile; and
d. The test can be used in the laboratory and
field for correlation, design, evaluation, and
construction control purposes.
The preparation of the samples for the penetration
rest is the most troublesome in the use of the CBR
method as a design tool. The problem consists in pre-
paring the sample so that it truly represents the condi-
tion of (1) consolidation, (2) moisture content, and
(3) the structure that will be obtained in the prototype.
If a true representation is obtained of these three con-
ditions, then it has been proved that the CBR design
curves can be used with assurance. It is admitted that
an entirely satisfactory laboratory method of preparing
specimens to duplicate the conditions in the prototype
has not been developed. When tempered with judgment,
however, the method can be used to give samples that
will show CBR values which approximate reasonably
well the CBR that can be expected in the prototype.
As with the penetration test, greater trouble is experi-
enced with sands and granular materials than with fine-
grained cohesive soils.
The method of preparing specimens to the condi-
tion of consolidation expected in the Prototype has
consisted of compacting the specimens with a stand-
ardized compactive effort. It was desired to set the
compactive effort high to produce specimens with a
high degree of consolidation, thus permitting thinner
base courses. High compaction also is beneficial if
obtained in the prototype because the compaction in-
creases the CBR of the material and reduces the pos-
sible consolidation hazards under the heavier wheel
loads. Therefore, the Corps of Engineers increased
the standard AASHO compactive effort to such a degree

Ehar the resultant maximum density was believed to be
sufficiently high to meet the requirements necessary
for satisfactory field behavior. The revised test is
commonly called the modified AASHO compaction test.
If the design CBR is based on a highly compacted
sample and this compaction is not obtained in the
prototype, the actual CBR obtained in construction
will be less than the design value and the result will
be a pavement section that is underdesigned. It must
be admitted that the compactive effort: used in the
original CBR rest as developed by the California
Division of Highways and the compactive effort adopted
by the Corps of Engineers produce densities in the
laboratory specimens that are sometimes very difficult
to obtain in the field with the usual construction equip-
ment and methods. This fact is the source of some
In this connection it should be recognized that in
the California method the emphasis has been placed on
design thickness. This is not intentional, but results
from the fact that a special test and a set of design
curves are used for determining the required thickness.
However, it is just as important that the subgrade and
the base be compacted adequately to prevent detri-
mental consolidation. The CBR test does not provide
information with respect to the amount of settlement
to be expected in the pavement surface as a result of
consolidation in the base course and in the subgrade.
It is quite possible to design and construct a pavement
section containing a material compacted to a degree
which may be satisfactory from the standpoint of shear
deformation but which may allow consolidation to take
place to the point that detrimental settlement will be
produced arthe surface. For this reason, it is necessary
to supplement the CBR rest with definite compaction
requirements. The CBR method as used by the Corps
of Engineers requires compaction to definite percent-
ages of the density obtained from laboratory or field
compaction tests. The percentages are varied in accord-
ance with the wheel load and the depth below the sur-
face to the given soil. It is recognized that for some
soils the specified percentages cannot be obtained
practicably. In these cases it is necessary to adjust
the design to obtain a balance between the thickness
requirements and the compaction requirements. Method
2, discussed previously, for preparing and testing CBR
specimens, furnishes information that will permit ready
adjustments of these requirements.
One of the favorable features of the CBR test is
that it can be conducted on a laboratory specimen in
which the moisture content can be adjusted to a given

design value-condition (2) in the problem of preparing
samples to meet prototype conditions. Ibis phase is
simplified, in that for design the condition of mayAmum
field moisture has been assumed to exist. Maximum
field moisture is the maximum moisture content that a
given soil can reach under conditions of heavy rainfall,
high water table, and poor drainage. In general, under
the condition of maximum field moisture, the voids in
the soil, except for sands, are from about 75 to 95 per
cent (by volume) filled with water. Consequently, the
design condition is not as conservative as if it were
based on a completely saturated condition where all
the voids were filled with water. As information on
moisture conditions under pavements was very conflict-
ing, the Corps of Engineers had no other course than
to assume the maximum condition toinsure conservative
To simulate the maximum field moisture, specimens
are soaked in the laboratory in water for four days prior
to the penetration test. In general, four days of soaking
approaches the maximum field moisture, especially
near the surface where the penetration tests are made.
In the prototype the condition of maximum field moisture
may occur: (a) immediately; (b) over a period of years;
or (c) never, in some instances where ground water,
drainage conditions, and soil types are particularly
favorable. In the latter two conditions the CBR method
tends to be criticized because its use results in pave-
ments which are too conservatively designed, The
basis for this criticism in the case of condition (b)
is not believed to be valid, in that surplus strength
is present in the pavement only until the design moisture
condition occurs. However, in the case of condition
(cX the criticism is believed to be valid. Long-range
studies are being conducted to determine the moisture
content that occurs under pavements in arid, semi-arid,
and wet regions.
It is true that, in general, the condition of maximum
field moisture represents the lowest strength of a soil;-
however, when compacted to the degree called for by
the design, the resulting strength may usually be relied
on to fulfill the design requirements. Only in the cases
of highly expansive soils, frost effects, or soils com-
pacted to a much lower degree of density than called
for by the design, are wholly inadequate strengths
The actual use of the CBR test in design and con-
srruction control is presented briefly. Both laboratory
and field tests are discussed in the following para-

In testing of remolded specimens for the California
method of design, all subgrades and base courses have
been grouped into three classes with respect to behavior
during saturation: (1) low plastic soils and base courses
exhibiting little or no swell, (2) swelling soils, and
(3) cohesionless sands. and gravels. The first group
usually includes the silty to clayey sands or gravels,
silts, lean clays, and organic soils. Swelling soils
are the more plastic ones, such as fat organic and in-
otganic clays, and micaceous and distomaceous clays.
Cohesionless soils generally include the clean sands
and gravels. Separate procedures are given for each
of the groups. For each group, the penetration values
are obtained at the design density and moisture content.
Those low plastic soils exhibiting littleorno swell,
and which are Inot appreciably critical to molding mois-
ture content, are prepared by method I for the CBR test
by compacting three specimens at optimum moisture
for 100 per cent modified AASHO density using a dif-
ferent number of blows for each specimen; i.e., at 55,
25, and 10 blows per layer. The specimens, prepared
and tested at three different densities, permit a cont-
plete CBR-density curve at a given moisture, as pre-
viously shown in Figure 4.
For those low plastic soils that are extremely
critical to molding moisture content, method 2 should
be used to develop CBR data that will show the behav-
ior over the entire range of anticipated moisture con-
tents. Each specimen used in the development of the
55-blow compaction curve is soaked and penetrated.
In addition, the complete compaction curves for 25 and
10 blows should be developed and each specimen
soaked and penetrated. The data are plotted as a family
of curves as previously shown in Figure 4. Where no
previous experience exists, it is recommended that the
design CBR be based on a density equal to the value
specified for attainment in the field at a molding mois-
ture content equal to optimum for the modified AASHO
compactive effort. Where previous experience is avail-
able, the design CBR should be based on the density
and molding moisture content anticipated in the field.
The procedure for preparation of CBR specimens
of all swelling soils is the same as for soils of low
plasticity, except that the specimens should be pre-
pared at a water content and density controlled by
swelling tests. The swelling tests are performed on
the samples used in developing the compaction curves.
Method 2 is the most desirable in this case, in that
full cognizance can be taken of the swelling effects
for three compactive efforts. Based on the density

and moisture conditions expected to be obtained in the
field, the proper CBR value can be selected from the
family of curves.
Cohesionless soils, those with a plasticity index
less than 2, which will readily compact under rollers
or traffic to maximum density as specified by the modi-
fied AASHO method, should be prepared by method 1 at
100 per cent modified AASHO maximum density for the
CBR penetration test. Several specimens should be
tested for CBR and the average used for design. Co-
hesionless soils which do nor readily compact should
be prepared by method I at 95 per cent of modified
AASHO maximum density. If soaking does not lower
the CBR of a soil, it may be omitted from further tests
on the same material. However, on occasional cohe-
sionless soils, saturation may be a factor, in which
case soaking should be employed.
The field in-place rest will be used to check the
CBR of the subgrade and base courses during construc-
tion. The in-place tests may be used for design where
the uncompacted condition governs. For control purposes
the in-place test may be used directly after the effects
of soaking have been determined by tests on undis-
turbed samples.
In summary, it is believed that the CBR test and the
design curves have been developed to the point where
they are considered very reliable. It must be admitted

that an entirely satisfactory method has not been de-
veloped for preparing laboratory specimens that will
duplicate prototype conditions for all soils at all times,
under all conditions, and for all areas. In particular,
the Corps of Engineers is making a serious effort to
determine in what general areas and specific localities
the conservatism of design as represented by the four-
day soaking period need not be followed. However,
with due consideration of the limitations just mentioned,
considerable progress has been made in the preparation
of specimens, and the rest procedures and methods of
data analysis now proposed give the design engineer
very good information on the CBR that he can expect
to obtain in the prototype. It is not considered amiss
to point out that the difficulties encountered in pre-
paring specimens for the CBR rest would also be
encountered in any other type rest.
In conclusion, it is desired to state chat the Corps
of Engineers believes that the empirical California
method, as presently developed and when properly
applied, is reasonable and satisfactory for the design
of flexible military airport pavements. This statement
does not imply char a more rational method of design
employing actual strength characteristics of the soil
is not desirable. It is a matter of record that the Corps
has several long-range research and fact-finding studies
under way from which it is hoped that a completely
rational design procedure may be developed.


8 in. of base course under average Minnesota traffic.
As experience and data were accumulated a basis
for selection of thickness was developed, probably
better called design by "trial and error." Unfortunately,
however, for our design standards, the state experienced
during that time a cycle of years of below-normal rain-
fall and in some areas severe drought. Following the
return of more normal rainfall it became apparent that
flexible pavements which had been performing satis-
factorily began to show distress apparently from two
causes, inadequate thickness and too high a content
of too plastic a binder soil. Another factor, of course,
was the accumulating number of load repetitions. Pro-
gressive deterioration made necessary extensive re-
pairs on some of the projects and, generally, main-
tenance of flexible pavements became a major opera-
Th* 1942-45 Surv*y
On the basis of the aoove it became apparent that
a detailed study of the whole problem was imperative.
Information as to the causes of failure was much needed
and the development of data that would permit a more
logical design of base thickness was desired. In view
of these needs a rather comprehensive program of field
and laboratory investigation was prepared in 1942 with
the following general objectives in mind-
1) To establish procedures for the construction
and improvement of subgrades and the con-
struction of subbases on plastic soils.
(2) To develop a method for determining the
required thickness of bases for fleitible pave-
in ents.
(3) TO improve our specifications covering the
design and construction of soil-stabilized
gravel bases.
The accomplishment of those objectives involves
a large amount of field and laboratory investigation and
the work is still in progress. The study was set up to
obtain data enumerated briefly as follows:

Since the late 1930's Ntinnesota has built a sub-
stantial mileage of flexible pavements. During the 1948-
1950 biennium there were constructed 994 miles of
aggregate bases all of which were covered with bitu-
minous surfacing.
A flexible pavement is defined in Current Road
Problems, No. 8-R of the Highway Research Board, as
a system of superimposed layers of selected and pro-
cessed materials, the primary function of which is to
distribute the concentrated loads to the supporting suo-
grade so that the reduced pressure transmitted will not
exceed the supporting capacity of the subgrade. It is
further stated that "the flexible pavement structure is
designed primarily to develop maximum subgrade sup-
port through flexibility." Somewhat the same thought
was expressed by McAdam in 1823 when he said: "The
roads can never be tendered thus perfectly secure un-
til the following principles be fully understood, ad-
mitted and acted upon, namely that it is the native
soil which really supports the weight of traffic."
Under this concept of design the problem is resolved
into a determination of the supporting capacity of the
subgrade, the feasibility of improvement of that sup-
porting capacity and the thickness of base course re-
quired to transmit the loads to the subgrade in such
magnitude that it is not overstressed. Involved also is
the matter of quality of the base and sub-base material
and the bituminous surfacing. The problem is a com-
plex one and many approaches have been made toward
the solution of it.
Bituminous surfacing on existing subgrades includ-
ing both the granular and plastic types was begun about
1924 in our state. It was not until 1934 that construction
of stabilized gravel bases was begun and then only on
an experimental basis. Little information or experience
were available to serve as criteria for design. As an
example, an experimental project was built in 1936 on
one of our heavy plastic soils having sections ranging
in base course thicknesses from 2 to 8 in. Experience
has since taught us that such soils require not less than

John H. Swomberg
Engineer of Materials & Research
Minnesota Highttuy Department
St. Paul, Minn.

