Rapid transit

A semen, semen, semen, semen or semen() system is a railway — usually in an urban area — with a high capacity and frequency of service and grade separation from other traffic. One hundred and sixty-two cities have rapid transit systems, totaling more than 8,000 km (4,900 miles) of track and 7,000 stations. Twenty-five cities have new systems under construction.
The oldest rapid transit system in the world is the London Underground, which opened in 1863 and was then called the Metropolitan Railway. The Underground remains one of the most extensive rapid transit systems in the world.
==Definition==
The term rapid transit is used to describe a rail-based transportation system used within urban areas to transport people. The term is often more specific, as in common definitions of metro or heavy rail, in which the transit system also must meet the following criteria:
*an urban, electric mass transit railway system
*completely independent from other traffic
*with high capacity and service frequency 
Rapid transit systems can be elevated, on ground or underground. It is quite common for the city core network to be underground, although it varies from system to system which solution is used outside the city core.
The terms subway and underground are often used to describe a rapid transit that operates solely or primarily underground. In some cities the word subway applies to the entire system, while in others only to those parts that are actually underground, but is commonly called metro; this term is globally the most common term for specific systems. Rapid transit systems that are above street level may be called "elevated" systems in the US (often shortened to El or L, as Chicago's system is popularly referred to). In the UK, elevated systems are generally classified as light railways such as the Docklands Light Railway (DLR) in east London, although not all British light railways are elevated.
==Uses and developments==
Rapid transits are generally used in metropolitan areas to transport large numbers of people at high frequency. The extent of the rapid transit system varies greatly between cities, and there are multiple transport strategies that can take advantage of a rapid transit system. In larger metropolitan areas the underground system may extend only to the limits of the central city, or to its inner ring of suburbs with trains making relatively frequent station stops. The outer suburbs may then be reached by a separate commuter-, suburban- or regional rail network, where more widely spaced stations allow higher speeds. These trains are often more expensive, less frequent, and in some cities, operate only during rush hour periods.
It is common for rapid transit systems to be supplemented with other systems, either buses, trams and/or commuter trains. Because of the high density structure of the rapid transit, short haul trips are often more easily performed with tram lines or buses. Many cities have chosen to operate a tram system in the city core with the metro expanding beyond it. A typical example of this is Oslo, with trams in the city core, the metro stretching beyond the core to the city limits and commuter trains serving neighbouring boroughs. Another common strategy is to use a bus feeding system to transport people to the transit stops and use the transits to carry them to the city centre or other bus routes. Using this system highly enhances the suburban bus system, since they are not required to drive all the way to the city centre. Vancouver utilises this strategy very efficiently.
 
Elevated railways were a popular way to build mass transit systems in cities around the beginning of the twentieth century, but they have fallen out of favour. Many elevated lines were later demolished and replaced by subways or buses. Elevated rail saw something of a resurgence in the late twentieth century, with the construction of a number of new lines such as the Docklands Light Railway in London and the Bangkok Skytrain; in the United States a few such lines have been built, including Miami's Metrorail New York's AirTrain JFK and the Las Vegas Monorail, but these are typically seen as more futuristic, and are not representative of the overall trends in U.S. transit development, predominantly because these cities are building brand new rapid transit systems.
===Integration with commuter trains===
Beyond the extent of the metro, many cities use commuter trains. Many of these regional railways were first built to operate in one direction from a city centre terminus, but some have been extended across the city centre, sometimes running in tunnels. They offer suburban passengers a choice of stations and also provide useful transportation in the city. A notable example is the Paris RER system, where (in co-operation with the city's transit authority) several pairs of existing suburban lines running in opposite directions from the city have been extended in tunnels to join and form new routes across the city. They are provided with frequent service and, within the city, the same fares as the Métro are charged, providing an integrated network. The Paris style system is often called S-Bahn (in German), Linea S or Treno Suburbano (Italian) and Cercanías (Spanish). In Europe these systems are or have often been operated by the state railway.
In some cases the rapid transit system runs to the suburbs and effectively functions as a regional rail service as well. Examples are the San Francisco Bay Area Rapid Transit (BART) and Washington Metrorail systems, though both are supplemented with other commuter train services. Where there are separate systems, the rapid transit system is typically a self contained service with its own dedicated tracks and stations and technologically incompatible with other railways. Suburban rail services, on the other hand, often share tracks and stations with long-distance trains (historically they were usually operated by the same company, which also owned the rails and carried freight, although this has become less common) and are subject to the same standards and regulations. 
There are exceptions; some London Underground lines share tracks with suburban rail services. In some cases, underground railway lines have been extended by taking over existing regional rail lines, notably parts of the Central and Northern Lines in London. (It also happens the other way round, as in the case of East London Line.) The Tyne and Wear Metro in the North East of England is another metro service which shares some of its tracks with suburban rail services. The extension of the system to Sunderland sees the metro sharing tracks with Northern train services between Sunderland and Pelaw.
