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Rapid transit or mass rapid transit (MRT), also known as heavy rail or metro, is a type of high-capacity
public transport Public transport (also known as public transportation, public transit, mass transit, or simply transit) is a system of transport for passengers by group travel systems available for use by the general public unlike private transport, typi ...
generally found in
urban area An urban area, built-up area or urban agglomeration is a human settlement with a high population density and infrastructure of built environment. Urban areas are created through urbanization and are categorized by urban morphology as cities ...
s. A rapid transit system that primarily or traditionally runs below the surface may be called a subway, tube, or underground. Unlike
bus A bus (contracted from omnibus, with variants multibus, motorbus, autobus, etc.) is a road vehicle that carries significantly more passengers than an average car or van. It is most commonly used in public transport, but is also in use for cha ...
es or
tram A tram (called a streetcar or trolley in North America) is a rail vehicle that travels on tramway tracks on public urban streets; some include segments on segregated right-of-way. The tramlines or networks operated as public transport ...
s, rapid transit systems are railways (usually
electric Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by ...
) that operate on an exclusive
right-of-way Right of way is the legal right, established by grant from a landowner or long usage (i.e. by prescription), to pass along a specific route through property belonging to another. A similar ''right of access'' also exists on land held by a gov ...
, which cannot be accessed by pedestrians or other vehicles, and which is often
grade-separated In civil engineering (more specifically highway engineering), grade separation is a method of aligning a junction of two or more surface transport axes at different heights (grades) so that they will not disrupt the traffic flow on other tr ...
in
tunnel A tunnel is an underground passageway, dug through surrounding soil, earth or rock, and enclosed except for the entrance and exit, commonly at each end. A pipeline is not a tunnel, though some recent tunnels have used immersed tube cons ...
s or on
elevated railway An elevated railway or elevated train (also known as an el train for short) is a rapid transit railway with the tracks above street level on a viaduct or other elevated structure (usually constructed from steel, cast iron, concrete, or bricks ...
s. Modern services on rapid transit systems are provided on designated lines between
stations Station may refer to: Agriculture * Station (Australian agriculture), a large Australian landholding used for livestock production * Station (New Zealand agriculture), a large New Zealand farm used for grazing by sheep and cattle ** Cattle statio ...
typically using
electric multiple unit An electric multiple unit or EMU is a multiple-unit train consisting of self-propelled carriages using electricity as the motive power. An EMU requires no separate locomotive, as electric traction motors are incorporated within one or a number ...
s on
rail track A railway track (British English and UIC terminology) or railroad track (American English), also known as permanent way or simply track, is the structure on a railway or railroad consisting of the rails, fasteners, railroad ties (sleeper ...
s, although some systems use guided rubber tires, magnetic levitation (''
maglev Maglev (derived from '' magnetic levitation''), is a system of train transportation that uses two sets of electromagnets: one set to repel and push the train up off the track, and another set to move the elevated train ahead, taking advantage ...
''), or
monorail A monorail (from "mono", meaning "one", and " rail") is a railway in which the track consists of a single rail or a beam. Colloquially, the term "monorail" is often used to describe any form of elevated rail or people mover. More accurat ...
. The stations typically have high platforms, without steps inside the trains, requiring custom-made trains in order to minimize gaps between train and platform. 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. The world's first rapid transit system was the partially underground
Metropolitan Railway The Metropolitan Railway (also known as the Met) was a passenger and goods railway that served London from 1863 to 1933, its main line heading north-west from the capital's financial heart in the City to what were to become the Middlesex su ...
which opened in 1863 using
steam locomotive A steam locomotive is a locomotive that provides the force to move itself and other vehicles by means of the expansion of steam. It is fuelled by burning combustible material (usually coal, oil or, rarely, wood) to heat water in the loco ...
s, and now forms part of the
London Underground The London Underground (also known simply as the Underground or by its nickname the Tube) is a rapid transit system serving Greater London and some parts of the adjacent counties of Buckinghamshire, Essex and Hertfordshire in England. The ...