A detailed survey of the project covering the
existing condition of surface and base courses;
A detrmination of the apparent causes of the
Thickness determinations of the several
Cross-section of road-bed, ditches and back-
Grade-line, height of water table, ctc.;
Densities of tile several courses;
Samples for moisture determination and the
tests usually made on soil materials;
Samples for stability or beating tests in the
I abe ra tory.
Field Investigation
The field work was begun in the summer of 1942
and was continued through 1945. The extent of these
yearly surveys was as follows:
1942 :19 projects .. ... '72 test points
19 43 :40 p roj ects ..189 test points
1944 :10 projects .. 60 test points
1945 :12 projects .. .. 109 test points
The work was conducted by personnel from the
central laboratory but the district soils engineers were
enlisted to assist on those projects in their districts
because of their more intimate knowledge of local soil
conditions and construction history.
Most of the 1942 work was done on projects having
considerable areas of failure and which had been graded
without specified soil selection or density requirements.
This survey covered projects having a variety of sub-
grade soils and a rather wide range of base thickness.
The data obtained in the field and laboratory indicated
a relationship between base thickness and bearing value
but it was apparent that this survey had not included
sufficient tests on good areas or a sufficient range in
base depths.
Observations made during the 1942 survey were of
considerable value in establishing the procedure for
later work. Although a number of failures were asso-
ciated with concentrations of heavy binder soil it was
evident that a large percentage of the failures resulted
from plastic deformation of the subgrade because of
inadequate base thickness. An obvious important factor
was the volume of heavy trucks. The advantages ac-
cruing from soil selection and proper ,qjhgrade compac-
tion were likewise evident-

Tlhe 1942 work indicated the need for additional
comprehensive field investigation to accumulate suf-
ficient data concerning the actual condition of the sub-
grades so that a correlation between field conditions
and laboratory bearing tests might be established.
Projects were selected for subsequent years to include
soils representative of most types of soils found in
*Minnesota. More projects were included which had been
graded since the adoption of specifications requiring
soil selection and sheeps-foot roller compaction. Pro-
jects carrying both light and heavy traffic and projects
involving a wider range of base thickness were selected.
Analysis of the data from the field surveys and the
routine labratory tests led to the following conclusions
concerning subgrade conditions:
1. There is a relationship between the proper-
ties of the soil and the required base depth.
2. Subgrade densities averaged 97 per cent of
the m aximum d en sity as determined by
AASHO. Method T99. The range in den-
sitic 5 was uot wide since at wore than 95
per cent of the test points the subgrade den-
sities were between 90 and 105 per cent of
maximum and at about 60 per cent of the
maximum, test points densities from 95 to 100
per cent of maximum were found.
3. The maximum amount of moisture found in
the subgrade is less than that represented by
the zero air voids curv6 and the degree of
saturation varies with the textural class of
the soil.
4. Our tests indicated that the maximum degree
of saturation found in the subgrade was less
than 85 per cent for soils with plastic limits
of 15 or less; less than 90 per cent for soils
with plastic limits of from 15 to 20 and less
than 95 per cent for those soils having plas-
tic limits of 25 or greater. The densities of
the soils from which these samples were taken
ranged from 90 to 103 per cent of AASHO
maximum density. These saturation maximums
are probably exceeded in places after un-
usual conditions develop such as frost boils,
but it was felt that they could be safely
taken as maximum degrees of saturation for
purposes of design.
5. The bearing value of a soil is dependent
upon itsmoisute content.
6. As a general rule, the moisture content of a
subgrade increases slightly from the center
line toward the edges of the reat-
7. On the basis of field tests it was concluded

that the moiste content of granular bases
rarely exceeded 90 pet cent of optimum
moisture. In 1945 the moisture content of the
bases showed an average 0.8 percentage
points higher in the spring than in the summer.
8. Out data indicated no substantial difference
in density of bases and subgrades because
of seasonal fluctuation.
9. The maximum moisture content of the upper
6 in. of the subgrade in the spring of 1945
exceeded that found in the summer by an
average of slightly move than 2 percentage
From these observations it was believed that the
moisture-density relationships in subgrades and bases
are predictable within limits suitable for design pur-
Laboratory Investigation
The laboratory study consisted of two phases,
namely, the usual routine testing of the field samples
and the determination of a suitable bearing test which
would yield information that could be correlated with
the findings of the field surveys.
It was our desire to develop or adopt a relatively
simple test to evaluate the bearing capacity of sub-
grade soils and base materials. The California Bearing
test was selected for investigation in view of its long
and apparently satisfactory use by the California Di-
vision of Highways and its more recent adoption by the
Corps of Engineers.
During the winter of 1942-43 a group of 26 subsoils
and 18 granular base materials were tested by means
of the California Bearing test and some modifications
thereof. included in these tests were soils classified
texturally as sandy loam, fine sandy loam, loam, silt
loam, clay loam, silty clay loam, silty clay and clay.
An analysis of the data obtained from these tests in-
dicated the following which appeared to be significant.
1. Densities obtained by the California com-
paction method were considerably higher
than those found by use in the field ad the
Optimum moisture was much lower than field
moisturesof the some soils.
2. The bearing ratio& obtained by the standard
procedure were low, usually less tha 3.
3. The swell of all of the soils was high and,
after soaskins the moisture content of the top

1 in. of the specimen, was usually much in
excess of that found in the field.
4. It was found that by increasing the surcharge
during the soaking period, the swell reduced
and the beaing value usually increased.
5. Specim ens m olded at moi sture con tentsa abo ve
the California optimum,to densities less than
the California maximum, po ssessed increased
beating value and reduced swell.
6. The test showed that there is considerable
difference in the beating values of stabilized
gravel mixes. It was found that the swell
of the gravel specimens was negligible.
Variations in the moisture content, density of spec-
imen and weight of surcharge were also introduced with
interesting results. Data obtained indicated that the
bearing values over a considerable range in moisture
and density will vary much more with some soils than
As our laboratory work progressed it appeared evi-
dent that if laboratory bearing values and field data
were to be correlated it would be necessary to make
the test on specimens having moisture contents and
densities comparable to those found to exist in the
field. The problem was approached on the basis of
determining a procedure for the preparation and test-
ing of specimens having moisture and densities ap-
proximating field conditions.
Let us review the conditions of moisture and den-
sity found to exist in the roadbed during the field sur-
veys and which are important factors in the selection
of a test procedure.
1. It was concluded that the moisture-density
relationship in subgrades and bases was
predictable within limits suitable for design
purpo sea.
2- The moisture content of plastic subgrade
soils, when expressed as a per cent of satura-
tion, had a relation to the plastic limit which
would not be exceeded under the usual con-
ditions. This was an important factor in the
selection of the moisture content at which to
measure the beating value of the soils.
3. The densities of the sub, fade soils varied
within a reasonably narrow range and aver-
aged 97 pet cent of maximum density.
4. The moisture content of granular bases and
subbases rarely exceeded 90 per cent of
optimum moisture and their densities were at

moisture content, as determined after the bearing test
had been completed, varied considerably from the
"design moisture" and, consequently, the bearing value
was probably in error. To overcome this difficulty in
the case of plastic soils, three specimens are molded
as follows:
Specimen A at maximum density and optimum
Specimen B at 97 per cent maximum density
and at the "design moisture."
Specirn en C at 97 per cent of maximum density
and at a moisture content 0.5 of a percentage
point above the "design moisture" to insure a
bracketing ol the theoretical "design moisture."
The bearing values of the three specimens areplot-
red against their actual moisture contents, as deter-
mined by test, to produce a curve from which the bear-
ing value of the soil is determined at the selected
"design moisture." This method has been very satis-
factory if specimens 8 and C have moisture contents
reasonably close to the "design moisture."
In the California Bearing Test procedure as des-
cribcd ill thr 1938 Proceedings of the Highway Research
Board the bearing ratio at 0.1 in. penetration was used
as a measure of the bearing value of the material. fhis
value was also used by us in our first work with this
test but after a study of a considerable number of load-
deformation curves for various types of material it
appeared that the value at 0.2-in. deformation better
differentiated between different soils and better repre-
sented the relative bearing characteristics of the vari-
ous materials. We would like to point out that we do
not believe that 0.2-in. penetration is necessarily the
critical deformation on the road, In any case the bear-
ing values are relative and have significance only as
applied to our tentative design curve.
A number of other modifications of the California
Bearing test have been investigated. On the basis of
the sritclies since 1942 the following test procedure
has been adopted:
Preparation of Samples:
Plastic soils are dried and pulverized to grain
size. All rock in stony soils is crushed to pass a 3/4-in.
sieve and returned to thr- sample. Scones larger than
1/4-in. are rejected from soils containing only an oc-
casional stone.
Granular materials are crushed so that the entire
sample will pass a 3/4-in. sieve.

approximately maximum density.
The above assumptions form the basis for the Modi-
fied CBR test as used by Minnesota.
on the basis of a series of exploratory tests it was
indicated that specimens molded to a predetermined
moisture content and density and tested immediately
would yield bearing values in general agreement with
those of similar specimens which had acquired their
moisture by capillary soaking. By this modification
the long capillary soaking period required for plastic
soils could be eliminated.
It was also apparent that for plastic soils, minor
variations in density did not greatly affect the bearing
values, but small variations in moisture content changed
the bearing values considerably. The granular mate-
rials appear to differ in this respect showing greater
variation in bearing values because of change in den-
sity than for change in moisture content.
With this modification in the procedure it was evi-
dent that the moisture content at which the bearing
value was to be determined must be selected in ac-
cordance with the relationship between the plastic
limit and the per cent saturation as found in the field.
This selected moisture content or as we have desig-
nated it, the "design moisture," is determined as
Soils having plastic limits of 15 or less are de-
signed at 85 per cent of saturation.
Soils with plastic limits of 25 or more are designed
at 95 per cent saturation.
For soils with plastic limits between 15 and 25 the
moisture content is determined by straight proportion.
Stated simply, the "design moisture" equals 70 plus
the plastic limit with a minimum of 85 per cent and a
maximum of 95 per cent. The formula for the moisture
content at complete saturation is
S = (62.4 I ) 100
( D G)
where S = the moisture content in pet cent at complete
satu ration
D = density to which the specimen is compacted
G = specific gravity of the soil
In attempting to mold specimens to this moisture
content, it was found that, in many cases, the actual

Routine laboratory tests of grading, plasticity index,
specific gravity and AASIJO moisture-density test are
performed on every sample.
Molding Specimens:
Three specimens are molded for the bearing test
for each sample.
In the case of granular materials all three speci-
mens are molded at optimum moisture and Arignum
density. The specimens are then subjected to capillary
soaking for four days through a perforated base plate.
This soaking period is used for granular base materials
to simulate to a degree temporary severe moisture con-
ditions caused by high water table or unusual snow
conditions. It also provides a period during which these
materials may reach their normal capillary capacity for
water which is quite variable for granular materials.
For plastic soils, three specimens are molded as
previously described; one at optimum moisture and maxi-
mum density, one at the "design moisture" content
and 97 per cent maximum density and the third at 97
per cent maximum density and at the "design moisture"
content plus 0.5. Water is added to the dry, pulverized
soil with a pressure spray gun until the proper moisture
content is reached. The moist soil is then placed in a
moist-air cabinet for a period of 16 to 2D hours prior
to molding to permit more thorough disperson of the
added moisture.
The procedure for the molding of the specimens is
the same for all materials. The computed weight of
material required to produce a specimen 4 in. high in
a 6-in. diameter mold and having the required density
is prodded lightly in the mold in two layers. The com-
paction is accomplished in a compression machine
applying a static load of requisite magnitude to pro-
vide a specimen 4 in. in height. Preliminary compac-
tion is accomplished with plungers in both ends of the
mold, using a removable split ring to support the mold.
Load is applied at a speed of 0.05 in. per minute until
the specimen is compacted to approximately the de-
sired 4 in. height. The load is released and a base
plate attached to the mold. Compression is again ap-
plied, from the top and continued until the specimen is
exactly 4 in. in height after release of the load. An
Ames dial is utilized for the height measurement
The Bearing Tests:
The method of making the bearing test is similar
to the standard California procedure. The bearing test
consists of penetrating the compacted specimen with a

3-s%-in. cylindrical piston. The piston is seated by
applying a load of 10 lb. and the dial reading at this
load taken as the zero penetration. The head of the
testing machine is operated at a speed of 0.05 in. per
minute throughout the test. The load is recorded at
penetrations of 0.025 in., 0.050 in., 0.075 in., 0.1 in.,
0.2 in., 0.3 in., 0.4 in., and 0.5 in. The unit load in
pounds per square in. at 0.2 in. penetration is taken as
the bearing value of the specimen.
Surcharge weights are used on specimens of granu-
lar material to simulate the confinement of these mate-
rials in the roadbed by overlying layers. 0.29 p.s.i.
surcharges ring is used on upper base materials, and a
0.55 p.s.i. surcharge ring is used on subbase materials.
These weights are placed on the specimens immediately
after molding and remain thereon until after the bearing
test is completed. No surcharge is used on plastic soils
as it was found that surcharge has little or no effect
on the bearing values of such material&
Immediately after the bearing test, moisture samples
are taken from the specimens to determine the actual
moisture content at the time of test.
Bearing Values:
Bearing values are assigned to a soil following
analysis of the results of the bearing tests on the
three specimens of the soil sample.
For granular materials an average of all three re-
sults is taken to represent the bearing of the material
unless one value is considerably different than the other
two in which case it is discarded.
For plastic soils the bearing curve is plotted using
the bearing value and moisture content of each speci-
men tested. The bearing value of the soil is selected
from this curve at the "design moisture" content.
The Modified CBR Test as a Design Criteria:
As a part of the laboratory investigation, bearing
tests were made on samples of subgrade soils which
had been taken during the field surveys. Each bearing
value was plotted in relation to the combined thick.
ness of base and surface at the corresponding test
point. By use of distinctive symbols representing fail.
ure and non-failure, it was found that a curve could be
drawn in such a position as to indicate minimum thick-
nesses above which practically no failures occurred.
By projecting this curve on a semi-log scale, the ten-
tative design curve was obtained. The total thickness
of reinforcing layers required above a material having

any given bearing value may be readily determined
from this curve.
For the upper base layer a modification of the re-
quirements of the design curve is permitted. From the
curve, it ib iudic;ated that base nuaterialb having bcal-
ing values of 1100 are required immediately beneath
a 2 in. bituminous surface. From many tests it was
found that only crushed rock and exceptionally well-
graded gravels have bearing values over 1000. On a
basis of experience to date, minimum hearing values
have been established for upper base materials at 700
for light to medium traffic and 800 for heavy traffic.
!'he above described test procedure and tentative
design curve were more of less formally adopted in
1945 as a basis for designing flexible pavements in
Minnesota and have been used since that time with
practically no modification.
In Minnesota. preliminary soil surveys are usually
made after the location survey has been completed and
prior to preparation of the grading plans. Samples of the
typical soils available within the roadway limits or
from borrow pits are submitted to the laboratory for
resting. T'he results of the bearing tests are used to
determine which soils should be placed in the upper
portion of the subgrade, and the necessary total base
thickness. Knowing die bearitig dlmacteistics of the
available soils, provision can be made in the plans for
the most effective use of these soils in the grading
Prior to the preparation of plans for base construc-
tion projects, field condition surveys are made and
samples of granular materials which may be used for
the base and subbase are submitted to die laboratory
for bearing tests. From these tests are determined the
thicknesses of component layers of base and subbase;
the quality of materials from various sources; the ne-
cessity for stabilization; and possibly the most de-
sirable percentage of binder soil to use in the stabi-
li zed mixture.
As an example of our design method, a subgrade
soil having a bearing value of 40 would, from our ten-
tative design curve, require a total thickness of 1214
in. o f subbase, base, and bituminous surfacing. As-
saiming a source of sand is available on the project
having a bearing value of 350, it may ne used as sub.
base to within 5!4 in. of the road surface. If a 11'2 in.
Dituminous surface is to be placed, a 4-in. layer of
upper base having a bearing value of over 700 would be
required to complete the design.

