page_title: United States Numbered Highway System
section_title: Expansion and adjustment, 1926–56
hierarchical_section_title: United States Numbered Highway System / History / Expansion and adjustment, 1926–56
caption_attribution_description: English: Sign on main highway between Portland, Oregon, and Seattle, Washington.
context_page_description: The United States Numbered Highway System 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. The only federal involvement in AASHTO is a nonvoting seat for the United States Department of Transportation. Generally, most north-to-south highways are odd-numbered, with the lowest numbers in the east, and the highest in the west. Similarly, east-to-west highways are typically even-numbered, with the lowest numbers in the north, and the highest in the south. Some exceptions exist, however, such as spur routes. Major north–south routes have numbers ending in "1" or "5", while major east–west routes have numbers ending in "0". Three-digit numbered highways are generally spur routes of parent highways.
context_section_description: When the U.S. numbered system was started in 1925, a few optional routings were established which were designated with a suffixed letter after the number indicating "north", "south", "east", or "west". While a few roads in the system are still numbered in this manner, AASHO believes that they should be eliminated wherever possible, by the absorption of one of the optional routes into another route.
  In 1934, AASHO tried to eliminate many of the split routes by removing them from the log, and designating one of each pair as a three-digit or alternate route, or in one case US 37. AASHO described its renumbering concept in the October 1934 issue of American Highways:
  "Wherever an alternate route is not suitable for its own unique two-digit designation, standard procedure assigns the unqualified number to the older or shorter route, while the other route uses the same number marked by a standard strip above its shield carrying the word 'Alternate'."
  Most states adhere to this approach. However, some maintain legacy routes that violate the rules in various ways.  Examples can be found in California, Mississippi, Nebraska, Oregon, and Tennessee. In 1952, AASHO permanently recognized the splits in US 11, US 19, US 25, US 31, US 45, US 49, US 73, and US 99.
  For the most part, the U.S. Routes were the primary means of inter-city vehicle travel; the main exceptions were toll roads such as the Pennsylvania Turnpike and parkway routes such as the Merritt Parkway. Many of the first high-speed roads were U.S. Highways: the Gulf Freeway carried US 75, the Pasadena Freeway carried US 66, and the Pulaski Skyway carried US 1 and US 9.
caption: This sign, photographed in 1941 on US 99 between Seattle, Washington, and Portland, Oregon, illustrates one rationale for a federal highway system: national defense.
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