. In 1868, New York opened the elevated West Side and Yonkers Patent Railway, initially a cable-hauled line using static
steam engine A steam engine is a heat engine that performs mechanical work using steam as its working fluid. The steam engine uses the force produced by steam pressure to push a piston back and forth inside a cylinder. This pushing force can be ...
s. ,
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
has the largest number of rapid transit systems in the world—40 in number, running on over of track—and was responsible for most of the world's rapid-transit expansion in the 2010s. The world's longest single-operator rapid transit system by route length is the
Shanghai Metro The Shanghai Metro (; Shanghainese: ''Zaon6he5 Di6thiq7'') is a rapid transit system in Shanghai, operating urban and suburban transit services to 14 of its 16 municipal districts and to Kunshan, Jiangsu Province. Served as a part of Shang ...
. The world's largest single rapid transit service provider by number of stations (472 stations in total) is the
New York City Subway The New York City Subway is a rapid transit system owned by the government of New York City and leased to the New York City Transit Authority, an affiliate agency of the state-run Metropolitan Transportation Authority (MTA). Opened on October ...
. The three busiest rapid transit systems in the world by annual ridership are the
Shanghai Metro The Shanghai Metro (; Shanghainese: ''Zaon6he5 Di6thiq7'') is a rapid transit system in Shanghai, operating urban and suburban transit services to 14 of its 16 municipal districts and to Kunshan, Jiangsu Province. Served as a part of Shang ...
, Tokyo subway system and the
Moscow Metro The Moscow Metro) is a metro system serving the Russian capital of Moscow as well as the neighbouring cities of Krasnogorsk, Reutov, Lyubertsy and Kotelniki in Moscow Oblast. Opened in 1935 with one line and 13 stations, it was the first ...
.


Terminology

''Metro'' is the most common term for underground rapid transit systems used by non-native English speakers. Rapid transit systems may be named after the medium by which passengers travel in busy
central business district A central business district (CBD) is the commercial and business centre of a city. It contains commercial space and offices, and in larger cities will often be described as a financial district. Geographically, it often coincides with the "city ...
s; the use of
tunnel A tunnel is an underground passageway, dug through surrounding soil, earth or rock, and enclosed except for the entrance and exit, commonly at each end. A pipeline is not a tunnel, though some recent tunnels have used immersed tube cons ...
s inspires names such as ''subway'', ''underground'', ''Untergrundbahn (
U-Bahn Rapid transit in Germany consists of four U-Bahn systems and fourteen S-Bahn systems. The U-Bahn commonly understood to stand for Untergrundbahn (''underground railway'') are conventional rapid transit systems that run mostly underground, while ...
)'' in German,White, 2002: 63 or the ''Tunnelbana (T-bana)'' in Swedish;Ovenden, 2007: 93 the use of
viaduct A viaduct is a specific type of bridge that consists of a series of arches, piers or columns supporting a long elevated railway or road. Typically a viaduct connects two points of roughly equal elevation, allowing direct overpass across a wide v ...
s inspires names such as ''elevated'' (''L'' or ''el''), ''skytrain'', Ovenden, 2007: 16 ''overhead'', ''overground'' or ''Hochbahn'' in German. One of these terms may apply to an entire system, even if a large part of the network (for example, in outer suburbs) runs at ground level. In most of
Britain Britain most often refers to: * The United Kingdom, a sovereign state in Europe comprising the island of Great Britain, the north-eastern part of the island of Ireland and many smaller islands * Great Britain, the largest island in the United King ...
, a ''subway'' is a
pedestrian underpass A subway, also known as an underpass, is a grade-separated pedestrian crossing which crosses underneath a road or railway in order to entirely separate pedestrians and cyclists from motor traffic or trains respectively. Terminology In the Un ...
; the terms ''Underground'' and ''Tube'' are used for the London Underground, and the North East England
Tyne and Wear Metro The Tyne and Wear Metro is an overground and underground light rail rapid transit system serving Newcastle upon Tyne, Gateshead, North Tyneside, South Tyneside, and the City of Sunderland (together forming Tyne and Wear). The network opened in ...
, mostly overground, is known as the ''Metro''. In
Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to ...
, however, the
Glasgow Subway The Glasgow Subway is an underground light metro system in Glasgow, Scotland. Opened on 14 December 1896, it is the fourth-oldest underground rail transit system in Europe after the London Underground, Liverpool's Mersey Railway and the Budap ...
underground rapid transit system is known as the ''Subway''. Various terms are used for rapid transit systems around
North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...
. The term ''metro'' is a shortened reference to a
metropolitan area A metropolitan area or metro is a region that consists of a densely populated urban agglomeration and its surrounding territories sharing industries, commercial areas, transport network, infrastructures and housing. A metro area usually ...
