United States Numbered Routes
| United States Numbered Highway System | |
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Map of the present U.S. Highway network
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| System information | |
| Maintained by state or local governments; numbers and routings assigned by AASHTO | |
| Length | 157,724 mi (253,832 km) |
| Formed | November 11, 1926 |
| Highway names | |
| US Highways | U.S. Highway nn (US nn) U.S. Route nn (US nn) |
| System links | |
The United States Numbered Highway System (often called U.S. Routes or U.S. Highways) is an integrated network of roads and highways numbered within a nationwide grid in the contiguous United States. As the designation and numbering of these highways were coordinated among the states, they are sometimes called Federal Highways, but the roadways were built and have always been maintained by state or local governments since their initial designation in 1926.
The route numbers and locations are coordinated by the American Association of State Highway and Transportation Officials (AASHTO). The only federal involvement in AASHTO is a nonvoting seat for the United States Department of Transportation. Generally, north-to-south highways are odd-numbered, with lowest numbers in the east, the area of the founding thirteen states of the United States, and highest in the west. Similarly, east-to-west highways are typically even-numbered, with the lowest numbers in the north, where roads were first improved most intensively, and highest 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 parent highways but are not necessarily connected to their parents. Some divided routes exist to provide two alignments for one route, even though many splits have been eliminated. Special routes, usually posted with a banner, can provide various routes, such as an alternate, bypass or business route, for a U.S. Highway.
Before the U.S. Routes were designated, auto trails designated by auto trail associations were the main means of marking roads through the United States. In 1925, the Joint Board on Interstate Highways, recommended by the American Association of State Highway Officials (AASHO), worked to form a national numbering system to rationalize the roads. After several meetings, a final report was approved by the U.S. Department of Agriculture in November 1925. They received complaints from across the country about the assignment of routes, so the Board made several modifications; 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 were divided, with alignments to serve different towns. In subsequent years, AASHTO called for such splits in U.S. Routes to be eliminated.
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