The United States Highway System is an integrated system of roads in the United States numbered within a nationwide grid. As these highways were coordinated by the United States Federal Government in the early days, they are sometimes referred to as Federal Highways. Nowadays, there is no funding difference between these routes and any other state highways. The numbers are coordinated by the American Association of State Highway and Transportation Officials (AASHTO), in which the only current federal involvement is a non-voting seat for the U.S. Department of Transportation.
Similar systems are the informal National Auto Trail system (which was used before the U.S. Highway System), the Interstate Highway System (which has partially replaced the U.S. Highway System), and the National Highway System (which is an unsigned system of major roads that supplement the Interstates).
Early named system
The first United States automobile highway system originated in the 1910s with a series of named highways, known collectively as National Auto Trails. The major routes were named for American Presidents; for example the Lincoln Highway ran from New York City on the Atlantic coast to San Francisco on the Pacific; the Jefferson Highway from New Orleans north to Winnipeg, Manitoba, Canada. A major exception to the presidential names was the Dixie Highway, running from Miami, Florida to Sault Ste. Marie, Michigan. Such obsolete highway names survive only in scattered locations in the United States, mostly on old highway routes that have been bypassed by later larger highways and now are used mostly by local traffic. The old named highways were marked with horizontal bands of color on telephone & telegraph poles and posts beside their routes, sometimes suplimented by letters (eg; a red, a white and a blue stripe with an "L" indicated the Lincoln Highway; two blue stripes with "JH" indicated the Jefferson Highway; two white and one red stripe with "DH" showed the Dixie Highway).
Discussion about the form of the proposed United States Numbered Highway system began in 1924, a preliminary list was ready by the next year. The final list was approved on November 11, 1926. During 1927, the named highways began to be replaced with numbers. US numbered highways do not have a minimum design standard, unlike the later Interstate highway system. Roads on the United States highway system are not usually controlled-access (stoplight free) roads. Many are the main streets of the cities and towns they run through. The United States Highways are state highways, funded just like any other state highway.
Numbering of US highways is not controlled by the Federal government. The American Association of State Highway and Transportation Officials (AASHTO) collectively agrees on the routes to be signed.
On maps and the road, a US highway is indicated by a number on a white sign in a shape of a shield with six points, five above, one below. Until the 1980s, the regulations which describe the sign did not explicitly state that they should be white, leading the state of Florida to use different colors for different roads from the 1956 until 1994 - http://www.us-highways.com/.
The numbering system consists of a one, two, or three digit number. For routes 1 through 101, odd numbers represent north-south highways and even numbers represent east-west. Major North-South US routes were designated by ending in 1. Major East-West US routes ended in zero. The numbers increase moving east to west and north to south. In contrast, the modern Interstate reverses the grid. Route numbers greater than 101 are spur or secondary routes given a number consisting of a single digit prefixed to the number of the "parent" route; for example, US highway 331 is the third secondary route that branches off US 31.
Further defining the system, suffixes have been used. Equal splits in a route were designated E and W for East / West and N and S for North / South. Existing examples include US 31E, US 31W, US 70N and US 70S. This sort of equally split route is not as common as it used to be.
Additional loop and spur routes are defined as Alternate routes (A routes) Bypass and Business Routes (B routes).
The Interstate highway system of limited access highways was begun in the 1950s as the National Defense Highway System. These new highways were to supplement the existing United States highway system, not to replace the US highway system, although in some areas an interstate did replace an older US highway.