The
Dwight D. Eisenhower National System of Interstate and Defense Highways (commonly known as the
Interstate Highway System,
Interstate Freeway System,
Interstate System, or simply
the Interstate) is a network of
controlled-access highways that forms a part of the
National Highway System of the
United States. The system is named for President
Dwight D. Eisenhower who championed its formation. Construction was authorized by the
Federal Aid Highway Act of 1956, and the original portion was completed 35 years later, although some urban routes were cancelled and never built. The network has since been extended and, , it had a total length of , making it the world's second longest after
China's. , about one-quarter of all vehicle miles driven in the country use the Interstate system. The cost of construction has been estimated at $425 billion (in 2006 dollars).