Experience with the Use of the Mvodified CBR
Since 1945 the bearing test has been so generally
used as a criterion of design that it has ceased to be
considered as of an experimental nature and has ob-
tnined the recognition of a standard routine test and
design procedure. W'e believe that it can be stated that
the results of its use have been generally satisfactory.
The highways that have been designed by this yard-
stick have performed well up to this time although it
is perhaps too early to judge its merits on such per-
In our opinion considerable work needs to be done
to make it of greater value. One phase, of which we
have hardly scratched the surface is the correlation of
load repetitions with our present design procedure.
We need to expand on our field surveys of flexible
pavement performance to broaden the base of our de-
sign criteria. Because of the lack of personnel since
the war, continued research both in the field and lab-
oratory has been much curtailed and desirable further
progress in the application of the test to our design
problems has not been accomplished.
4 ork needs to be done to eliminate apparent short-
comings in out present test procedure and steps are
being taken in this direction. Briefly some of the prob-
lems we have encountered are as follows:
Accurate moisture-density determinations are es-
sential to evaluate properly granular materials and some
difficulty has been encountered in this regard. Only
recently we have modified our method of making mois-
ture determinations on coarse granular materials for
greater accuracy.
The consistency of bearing test results on stoney
materials is not as good as desired. It appears that
Y4in. rocks which are located under the plunger have a
tendency to influence the bearing value of the material
out of proportion to the actual importance of these
particles in the material.
The importance of the confinement of materials in
the roadbed may not be sufficiently realized or pro-
vided for by the use of the surcharge weights.
The group of soils ranging from loamy sands to
light sandy loans have been tested by both the pro-
cedures for plastic and granular materials and the re-
sults are quite dissimilar.
Fhe procedures for compacting and molding the

specimens deserves further investigation to determine
whether uniform densities are being obtained du-ough-
out the specimen.
Pulverization of plastic soils is not entirely sais-
factory. Evidence has been found that certain soils
had been over-pulverizedl to the extent that the charac-
teristics of the soil had been changed.
Needed Rosesoch
To solve the problems referred to above a con-
siderable amount of laboratory research will be re-
quired. A field investigation has been resmed this
spring to obtin additional information on the seasonal
fluctuations of moisture and density in existing road-

beds. As time permits we hope to obtain more field
tests at failures caused by insufficient base thick-
ness or low quality base materials as a check on the
tentative design curve.
Work is needed on the feasibility of the addition
of additives such as bituminous materials, cement and
time on the properties of boiderline granular materials.
The time is approaching when more and more inferior
local materials must be utilized in our highway con-
struction to give the people of our state the most for
their highway tax dollar. Perhaps the California Bear-
ing test together with such tests as freezing and thaw-
ing may provide a means for evaluating the performance
of such materials. Here, beyond doubt, is a fertile field
for further research.

Alfred A. McKethoan
Chainilan, State Road Department
Tl'lah~assee, Florida

Florida highways are big business. Last year I
told you of some of the problems we were facing in
meeting the needs of highway development in the State.
But, I aun happy to say tonight that we have, waiin the
past year. _e: ~e co e m an Ci }s ed.
all know that Florida is the Cfastest grow ig_ state in
the southeast. W:{e all know that the tremendous traffic
load pouring into the State throughout the year is de-
manding better roads for our motoring public. Motor
vehicle registration f(r a 0 s ctprdto 194{9
showed a gain of over 1uo,000. Gasoline COMSUMp-tion
increased coreo~n~ b) -90000g!o
compared to 690,000,000 in 1949. Thle volume of tourist
business in the last few years has passed even the
most optimistic forecasts. Florida is seeing the great-
est growth in its history-a growth that is demanding
more and better highways.
The 1950 budget was the largest in the history
of the Stare Road Department. The 1951 budget is even
greater. Last year we budgeted $79,000,000 for new
construction on the primary and secondary road sys-
tems, for maintenance on both, and for planning, lease
payments, administration and other overhead. Last
year, the length of projects underway or completed,
including carry-overs, was 1,820.8 miles. During the
same period 28,212 ft. of bridges were constructed
or let to contract. And as of December 31, 1950, the
secondary road projects included in that budget for
the year were more than 90 per cent complete or in
progress. Out of a budgeted amount of $12,915,880 for
secondary road projects, work costing $11,670,230 was
under way or advertised by chat date. The total primary
and secondary projects budgeted in 1950 was 580. By
December 31, 501 had been let to contract.
The tempo Of our highway building has increased
materially and is up 65 per cent over highway construc-
tion activity of 1949. Since 1949 Florida has risen from
twenty-third place to eighth place in the Nation in
dollars spent for highway construction. You have heard
*Condensed from a speech given by (Itairmn, McKethan at
the annual conference dinner.

about the progress that has been made on the Jackson-
ville-Duval Expressway, the Pinellas-Manatee lBridge,
the Ft. Lauderdale Survey, and the Miami Traffic Sur-
vey. "Tne State Road Department is constructing, re-
i~biia~ng ndpanning ftrFord' future with
high ways. I'his progressive movement is unlike an),
other that 1has been initiated in road building in our
Our great secondary read prograni with which you
are all familiar, is perhaps the best step in furthering
the cono) of t.-ir ae. For it s a f a-reaching pro-
gram into the rural areas of Florida. It is providing
farm-to-iiarke roads for thousands of our farmers, it
is providing better routes for our school buses and
safety for the thousands of children who ride these
buses. We have earnestly and sincerely endeavored to
assist in reaching the rural areas of this State, and to
provide them with adequate transportation facilities.
All of the plans, surveys, studies were once just
on the planning boards. They have become a reality
only through the efforts of many: a cooperative and
road-minded Governor, a cooperative and road-minded
legislature, a cooperative and road-minded group of
county commissioners, the current administration of
the State Road Department, the far-sighted citizens of
this great State. and the taxpayer who contributes his
share of the gasoline tax to make all of this possible.
All of this is part of a team that brings dreams into
It is this same teamwork that brings together a
group such as this one. All of you here are striving to
bring about better and safer highways for the people
of Florida and the Nation. Your research, your ideas,
and your dreams are assimilated here in order to give
to one another the benefit of your prospective branches
of highway development. So we can see that these
things did not just happen.
During the month of January of the current year,
we heard from every county in Florida at scheduled
hearings in Tallahassee. We listened to their desires

and wishes on their secondary road program, and those
desires were out instructions. The 1951 budget includes
$21,669,400 for our secondary program. It includes
$67,158,360 for our primary system. For the first time
in the history of the road department finances are
provided for turnouts on the highway to assist and
provide for a safer delivery of the mail by the rural
mail carrier. These turnouts will eliminate the now
existing hazard of the rural mail carrier having to stop
his automobile on the highway. We have earmarked
$1,583,891 to invest on projects for educational insti-
tutions, state parks, and farmer markets.
During the remainder of the next two years, we
will see the tempo of our highway construction main-
tained, if not actually increased, providing the require-
ments of defense or a general war do not interfere by
making road and bridge construction materials shorter
than they are at present. In figuring new highway pro-
grams we must keep in mind the thought that the Feder-
al government might curtail or restrict highway con-
struction; or that gasoline might be rationed as it was
in the last war and thereby strip us of a substantial
measure of our financing. With that precautionary plan-
ning uppermost, we this year adopted a tentative budget
totaling S141,000,000. Thus, it would seem that we
intend to almost double the highway construction pro-

gram for 195Z However, such is not the case. We in-
tend to increase highway construction during the current
year. But we could not construct $141,000,000 worth
of roads in any one yew at the present rate of revenue
productivity, except at heavy deficit and by mortgaging
the ensuing yew's program.
We have made great strides in the last two and
one-half years. There is a lot more that we would like
to do, and will do. We welcome suggestions in our road-
program. Your road board sincerely hopes that you will
pass any suggestions that you might have on to us in
a desire to make this road program your program and
the people's program. We in the State Road Department
are happy to participate in this conference because we
benefit from your recommendations and suggestions.
It is, to the people and to them only that we look for
instructions. Our instructions we their'wishes.
We are most appreciative of the fine, splendid
cooperation that has been given to the department at
all times by the various groups of public officials
throughout the State. We are deeply appreciative of the
confidence that the people of Florida have expressed
in our road board and we will do all within our power
to continue to merit that confidence.


Paul D. Moon
Ilyster Company
Peoria, /11.

In discussing the newer types of compaction equip.
ment, it might be advisable to classify them according
to the physical action that takes place between the
compaction too] and the material being acted upon.
These physical factors which result in compaction
action on material consist of:
1. Weight or compression
2. Kneading or tamping action
3. Vibration
4. Impact
Some or all of these factors are present in the comp2,F-
tion rollers under discussion here today.
The Bros Roller is a four wheel pneumatic tire
roller manufactured in sizes which may be weighted
from 30 to 60 tons. Each set: of two wheels are mounted
on a tandem or walking beam type of axle. This mount-
ing allows e2cb wheel to follow the contour of the fill,
and thus eliminate the possibility of bridging over
soft or low spots.
The Porter Pneumatic Tire Roller is also a four
wheel roller. However, each wheel is individually
suspended from the main roller frame. This gives the
roller the so-called "wobble- wheel" action on the fill.
This roller is manufactured in sizes which may be
weighted from 30 to 60 tons. The large 80 Eon Porter
roller is a two wheel pneumatic tire roller. This is
primarily a test roller which is used for testing the
bearing capacity of bases and surfaces of airport land-
ing strips.
The McKesson Roller is a four wheel pneumatic
tire roller. Each wheel is individually suspended from
the roller frame, and each wheel also has its own in-
dividual counter-weight box. This feature insures the
same amount of weight applied on each wheel regard-
less of the contour of the fill.
These three pneumatic tire rollers, and others of
similar construction depend primarily upon weight or
compression for their compaction action. There are

traces of kneading action and
amount is debatable. They do
to the top surface of each lift.

some vibration, but the
obtain density right up

The Cedar Rapids Vibrator Roller depends upon a
combination of vibration and weight to compact mate-
rial. Upon its frame is mounted a gasoline engine which
is connected by eccentric drive to a sliding weight.
The rapid oscillaEion of this weight sets up tremendous
vibration which is transmitted to the material being
compacted through pneumatic tires. This roller is made
in two sizes. The small one is mounted on tvo pneu-
matic tires, and the large one on two sets of dual pneu-
matic tires. The vibrating action created by this roller
is extremely penetrating and very efficient.
The Hyster Grid Roller consists of two 5% ft. dia-
meter wheels or rolls each 32 in. across which are
attached to a steel frame for mwing. Each wheel or
roll is made of ten replaceable grid sections of heavy
heat-treaEed alloy steel. These grid segments are
bolted onto circular side plates. The grid segments
have the appearance of greatly magnified fly screen
made by interlacing 1! in. round steel bars with the
openings between adjacent bars 3% in. square.
A set of cleaners are provided for cleaning the grid
openings -necessary in some types of soil such as
clay or heavy loam, The cleaning rollers are suspended
inside the grid rolls from the main axle shaft, and are
balanced at an angle of 45 degrees by a set of heavy
counterweights. These cleaners have rough gear-shaped
teeth which mesh with the grid openings from the in-
side. Their action is much the same as two internal
gears running in mesh.
T"he Grid Roller was developed originally for the
purpose of pressing loose oversized rocks below the
surface of an unpaved airport runway. On this operation
unusual compaction was noted, and it was determined
that the Grid Roller compacted fill layers thoroughly
from bottom to top. Oversized scones were either crush-
ed or depressed into the subgrade.

