the past year. This work is of importance since it is hoped that ultimately it will lead to the development of tests which will insure tre durability of this type of bituminous material which is used extensively in low-cost surfaces. A progress report of the work to date has been prepared. Similar materials from other refineries, as well as liquid asphaltic materials of the rapid-curing type and tars from various producers, are to be studied during the coming year. The development of a satisfactory accelerated laboratory test, to supplement the tests more commonly used for the control of quality of liquid bituminous products, should aid greatly in securing longer life and greater durability of the materials.

Laboratory investigations to determine and evaluate the factors essential to the proper design of hot bituminous paving mixtures have been continued. These investigations involve tests of laboratory and field samples both with the Hubbard-Field stability apparatus and with the roller stability machine designed by the Bureau to simulate the action of traffic. A progress report is now being prepared.

There has recently been built for testing purposes a small circular test track having an outside diameter of 14 feet and a width of 18 inches. Facilities are provided for temperature control and provisions are made for variations in the type and condition of the base. Traffic is applied to the test surface with full size rubber-tired automobile wheels. This permits the testing of low-cost bituminous surfaces under controlled conditions which are essentially comparable to those of actual service. To date, the effect of various quantities and consistencies of the bituminous material, in mats of the road or plant-mixed type, has been studied. As the work progresses, tests will be made to determine the relative importance of other factors which influence the stability and durability of the different types of low-cost bituminous surfaces, such as type of bituminous material, type and grading of mineral aggregate and character and condition of the base.

Concrete pavement design.-This investigation, which has for its object the development of information that will assist in a better understanding of the structural action of concrete pavement slabs and thus lead to improved structural design, has been actively prosecuted during the past year. Observations of the effect of loads and temperature are being made on 10 full-size concrete pavement slabs of various designs and a considerable amount of new information of a definite and conclusive nature has been developed.

Motor-vehicle impact investigations. The past investigations of motor-truck impact have involved primarily the determination of the magnitude of impact reactions on road surfaces and the variables which exert a major influence. Attention is now being directed to the effect on the road surface itself of these suddenly applied impact forces.

In the study of concrete pavement design, described above, much has been learned of the relation between static loads and stresses in the pavement slab. For loads due to impact the same relationships do not necessarily exist and, although definite information is lacking, there are indications that the relationships may be quite different.

The program of study which has been outlined includes a series of tests to determine the relative effects of static and impact forces on massive concrete specimens under carefully controlled conditions. For this work a specially designed pendulum-type impact machine has been designed and is being built. The program also includes comparative static and impact tests on actual pavement slabs, to follow the series of laboratory tests.

The degree of road roughness is one of the major variables which influence the magnitude of impact reactions produced by vehicles and it is, therefore, highly desirable to have some method by which it may be measured. Several years

ago the Bureau developed a device, to be mounted on a motor vehicle, by which the successive deflections of the front springs of the vehicle, caused by the surface roughness of any road over which it might be driven, could be summed up and recorded in inches. The device was intended to indicate the relative roughness of road surfaces by the relative amounts of spring deflection recorded on different roads. There was full realization of its limitations, but it is useful nevertheless and has been used in many parts of the country. Its principal shortcoming is that the general level of the values recorded is affected by the vehicle characteristics (springs, weight, tire equipment, etc.), so that it is not possible satisfactorily to compare data obtained with the instrument mounted on different vehicles. This deficiency led to an investigation of the possibility of developing a standardized vehicle that could be used with the relative roughness indicator.

During the past year considerable study has been given to this problem. A single-wheel trailer has been built, capable of standardization in all of it parts, and the work done with it thus far gives promise that it may be satisfactory. It is relatively simple to build and can be readily attached to the rear bumper of any automobile. With such a vehicle it should be possible to compare directly data taken with different units at widely separated points or to compare data taken from time to time with the same unit. If this becomes possible, the usefulness of the relative roughness indicator will be greatly increased.

INVESTIGATIONS OF CONCRETE AND CONCRETE AGGREGATES

During recent years considerable attention has been given to studies of the effect on the quality of pavement concrete of variations in the concrete mixture and in the construction operations incident to placing and finishing it. These studies have been of such character that they could not be made with laboratory specimens but required that the concrete be mixed and placed under actual field conditions and with full-size construction equipment.

