how many miles of interstate highways are there in the us
Interstate Highway System The Dwight D. Eisenhower National System of Interstate and Defense Highways (commonly known as the Interstate Highway System, Interstate Freeways, 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, as of 2013[update], it had a total length of 47,856 miles (77,017 km).[2] As of 2013[update], about one-quarter of all vehicle miles driven in the country use the Interstate system.[3] In 2006, the cost of construction was estimated at about $425 billion[4] (equivalent to $526 billion in 2016[5]).