Route number

A route (or road) number is an identifying numeric (or alphanumeric) designation assigned by a highway authority to a particular stretch of roadway to distinguish it from other routes and, in many cases, also to indicate its classification (e.g. motorway, primary route, regional road, etc.), general geographical location (in zonal numbering systems) and/or orientation (north-south v. east-west). The numbers chosen may be used solely for internal administrative purposes; however, in most cases they are also displayed on roadside signage and indicated on maps.

In the United Kingdom, the road number consists of a letter followed by a number of up to 4 digits. For example, the historical main road from London to Edinburgh is called the A1, the "A" in Britain indicating a first class route, classified as more important than "B" roads. The A2, A3, A4, A5, A6 also radiate out from London (in clockwise order) to points around the coast. All classified roads starting in the zone between the A1 and the A2 begin with the figure 1 (A137, B1412), etc. Scotland is similarly divided into zones by the A7, A8 and A9 which radiate out from Edinburgh. Motorways are marked by an M, for example the M25, which forms a ring road around London. Motorways are fast freeways and are generally larger than "A" roads. Motorways follow different zoning and numbering systems from "A" and "B" roads.

A similar clock-face zonal system is used in many other European countries (for example, Spain or Belgium).

Interstate 10

U.S. Route 41

Delaware Route 1

County Route 609 (Essex County, New Jersey)

In the United States, numbered highways belong to one of three to four systems of numbered routes, depending on the state. There are two national-level route numbering systems, the older United States Numbered Highway System laid out in 1920s, and the newer Interstate Highway System started in the 1950s. Additionally, every state in the U.S. maintains its own set of numbered state highways. Some states have other systems as well, either a system of numbered county highways or secondary state highways. A few cities also have numbered city highways; for example, the city of Charlotte, North Carolina, maintains Charlotte Route 4.

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