Interstate Highway System

The Beginning of the Interstate System

Although it would informally become known simply as “the Interstate,” the official name of the proposed system was “The National System of Interstate and Defense Highways.” Final changes expanded the system to 41,000 miles (65,983 kilometers) and authorized $25 billion to be made available in fiscal years 1957 through 1969. The share paid by the federal government would be 90 percent. The money was the sticking point in Congress—no one wanted to pay the bill. The Federal Aid Highway Act of 1956 did not win approval until Representative Hale Boggs (D-Louisiana) of the House Ways and Means Committee, at the suggestion of Secretary of the Treasury George Humphrey, proposed the creation of the Highway Trust Fund, modeled after the Social Security Trust Fund. Revenue from taxes on highway-user products would be credited to the highway fund for use exclusively on the interstate system and other federal-aid highway and bridge projects.

In July 1956, the Bureau of Public Roads (BPR) and the American Association of State Highway Officials (AASHO) collaborated on the design standards. They agreed that the system would consist of divided highways with four or more 12-foot (3.7-meter) lanes. Controlled access would be the rule, with any crossroads moving over or under the routes. All overpasses had to have a 16.5-foot vertical clearance above the freeway, although 14-foot overpasses were permissible within urban areas. This particular specification was included to enable military equipment to pass clearly below an overpass, a reminder that national defense was paramount in the minds of the system's designers. Although military equipment of this size is not commonly transported on the Interstate Highway System, the standard remains. The highways were designed for speeds of 50 miles per hour (mph; 80.5 kilometers per hour, km/h) in mountain terrain, 60 mph (96.6 km/h) in rolling terrain, and 70 mph (112.7 km/h) in flat terrain.

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