The Dwight D. Eisenhower National System of Interstate and Defense Highways, commonly known as the Interstate Highway System, is a network of controlled-access highways that forms part of the National Highway System in the United States. The system extends throughout the contiguous United States and has routes in Hawaii, Alaska, and Puerto Rico. As of 2020, about one-quarter of all vehicle miles driven in the country used the Interstate Highway System, which had a total length of 48,756 miles (78,465 km).