interstate

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. Construction of the system was authorized by the Federal Aid Highway Act of 1956. The system extends throughout the contiguous United States and has routes in Hawaii, Alaska, and Puerto Rico.
The U.S. federal government first funded roadways through the Federal Aid Road Act of 1916, and began an effort to construct a national road grid with the passage of the Federal Aid Highway Act of 1921. After Dwight D. Eisenhower became president in 1953, his administration developed a proposal for an interstate highway system, eventually resulting in the passage of the Federal Aid Highway Act of 1956. Construction of the Interstate Highway System was proclaimed complete in 1992, though some planned routes were canceled and several routes have stretches that do not fully conform with federal standards. The cost of construction of the Interstate Highway System was approximately $114 billion (equivalent to $521 billion in 2018). The original system has been expanded numerous times through the creation of new designations and the extension of existing designations.
Though much of their construction was funded by the federal government, Interstate Highways are owned by the state in which they were built. All Interstates must meet federal standards such as having controlled access, using a minimal number of traffic lights, and complying with federal traffic sign specifications. Interstate Highways use a numbering scheme in which primary Interstates are assigned one- or two-digit numbers and shorter routes are assigned three-digit numbers where the last two digits match the parent route. The Interstate Highway System is partially financed through the Highway Trust Fund, which itself is funded by a federal fuel tax. Though federal legislation initially banned the collection of tolls, some Interstate routes are toll roads.
As of 2016, about one-quarter of all vehicle miles driven in the country used the Interstate Highway System, which had a total length of 48,191 miles (77,556 km). Several future routes are in development.

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