. Rapid transit systems such as the
Washington Metro The Washington Metro (or simply Metro), formally the Metrorail,Google Books search/preview
,
Los Angeles Metro Rail The Los Angeles Metro Rail is an urban rail transit system serving Los Angeles County, California, United States. It consists of seven lines, including five light rail lines (the A, C, E, K, L lines) and two rapid transit (known locally as ...
, the Miami Metrorail, and the
Montreal Metro The Montreal Metro (french: Métro de Montréal) is a rubber-tired underground rapid transit system serving Greater Montreal, Quebec, Canada. The metro, operated by the Société de transport de Montréal (STM), was inaugurated on October 14, ...
are generally called the ''Metro''. In
Philadelphia Philadelphia, often called Philly, is the largest city in the Commonwealth of Pennsylvania, the sixth-largest city in the U.S., the second-largest city in both the Northeast megalopolis and Mid-Atlantic regions after New York City. Since ...
, the term “El” is used for the Market–Frankford Line which runs mostly on an elevated track, while the term “subway” applies to the
Broad Street Line The Broad Street Line (BSL), also known as the Broad Street subway (BSS), Orange Line, or Broad Line, is a subway line owned by the city of Philadelphia and operated by the Southeastern Pennsylvania Transportation Authority (SEPTA). The line ru ...
which is almost entirely underground.
Chicago (''City in a Garden''); I Will , image_map = , map_caption = Interactive Map of Chicago , coordinates = , coordinates_footnotes = , subdivision_type = List of sovereign states, Count ...
's
commuter rail Commuter rail, or suburban rail, is a passenger rail transport service that primarily operates within a metropolitan area, connecting commuters to a central city from adjacent suburbs or commuter towns. Generally commuter rail systems are con ...
system that serves the entire metropolitan area is called ''
Metra Metra is the commuter rail system in the Chicago metropolitan area serving the city of Chicago and its surrounding suburbs via the Union Pacific Railroad, BNSF Railway, and other railroads. The system operates 242 stations on 11 rail lines ...
'' (short for "Metropolitan Rail"), while its rapid transit system that serves the city is called the "L". Boston's subway system is known locally as "The T", while in the
San Francisco Bay Area The San Francisco Bay Area, often referred to as simply the Bay Area, is a populous region surrounding the San Francisco, San Pablo, and Suisun Bay estuaries in Northern California. The Bay Area is defined by the Association of Bay Area G ...
, residents refer to
Bay Area Rapid Transit Bay Area Rapid Transit (BART) is a rapid transit system serving the San Francisco Bay Area in California. BART serves 50 stations along six routes on of rapid transit lines, including a spur line in eastern Contra Costa County which u ...
by its acronym "BART". The
New York City Subway The New York City Subway is a rapid transit system owned by the government of New York City and leased to the New York City Transit Authority, an affiliate agency of the state-run Metropolitan Transportation Authority (MTA). Opened on October ...
is referred to simply as “the subway”, despite 40% of the system running above ground. The term “L” or “El” is not used for elevated lines in general as the lines in the system are already designated with letters and numbers. The “L” train or
L (New York City Subway service) The L 14th Street–Canarsie Local is a rapid transit service in the B Division of the New York City Subway. Its route emblem, or "bullet", is colored since it serves the BMT Canarsie Line. The L operates at all times between Eighth Avenue in ...
refers specifically to the 14th Street–Canarsie Local line, and not other elevated trains. In most of
Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical south-eastern region of Asia, consisting of the regions that are situated south of mainland ...
and in
Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the no ...
, rapid transit systems are primarily known by the
acronym An acronym is a word or name formed from the initial components of a longer name or phrase. Acronyms are usually formed from the initial letters of words, as in ''NATO'' (''North Atlantic Treaty Organization''), but sometimes use syllables, as ...
''MRT''. The meaning however varies from one country to another. In
Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Gui ...
, the acronym stands for '' Moda Raya Terpadu'' or ''Integrated Mass ransitMode'' in English. In the
Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...
, it stands for '' Metro Rail Transit'', with two lines also using the term ''subway'' being underground lines. In
Thailand Thailand ( ), historically known as Siam () and officially the Kingdom of Thailand, is a country in Southeast Asia, located at the centre of the Indochinese Peninsula, spanning , with a population of almost 70 million. The country is b ...
