Route Number - United States

United States

Further information: Numbered highways in the United States

In other countries, such as the United States, the situation is a bit more complicated. The numbers can be broken up into several major classifications, such as Interstate highways, or high-speed limited-access highways. For instance, the interstate between Boston and Seattle is called Interstate 90. The United States highways are often more local routes that can span multiple states and can include multiple roadway classifications. An example of this is the U.S. highway linking Maine to Florida called U.S. Route 1. There are also state highways, or roadways under the control of the state government and are usually more minor than those of U.S. highways. These are often titled with the state name followed by the route number; Kentucky Route 67 indicates a Kentucky state road numbered 67.

Under the current numbering system for Interstate highways, odd numbers generally indicate a north-south route, and even numbers mean an east-west route. The numbering system creates a sort of grid; east-west Interstates increase in number as one goes north, and north-south Interstates increase in number as one goes east. For example, Interstate 4 is in central Florida, while Interstate 94 runs in the northern part of the country. Also, Interstate 5 travels along the Pacific Ocean while Interstate 95 runs up the East Coast. Conversely, north-south U.S. routes increase in number as one goes west (U.S. Route 1 parallels Interstate 95 and U.S. Route 97 runs in the Pacific Northwest) and the number of east-west U.S. routes increase as one goes south (U.S. Route 2 travels along the Canadian border and U.S. Route 98 runs along the Gulf of Mexico). States may or may not follow the odd and even rules and usually do not number their routes according to a grid. Some exceptions are Iowa, which uses a grid to number its county routes, and Ohio, which has "clusters" of similarly numbered routes.

The numbering system for state highways varies widely from state to state. A state may choose to use letter prefixes for all, some, or none of its state roads. For example, the Virginia Department of Transportation does not use letter prefixes for state primary or secondary routes, but does use an "F" prefix for frontage roads. Although the state's two-letter designation usually becomes a prefix for the route, some states, like Michigan, prefer to use a single-letter prefix (such as "M-28"). Indeed, a state may choose to give a route an entirely alphabetic designation, such as the lettered county routes in Wisconsin and the Missouri supplemental routes.

Some states (Southern and Midwestern states in particular) tend to use the term "Highway" for state routes and their sections of U.S. highways, while others prefer the term "Route."

Some routes may carry a letter suffix, such as E/W (for East/West) or N/S (for North/South). Other lesser-known suffixes include A (for Alternate), B (for Business) and C (for City), but not all states practice this convention. For example, in New York State, there has been or currently are routes 17, 17A, 17B, 17C, 17D, 17E, 17F, 17G, 17H, 17J, 17K, and 17M.

Complicating the issue further is the fact that some states have distinct numbering systems for primary and secondary routes or for state routes and county highways. For example, in Virginia, the primary and secondary road systems have numbering ranges that are, with rare exceptions, mutually exclusive.