The latest of these investigations to be completed involved a study of the effect of high-speed vibrators mounted on the screeds of a standard finishing machine for compacting and finishing the concrete, and the effect of "delayed finishing", or the continued surface manipulation of the concrete, to remove excess water and consolidate the mass.

The tests have shown that, as compared with the standard finishing machine, the employment of vibratory equipment will permit the use of considerably more coarse aggregate and less cement in the mix without detriment to the quality of the concrete. Similar results were obtained with "delayed finishing" as compared with the standard method of machine finishing.

It is generally difficult, if not impossible, to estimate the saving in money which may result from the information developed by research. This project is somewhat unique in that the results are of a character which permit such an estimate to be made. It is estimated conservatively that if the results of the study of vibratory finishing machines were applied to all the concrete pavement construction in the United States, it would result in an annual saving in excess of one and a half million dollars. The investigation cost approximately $25,000.

Several studies having to do with the general question of improving concrete from the standpoint of durability or resistance to weathering are being continued. In one series, a number of mortar specimens containing various types of concrete sand are being subjected to alternate freezing and thawing for the purpose of developing information which will make it possible to include in specifications definite quantitative requirements designed to insure durability of fine aggregates. In an effort to improve existing methods of testing the wear-resisting qualities of coarse aggregate, a study was undertaken of the so-called "Los Angeles Rattler" test used by the State of California. It has been claimed that this test is superior to the existing standard method because it is possible to test both crushed stone and gravel by the same method, thus eliminating the necessity for two separate specification requirements as at present. These tests were conducted in cooperation with the American Association of State Highway Officials.

During the past year an investigation has been started which has for its major object the development of a standard laboratory method for testing the numer ous new methods and materials continually developed and promoted for curing concrete. Some of these methods have merit and some do not. No standard method of testing exists and in the past it has been customary quite generally to investigate methods of curing by studies in the field on actual construction work. This has been expensive and, on account of the presence of variables that could not be controlled, the results frequently have been inconclusive. It is becoming increasingly necessary to have a relatively simple, rapid, and inexpensive test that can be conducted under controlled conditions in the laboratory.

One of the new curing methods that presents interesting possibilities, not only as a means of curing but also as a means of insulation, involves the use of a cotton mat formed of one or more layers of raw cotton or cotton waste placed between sheets of cotton cloth. A laboratory study of this material showed quite definitely that the cotton mats were not only effective in providing insulation against the heat of the sun but also that, with only one wetting, they were as effective in providing good curing as the standard method of using a double thickness of burlap kept wet continuously for 3 days. One State highway department has already begun the use of this method in a limited way and others are express

ing interest. If generally adopted, the method will not only provide an effective method of curing but also will provide another market for cotton.

Attention has been called recently to the extreme importance of controlling the temperature and moisture content of concrete specimens at time of test if reliable results are to be obtained. One series of tests, conducted for the purpose of developing information along this line, has been completed. Another series involves tests, at various periods up to 1 year, of concrete containing both normal and light-weight aggregates stored and tested under both wet and dry conditions. These tests should also yield information of value as to the effect of artificial light-weight aggregates on the strength of concrete at different ages and under various curing conditions.

Highway bridge investigations.-A complete report of the cooperative investigation of the Freyssinet method of arch construction as applied to the Rogue River bridge in Oregon has been completed and is being published as a bulletin of the Oregon Highway Commission.

A cooperative study of multiple-span reinforced concrete arch bridges has been completed at the University of Illinois. This study was made for the purpose of determining the effect of spandrel structures of various types and elastic piers of various heights on the action of concrete arches. For this pur

pose several multiple-span arch ribs, each of three 26-foot spans, were built in the laboratory, and deformation measurements were made under loads of different intensities and distribution. The factors studied were spacing of expansion joints in the deck, height of deck above the rib at the crown and height of elastic piers. Much information that will be useful to bridge designers was developed by this study. A complete report is now being compiled.

Tests to determine the friction developed in the sliding of expansion bearings in highway bridges, when the bearing plates are made of various materials and finished in different ways, were mentioned in last year's report. During the past year the schedule of tests has progressed steadily. Several hundred tests have been made and an appreciable range in the coefficient of friction has been found to exist. The publication of the information obtained in this investigation should assist bridge engineers materially in the deisgn of sliding bearings.