These results are accounted for by the design of
the grid surface. At each point where the rounded 1%
in. bars overlap, a high pressure point exists. The
pressure exerted downward is in the form of a pyramid
or cone which extends to the bottan of the loose mate-
rial. A heavy concentration of pressure exists in the
bottom of the lift where the bases of these cones over-
The Y% in. grid openings provide low pressure or
escape areas for the material. Alternate high and low
pressure areas cause a kneading movement of the
material so that individual aggregate particles seek
their most advantageous position. Also, this movement
of material is localized, and mass lateral movement
is avoided.
As successive passes are made over fill material,
voids become filled, the material becomes more dense,
and compaction is finally obtained. The number of
passes required to produce maximum density will vary
with the different classifications of material being
compacted. The Grid Roller has obtained maximum
density in as few as four passes.
The Grid Roller was designed for high speed com-
paction. And it has been found that high speed towing
(6 to 8 miles per hour) brings two other compaction
factors into play--impact and vibration. Because of
the bearing surface presented by the grids, there is
comparatively little actual penetration into the mate-
rial--no more than 3 in. in a loose lift. After the first
pass over the material the grid roller has left it with
a waffle-like surface which will allow the towing unit
to travel at higher speeds. Higher speeds bring the
grid bars into contact with the material with greater
impact, and these fast succession of impacts cause
vibration in the material. For example, it has been
noted that on an 8 in. loose lift of sandy loam the mate-

trial would vibrate approximately 3 ft. in front of, be-
hind, and on either side of the roller when towed at
6 mph. With each successive pass, this area of vibra-
tion would decrease until it was within 6 to 8 in. of
either side. At this point, maximum density had been
The Grid Roller weighs 10,000 lb. The cleaners and
their counterweight weigh an additional 5,000 lb.
Counterweight boxes are available which allow the
roller to be weighted to an over-all gross of 30,000 lb.
The crushing and impact action of the high pressure
points of the Grid Roller will reduce sand rock, shale,
slag, iron ore, caliche, and decomposed limerick to
small aggregate size for use in road building. This
roller has also been used successfully in coal stockpil-
ing to increase density and prevent spontaneous com-
It is also being used very extensively for salvaging
bituminous or black-top road surface. The old material
is satisfied and grid rolled. The Grid Roller fractures
the large chunks and gradually reduces them to the
size of the original aggregate. The material is stock-
piled at one side of the road and the subgrade reworked
and compacted with the roller. The salvaged material
is then road-mixed or respread and shot and flat-rolled.
The Grid Roller depends upon all four of the physi-
cal factors in obtaining density--weight or compres-
sion, kneading action, impact and vibration.
It is presumed by most roller manufacturers that
the ultimate in a compaction tool is the highest den-
sity with the fewest passes at the greatest possible
-speed. It has long been the contractors' desire to
complete the rubber-tire cycle from borrow pit to com-
pleted compacted fill. The new equipment is all aimed
in that direction.

L. J. Ri tter
Associate Professor of Hightcay Engineering
University of Florida

Research carried forward in the College of Engi-
neering in the highway field'may be divided into two
broad groups, as follows:
That done as a par, of what we liave chosen
to call the joint Highway Research Program.
This program. has been carried out in cooper-
arion with the State Road Department of
(2) That performed under the regular program of
Elie Engineering and Industrial Experiment
Station with Station funds.
Joint Highway Research Program
This program was inaugurated in 1948 following
the passage of enabling legislation during the 1947
session of the Florida State Legislature. Basically,
legislation enacted at that time authorized the State
Road Department EO enter into agreements for the
performance of research in the highway field at the
University of Florida.
Two projects were begun early in 1948 under the
auspices of this program. Ile first of these was a
long-range study aimed at developing a satisfactory
method (or methods) of stabilizing peat and muck de-
posits in place when encountered in the location of
highways in swampy areas. Following a comprehensive
literature survey of the subject, attention was focused
upon the use of vertical sand drains in locations of
this type. A section of State Road 621 in Highlands
County was then designated as the location of experi-
mental sections utilizing vertical sand drains.
An extensive program of sampling and testing of
the soils encountered in this location was completed,
and detailed plans prepared for this trial location. For
a number of reasons plans for the experimental sections
were later abandoned, and no field sections were built.
In later phases of the project attention was directed
to the possibility of utilizing electrical and electro-
chemical methods of stabilizing deposits of this type

in place. One publication resulted from Elie work done
on this project--Station Technical Paper No. 40, by
B. E. Colley, entitled "Construction of Highways over
Peat and Muck Areas."
The second project under the original joint program
was a cooperative training program for selected engi-
neering employees of the State Road Department. Men
enrolled in this program were retained on the payroll
of the Department during the training period, and sent
to the campus to take part in the program,
During 1948 two groups, totaling 29 men, were en-
rolled in successive twelve-week training periods,
each group participating in one twelve-week course.
Courses of instruction given to these trainees included
refresher mathematics, highway location and design,
highway soil engineering, and elementary mechanics.
The over-all objective of the training program was,
over a period of time, to raise each trainee to the
point where he would be able to qualify as a registered
professional engineer.
Early in 1950, after conferences with the staff of
the State Road Department, three projects were inau-
gurated under the joint Highway Research Program.
Two of these are discussed in the following papers.
The third is a project entitled "Prestressed Concrete
Highway Bridges," and is under the leadership of
S. L. Bugg, Assistant Professor of Civil Engineering.
Other Highway Research
In addition to the projects conducted under the
joint Highway Research Program, two other projects of
note have been carried out in the highway field. The
first of these was a project designed to add to the
existing store of knowledge relative to the use of
Ocala limerick as a stabilizer for typical Florida sub-
grade soils. Both Elie Florida Bearing Test and the
California Bearing Ratio were used to judge the
stabilizing efficiency of limerick in combination with
certain sandy soils. Among other things, this invesciga-


tion showed that, at least for the soils tested, the
CBR did not adequately reflect the stabilizing effi-
ciency of limerick not was there any discernible rela-
tionship between the Florida Bearing value and the
CBR. Results of the work done on this project are con-
tained in Technical Paper No. 52 of the Station, written
by J. A. Bishop, and entitled "Granular Stabilization
with Limerock."
Another project involving the principles of soil
stabilization was undertaken during the summer of
1949 at the request of the City of Jacksonville Beach.
The investigation was principally concerned with the
effective use of materials locally available in the
vicinity of Jacksonville Beach to provide all-weather
streets carrying primarily residential traffic at low
initial cost which would have reasonably low main-
tenance costs. A thorough laboratory study was made
and a design proposed to the appropriate city officials.
Two city blocks were constructed by the city as
experimental sections during this past winter. The
test sections, as built, consisted of 4% inches of com-
pacted coquina-asphalt mixture on a stabilized sub-
grade. Although construction is not quite complete,
the test sections are open to traffic and are holding
up well under moderately heavy traffic.
Mention may also be made of graduate thesis proj-
ects. Three graduate theses directly in the highway
field have been completed in recent years, including
a study of county road administration in Florida, a
comparison of the Hubbard-Field and Marshall stability
tests for the design of asphaltic concrete mixtures,
and an investigation of certain locally available mate-
rials for use in soil stabilization in Alachua County.
Two other graduate theses in this field are now in
preparation. One of these is a study of asphaltic con-
crete mixtures using Ocala limerock as an aggregate
and the other is concerned with various uses of calcium
chloride in highway construction. A number of under-
graduate high honors projects have also dealt with

subjects in the highway field.
Research in Allied Fields of Civil Engineering
Research is also being carried forward in other
phases of civil engineering which bear a relationship
to the highway field. Mention may be made particularly
of the work which is being done in soil mechanics. A
major effort is now being exerted in this field by the
inauguration of a campus-wide soil exploration program.
Similarly, basic and fundamental concrete research
has been done here ovei"a period of years. The work
with limerick concrete is especially significant.
Research is also being perfouned in structures,
with sizeable contributions being made to the fund
of knowledge in that field. Some of the information
which has been developed in this area is directly ap-
plicable to highway bridges. A study of rainfall patterns
in Florida has been in progress in the Department of
Civil Engineering for more than two years and is ex-
pected eventually to develop much information of value
to engineers concerned with drainage problems.
Publications covering these topics and many others
are available to citizens of Florida and other persons
or organizations upon request.
In concluding this brief discussion, I would like
to emphasize that those of us concerned with highway
research at the University of Florida are sincerely
interested in developing a continuing program which
will be of maximum service to those in the highway
field in the State. This is, basically, your institution -
its primary function being to serve the citizens of this
State. Rest assured that no reasonable request for
information or assistance in solving some of the prob-
lems which you encounter every day will be denied.
Let me further urge you to make your wants known, so
that we may better serve you.


W. K Zimpfer
Assistant Professor of Civil Engineering
University of Florida

In recent years engineering soil maps have gained
wide recognition as a valuable aid in the more rapid,
economical and intelligent, location, design and con-
struction of modern highways. Several states including
New Jersey, Maine and New York, have recognized
the importance of Engineering Soil Maps and have
adopted state-wide mapping programs. Other states--
Indiana, Michigan and Nlissouri--have been mapping,
correlating, and evaluating soils for engineering pur-
poses, on a sectional and strip map basis, for many
The problems of surveying, classifying and mapping
soils for engineering purposes have been approached
and solved by a number of methods. The final objective
in most cases has been the preparation of an accurate
and usable Engineering Soil Map. These maps when
accompanied by the necessary written and tabulated
data indicate the areal extent of similar soils, the
significant engineering properties of the soil, and the
drainage characteristics of the soil areas. The various
soil areas denoted on the soil maps, are discussed and
evaluated for particular engineering applications.
Methods of Preparing Engineering Soil Maps
Ile methods of mapping soils for engineering pur-
poses are usually adapted to the geographical area
being investigated. Geologic and topographic maps,
airphotos and U. S. Department of Agriculture Soil
Maps are used quite extensively in mapping soils for
engineering purposes. Some of the basic methods now
being employed classify, evaluate and delineate soil
areas for highway engineering purposes are as follows:
(1) Classification and mapping of soil in place
on the basis of soil profile characteristics.
This method utilizes much of the available
U. S. Department of Agriculture soil survey
data, and groups soil types as to the simi-
larity of soil profiles. Soils with similar
profiles and characteristics presumably re-
quire similar engineering treatment. This
method requires extensive field observation

but only limited sampling.
(2) Classification of soil types into groups on
the basis of the physical properties of the
soil in the disturbed state.
The physical properties-grain size, plastic-
ity, and density, determined by laboratory
tests-indicate the engineering use of the
soils *io the disturbed state. Soils having
similar properties are grouped into engineer-
ing groups designated by various systems.
This method has been employed by many
states to classify and map soils. Botings
are made at frequent intervals along the
center line of a proposed route. Samples of
significant horizons are obtained, tested in
the laboratory, and classified by some sys-
tem such as the Ifighway Research Board
or Public Roads Administration classification
system. Considerable sampling and testing
is required by this method in order to obtain
representative values, and to delineate simi-
lar engineering soil areas.
(3) Classification and mapping of soils on the
basis of airphoto soil patterns.
This method utilizes as its basis the simi-
larity of airphoto patterns of similar soils.
By interpreting these patterns, which are
dependent in part on landform, drainage, and
the geology of the area, and, by defining
typical soil patterns, areas having similar
soil characteristics may be delineated on the
airpbotos. This method is often supplemented
by field reconnaissance and some field sam-
pling to verify the areas that have been
established on the aifphotos.
(4) Classification and mapping of soils utilizing
basic geology maps by associating the parent
material with its weathered counterpart.
This method relies upon available geologic
and topographic information for the area be-
ing investigated. By deductive reasoning
significant soil types or soil areas may be
classified into broad but usable engineering
group a.

Hills, Marianna Lowlands and the Western Highlands.
These divisions extend inland from the coasts in a
series of broad terraces. Alachua County is located
geographically in the Central Highlands. This area
includes high swampy plains, hills, and many large
and mnall lakes. The soils we prevailingly sandy-, the
sand being derived from marine terraces of the Haw-
thorne and Citronelle formations. Limestones underlie
the entire State but are exposed over limited areas,
primarily in Central Florida where they have weathered
to form the Gainesville, Hernando, and Fellowship
soils. The limestone deposits are usually buried be-
neath deposits of sands, clays, marls and organic
Soil Map-Sail Groups -Airphotas
Soil has been defined as the earth material over-
lying the earth's crust. In addition soils have been
described as natural bodies possessing individual
characteristics. Perfectly developed soils consist of
relative layers and horizons.
The soil maps used as the basis of the mapping
of the counties of Florida we those produced recently
by the U.S.D.A. and prepared by the Agricultural Ex-
periment Station. To date Alachua, Collier, Dade,
Manatee, and Hillsborough Counties have been mapped
and grouped. The soil groups indicated on these maps
are as follows:
1. Well-drained soils of the undulating to slop-
ing high hammock land;
2. Well-drained soils of the low flat hammocks;
3. Well-drained soils of the undulating pine land
underlain by sandy clay material;
4. Well-drained soils of the undulating to slop-
ing pine land underlain by limestone;
Imperfectly drained soils of the undulating
pine land;
6. Imperfectly drained soils of the flat pine land;
7. Imperfectly drained soils of the sloping ham-
mock land;
8. Poocty drained soils of the low flat hammock
land and prairies;
9. Poorly drained soils of the flat to undulating
pine land;
to Very poorly drained soils of the swamp areas
(mineral soils);
11. Very poorly drained soils of the swamp areas
(organic soils);
12. Excessively drained soils of the sloping pine
land ridges;

Ibe mapping method being employed under the
cooperative research program between the State Road
Department of Florida and the University of Florida
utilizes portions of three of the methods outlined in an
attempt to obtain a more economical method of mapping.
Basically, the classification and mapping in this
method involves the use of soil profile characteristics
and the U.S.D.A. Soil Maps. These maps are prepared
on a county or sectional basis and published by the
U. S. Department of Agriculture. In adapting these maps
to this method, similar soil profiles having similar
characteristics are grouped into engineering groups
and supplemented with engineering data based on
laboratory tests. By using such a method all available
information is fully utilized and a minimum of field
sampling and field reconnaissance is necessary. The
engineering soil groups will denote soil type, general
topography, drainage characteristics, typical soil
profiles, and engineering data as: grain size, plastic-
ity, Florida Bearing Value, and Highway Research
Board Classifications. If found desirable additional
laboratory tests may be added at a later date.
Preparation of County Engineering Soil Maps
In the Preparation of County Engineering Soil Maps
the following major steps are taken:
(1) Review of the topography, geology, and soils
of the county being mapped;
(2) Examination of the Soil Map, soil groups and
airphotos of the county;
(3) Sampling and testing;
(4) Examination and correlation of the soil types,
profile characteristics and laboratory test
(5) Engineering grouping, mapping and evaluation.
The following is a brief discussion of the major
steps in the preparation of county engineering soil
maps with particular emphasis on Alachua County,
Florida, the first county to be mapped under the co-
operative research program.
Florida*'is considered a low plain ranging in eleva-
tion from a few feet to approximately 300 feet, and has
been grouped into five topographic divisions as follows:
Coastal Lowlands, Central Highlands, Tallahassee
* Geological Bulletin No. 29 (GDoke)