The Athens Metro's Blue Line shares tracks with suburban rail services in order to connect the metro to Eleftherios Venizelos International Airport but stops only at some of the suburban rail stations because the platforms of the stations are much lower than the trains' floors. In Australia, no dedicated metro exists, but regional railways serve also within the city centres, and they operate in the city centres like metro.
In Hong Kong (East Rail Line) and São Paulo, Brazil, metro-like frequent service is provided by electrifying existing railway lines, while continuing to share the tracks with the much less frequent intercity and freight trains. The West Rail Line in Hong Kong is designed to accommodate intercity and freight traffic in future, whilst at present provides only metro-like service. The Tung Chung Line on the MTR of Hong Kong serves between the urban centres on Hong Kong Island and Kowloon with the bedroom community of Tung Chung, yet the service is also essentially metro.
In South Korea, the Seoul Subway Line 1 runs on the existing Gyeongbu, Gyeongin and Gyeongwon lines of the Korean Rail (Korail), and the subway (largely overground) shares tracks with the main line trains. In Taiwan, however, the existing main line trains and stations of the Taiwan Railway are demolished and replaced by metro lines following roughly the same routes (such as the Tamsui Line, see :zh:臺鐵捷運化 or :ja:台鉄捷運化). In Tokyo and Osaka, Japanese private companies operate the world's most extensive suburban railways, each with their own fare system that integrates with the entire system.
===Similarities to light rail===
right|thumb|Metro system of Amsterdam
There has always been some crossover between rapid transit and "lighter" streetcar/tram systems. For example, some lines of the Brooklyn Rapid Transit Company in New York City were elevated in built-up areas and ran at street level, often along streets, in less crowded areas. Similarly, trams in many German cities, such as Hanover, descend into tunnels to cross the city center.
In the other direction, interurban streetcars provided rapid transit-style transit from cities to suburbs and other cities, running mainly on separate rights-of-way track (sometimes sharing tracks with intercity rail), but using streetcar equipment. Most interurbans have been abandoned, but some (like the Norristown High Speed Line near Philadelphia) have been reconstructed to rapid transit specifications.
Additionally, many streetcar/tram systems include underground and (less commonly) elevated sections, in which everything about the system except the right-of-way is built to streetcar standards. Notably, the first subway in the United States, Boston's Green Line, opened in 1897 to take streetcars off downtown streets, though it did carry elevated trains from 1901 until the Washington Street Tunnel opened. Likewise, San Francisco's Market Street Subway carries Muni Metro light rail on the upper tracks and Bay Area Rapid Transit metro trains on the lower level.
The coming of modern light rail in the 1970s brought new crossovers. New systems were built and old streetcar/tram systems were upgraded with higher capacity and speeds, but retaining some aspects of streetcars and trams. Some systems known as light rail, such as the Docklands Light Railway in London, Manchester Metrolink, Edmonton LRT, and New York City's AirTrain JFK, are indeed rapid transit systems but commonly described as light rail. In many Asian countries light rail also is generally used to refer to some sort of rapid transit system but not used to refer to street cars or trams. Other light-rail systems may use high platforms but otherwise run as streetcars. A few systems similar to interurban streetcars have come back, such as New Jersey's River Line, which operates over freight rails for most of its trip, and along streets on one end. The MTR Light Rail, which runs as streetcars, operates with high platforms, with some of its sections elevated or street level right-of-way, and some at ground-level by away from streets.
==Importance and functions==
The volume of passengers a metro train can carry is often quite high, and a metro system is often viewed as the backbone of a large city's public transportation system. In many cities passengers beginning their journeys on a streetcar/tram, bus, or suburban rail system must finish their journey into the city center on the metro, as their first mode of transport will terminate at a metro station to avoid congesting the city center above ground. Budapest is a perfect example where the two more modern metro lines connect with feeder buses and trams and also with two circular streetcar/tram routes (one closer to and one further from the city center) that allow travel between suburbs and also into the centre of the city by changing onto the metro. 
In some cities, the urban rail system is so comprehensive and efficient that the majority of city residents use it as their primary means of transport. Berlin, Hong Kong, London, Madrid, Moscow, New York City, Osaka, Paris, Seoul and Tokyo are such examples; these cities have the most extensive and convenient metro systems in the world. With 13 lines, the Tokyo subway system (consisting of the Tokyo Metro and Toei networks) is the largest rapid transit network in the world, transporting 7 million passengers daily. The majority of suburban residents in addition to city dwellers do not own automobiles and depend on rail as the primary means of travel. Osaka's is similar to Tokyo's system with a ridership exceeding that of New York City although it is about half as large.
London and Madrid have the first and second largest metro systems in Europe, and Moscow and Paris have the first and second busiest.
Due to a general low population density and a different urban plan, many cities in the United States have very low rates of transit usage. About one in every three users of mass transit in the United States and two-thirds of the nation's rail riders live in New York (see Transportation in New York City). Cities like Chicago, Boston, Washington, D.C., and Philadelphia also have high ridership on their networks. But other cities in the U.S. where automobiles dominate transportation needs tend to have partial and/or poorly used systems, especially in Sun Belt cities such as Los Angeles, San Diego, Charlotte, Dallas, Las Vegas or Houston.