, it stands for ''
Metropolitan Rapid Transit The Metropolitan Rapid Transit or MRT is a mass rapid transit system serving the Bangkok Metropolitan Region in Thailand. The MRT system comprises two rapid transit lines, with a further three lines (one rapid transit line and two monorail lines) ...
'', and previously also used the ''Mass Rapid Transit'' name. Outside of Southeast Asia,
Kaohsiung Kaohsiung City ( Mandarin Chinese: ; Wade–Giles: ''Kao¹-hsiung²;'' Pinyin: ''Gāoxióng'') is a special municipality located in southern Taiwan. It ranges from the coastal urban center to the rural Yushan Range with an area of . Ka ...
and
Taoyuan, Taiwan Taoyuan () is a special municipality of the Republic of China (Taiwan) located in northwestern Taiwan, neighboring New Taipei City to the north-east, Yilan County to the south-east, and Hsinchu County to the south-west. Taoyuan Distri ...
have their own ''MRT'' systems which also stands for ''Mass Rapid Transit'' as with
Singapore Singapore (), officially the Republic of Singapore, is a sovereign island country and city-state in maritime Southeast Asia. It lies about one degree of latitude () north of the equator, off the southern tip of the Malay Peninsula, bor ...
.


History

The opening of London's steam-hauled
Metropolitan Railway The Metropolitan Railway (also known as the Met) was a passenger and goods railway that served London from 1863 to 1933, its main line heading north-west from the capital's financial heart in the City to what were to become the Middlesex su ...
in 1863 marked the beginning of rapid transit. Initial experiences with steam engines, despite ventilation, were unpleasant. Experiments with
pneumatic railway An atmospheric railway uses differential air pressure to provide power for propulsion of a railway vehicle. A static power source can transmit motive power to the vehicle in this way, avoiding the necessity of carrying mobile power generating e ...
s failed in their extended adoption by cities. Electric traction was more efficient, faster and cleaner than steam and the natural choice for trains running in tunnels and proved superior for elevated services. In 1890, the
City & South London Railway The City and South London Railway (C&SLR) was the first successful deep-level underground "tube" railway in the world, and the first major railway to use Railway electrification in Great Britain, electric traction. The railway was originally in ...
was the first electric-traction rapid transit railway, which was also fully underground.Ovenden, 2007: 7 Prior to opening, the line was to be called the "City and South London Subway", thus introducing the term Subway into railway terminology. Both railways, alongside others, were eventually merged into
London Underground The London Underground (also known simply as the Underground or by its nickname the Tube) is a rapid transit system serving Greater London and some parts of the adjacent counties of Buckinghamshire, Essex and Hertfordshire in England. The ...
. The 1893
Liverpool Overhead Railway The Liverpool Overhead Railway (known locally as the Dockers' Umbrella or Ovee) was an overhead railway in Liverpool which operated along the Liverpool Docks and opened in 1893 with lightweight electric multiple units. The railway had a numbe ...
was designed to use electric traction from the outset. The technology quickly spread to other cities in Europe, the United States, Argentina, and Canada, with some railways being converted from steam and others being designed to be electric from the outset.
Budapest Budapest (, ; ) is the capital and most populous city of Hungary. It is the ninth-largest city in the European Union by population within city limits and the second-largest city on the Danube river; the city has an estimated population o ...
,
Chicago (''City in a Garden''); I Will , image_map = , map_caption = Interactive Map of Chicago , coordinates = , coordinates_footnotes = , subdivision_type = List of sovereign states, Count ...
,
Glasgow Glasgow ( ; sco, Glesca or ; gd, Glaschu ) is the most populous city in Scotland and the fourth-most populous city in the United Kingdom, as well as being the 27th largest city by population in Europe. In 2020, it had an estimated popu ...
and
New York City New York, often called New York City or NYC, is the List of United States cities by population, most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the L ...
all converted or purpose-designed and built electric rail services. Advancements in technology have allowed new automated services. Hybrid solutions have also evolved, such as
tram-train A tram-train is a type of light rail vehicle that meets the standards of a light rail system (usually an urban street running tramway), but which also meets national mainline standards permitting operation alongside mainline trains. This al ...
and
premetro A premetro is a tramway or light railway which includes segments built to rapid transit standards, generally as part of a process of conversion to a metro-standards railway usually by the construction of tunnels in the central city area. Hist ...