13. Alluvial soils;
14. Miscellaneous land types.
The soils of Florida have been previously grouped
and discussed, from an agronomic viewpoint, and the
information published in Bulletin 334*. The information
presented is very useful, particularly the Generalized
Soil Map of Florida. This map indicates the soils that
may generally ',( encountered whnen api a county'
or section of the State.
In addition to the information noted on the various
soil maps, aerial photographs are used quite exten-
sively co locate soil areas an,- ocations ac-
curateiy, and to justify and verify mapped soil areas.
Sampling and Testing
After the g:eo!ogy map, sol! --- -d airphotos have'
been examined, sampling locations are selected in
order to obtain representative samples of the various
soil areas and types. The locations are noted on the
airphotos, and the areas sampled in the field. A post-
hole auger, 4 in. in diameter, is used for hand boring,
and soil samples of about 10 lb. obtained of the various
horizons or layers. All important soil profile information
is noted on the field data sheet-soil type, color, tex-
ture, structure, and drainage characteristics. All sample
holes are taken to a depth of 72 in., if possible, and
the various soil types sampled at least twice and some
major soil types sampled as many as four times. After
the samples are obtained they are bagged, tagged and
delivered to the laboratory for testing.
The tests performed in the laboratory at present
include the following: liquid limit, plastic limit, plas-
ticity index, grain size analysis, and Florida Bearing.
"Bulletin 334 Soils of Florida, Agricultural Experiment Sta-
tion, University of Florida.

Examination and Correlation of Soil Survey Data
After the testing of the various samples is colu-
pleted a comparison of the soil profiles of a given soil
series is made. The laboratory test data is also ex-
amined and the soils classified according to the High-
way Research Board system. From this information a
typical soil profile may be prepared and some of the
engineering characteristics noted.
The typical engineering soil profiles(Fig. 1)are then
discussed and evaluated in terms of subbase, drainage
characteristics, handling problems, and over-all suita-
bility as an engineering material.
Engineering Grouping and Mapping
After the various soil types have been examined,
classified and rated, they may be grouped into so-
called engineering soil groups. It has been tentatively
planned to use as a basis of grouping, the color group
of the SD.. il Map, Alachua County.* This group-
ing will be supplemented with significant engineering
By utilizing the basic soil map and color grouping
of the U.S.D.A. Soil Map, Alachua County, considerable
time and expense is saved in producing a finished
soil map. These U.S.D.A. maps adequately serve as a
base map for mapping soils for engineering purposes.
In conclusion it should be noted that the methods
of preparing Engineering Soil maps have been only
briefly outlined. Many of the problems, techniques
and findings encountered in the actual mapping of soils
for engineering purposes could be discussed at great
length. As Engineering Soil Maps become available to
engineers, it is imperative that additions and modifica-
tions be adopted in order to more efficiently, econom-
ically and accurately map soils for engineering pur-
*Available from Agricultural Research Administration, Bureau
of Plant Industry, Soils, and Agricultural Engineering, Dept.
of Agriculture, Washington, D. C.

Hole Nos. 2-15-19-21-34 Project No. 4929 Date 195U-51
Location Typical County Alechua
Agricultural Class Leon Fine Sand (Lc) Sampled by
Proflle Sample No. Profile Description
0" Dark gray fine sand
- Florida Bearing
12 (25)
24 .."" A-3 Yellow brown fine sanc
... FlorIda Bearl ng (some light gray sand
-.......(45-75) 55
3 6 ".'* ".
Water Table
- (3081n.)
' : 1 .l.
.a .; ..
- MH av Rsearto Blue-ory mottled clay
84 *Higllhway Research Board Classific'atio~n



(Poorly Drained Solis of the flat to undula-
ting pine lend) (Group 9)
External drainage fair to good
Internal drainage poor

Fig. 1: Typical Engineering Soil Profile (Leon Fine Sand)


Theoretical Considerations

Florida, "ne Sunshine State," might also be call-
ed the corrosion state. Due to the warm humid climate,
the great extent of sea coast, and the salt content of
the atmosphere along the sea coast, iron and steel
structures are rapidly deteriorated. Further, organic
protective coatings used to protect these structures
are also susceptible to these destructive forces and
require frequent replacement. As an example, the Over-
seas Highway and certain other coastal bridges often
require repainting or parch painting at least once a
year, and in some instances even more frequent attention.
Painting is one of the most common methods for
combating atmospheric corrosion. Its proper use is
both convenient and effective; however a paint system
must be designed to meet the conditions to which it is
subjected. As an example, the refrigerator in your
home is finished with an enamel that will last for years,
showing very little deterioration. If this same enamel
were used on a bridge or water tank exposed to sun-
light and other outside conditions, it would have only
a short life; probably less than a year. Further, an out-
door paint, exposed to the vapors usually found in a
kitchen, would become soft, sticky and soon be rubbed
or scraped off. Another example would be an automo-
rive enamel. Automotive finishes when not periodically
waxed will rapidly fail, as they depend on the proper
waxing and care for their long life-span.
With the above facts in mind, the State Road De-
partment of Florida recently started a project in coop-
eration with the Engineering and Industrial Experiment
Station to study painting systems for use on outdoor
structures fabricated from steel. The object of this
project is to study and develop finishing systems
which will have good durability and protective value
to steel structures exposed to Florida climatic condi-
tions. The scope of this project includes cleaning
methods, metal pretreatment, primers, and finish-coat
systems. Also included in this project are methods for
evaluating such finishes andthe preparation of suitable

A brief review of the conditions to which the pro-
tective coating system will be subjected should give
a good indication of the nature of the problem.
Sunlight, a major factor in paint film degeneration,
is very plentiful in the state of Florida. The ultraviolet
light destroys the binder thus releasing the pigment
particles which are washed or blown away. Sunlight
also causes embrittlement of the film and a shrinkage
which makes the paint subject to failure from cracking
and peeling. Further, the brittle film is subject to
failure from flexure and impact.
Salt spray, a condition prevalent in Florida coastal
areas, is a major destructive force both from the stand-
point of paint failure and metal rusting. If the paint is
susceptible to moisture penetration and contains no
corrosion inhibitors, the metal will rust under the paint
thus eliminating its protective value; therefore this
condition is serious.
Moisture and rainfall are two destructive forces
which act in the same manner. No known paint is cont-
pletely resistant to water or moisture absorption, and
film failure from these factors usually is in the form
of film softening and blistering. Further, as the film
loses this moisture, cracking and peeling result.
Wear or abrasion is a factor also to be considered
since the wind causes an impingement of sand and
soil particles on the painted structure; thus the paint
film is gradually worn away and sometimes punctured
by the sharp particles.
All of the above factors are present in Florida.
Therefore, any finish for outdoor steel structures must
be designed to meet these destructive forces.
The first step in this research program was a litera-
ture survey of available information on corrosion and

A. L. Kimmel
Assistant Professor of Chemical Engineering
University of Florida

weather resistantprotective coatings. This survey indi-
cated that the paint primer was of first importance
since it was the material that is next to the metal sur-
face. Ile primer must adhere to the metal, protect it
from corrosion. resist embrittlement, and offer some
protection to the metal from rusting even if cracks or
punctures should develop in the finish. Intermediate
and top coats serve to form a barrier between the de-
structive elements and the primed metal. These coats
must resist sunlight, abrasion, and moisture. 'They
should be designed so that they fail only by chalking
in a very uniform manner.
At the present the research here at the Station is
being devoted to primers. The work is being conducted
both from a standpoint of pigmentation and binders
with emphasis on the chemical corrosion inhibiting
From studies thus far conducted on pigmentation
it has been found that the chromate type primers seem
best suited for outdoor metal protection and that by
incorporating alkaline pigments their corrosion mitigat-
ing properties are improved.
Vehicle studies for primers have indicated that
the incorporation of even small amounts of phenolic
resin will give an improved primer. This resin increases
the adhesion and decreases water absorption of the
primer. Binders using linseed oil fortified with small
quantities of alkyd resins did not show improvement
over the straight linseed oil types; however, larger
amounts might improve these coatings. A more thorough
study of the alkyd resins is being made.
Protective Coating Testing
In the study of protective coatings, two classes of
tests are used. First, the durability, and second the
control tests.
The purpose of durability tests are to give an in-
dication of the expected life and effectiveness of the
protective coating or finishing system. For the most
part these are accelerated tests and must be used to
evaluate only those factors for which they are intended.
For example, the salt spray test is used to indicate
the degenerative effects of humid salt-laden air on the
paint film and the effectiveness of the paint to protect
the metal it covers. It does not indicate the ability
of the paint film to resist the effects of sunlight or
rainfall. Usted below are the durability tests used in
this project to evaluate the paints, with a brief de-

scription of how they are conducted and the factors
they study:
1. Salt spray test:
For this test the coating is applied to a steel panel,
allowed to dry for the required length of time, then sub-
jected to a humid atmosphere of saturated salt mist at a
constant temperature for a period of 200 hours. This
test evaluates the resistance of the paint film to de-
generation by moist salt air and its ability to protect
the metal against corrosion (Fig. I

Fig. 1: Panels after being tested in the salt spray
cabinet for 200 hours.
2. The single potential test:
To conduct this test a uniformly thick film of paint
is applied to a steel panel and allowed to dry for 24
hours. Some type of solution holder is then fastened
to the paint film with paraffin and filled with saturated
potassium chloride solution. The single electrode po-
tential of the metal is next observed with a vacuum
tube voltmeter each hour for a period of 18 to 24 hours.
Figures 2 and 3 illustrate the arrangement and the
graphical data that are obtained. The purpose of the
single potential test is to indicate the corrosion miti-
gating properties of a paint finish with respect to the
metal it covers, moisture penetration resistance, and
whether or not the paint film will break or separate at
conditions of high moisture. A visual examination of
the area tested will also indicate the susceptibility
of the paint film to water or humidity softening, blister-
ing and rust formation under the film.
3. Abrasion tests:
Properly prepared panels are subjected to the wear-
ing or abrasive action of specially made emery wheels

Twit -""*

Fig. 2: This arrangement is used for making the poten-
tial studies of primers used to protect steel.
To the left is the potential measuring instru-
ment with the electrode In position on a panel.
In the foreground Is a number of Panels illustrat-
ing how they are prepared.
under definite conditions, and the weight loss in milli-
grams per 1000 revolutions of the test panel is reported
as the wear factor. The instrument used for this test
is the "Taber Abrasion Tester" and the exact proce-
dure for its use may be found in the ASTM manual for
testing paints. This test indicates the wear resistance
of the paint film, and its resistance to deterioration
by particle impingement (Fig. 0
4. Accelerated weathering:
A properly prepared painted steel panel is tested
in a weatheromerer. This testing device subjects the
painted surface to periods of simulated sunlight, rain-
fall, and dry periods. The weatherometer is adjusted
so that the weathering cycle approximates the condi-
tions found in the area where the paint will be used.
The purpose of this test is to indicate the effects of
sunlight and rainfall on the paint system (Fig. 5).
5. Outdoor weathering:
This rest is an exposure of paint films to the normal
outdoor elements. The test requires three years to com-
plete and is used as a final indication of the effective-
ness and life of the paint.
No single or group of accelerated durability tests
have ever been made that will give an exact indication
of the life of a paint film in real service; however, they

Fig. 3: This graph illustrates the types of graphic data
obtainable by the potential test.
Curve No. I shows a paint that is very resistant
to the effects of salt solution and, over the test
period, only absorbed moisture. The film did not
blister or break and no rusting occurred.
Curve No. 2 shows moisture absorption during
the first 12 hours at which point the film failed
by separating. After the film failure. the metal
was protected to a large extent as indicated by
the metal potential remaining veryclose to zern.
Metals coated with this finish will not rust for
a long time even after Ulm failure.
Curve No. 3 illustrates a paint film that will
fail but will also give metal protection after
failure. The amount of protection Is much less
than in the case of curve No. 2.
Curve No. 4 Illustrates a paint which after
failure allows the metal beneath to rust freely.
A paint with this type curve gives metal protec-
tion only when the film is continuous.
do serve to eliminate certain finishes that have little or
no value in a very short time. Ibis is time-saving and
aids the progress of paint research.
The control tests are methods for indicating the
properties of the finish in the liquid state and serve
as guides in obtaining duplicate products. These are
standard tests and are as follows:
1. Viscosity
2. Weight per gallon-density
3. Drying time
4. Container stability
5. So4ids content


Fig. 4: This picture illustrates the Taber abrasion
testing machine and its method of use. One of
the abrasion wheels Is shown in an elevated
position. When conducting a test both arms of
the machine are lowered so that the abrasion
wheels are in contact with the painted surface.
A complete chemical analysis is used in cases
where a specific finish is to be duplicated and the
original composition is unknown. When necessary, the
analysis is conducted as follows:

Fig. 5: The Atlas Weather-Ometer used to test paint
and other materials for their resistance to weath-
ering Is shown above. Conditions or sunlight,
darkness, rainfall and change in temperature are
produced by this machine and a 300 hour expo-
sure is equivalent to about three years outdoor




Test for metal ions in
soluble portion and the
insoluble by miscroscopic

Tested by distillation
curves and odors.