ECONOMIC RESEARCH

All of the following research projects originated in requests from the State or other authorities involved, and have been organized and conducted for the purpose of arriving at specific information desired for some definite purpose in connection with either highway administration or State legislation.

Washington_regional area traffic survey.-A complete report on this project was completed for publication in December 1933. It covers a 12 months' investigation of traffic throughout the area surrounding the District of Columbia. The survey has developed information that will enable the cooperating agencies to plan a comprehensive and connected system of highways in the Washington regional area, and establish a priority program of highway construction and betterment which may include suitable belt lines, relief roads, or necessary relocations and extensions of existing highways. On this work the Bureau cooperated with the following agencies:

National Capital Park and Planning Commission

Maryland State Roads Commission

Virginia State Highway Commission

City of Alexandria, Va.

Prince Georges County, Md.

Montgomery County, Md.

Arlington County, Va.

Fairfax County, Va.

Maryland-National Capital Park and Planning Commission

New Jersey traffic survey.-Field work on a 12 months' traffic census throughout the State of New Jersey was completed in August 1933 and a report is now being compiled. This survey has produced data on the flow of traffic over the entire State highway system, and on a limited mileage of principal county roads as well. Special study was given to truck traffic, with results that are expected to provide the most detailed and accurate information thus far available on this important portion of highway traffic.

Indiana traffic survey.-Field work on a 12 months' survey of traffic in 11 counties of Indiana was completed in August 1933. This study has developed information regarding the relative proportions of foreign and local traffic on

township, county, and State roads. The Indiana State Highway Commission is compiling the resulting report.

Florida traffic survey.-Field work on a State-wide survey of traffic in Florida, to extend 12 months, began in September 1933. This survey will elicit, in additio to the usual data on traffic density, useful information on the flow of tourist traffic into and out of Florida, and motor truck movements of fruits and vegetables to northern markets.

Connecticut traffic survey.-Field work on a traffic census in Connecticut was begun in September 1933 to last 12 months. The results of this survey will be of special interest by affording comparison after 10 years with a similar survey conducted by the Bureau in 1922-23. Data will also be gathered with specia! reference to traffic between city and country points. Classification will be made of truck operation, and studies of prevailing speeds on congested, medium, and light traffic routes will be carried on during the survey.

Intersection studies.-Investigation has been continued to measure delays to vehicles caused by various types of traffic control, and to ascertain the conditions to which the common types of control are best adapted. Results of observations made in Washington, DC., and the immediate vicinity, and on the new viaduct across the Hackensack Meadows between Jersey City and Newark, N.J., have been complied. Successful results have been obtained by means of an electrical time recorder, and a technique for using this device has been perfected.

Highway tax studies.--A series of three tax studies in the States of Wisconsin. Michigan, and Illinois has been made in cooperation with the Department of Economics of the University of Wisconsin and the respective State highway departments, and results have been published. A new investigation of this nature is now under way in New Hampshire under the same cooperative arrangement. The purpose of these studies is to establish the relation of the highway taxes paid from different sources with highway expenditures on the different classes of roads, and to correlate the income and expenditures with the highway service furnished by the several classes of highways. These studies will establish a broad basis for the adjustment of highway taxes on a rational plan.

Reflector buttons.-Tests in cooperation with the United States Bureau of Standards designed to determine the comparative efficiency of various types of highway signs using reflector buttons have been completed and the results published. The tests were made by both photometric and personal visual observations. Supplemental tests on other types of reflector buttons are now being given consideration.

Lateral distribution of traffic.-In order to determine the distribution of vehicles on the highway surface, photographic observations have been made with a moving-picture camera on heavily traveled highways. The resulting films will show the width and length of highway utilized by vehicles in passing each other, the usual position taken by vehicles of various kinds on the highway when in motion, and similar pertinent data.

Special statistical investigation.-In order to determine for the first time the extent of fees and taxes imposed upon the numerous types of motor vehicles by the many taxing jurisdictions-Federal, State, county, municipal, and others-s special investigation has been undertaken throughout the 48 States and the District of Columbia. Figures in the great detail desired were compiled by special statisticians working in the motor-vehicle departments and other agencies of every State. The resulting report was completed at the end of 1933.

