Road number

A road number is often assigned to a stretch of public roadway. The number chosen is often dependent on the type of road, with numbers differentiating between interstates, motorways, arterial thoroughfares, two-lane roads, and so forth.

UK

In some countries, such as the United Kingdom, the road number has a letter followed by a number of up to 4 digits. For example, the main road from London to Edinburgh is called the A1, the "A" in Britain indicating a first class route; this is classified as being 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 must begin with the figure 1 (A137, B1412), etc, 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 beltway around London). Motorways are fast freeways and are larger than "A" roads. Motorways follow different zoning and numbering systems than "A" and "B" roads.

This clock-face zonal system is used in many other European countries (for example, Spain).

US

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 you go north, and north-south Interstates increase in number as you go 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 you go 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 you go 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, who uses a grid to number their 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) like 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 roads. For example, in Virginia, the primary and secondary road systems have numbering ranges that are, with rare exceptions, mutually exclusive.

Elsewhere

France still uses Route Nationale numbers from an 1824 revision of 1811 numbers made under Napoleon.

Some countries, such as Brazil, number their national highways by direction. (BR1xx = North/South highways, BR2xx = East/West, BR3xx = 'Diagonal' (ie NW/SE or NE/SW)).

ee also

*Asian Highway Network
*China road numbering
*International E-road network (Europe)
*Great Britain road numbering scheme
*State-numbered route (countries that are divided into states)
*Numbered highways in the United States
*Numbered highways in Canada

Further reading

* [http://www.cbrd.co.uk/roadsfaq/#22 Explanation of British road numbers]
* [http://www.us-highways.com/bus98.htm Explanation of U.S. highway numbers]