The Traffic Survey and Its Uses

By L. E. PEABODY, Highway Economist, U. S. Bureau of Public Roads, in the United States Daily THE highway traffic surveys made by the Bureau of Public Roads, in cooperation with state and local highway authorities, are much more than mere counts of the vehicles on the highways. They give to highway officials desirous of conducting their operations in a business-like manner the one sure means of dealing justly with the many demands made on them for highway improvements.

They afford the basis of a rational budget and program of road improvement. They show the real highway needs of the present traffic and they provide the necessary basis for estimation of future needs.

Such surveys have been made by the Bureau in the states of Maine, New Hampshire, Vermont, Connecticut, Pennsylvania and Ohio, and for the purpose of solving pressing metropolitan problems in the counties adjacent to Chicago and Cleveland. During the present year simultaneous surveys will be made with the Bureau's help on all the Federal Aid roads of the states of Washington, Oregon, California, Idaho, Montana, Utah, Nevada, Arizona, Wyoming, Colorado, New Mexico and Nebraska Thus, with the direct assistance of the Bureau a number of states have provided themselves with the factual information which is essential to the businesslike conduct of the work of road improvement, and others are about to profit in a similar manner. Others with which there have been no direct cooperation have followed the methods developed by the Bureau in making surveys under their own auspices; and the same methods are used by consulting experts employed by a number of cities to work out their traffic problems.

Simple counts of the vehicles using the highways on one or two days of each year have been made for a number of years by several of the state highway departments. Such counts are now found to be of limited usefulness and, when the counts are made at the wrong season of the year, as they often are, the information they supply may be actual ly misleading.

From this simple and inadequate form the methods of traffic analysis have been developed under the Bureau's leadership, so that there is now provided forthe guidance of administrative officials a complete and understandable picture of the existing highway situation and a clear indication of the future needs.

Contributing to the composite picture, in addition to data showing the average daily use of each section of the highway system, are detailed data that show the composition of the traffic, the number of passenger cars, trucks and other classes of vehicles, the origins and the destinations of these vehicles, whether they are owned by farmers or city dwellers, the regularity and frequency of the trips they make and a variety of other data.

The uses of such traffic data are as varied as the information itself. Tne constant urge of public opinion for more and better highways compels a selection of routes for first improvement, because obviously the amount of work possible at any time is limited by the construction equipment and money available.

The traffic survey provides a sure means of classifying highways in the order of their importance. The type and design of surface, the width necessary and sometimes the grades and curvature are directly related to the traffic data, which indicate the specific requirements to be met in design and construction.

The information regarding origin and designation enables one to place correct values on local and long-distance traffic as affecting the general layout of the highways and the construction program. This information also indicates the need of new roads or of alternate roads to carry traffic between definite points.

In city areas proper control and regulation require traffic information to locate congestion points or congested routes as a basis for establishing traffic lights and controls and to determine the specific needs for new streets and structures. Many surveys have demonstrated that present facilities are ample if traffic is properly redistributed and con trolled.

Studies of parking practices and resulting reforms in such practices have been of prime importance in city work. The separation of traffic, by routing passenger cars and light vehicles on one street or level and heavier on another, has been helpful in raising the traffic efficiency of existing facilities.

In addition to these uses of the census data for purpose of broad planning, there are a number of special problems, in dealing with which an exact knowledge of the traffic density and other characteristics is of primary value. Some of these other uses are suggested simply by stating a few of the more common highway problems:

The above list is not exhaustive, but it is clear that the proper solution of each of the problems mentioned is dependent upon a precise knowledge of the traffic to be served; and it is also apparent that a variety of facts concerning the ... required for the solution of the various problems.

For some the data required are those which will furnish an accurate idea of the flow of traffic throughout the year; others require a knowledge of winter traffic, others of peak density, others of some fraction of the total traffic, such as motor trucks, foreign vehicles, etc.

In planning a traffic survey it is essential that there shall be a clear understanding of the method be employed in converting the basic data to the solution of the various problems. Otherwise essential data may not be obtained and much gathered that is later found to be useless. The method employed must be carefully designed to supply a maximum of information, precisely the kind required, at a minimum of expense.