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 by joint action of the State highway departments of each State and the adjoining States. All routes so selected were automatically to become part of the Federal-Aid Primary System without regard to previous mileage limits on that System.

In February 1945 the PEA requested each State to submit recommendations for the Interstate System routes within its boundaries. When these recommendations were all in, they totaled 45,070 miles—considerably over the legal limit and far above the 33,920 miles recommended by the Interregional Highway Committee. Two thousand miles were circum- ferential or distributing routes around the large cities. The PRA decided to defer consideration of these to a later date and concentrate on getting the States to agree on the main routes between the cities.

After weeding out the routes with the weakest justifications and adding a small mileage requested by the War Department, the PRA came up with a total of 37,324 miles for the main routes. In March 1946 the PRA sent each of the States a map showing this tentative integrated system and asked for their concurrence. The first State to concur was Nebraska, and by June 1946 acceptances had been received from 37 States.

It required a year for the PRA and the remaining 11 States to iron out their differences, but agreement was finally reached on a 37,681-mile System, including 2,882 miles of urban thoroughfares. Some 2,319 miles were reserved for urban circumferential and distributing routes, to be selected later. The Federal Works Administrator approved this System on August 2, 1947.

While the States were selecting the Interstate routes, the PRA asked the American Association of State Highway Officials to propose standards to control the location and design of the Interstate highways. “There was no thought of requiring that every mile of the system be built according to a rigid pattern but it was believed essential that there be a high degree of uniformity where conditions as to traffic, population density, topography, and other factors are similar.”

The projected routes of the Interstate System as approved by the Federal Works Administrator, 1947.

AASHO’s Committee on Planning and Design Policies had been formed in 1937 to review and evaluate the immense amount of research and operational information on highways that had accumulated since the 1920’s. Between 1938 and 1944 the Committee summarized the existing knowledge of geometric design and good design practice in seven “Policies” which were adopted by the Association and became, in effect, the national design policies for highways. Because of this prior work, the Committee was able

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