How long is the Interstate System?
Currently, the Interstate System is 46,876 miles long. The Federal-Aid Highway Act of 1956 imposed a statutory limitation on the Interstate mileage that would be built with Interstate Construction funds under the new program (41,000 miles at the time). Later legislation increased the limitation to 43,000 miles, of which a total of 42,795 miles has been used. Separate legislation allows the Federal Highway Administration to approve additional mileage if it meets full Interstate standards and would be a logical addition or connection. Beyond the 42,795 miles, this additional mileage is not “chargeable”—that is, it is not eligible for Interstate Construction funds under the 1956 Act, as amended, although the State may use other Federal-aid funds to help with construction.
