United States Numbered Highways

The system of United States Numbered Highways (often called U.S. Routes or U.S. Highways) is an integrated system of roads and highways in the United States numbered within a nationwide grid. As these highways were coordinated among the states, they are infrequently referred to as Federal Highways, but they have always been maintained by state or local governments since their initial designation in 1926. The numbers and locations are coordinated by the American Association of State Highway and Transportation Officials (AASHTO). The only federal involvement in the AASHTO is a non-voting seat for the United States Department of Transportation. North-to-south highways are odd-numbered, with lowest numbers in the east and highest numbers in the west. Similarly, west-to-east highways are even-numbered, with the lowest numbers in the north and highest numbers in the south. Major north–south routes have numbers ending in "1" while major east–west routes have numbers ending in "0". Three-digit numbered highways are spur routes of each parent highway but are not necessarily connected to their parent route. Divided routes exist to provide two alignments to one route, even though many have been eliminated, while special routes, usually posted with a banner, can provide various routes, such as an alternate or bypass route, for a U.S. Highway. The Interstate Highway System has largely replaced the U.S. Highways for through traffic, though many important regional connections are still made by U.S. Highways and new routes are still being added.

Prior to the U.S. Routes, auto trails were predominant in marking roads through the United States. In 1925, the Joint Board on Interstate Highways, recommended by American Association of State Highway Officials (AASHO), worked to form a national numbering system for roads. After several meetings, a final report was approved by the Department of Agriculture in November 1925. After numerous complaints from across the country about the assignment of routes, several modifications were made and the U.S. Highway System was approved in November 1926. As a result of compromises made to get the U.S. Highway System approved, many routes divided into two alignments to serve different towns. In subsequent years, the AASHTO called for splits in U.S. Routes to be eliminated. Expansion of the system continued until 1956 when the Interstate Highway System was formed and many U.S. Routes were replaced by Interstate Highways. Despite the Interstate system, U.S. Routes are still used, and often used as alternate routes for Interstate highways during heavy traffic or accidents.