A multiplex or concurrency on a road network occurs where a single physical road carries two or more different highway, motorway, or other road numbers. It has been suggested that Highway Transportation System be merged into this article or section. ... Motorway mark in Europe A motorway (in the United Kingdom, Ireland, New Zealand and some Commonwealth nations) is both a type of road and a classification. ... A road number is a number assigned to a stretch of road, or of a long distance route. ...

The practice is relatively common; where two roads must pass through a single geological feature, or crowded city streets, it is advantageous for road designers to merely divert them down the same road, saving on the cost of a new road.

In the United States, highways often form multiplexes in rural areas. As highways in the U.S. are signed with a cardinal direction, it is possible for two highways signed with opposite directions to be running along the same piece of road; a "wrong-way multiplex". Most of the time, multiplexes are simply marked by placing signs for both routes on the same post; occasionally a state will instead sign the road as "to" the less major route. Several states don't officially have any multiplexes, instead officially ending routes on each side of one. In these states, multiplexes are typically poorly signed. In the mid-20th century, California had numerous multiplexes, but the California Legislature removed most multiplexes in a comprehensive reform of highway numbering in 1964. Cardinal directions or cardinal points are the four principal directions or points of the compass, north, east, south and west. ... A wrong-way multiplex in the interior of British Columbia; 97 south is 5 north is 1 east A wrong-way multiplex occurs in highway numbering systems when two multiplexed routes, nominally going in opposite directions, are routed in the same direction along one stretch of physical road. ... (19th century - 20th century - 21st century - more centuries) Decades: 1900s 1910s 1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s As a means of recording the passage of time, the 20th century was that century which lasted from 1901–2000 in the sense of the Gregorian calendar (1900–1999 in the... State nickname: The Golden State Official languages English Capital Sacramento Largest city Los Angeles Governor Arnold Schwarzenegger (R) Senators Dianne Feinstein (D) Barbara Boxer (D) Area  - Total  - % water Ranked 3rd 410,000 km² 4. ... The California State Legislature is the legislative branch of the state government of California. ... For the Nintendo 64 emulator, see 1964 (Emulator). ...

In the United Kingdom, it is common for major through routes to multiplex with others. Only one road number (typically that of the more heavily used route) is ever shown on road signs however; the other road is either bracketed on the sign, implying that the major route leads to a junction with the minor route (which it will do at the end of the multiplex), or left off altogether. For example, the A82 multiplexes with the A85 for five miles in western Scotland. Each route-confirmation sign-header gives the road number as "A82 (A85)". The A82 is the major road to the western Scottish Highlands, running from Glasgow to Inverness. ... The A85 is a major road in Scotland. ... Scottish Executive - official site of the Scottish Executive Scottish Parliament - official site of The Scottish Parliament BBC Scotland - Scottish history, news and travel pages from BBC The Gazetteer for Scotland - Extensive guide to the places and people of Scotland, by the Royal Scottish Geographical Society and University of Edinburgh Scotland...

This use of the term "multiplex" is a neologism, albeit well-used, as an extension of other meanings of the term. "Concurrency" is used by some road authorities. A neologism is word, term, or phrase which has been recently created (coined) —often to apply to new concepts, or to reshape older terms in newer language form. ... Multiplex may mean: Multiplex (comics), a DC Comics character. ...