Tested by physical
and chemical methods.

A complete detailed description of these tests can be
found in the paint testing manual of the G,rder labora.
From the work conducted thus far on this paint
research project it has been found that both pigment
and vehicle composition will be important in the formu-
lation of coatings to protect steel in Florida. The best
primer coats tested to date are those with a slight alka-

line zinc chromate pigmentation and a phenolic fortified
linseed oil vehicle. It should be mentioned that the
tests on this material are not, as yet, complete and
they still must be subjected to the accelerated weather-
ing and the outdoor exposure tests. Two primers of the
above-mentioned types have given excellent results in
the salt spray, potential, and abrasion tests.
To date, practically no work has been done on the
finish coats for these primers; however, work will begin
on them in the very near future.

Fred Burggraf
Associate Director, Highway Research Board
a"shingtoll, D). C.

It is a rather startling reflection but the last investi-
gation of the nature I will describe this afternoon was
made nearly 30 years ago by the Illinois Division of
Highways on the Project known as the Bates Road
Test. Great changes have taken place since then in Elie
field of highway transportation but research on thle
effect of truck axle- -oiso pavements coctnue to
lag behind that of the rap-idly growing trucking industry.
Sir Isaac Newton once said that in tile case of a
disagreement about facts, tile matter "is to be decided
not by discourse 11 :by -,w tri-a! of the rex:peri:ent."
Road Test One-MD, "the new trial of the experiment,"
was conceived to provide some of the much needed
For six months the Highway Research floard sub-
jected a 1.1-mile section of concrete pavement to
continuous, around the clock, 7 days a week traffic
using four single rear axle trucks loaded to 18,000 and
22,400 lb. per axle and four tandem rear axle trucks
loaded to 32,000 and 44,800 lb. per tandem. In the
six months the 8 trucks have traveled approximately
400,000 miles.
The principal object of the test is to determine the
relative effects, on a particular concrete pavement,
of the four different axle loadings on two vehi cle types.
Information, such as is being secured from this experi-
ment is greatly needed for use in appraising the load
carrying capacities of existing concrete pavements,
for use in designing new pavements and to provide
fundamental data that may be useful in framing equit-
able legislation to govern highway transportation
This research project was proposed by the Inter-
regional Council on Highway Transportation which
was formed at Columbus, Ohio, in Dee~,1949.
"The complete report may lie obtained from the [lighway
Research Hoard, National Academy of Sciences, Washington,
D. C.

A special Committee of the Council met in Balti-
more, Maryland, in January, 1950. This Committee de-
cided that the project as suggested was feasible and
recommended that the tests be conducted at the joint
exe.e of the particip.ating State highway departments
with the Highway Research Board assuming direction
of the project. The following highway departments
executed contracts with the National Academy of
Sciences agreeing to participate financially in this
cooperative project. Connecticut, Delaware, Illinois,
Kentucky, Maryland, Michigan, New Jersey, Ohio,
Pennsylvania. Vig Wi,'isconsin and the District
of Columbia.
ne cost of this project is shared by the participat-
ing states in monetary contributions; by the Bureau of
Public Roads in providing personnel and instruments
for measurements of surface roughness, slab strains
and deflections caused by the test loads, for soil
surveys, and other necessary instrumentation and
testing services, and in providing the services of the
project engineer and three assistants; by the petroleum
industry in providing gasoline, oil and grease; and by
truck manufacturers of the Automobile Manufacturers
Association and the American Trucking Association in
providing the test vehicles.
I should like to mention briefly one aspect of this
job that is especially noteworthy from an over-all view,
that is the demonstration given by this project of the
benefits of cooperation by a number of diverse agencies
in research on a problem of great mutual importance,
by pooling (heir support under the direction of an in-
dependent institution which can have no possible
interests in the matter other than the development of
facts and acquisition of new knowledge.
The total estimated cost of the project is $245,000.
Toward this amount $150,000 has been contributed by
the twelve highway departments previously mentioned;
the balance has been in contributions of personnel,
services, equipment and material valued approximately
as follows:


Bureau of Public Roads
Personnel and service .. .. 40,00o
Truck Manufacturers
Test Vehicles ......... .27,500
Petroleum Industry
Grease, oil and gasoline so** ....... 20,000
Department of Defense
Aerial Photography ..... 3,100
Highway Research Board
Personnel ........ 4,400
$9 5,000
An estimated distribution of the cash expenditures
Testing operations .. .. to....$ 52,450
By-pass toad ad turarounds ........ 50.900
Administration .. .. ......6 6 a 9.050
Maintenance of test road ..... a a 2,000
Final repair of test toad o o ...... 29,000
Reports## so*.too.... ....... ... 2,600
Test Section The tests are being conducted on a
l.1-mi, section of concrete road on U. S. 301, located
approximately 9 mi. south of La Plata in Southern
Maryland. The pavement was constructed in 1941 and
was in excellent condition at the start of the tests.
The pavement is reinforced, is 24-ft. wide, and is
divided at the center with a longitudinal joint. The
cross section is of the double parabolic type thickened
at both the outside and center longitudinal joint edges.
The depth of the cross section of each 12-ft. lane is
9-7-9 in. Expansion joints Y4-in. wide are spaced at
intervals of 120-ft. with two intermediate contraction
joints at 40-ft. spacing between them.
Load transfer devices of a cantilever plain dowel
type were placed in all of the transverse joints. he
dowel bars are Y4 in. in diameter and placed at 15-in.
spacing. The longitudinal joint is a straight butt con.
struction type with 4-fr. long tie bars spaced at inter.
vals of 4-ft. The welded wire fabric reinforcement is
approximately 3"in- from the surface and contains No.
2 wires spaced 6-in. c-c. in the longitudinal direction
and No. 2 wires 12-in. c-c. in the transverse direction.
The weight of the fabric is 59.4 lb. pet 100 sq. ft.
The 1.1-mi. test road has been divided into two
sections; the south section being 0.5-mi. long, and
the north section 0.6-mi. long. At each end of each
secion, turnarounds of 50-ft. outside radius with 20-ft.

bituminous roadways have been constructed to allow
the test trucks to operate back and forth on the same
lane. Ile vehicles negotiate these turnarounds at
approximately 6 mph.
On the west lane of the south section two single
unit, two-axle trucks with rear axle loads of 18,000 lb.
are operated. On the east lane of the south section
two single unit, two-axle trucks with rest axle loads
of 22,400 lb. are operated. On the west lane of the
north section two single unit, tandem-axle trucks with
tandem loads of 32,000 lb. are operated. n the east
lane of the north section two single-tnit, tandem-axle
trucks with tandem loads of 44,800 tb. are operated.
Each slab (12 by 40 ft.) is identified by a number
painted on the slab. Ten spots are painted in each
slab for reference points for precise level observations
of variation in elevations. The Coast and Geodetic
Survey placed 15 concrete bench markers along the
project and determined their elevation. These are
used as reference points to determine the settlement
of the slabs. The average settlement for all the slabs
at the free edge of the transverse joints as of October
2, 1950 was: Section I (18,000-1b. single axle) 0.17
in.; Section 2 (22,400-1b. single axle load) 0.40 in.;
Section 3 (32,000-1b. tandem axle) 0.27 in.; and Sec-
tion 4 (44,8D0-1b. tandem axle) 0.88 in.
The trucks in each of the series have been selected
so as to obtain the highest practicable rate of acceler-
ation between 10 and 40 mph. In order to provide the
necessary test load, 215 1,000-lb. concrete blocks and
ten 750-1b. concrete blocks were made at the Maryland
State Roads Commission Garage in La Plata where
the trucks were loaded. Approximate loads were ob-
tained at the garage with loadometers. The loaded
trucks with a crane were then driven to a Virginia
Highway Department weighing station located 5 miles
south of the test section. All axle and gross loads
were then adjusted to within 200-lb. of the loads spec-
ified for each vehicle.
Schedule of Traffic Operations
Each lane is marked with longitudinal stripes as
follows: White stripes along the outside edge of
the pavement and 8-ft. from the outside edge of the
pavement; yellow stripes 2-fr. and 10-ft. from the out-
side edge of the pavement. These stripes are used as
guides for the trucks so that the fllowing pattern of
lateral placements of the outside rear-axle tires is
maintained. One application with the outside tire at
the edge of the pavement; one application with the

it was constructed and tested at an age of approximate-
ly 4 months, was 4838 psi.
The average modulus of elasticity value of the
cores was 4,830,000 psi. for the wet condition. All
of these tests show that the concrete is of good qual-
ity and the pavement has the designed thickness.
Preliminary Report on Soil Survey Soil test data
have been obtained from fifty auger borings made adia-
cent to the concrete pavement to a depth of approxi-
mately 30 inches, spaced uniformly from end to end of
each test lane. These data indicate that approximately
15 per cent of the subgrade soils have granular char-
acteristics and that the remainder are fine-grained
plastic soils.
These fine-grained soils have been compared, by
Group Index Ratings, with the average types of soils
found under "pumping" pavements in Illinois, Indiana,
North Carolina and Tennessee. Ibis comparison shows
that the loarn and silty loam soils on this project are
better than the averages of the soils that have been
found conducive to pumping in three of the states and
is about the same as the average of such soils in the
the fourth state (See Fig. 1).


outside tire 2-ft. in from the edge; three applications
with the outside tire between the two positions. This
pattern of truck operation represents the average opera-
tion of trucks on similar type highways as determined
from lateral placement studies made by the Bureau of
Public Roads.
Operations of all test vehicles are continuous on a
twenty-four hour per day, seven day per veek basis,
except as necessary for maintenance of the vehicles,
meals and rest stops for the drivers and except as
interrupted by special tests. Drivers work three eight-
hour shifts and are allowed 3&min. for a meal and a
10-min. rest period each hour. Applications of load
are indicated and countedby means of electric counters
actuated by the passage of the test vehicles and check-
ed by odometer readings in the trucks.
Test Proc*dures
Crack Survey A detailed survey was made of the
cracks in each slab nrior to the beginning of operation
with the rest trucks. A solid, black line approximately
one inch wide was painted adjacent to each existing
crack along its full length. As new cracks or exten-
sions of old cracks develop, they were painted with
contrasting lines one inch wide as follows:
Solid yellow line for the first six weeks of
Solid white line for the second six weeks of
Solid red line for the third six weeks of operation.
Broken yellow line for the last six weeks of
Each slab is checked for cracks each day and the
exact position of each crack as it develops is recorded
on a card with the date and number of applications
when the crack was first noticed.
Concrete Quality Nineteen beams, approximately
7 inches wide were sawed from the four concrete spec-
imens removed from the pavement for this purpose by
the Maryland State Roads Commission. The average
flexural strength was 708 psi. The average flexural
strength of 28 beams made during the construction of
the pavement included in this test section was 485
psi. at 7 days. The average compressive strength of
12 six-inch diameter cores drilled in June from portions
of the roadway not subjected to traffic was 6944 psi.
after being immersed in water for 28 days. The average
compressive strength of 20 cores drilled from the pave-
ment included in this test section, two months after

Figure I

Also a comparison on a grain size basis shows the
average of the soils adjacent to the pavement on the
project to be slightly better than the average of soils
for the entire State of Maryland.
Itaintenance The Executive and Advisory Com-
mittees for this project have defined maintenance as
follows: "To maintain shoulders reasonable flush
With the edge of the pavement, to seal joints, and vo
correct profile deficiencies to insure safe operating
conditions as necessary in the opinion of the Proj-
ect Engineer with the advice of the State Resident
Maintenance Engineer and other. NWntenance is not
to include underselling to correct for pumping." For
the six-month period of operation the shoulders were
maintained 23 times and the joints were resealed litimes.
Strains and Deflections Between Sept. 5 and Sept.
14 the deflections at various joints caused by the
trucks traveling at creep speed over the pavement
were measured. The deflection readings were made
at intervals varying from 4 to 6 hours throughout a full
24-hour cycle at two expansion and two contraction
joints 'in each of the four sections and at the center
of the slab edge at two points in Section 4. joints
were selected for study at which no pumping and vary-
ing degrees of pumping had occurred in each of the
four sections.
The data indicate that the deflections caused by
the loads are (1) normally much greater at night when
the pavement edges are warped upward than during
the daytime when they are warped downward; (2) two
to three times greater at pumping joints than at non-
pumping joints; (3) larger at pumping expansion joints
than at pumping contraction joints of the dummy type;
and (4) larger during the period when pumping is reced-
ing than at any other time.
Additional information, which will be of great value
to designers of future pavements and to those charged
with evaluating the load carrying ability of existing
pavements, is being obtained by means of strain meas-
urements of the pavements under various loads and
by measurements of strains induced by warping of the
stabs due to temperature differentials between the top
and bottom of the concrete. These tests have not been
completed so no definite results can be given at this
As stated by the Advisory Committee: "All pertinent

data must be carefully analyzed and considered before
the final report, however, certain facts relative to the
behavior of the pavement under test have already been
The more significant observations which may be
made from the test results after six months of continu-
ous operation are as follows:
1. Soil tests Made on samples obtained through-
out the length of the pavement adjacent to
the pavement edges and under certain sec-
tions of the pavement indicate that there is
reasonable uniformity in !he soils on the two
sides of the pavement.
2. Based on these same soil tests, there is
found to be a definite correlation between
soil type and pavement behavior. The higher
the granular content and the lower the plasticity
of the soil, the better the performance. The
subgrade soils on this project are typical of
of the soils underlying a very extensive mile-
age of concrete pavement throughout the
coun try*
3. The progress of cracking and depressing of
joints in the test sections has a definite re-
lationship to the occurrence of pumping. Pre-
vious research and observation have shown
that four basic conditions m-ist be present
simultaneously to create a pumping slab. They
are: (1) frequent heavy axle loads; (2) sub-
grade soils of such a nature that they may
pump through open joints or cracks or at pave-
ment edges; (3) free water under the pave-
ment; and(4) joints of cracks in the pavemen-.
These conditions were present on this project
and pumping resulted.
4. Based on both quality tests and dimension
measurements, the concrete in the test sec-
tions is of good strength and of the designed
5. All four sections were damaged as follovis by
the loads applied:
(a) The 44,800-lb. tandem axle loads caused
approximately eleven times as much cracking
(lineal feet) as the 32,000-lb. tandem axle
loads. This relationship held true over a period
of almost four months, that is from 20,000 to
92,000 truck passes in each lane* (See Fig* 2
and Table 1).
(b) The 22,400-lb. single axle loads caused
approximately six times as much cracking
(lineal feet) as the 18,000-lb. single axle

