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Rh UNIFORM APPLICATION OF GEOMETRIC AND CONSTRUCTION STANDARDS

Section 108 (i) of the 1956 act requires the geometric and construction standards for the Interstate System to be approved by the Secretary of Commerce in cooperation with the State highway departments, and that these standards shall be adequate for the types and volumes of traffic forecast for the year 1975. Appropriate committees composed of State highway department and Bureau of Public Roads engineers had been working for several years under sponsorship of the American Association of State Highway Officials in developing design standards for the Interstate System. The standards used in making the estimate reported herein were adopted by full membership vote of the American Association of State Highway Officials on July 12, 1956, and approved July 17, 1956, by the Commissioner of Public Roads acting for the Secretary of Commerce.

To serve as a standard guide, the Bureau of Public Roads, working with representatives from the State highway departments, prepared in October 1956 an Instruction Manual for Preparation and Submission of Detailed Estimate of the Cost of Completing the Interstate System in Accordance with Section 108 (d) of the Federal-Aid Highway Act of 1956.

This manual outlined in detail the procedures to be followed in preparation of the estimate. It was furnished to all State highway departments. An additional guide was prepared by the Bureau of Public Roads and furnished to the States to serve as a means of checking their forecasts of traffic. Since everyone working on the estimate was provided with the same guides, maximum uniformity has been obtained.

Uniformity as used here does not mean that the average cost of constructing a mile of road, or any other average factors, will be the same in all States. Such a comparison of averages is meaningless because of wide variations in conditions such as traffic, terrain, climate, and other factors peculiar to individual States and even within different portions of the same State.

Within the scope of practical uniformity there is a balance between traffic needs in a particular circumstance and the highway design used to satisfy that need. There are and should be provisions for some range and variation in design. These variations will include such things as widths of rights-of-way and the kind of improvements to be removed therefrom, pavement-and subbase thickness, bridge foundations and types and the frequency and length of structures, number of traffic lanes, frequency and complexity of interchanges and grade separations, and many other elements involved under various local conditions. Uniformity in this sense, therefore, means the application in all of the States of the design range provided in the Geometric Design Standards approved for the Interstate System Pursuant to section 108 (i) of the 1956 act.

PREPARATION OF THE ESTIMATE AND THE BASIC PRINCIPLES AND PROCEDURES FOLLOWED

The estimate of cost of completing the Interstate System was prepared in each State by personnel from the State highway departments and the division offices of the Bureau of Public Roads.