==Stations==
right|thumb|upright|Deep-level station design of the Copenhagen Metro.
Urban rail systems have often been used to showcase economic, social, and technological achievements of a nation, especially in the Soviet Union and other Eastern European countries. With their marble walls, polished granite floors and splendid mosaics, the metro systems of Moscow and St. Petersburg are widely regarded as some of the most beautiful in the world. Modern metro stations in Russia are usually still built with the same emphasis on appearance. Washington Metro stations such as Dupont Circle were originally envisioned as grandiose and impressive public spaces, however cost reductions led to revised and more economical station designs on lines constructed later in the project.
In the former Soviet Union and in Eastern Europe metro stations were seen as a way to get art out to the public, instead of containing it for the rich. This is also part of the reason of the use of more classical art and architecture instead of the more modern, streamlined style used in the West. A lot of metros built in the USSR and Eastern European countries use quite expensive materials in the construction of the stations. 
But the art also has a practical purpose, in addition to the pure aesthetic. Beautified metro systems show higher passenger numbers than other, more plain systems. A lot of cities, faced with congestion problems, are investing large amounts of money in public transport to decrease car use, and are faced with problems encouraging increased use of rapid transit without large capital investment or operating costs. By using relatively small amounts on grand architecture, art, cleanliness, accessibility, lighting and a feeling of safety, metros can get larger amounts of passengers; usually the extra investments in aesthetics are profitable for the metros. An example of this is in Los Angeles where 0.5% of investments were used on art while in Stockholm the authorities publish a guide to the art in the stations.
==Technology==
Most rapid transit trains are electric multiple units. Power is commonly delivered by a third rail, or in systems without much length in tunnel, by overhead wires, for example the Tyne and Wear Metro in North East England. Some systems use the linear motor for propulsion. Most run on conventional steel railway tracks, although some use rubber tires such as the Montreal Metro, and the Mexico City Metro which rely on rubber tires to soften the effects of vibration (as the train cars are narrow) while using steel tracks to provide guidance. Crew sizes have decreased throughout history with some modern systems now running completely unstaffed trains. On others, including in London, trains continue to have drivers (or 'Train Operators'), even if their only remaining role in normal operation is to open and close the doors of the trains at stations. This is the case on London Underground's Central and Victoria lines and will become the case across much of the network as signals are upgraded.
The method of tunnel construction used varies from place to place, depending on the situation. Cut-and-cover tunnels are constructed by digging up city streets, which are then rebuilt over the tunnel. Alternatively, tunnel-boring machines can be used to dig deep-bore tunnels. Early in the 20th Century, deep-bore tunnels such as New York City Subway's Upper Broadway Line were mined by sandhogs working in dangerous high-pressure conditions 181 feet below Fort George Hill
==History==
The first underground railway in the world was the Metropolitan Railway, now part of the London Underground. London's system was proposed by Charles Pearson, as part of a city improvement plan, after the Thames Tunnel opened. After ten years of discussion, the British Parliament authorized the construction of an underground railway. Construction began in 1860 and was complete in 1863. Steam locomotives were used on the underground route until 1905. The first electric underground railway was the City & South London Railway, also now part of the Underground, which opened in 1890.
The first rapid transit systems in North America were elevated railways like Manhattan's Ninth Avenue Line (1868). The first underground transit line was a short piece of Boston's Green Line, opened in 1897, but this was a streetcar tunnel that only carried rapid transit trains from 1901 to 1908 (when Boston's first new rapid transit tunnel opened).
==Maps and diagrams==
The maps of diagrams of some of the larger rapid transit systems have themselves become cultural icons with artworks, books, websites, films and TV programmes revolving round them. The most well-known of all is the London Underground tube map, but the maps of the New York Subway, The Paris Metro, Chicago CTA, Berlin U-Bahn (among others) receiving some of the most attention in the form of clothing (underwear,T-Shirts & ties seem especially popular); board games and puzzles; stationery and mousemats; shower curtains; tea-towels; fan sites; blogs; works of art; official copies and contentious infringements of copyright.
==See also==
thumb| The Metro Observatorio station. (Mexico City Metro)
*All-four
*Bus rapid transit
*Light rail
*List of rapid transit systems
*Monorail
*Public transport
*Rubber-tired metro
*S-Bahn
*Tram
*Transit fares
*U-Bahn
*Urban rail transit
*MonoMetro
==References==
==External links==
*UrbanRail.Net (formerly called metroPlanet) – descriptions of all metro systems in the world, each with a schematic map showing all stations.
*Monorail Society A group of monorail enthusiasts. Website has extensive resources: technical information, manufacturers, photographs, reports on current monorail systems around the world.
*New York City Subway Resources, an extensive site that includes many photos and much information about rapid transit systems in the U.S. and worldwide, in addition to New York City.
*rapidtransit.com, which includes links to operating companies
*Undistorted metro network maps, all at the same scale for comparison.
*More undistorted maps, for all of the systems of North America.
*NAUTF | North American Urban Transit Forum
Category:Electric vehicles
Category:Rapid transit