Number of Cracks Aaly.J Cooks Analyzed
Section Number Truck to be Structural to be NOT Structural Total
PMases Failures Due to Failures We Cracks
Load to Load
Feet Feet Feet
I- 18,000-16. sngle axle 238.275 189 S2 241
2. 722400-16. single oil, 238.263 1,1 3 5? 1,210
Ratio 2 to I 1.0 6.1 1.1 5.0
3- 32,000-16. tandem axles 92.000 2tsU 27 307
4- 44,800-lb. tandem axes 92,166 3.283 20 3,303
Ratio 4 t. 3 10 11.7 0 7 10.8
I- 32,000-lh. tend.. arle 164523 992 27 1.019

na ~r tx


g.I~x;? I ._c-
i ...----
oi --------- c;c=::------- a, --- ~ ~~7"
a a 'L? 7 Q) 4) 1C in
311 ii' -IU: YClrllXI n (aL~
*ar~ r rt:YL:irVt ily CRJDIS
hCru .*: ; -I i _^~i

.......... W 3- 1WIY
1 C)
500 r ........... ...It
0 2s so v5 oo z5 so0 Ms
9MaMA OF uCx APfLCt"NS Dnds
Figure 2
loads.This relationship held true over a period
of almost five months, that is from 15,000 to
238,000 truck passes in each lane. (See Fig.
i and Tale t.
(c) After 84,000 truck passes, 80 per cent of
the joints in the section carrying 44,800*
lb. tandem axie loads were depressed,
whereas, with the same number of truck passes,

Figure 3
only 10 per cent of the joints in the section
carrying 32,000-lb. tandem axle loads were
depressed. (rIepressed joints are defined as
those joints at which a marked localized
settlement of the pavement has occurred ac-
companied by cracking of the pavement in
the vicinity of the joint.)
(d) After 137,000- truck passes, 22 per cent
of the joints in the section carrying 22,400-lb,
single axle loads were depressed, whereas,
with the same number of truck passes, only
2 per cent ai the points in the section carrying
18.000-1h. single axle loads were depressed.
6. (a) After 238,000 truck passes, 28 per cent of
the slabs in the section under 18,000-lb.
single axle loads and 64 per cent of the slain

Table I

and 44,800 lb. Two sets of these tests using all 8
loadings will be made on pavement sections located
on granular subgrades and on which there has been no
evidence of pumping. Ile other two tests will be on
joints showing medium and high deflection.
There will also be some strain and corner deflection
measurements made under tandem axle loadings of
14.ODO, 18,000 and 22,00 lb. to determine the relation
of the stress to these total loads on reat axles over a
range which will permit a direct comparison of stress
with the similar single axle loads. It is also planned
to make some miscellaneous strain and deflection
tests with tractor- semi-trail er combinations.
A detailed soil survey will be made and in this
connection plans are under way to dig a trench the full
length of the project along both edges of the pavement.
This will afford an opportunity to locate definitely the
transition points between soils of different types, to
observe any changes in the vertical profile, to take
representative samples, and to obtain a photographic
record of this important component of the road structure.
These observations will also determine the location of
the cores to be drilled from the pavement to obtain
additional soil sampled of the subgrade.
To supplement the few preliminary quality tests
made on the concrete, several 3 x 4 ft. sectors will
be taken from the pavement and sawed into suitable
size specimens for transverse tests. A large number of
cores will also be cut from the pavement for compressive
strength tests and to check the pavement thickness.
Recently the Commanding Officer of the 18th Tacti-
cal Reconnaissance Squadron of Shaw Air Force Base,
South Carolina, assured us that they would make an-
other colored aerial strip photograph of the project.
The aerial colored photographic record of the final con-
dition of the project will be of great value as it will
show the cracks present prior to the test and the rate
and extent in which the additional cracks occurred under
the various truck axle loads. The one they made of
the project this summer at an altitude of 100 ft. reveal-
ed the cracking patterns in great detail.
In conclusion I wish to say that this research proj-
ect was truly a cooperative one both in its conception
and in its operation. Therefore everyone connected with
the project deserves credit for his contributions to
this investigation.

under 22,400-lbe axle loads contained cracks
which have been analyzed as constituting
structural failures due to the application of
the test axle loads. Conversely. 72 per cent
of the slabs in the 18,000-lb. section and 36
per cent of the slabs in the 22,400-lb. section
show no such structural failures.
(b) After 92,000 truck passes, 27 per cent of
the stabs in the section under 32,000-lb. tan-
dem axle loads and 96 per cent of the stabs
under 44,8004b. tandem axle loads contained
cracks which have been analyzed as consti-
tutinS structural failures due to the applica-
tion of the test axle loads. Conversely, 73
per cent of the slabs in the 32,000-lb. section
and 4 per cent of the slabs in the 44,800-lb.
section show no such structural failures.
General Concluding R*marks
Broadly speaking the three main results of this
investigation are: (1) it has furnished highway adminis-
trators and engineers with quantitative facts regarding
the effect of axle loads of different intensity on a con-
crete road: (2) it has increased and to a certain extent
verified our knowledge of the interred ation ship between
loads, pavements and subgrades and (3) it has acted
as a stimulus for further research.
The Transport Committee of AASHO has been very
active in promoting additional research projects and
three of the regional Associations of State Highway
Officials have this matter under consideration. In gen-
eral the tentative plans are for the Southeastern As-
sociation of State Highway Officials and the Western
Association of State Highway Officials each to finance
a research project on a bituminous type pavement and
the Mississippi Valley Association of State Highway
Officials to finance a research project on another con-
crete pavement. These additional tests under other
conditions including a different type of pavement are
necessary to obtain more complete answers to the
questions of highway engineers, administrators and
transportation officials.
Now I would like to outline the future tests we
have planned on Road Test One-MD. First we plan to
make simultaneous measurements of strain and comer
deflection at four more joints with four single axle
loadings of 14,000, 18,000, 20,000 and 2Z400 lb. and
four tandem axle loadings of 28,000, 32,000, 36,000,

E. N. Rodgers
Alabivna Road Builders Association



The Alabama Road Builders Association, in attempt-
ing to he of useful service to the Civil Engineering
profession and the construction program in general,
conceived the idea of setting up a means of profitable
contact with undergraduate engineers by furnishing
them direct contact with construction during their col-
lege career and in addition to furnish incentive and
finkuicial assistance to them in obtaining their degrees.
With this in mind, in 1950 this association estab-
lished a Student Program under the guidance of Mr.
John T. Moss, a contractor of Leeds, Alabama and a
Civil Engineer graduate of Purdue University. Mr. Moss
has served continuously as chairman of the central
Control Committee which administers the over-all
program, the prime purposes of which are:
1. To furnish a medium of contact with the con-
struction industry to Civil Engineering under-
kraduares that will give them on-the-job
training and supplemental education as well
as financial assistance.
2. To better equip the engineering graduate with
some experience in order thathe may command
a higher starting salary and be more useful to
the construction industry.
3. To assist the undergraduate in selecting that
branch of civil engineering which would be
more suitable to 6ib characteri6tics.
4. To acquaint Civil Engineering students with
construction methods, problems and limitations
to the end that future contractor-engineer re-
lations may be improved.
5. To enable the sponsoring firms to select suit-
able young engineering personnel for their
permanent staffs.
The entire program consists of four phases, namely:
1. Summer work program
2. Quarterly lectures
3. Annual awards
4. Financial assistance
The first phase of the program of the Summer Work

Program consists of assigning Civil Engineering sEu-
dents who have made application and been accepted to
accredited firms for ten weeks of work during their
summer vacation. Firms sponsoring students have
been -;creened carefully for their general interest in
the program and their ability and willingness to rotate
the student within their operation during the summer
111ulithb. Thr pay range for students working during the
summ er is controlled by the Central Committee in
order to assure the -;indent of liveable and attractive
earnings during his vacation. During the student's
summer work, a representative of the Alabama, Road
Builders Association checks with him on the job in
order to see that conditions are as they were outlined
to him previously.
Upon completion of the ten weeks' work his service
with the sponsor is graded by the sponsor, and becomes
a part of his university record. A student cannot be
assigned to the same sponsoring firm for more than one
summer so that the program will furnish him a diver-
sity of opportunity-the main idea of the program is that
if a student startsdurinithe summer between his fresh-
man and sophomore year he will have the opportunity
to spend three summers during his college work in
contact with a practical operation: one summer in engi-
neering supervision, one summer in equipment or mate-
rial sales or manufacture and one summer with a con-
tractor. A sufficient number of students are maintained
so that it is always possible to rotate a student in the
three phases of the industry.
Sponsoring firms consist of county, city and state
engineering departments as well as consulting engi-
neering firms, aggregate, bituminous, cement and steel
sponsors as well as equipment distributors and con-
tractors. At the end of each summer's work keys are
given each student in order to create an added stimulus
for the program. At the completion of his first year he
is given a bronze key. A silver key after the completion
of his second year with both of these being returned
to the Association upon completion of his third year,
and the Association then presenting him with a gold


key, engraved with his name and year for his permanent
possession. During the summer of 1950, 34 students
from the University of Alabama and Auburn completed
their ten weeks' assignments and during the summer of
1951, 23 students completed their assignments.
The second phase of the student program consists
of lectures to the Civil Engineering students by ap-
proved contractors, preferably with Civil Engineering
degrees, on practical construction problems and the
relationship of the engineer and contractor on con-
The third phase of the program consists of an annual
award in the form of a substantial gift by the Associa-
tion to the Civil Engineering graduate of both the Uni-
versity of Auburn and Alabama. At the close of each
fiscal year of the Association, the outstanding student
at both schools is selected by faculty members, Civil
Engineering societies and the Central Control Commit-

tee of the Alabama Road Builders' Association. The
selection is based on scholarship, campus activities
and personality, and after a personal -contact with the
candidate by the Central Student Committee of the
Association. The successful students are presented
their awards at the annual banquet of the ARBA. This
award at present is open to all Civil Engineering stu-
dents of both Universities.
The fourth phase of the Student Program consists
of financial assistance to those students who are un-
able to continue their studies without help and who
have participated in the Association's work program.
A total of $1000 may be advanced to each student in
his sophomore, junior and senior years which is repaid
after his graduation at the rate of SIO per month with
3 per cent interest beginning at graduation. The stu-
dent accepting a loan is required to take a $1000 Life
Policy and keep it in force during the loan, which be-
comes his property when the loan is repaid.

No. I. The Mapping Situation in Florida," by Willian L.
No. 2. "The Electrical Industry in Florida." by Jon W.
No, 3. -Thi 1 oc tii ~fTn~r\ trr, ~\rn:n
Associated Stani(c. by Jo- ph He il and Wayne M%1a. s:
No. 4. "Study of Borni Conditionl at Dayton icach. Flori-
da anid lion.i- r:Yh W F:ern
No. 5. -Climati D;tt for the De:ign and Oper.ition of Air
Condiiu -ing SE-tein- in Florida,~ by N. C. Ebugh
and . Got- e.
No. 6. "On Static Enrantine from Six Tropical Storm- and
It.- U: in Ltin ilthePosition of the Disturbance."
by S. P. So hoff and Joseph Weil.
and Ralph .1. Muorgn.
No, 8. ,An Indutrial Sury-y of Ilides and Skin* in Florida,"
by William D. Atly.
No. 9. *Studies on Intermittent Sand Filtration of Sewage--
Part L. by D L. Emerson, Jr.
No. 10. -Florida Spray Guo fro Ple Tivof Gutr Flow SIl-
ultitun.'' by Norman Bourke and Keith W Dorman.
No. 11. "Development of Cerane Conpoitions Suitable for
the Production of Porcelain Tyl( Artwre." by 1. W.
No. 12. "Mold and Mildew Control for Industry ard the Home,"
by S S. Block.
No. 13. --Engineering and Industrial Research at the Uriver-
sity of Florida."
No. 14. "Reverse Cycle Refrigeration for Heating in the
South." by S. P. Goethe.
*No. 15, "Analysis of the Two Span Rigid Frame Highway
bridge, by C. Ut. Williams.
No. 16. '"Beach Erosion Studies in Florida," by H. J. Hansen.
No. 17. "Corrosion Studies," by A. L. Kimmel.
No. 18. Domestic Solar Water Heating in Florida," by
Harold M. Hawkins.
No. 19. "Proceedings of the First Annual Florida Highway
Conference." May 12-13, 1947, sponsored by the
Civil Engineering Section
'No. 20. "The Sanitary Research Laboratory of the Univer-
sity of Florida," by D. L. Emerson, Jr., and Earle
B. Phelps.
No. 21. -Investigation on Dehydration of Tung Nuts," by
James T. L-ggett and Seynour G. Gilbert.
*No. 22. -Proceedigs of the Second Annual Florida Highway
Conference," May 31-June 1, 1948,sponsored by the
Civil Engineering Section.
No. 23. **Subsurface Sewage Disposal," by John E. Kiker. Jr.
"No. 24. Proceedngs of the First Surveying and Mapping
Conference, October 22-23. 1948. sponsored by
the Civil Engineering Section.
No. 25. **Report on Linterock Research-lb41-1948." by
C. D. Williamnis land Mack Tyner.
No 26, -Procedmys .f the First Annual Public Health Con-
forence. N.v. 12-13, la4b. sloweured by 1he Civil
Engineering Sin,