COMBINATION PHYSICAL AND ECONOMIC RESEARCH

The major purpose of these studies is to reduce highway construction costs. The method of attack is both simple and direct and the results obtained so far have been most gratifying.

Careful and repeated time studies of the various unit operations involved in regular methods of highway construction have shown that the time and energy expended by construction forces seldom if ever yield their possible maximum in productive results. This is largely due to the fact that most modern highway construction methods involve the almost constant repetition in some definite order of certain cycles or series of operations. Consequently any regular increase of the time required to perform any part of the cycle, or even any relatively small but recurring interruptions to the orderly progress of the various steps in the cycle. or any failure to properly coordinate or synchronize the various dependent operations is at once translated into a corresponding decrease in the production. Since, however, the daily or hourly operating cost of the construction organization

emains practically constant for any given set of conditions, the unit operating sts vary nearly inversely as the rate of production.

Several years of experience has therefore shown that reduced unit construction usts are most surely obtained by the elimination or reduction of the delays, lost notions and wastes of energy associated with our present construction methods. The studies, which are carried on in the field on going projects, have a dual purose, (1) to develop and put into practical operation ways, means, and methods hat will serve to enhance the efficiency of road construction operations of all inds, and (2) to disseminate a working knowledge of the more efficient methods thus developed and encourage their adoption in road construction work generally, with resultant lowering of costs and a consequent saving of highway funds.

The latter purpose is achieved in several ways. The contractors with whom the Bureau cooperates acquire a knowledge of the methods employed in analyzing the various operations, detecting losses and waste motion, and ascertaining the hanges and adjustments of plant and working force needed to improve efficiency. The better methods of operation developed by the demonstrations almost invariably become the standard practice of these contractors in their subsequent work.

While the number of contractors with whom the Bureau can cooperate thus directly is limited, the benefits of the studies are extended to a constantly inreasing number of the most progressive road builders by means of the example of the aided contractors, by published reports and by papers presented by representatives of the Bureau at meetings of contractors and highway engineers. The various associations of contractors have manifested a keen interest in all phases of the work and have made it the subject of discussion at many of their meetings.

As grading or earth-moving operations constitute a considerable item in all road construction the first work undertaken in these studies was directed to the operation of earth-moving equipment. Beginning with the lighter equipment, such as wheel scrapers, and fresnoes, the studies were extended to include the operation of elevating graders, steam shovels, and drag lines. Each type of equipment was studied in actual operation with the object of determining how and to what extent the preventable time losses were possible of elimination without incurring corresponding increase in operating costs. Increases in production rates of from 10 to 30 percent have been common on the various grading projects studied.

Comprehensive reports covering these studies have been published which outline in detail the principles involved. These reports also indicate the economic limits of various types of earth-moving equipment for various kinds of grading work and suggest further improvement in the design of the highway grade to permit more economical handling of the earthwork.

In

The studies, as extended to concrete paving, afford great opportunity for savings because of the amount of such work being done. These studies have centered largely on determining the preventable time losses in the various unit operations and on the development of practical methods of preventing such losses. concrete paving work the production rate is dependent on the mixer and all other operations must be balanced to accord with the mixer cycle. Any operations that delay the mixer restrict production. As in the grading studies, it has been found possible on all projects studied to increase the rate of production without incurring a corresponding increase in the hourly operating cost.

Similar studies have been made on other types of construction, including bituminous surfaces of various types. All of the work has been directed toward securing decreased construction costs without impairment of the quality of the finished product.

In the efforts to relieve unemployment there is a tendency toward substitution of hand labor for mechanical equipment. On Federal projects it is expected that hand-labor methods of construction will be required to the greatest extent possible without interfering with the quality of the work or unreasonably increasing its total cost. As a guide in determining how far this tendency may reasonably be carried, studies are being made to ascertain for each class or type of construction just what operations may be performed satisfactorily and profitably with hand labor and how and to what extent present methods, technique and rates of operation must be modified or discarded in order to accomplish this purpose. Last year a study was made of the extent to which labor profits from the construction of high-type pavements in which mechanical equipment plays an important part. In this study the money paid out by States or communities for the construction of a concrete pavement was traced through its various