legislation required all interstate highways to have at least four lanes (two in each direction). Rest areas would line the highways, but all commercial establishments, including gas stations, were prohibited. The 1966 revisions also allowed existing bridges, tunnels, and toll roads to become part of the system provided they met its strict standards and enhanced transport integration.

There is unresolved rivalry over which segment was first built: the states of Pennsylvania, Missouri, and Kansas all claim the first segment of the interstate system, but their entries were either started before the 1956 act or were upgrades of existing roads. Originally expected to take thirteen years, construction took, nearly forty, some of the delay being due to changes in plan, as well as environmental and social issues. In 1990 the project, finally extended to just under 42,800 miles (68,500 kilometers), was renamed the Dwight D. Eisenhower System of Interstate and Defense Highways. The network, completed in 1995, represents under 2 percent of total road mileage in the United States, but it accounts for almost 25 percent of all national travel miles. A 1958 estimate put the total cost of construction at $37.6 billion; that rose to $130 billion, mostly because of inflation.

The Dwight D. Eisenhower System of Interstate and Defense Highways has met at least its economic goals, a success that may be measured by its projected usage being reached ten years earlier than predicted. During construction it provided job opportunities throughout the country and enhanced the national economy. It allows the decentralization of commerce and industry, makes intercity travel much easier, and increases the mobility of the workforce. Indeed, some estimates claim it has already returned, in terms of economic productivity, six times its construction coat. Other statistics suggest another major socioeconomic benefit: dramatic reductions in the number of road fatalities and injuries, just as Eisenhower predicted.

Further reading

Cox, Wendell, and Jean Love. 1996. The Best Investment a Nation Ever Made: A Tribute to the Dwight D. Eisenhower System of Interstate and Defense Highways. Washington, DC: American Highway Users Alliance.

Rose, Mark H. 1990. Interstate Express Highway Politics,1941–1989. Knoxville: University of Tennessee Press.

Seely, Brute E. 1987. Building the American Highway System: Engineers as Policy Makers. Philadelphia: Temple University Press.

Weiner, Edward. 1992. Urban Transportation Planning in the United States: An Historical Overview. Washington, DC: Office of the Secretary of Transportation.