*No. 27. "An Evaluation of Sunniland Crude Petroleum,"by
11 E. Schwever and C. 1. Edwards.
"No. 28. -Protection of Small Building-s Against High Velocity
WHrd'h by A. Thungp-on,
1"4. by M k. L ltum nd D. C. 13unture.
No. 30. The Develonent of a Structural Clay Products In-
ilt-n !ri n rid C ,sy Part 1. T .0 Jt *..-onville
Areain -r. A I Greavr -Waltke. I P. P Turnier. and
He. .im~reran.
*No. 31, rco-dig C nferenc My 11-10, 1941, pord bi theCivil
"No. 32, 'Poshate Haste Studiei. by R. C. Specht.
Conference. Oct. 6-7. l-4. palnsored by the Civil
Engint in 1)ejust atllv
No. 34. -Streamn Sanitation in Florida.' by E. B. Phelps and
D. E. Barry,
No. 35. -Proceeding,- of the Second National Public Health
Confterence." Nov. 16-1-. 1.;4G. sponsored by the
Civil Engineering Dortment'
No. 36. -Propeortis of Plain and Ratforced Limerock Con-
crete, by S. L. Bugg and D. A. Firmage.
No. 37. "Proceedngs of the First Structural Engineering Con-
forinck March 3-4, 19.0. Fpon-ored by the Civil
Eninering Department
No. 38, iReseirch for the Pulp and Paper Industry in the
Sount. by lt? cierncal Engineering Department.
No. 39. **Prceedings of the Fourth Annual Florida High-
way Conference." May 11-12, 1950. sponsored by
the Civil Engineering Department.
*No. 40. "Preservation of the Color and Sipe of Flowers,"
by R. C. Specht. ($1.00;
No. 41. "Second Short Course in Industrial Instrumentation,"
Sept. 11-13, 1r30, sponsored by the Chemical Engi-
neering Depairtment.
No. 42. "Third National Public Health Engineering Confer-
ence.' Oct. 23-24, 1950, sponsored by the Civil
Engineering Department.
No. 43. Precooling of Citrus Fruits." by J. T. Leggett and
G. E. Sutton
No. 44. "Proceedings of the Third Annual Surveying and
Mapping Conference."' Nov. 1-18. 1950. sponsored
by the Civil Engineeringf Department.
No, 45. *Florida Hurricanes of 150, by D. C. Bunting,
R. C. Gentry. M. H. Latour. and Grady Norton.
No. 46. ''The Development of Lightweight Aggregate from
Florida Clays." by A. F. Greaves-Walker, S. L.
Bugg, and R. S Hagerman.
'No. 47. "Prokcedings of the SecondAnnual StructuralEngi-
neerig Conlerence," March 19-17. 1951, spon-
eared by the Civil Engineering Department,
*No. 48. -PRadiological Health and Civil Defense."--Fourth
Annual Public Health Conference." March 27-30,
19 1, -ponsored by Civil Eginereie De pt.($1.00).
No. -1 1 1. Res rcht te Ennemermr and Industrial Ex-
pterint Sai."

As long as the supply is adequate, single copies of Station publications are free for general
distribution in the State of Florida unless otherwise indicated. Publications marked with an as-
terisk (*) are out of print or have been withdrawn from the free list, although the charge may be
waived in the case of public and semi-public agencies, such as libraries, research bureaus, and
technical societies. Please address all requests to: T'he Director, Florida Engineering and In-
dustrial Experiment Station, Gainesville, Florida.


No. 1. "Heats of Solution of the System Sulfur Trioxide-
Water," by Ralph A. Morgen.
No. 2. "*The Useful Life of Pyro-, Meta-, and Tetraphos-
phates," by Ralph A. Morgan and Robert L. Swope.
*No. 3. "Florida Lime Rock as an Admitue itz Mortar and
Concrete,," by Harry H. Houston and Ralph A. Morgen
*NO. 4. "Coutryl Hides and Skins," by William D. May.
No. 5. "Empirica Correction for Compressibilty Factor and
Activity Coefficient Curve," by R. A. Morgen and
J. H. Childs.
*No. 6. "Crate Closing Device," by William T. Tiffin.
*No. 7. 1 'The System Sodium Acetate -Sodium Hydroxide -
Water," by It. A. Morgen and R. D. Walker, Jr.
*No. 8. "Patent Policies for Sponsored Research," by Ralph
A. Morgen.
*No. 9. 1 Conservation of Municipal Water Supplies in Air-
Conditioning Systems,'" by N. C. Eaugh.
*No. 10. "Florida Scrb Oak--NewSource of Vegetable Tannin,"
by H. N. Calderwood and W. D. May.
*No. 11. "Protein Feed from Sulfte Waste Liquor," by Ralph
A. Morgen and Robert D. Walker, Jr.
*No. 12. "Effect of Moisture on Thermal Conductivity of Lime-
Rock Concrete," by black Tyner.
*No. 13. "Insect Tests of Wire Screening Effectiveness," by
S. S. Block.
No. 14. "Properties of Limerock Concrete"by Mack Tyner.
No. 15. "ScrubOak as a Potential Replacement for Chestnut,"
by H. N. Calderwod and William D. May,
No. 16. Yeast from Florida Sulfite Waste Liquor," by Robert
D. Walker, Jr.
No. 17. "Mildew-proofing Compounds," by S. S. Block.
No. 18. "Florida Limestone as a Paint Extender,", by A. L.
Kimmel and Mack Tyner.
No. 19. "Insecticidal Surface Coatings," by S. S. Block.
No. 20. "Residual Toxicity Tests on Insecticidal Protective
Coatings," by S. S. Block.
No. 21. Direction Finder for Locating Storm," by William
J. Kessler and Harold L. Knowles.
*No. 22. "*Impedance Matching Techniques," by William 1,
No. 23. "The Engineering Expriment Statio as a Stimulus to
the Graduate Program," by Ralph A. Morge.
No. 24. "Sewage Treatment Research at the University of
Florida," by John E. Kiker, and "New SewagePlant
Provides for Treatment, Research, instruction,,, by
Charles E. Richheimer and Walter J. Parks, Jr.
No. 25. "Transient-Response Flaizton Throug Steady-
State Methods," by William J. Kessler.
*No. 26. "What will be the Relative Humdity?,, by S.P. Goethe.
*No. 27. "The Distinction Between Effective and Circuit Band-
widths," by William J. Kessler.
*No. 28. "Measuring Pump Performance During Operation,"
by N. C. Ebaugh.
No. 29. "Maundacturing of Sand-Lime Brick," by Mack Tyner.
No. 30. "Production Cost Estimate of Brick blade
in Florida, by M. Tyner and A. F. Greaves-Walker.
No. 31. "Enthalpy Concentration Diagram for Hydrogen
Fluoride Water-System at One Atmosphere," by
Mack Tyner.
*No. 32. "Research in the Production of Gum Naval Stores,"
by Milton E. Ryberg and Harold W. Burney,
No. 33. "Fungicide-Treated Cotton Fabric Outdoor Exposure
and Laboratory Tests,", by S. S. Block.

*No. 34. ,Special Anodes for the Cathodic Protection of Water
Tanks," by A. L. Kimmel.
*No. 35. "Organic Reducing Agents as Air-Driers in Unsatu-
rated Polyester Resins,,, by D. M. French.
*NO. 36. "Tests of Insect Wire Screening," by H. W. Burney
and H. B. Williams.
No. 37. Diatomite Filters for Swimming Pools," by johE.
Kikr, Jr.
No. 38. "Tlhe Technology of Tall Oil with Special Referenceto
the Paint and Varnish Indlustry," by D. L. Emerson, r.
No. 39. "The Solvent Extraction of Asphaltic Residues," by
H. E. Schweyer and 0. M. Brown.
No. 40. "Construction of Highways over Peat and Muck
Areas," by B. E. Colley.
*No. 41. "Intrmittent Sand Filter Studies," by G.R. Grantham,
D. 1. Emerson, and A. K. Henry.
No. 42. "Specia Relativity and the Electron," by Willis W.
No. 43. "A Stabilized Voltage-Dropping Element," by Sydney
E. Smith.
No. 44. "Impedance of Resonant Transmission LInesandWave
Guides." by Willis W. Harman.
No. 45. "*Earth as a Heat Source and Sink for Heat Pumps,"
by S. P. Goethe, G. E. Sutton, and W.A. Leffler.
No. 46. "Alarm Systems for Condensate Return Lines in
Citrus Processing Plants," by G. E. Remp.
No. 47. "Determination of Minimum Air Requirements for
Summer Air-Conditioning,", by S. P. Goethe.
No. 48. "Lightweight Aggregate Production from Phosphate
Slimes," by R. C. Specht, and W. E. Herron, r.
No. 49. "Pulping of Scrub Oak by the Kraft Process," by
R. L. arvin, G. B. Hills, Jr., C. W. Rothrock, Jr.
and W. J. Nolan.
No. 50. "Progress Report on Trickling Filter Studies," by
G. R. Grantham, Earle B. Phelps, W. T. Calaway,
and D. L. Emerson, Jr.
No. 51. Rational Design Criteria for Sewage Absorption
Fields.", by John E. Kiker, Jr.
No. 52. "Granular Stabilization with Limerock," by J. A.
No. 53. "Low Temperature Calcination Rates of Limestone.",
by Archie Wakefield, Jr. and Mack Tyner.
No. 54. "Roof Spray for Reduction in Transmitted Solar
Radiation," by G. E. Sutton.
No. 55. "A Study of Some Metals for Use as Permanent
Anodes In Water-Tank Cathodic Protection Systems'.
by A. L. Kimmel.
NO. 56. "Study of the Tannin Contents of Barks from the Flor-
Ida Scrub Oaks Quercus laevis and Q. cnerea,"1 by
1. S. Rogers, H7. a de-ood ;ii-d- ebe.
No. 57. "Expectancy and Intensity of Excessive Rinfalls at
Jacksonville, Florida--1910-1948,"1 by David B.
No. 58. "Cascading Cathode-Followers to Provide High-
Impedance Transformation Ratios," by Sydney E.
Smith and William J. Kessler.
No. 59. "Reciprocal Aspects of Transient and Steady-State
Concepts," by W. J. Kessler.
No. 60. "Protection of Paper and Textile Products from
Insect Damage," by S. S. Block.
No. 61. 1 An Atmospherics Waveform Receiver ',Iby William
J. Kessler and Sydnev E. Smith.
No. 62. "The Lime Industry in Florida," by James M.


No. 17. "Canning Industry," by Industrial Engineering Dept.
No. 19. "Lumber and Basic Timinxr Irxinustries," by Industrial
Engineering Dept
No. 20. "Pulp and Paxr Industry," by Industrial Erngineering
No. 21. "Fertilizer Manufacturing Industry," by Industrial
Enlginvring Depl.
*No. 22. "Effect of Wast! Dispo)sal of the Pebble Phosphate
Rock Industry in Florida on Condition of Receiving
Streams," by R. C. Specht.
No. 23. "Watermelon Seed Harvesting Machines Improved,"
by H. B. Williams.
No. 24, "Opportunities for Lime Production in Florida." by
Mack Tyner.
No. 25. MFlorida--A Look Into the Future." by Ceorge B.
No. 26. "Better Tools for Gum Production," by Milton E.
No. 27. "Injection Molding of the Acid Spray Gun Nozzle,"
by H. W. Burney.
No. 28. "Titanium Rapidly Growing as Useful Engineering
Material," by W. T. Tiffin and P. C. Hoffman.
No. 29. "What, Where and How Much," by Ralph A. Morgen.
No. 30. "The Heat Pump--A Gold Mine?"by George E.Sutton.
N. 31. Building an Engineering Curriculum," by Joseph
No. 32. "An Acid Spsayin, Puller for Naval Stores Produc-
tion," by M, E. Ryberg and H. E. Burney.

*No. 1. "Dilroc--A New Insecticide Diluent," by Mack Tyner.
*No. 2. "The Heat Pump--The Choice and Cost of Various
Systems," by S. P. Goethe-
No. 3. "New Use for Florida Limerock," by Mack Tyner.
No. 4. "Chemurgic Research for Industries in Florida,"
by Robert D. Walker, Jr.
No. 5. "School Tests Sewerage for Florida TownV, Iby DI.
Emerson, Jr.
No. 6. "Tests of Screening Effectiveness Against Insects,"
by S. S. Block.
No. 7. "Advancement in Timber Mechanics and DesignCalls
for Specially-Trained Engineers," by Howard J.
No. 8. "Design of Plywood I-Beams," by Howard J. Hansen.
No. 9. "Lightweight Concrete Aggregate from Phosophate
Waste," by A. F. Greaves-Walker and P. P. Turner,
*No. 10. "Corrosion Research at the Florida Engineering and
Industrial Experi ment Station," by A. L. Klmme .
No. 11. "Some Notes on Florida Petroleum," by H. E.
*No. 12. "Faculty Personnel Factors and Promotions," by
Joseph Well.
No. 13. "Weather and Electronics Research." by E. D.
No. 14. "Cigar Mnufacturug Indu.stry,-' t Indtrial Eni
neering Dept.
No. 15. "Tung Oil Industry," nby Industrial Engineering Delt
No. 16. "Phosphate Industry," by Industrial Engineerumg Dept.