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From Wikipedia, the free encyclopedia
Rapid transit, also known as metro, subway, underground, or colloquially as "the train", is a type of high-capacity public transport generally found in urban areas.[1][2][3] Unlike buses, trams or light rail, rapid transit systems are electric railways that operate on an exclusive right-of-way, which cannot be accessed by pedestrians or other vehicles of any sort,[4] and which is often grade separated in tunnels or on elevated railways.
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/7/72/NYC_Subway_R160A_9237_on_the_E.jpg/640px-NYC_Subway_R160A_9237_on_the_E.jpg)
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/c/c8/Moscow_MetroCrowded_%28pixinn.net%29.jpg/640px-Moscow_MetroCrowded_%28pixinn.net%29.jpg)
Modern services on rapid transit systems are provided on designated lines between stations typically using electric multiple units on rail tracks, although some systems use guided rubber tyres, magnetic levitation, or monorail. The stations typically have high platforms, without steps inside the trains, requiring custom-made trains in order to avoid gaps. They are typically integrated with other public transport and often operated by the same public transport authorities. However, some rapid transit systems have at-grade intersections between a rapid transit line and a road or between two rapid transit lines.[5] It is unchallenged in its ability to transport large numbers of people quickly over short distances with little use of land. Variations of rapid transit include people movers, small-scale light metro, and the commuter rail hybrid S-Bahn.
The world's first rapid-transit system was the partially underground Metropolitan Railway which opened as a conventional railway in 1863, and now forms part of the London Underground.[6] In 1868, New York opened the elevated West Side and Yonkers Patent Railway, initially a cable-hauled line using static steam engines.
The world's largest rapid transit system by both length of track (842 miles (1,355 km), including non-revenue track)[7] and number of stations (468 stations in total)[8] is the New York City Subway. By length of passenger route, the world's longest single-operator rapid transit system is the Shanghai Metro.[9][10] The busiest rapid transit systems in the world by annual ridership are the Tokyo subway system, the Seoul Metropolitan Subway, the Moscow Metro, the Beijing Metro, and the Shanghai Metro.[11]