, which incorporate some of the features of rapid transit systems. In response to cost, engineering considerations and topological challenges some cities have opted to construct tram systems, particularly those in Australia, where density in cities was low and
suburb A suburb (more broadly suburban area) is an area within a metropolitan area, which may include commercial and mixed-use, that is primarily a residential area. A suburb can exist either as part of a larger city/urban area or as a separ ...
s tended to spread out. Since the 1970s, the viability of underground train systems in Australian cities, particularly
Sydney Sydney ( ) is the capital city of the state of New South Wales, and the most populous city in both Australia and Oceania. Located on Australia's east coast, the metropolis surrounds Sydney Harbour and extends about towards the Blue Mounta ...
and
Melbourne Melbourne ( ; Boonwurrung/ Woiwurrung: ''Narrm'' or ''Naarm'') is the capital and most populous city of the Australian state of Victoria, and the second-most populous city in both Australia and Oceania. Its name generally refers to a metro ...
, has been reconsidered and proposed as a solution to over-capacity. Melbourne had tunnels and stations developed in the 1970s and opened in 1980. The first line of
Sydney Metro The Sydney Metro is a fully automated rapid transit system serving the city of Sydney, New South Wales, Australia. Currently consisting of one line that opened on 26 May 2019, it runs from Tallawong to Chatswood and consists of 13 stat ...
, was opened in 2019. Since the 1960s, many new systems were introduced in
Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
,
Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...
and
Latin America Latin America or * french: Amérique Latine, link=no * ht, Amerik Latin, link=no * pt, América Latina, link=no, name=a, sometimes referred to as LatAm is a large cultural region in the Americas where Romance languages — languages derived ...
. In the 21st century, most new expansions and systems are located in Asia, with China becoming the world's leader in metro expansion, operating some of the largest and busiest systems while possessing almost 60 cities that are operating, constructing or planning a
rapid transit system Rapid transit or mass rapid transit (MRT), also known as heavy rail or metro, is a type of high-capacity public transport generally found in urban areas. A rapid transit system that primarily or traditionally runs below the surface may be c ...
.


Operation

Rapid transit is used in
cities A city is a human settlement of notable size.Goodall, B. (1987) ''The Penguin Dictionary of Human Geography''. London: Penguin.Kuper, A. and Kuper, J., eds (1996) ''The Social Science Encyclopedia''. 2nd edition. London: Routledge. It can be def ...
, agglomerations, and
metropolitan area A metropolitan area or metro is a region that consists of a densely populated urban agglomeration and its surrounding territories sharing industries, commercial areas, transport network, infrastructures and housing. A metro area usually ...
s to transport large numbers of people often short distances at high
frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
. The extent of the rapid transit system varies greatly between cities, with several transport strategies. Some systems may extend only to the limits of the inner city, or to its inner ring of
suburb A suburb (more broadly suburban area) is an area within a metropolitan area, which may include commercial and mixed-use, that is primarily a residential area. A suburb can exist either as part of a larger city/urban area or as a separ ...
s with trains making frequent station stops. The outer suburbs may then be reached by a separate
commuter rail Commuter rail, or suburban rail, is a passenger rail transport service that primarily operates within a metropolitan area, connecting commuters to a central city from adjacent suburbs or commuter towns. Generally commuter rail systems are con ...
network where more widely spaced stations allow higher speeds. In some cases the differences between urban rapid transit and suburban systems are not clear. Rapid transit systems may be supplemented by other systems such as
trolleybus A trolleybus (also known as trolley bus, trolley coach, trackless trolley, trackless tramin the 1910s and 1920sJoyce, J.; King, J. S.; and Newman, A. G. (1986). ''British Trolleybus Systems'', pp. 9, 12. London: Ian Allan Publishing. .or trol ...
es, regular
bus A bus (contracted from omnibus, with variants multibus, motorbus, autobus, etc.) is a road vehicle that carries significantly more passengers than an average car or van. It is most commonly used in public transport, but is also in use for cha ...
es,
tram A tram (called a streetcar or trolley in North America) is a rail vehicle that travels on tramway tracks on public urban streets; some include segments on segregated right-of-way. The tramlines or networks operated as public transport ...
s, or
commuter rail Commuter rail, or suburban rail, is a passenger rail transport service that primarily operates within a metropolitan area, connecting commuters to a central city from adjacent suburbs or commuter towns. Generally commuter rail systems are con ...
. This combination of transit modes serves to offset certain limitations of rapid transit such as limited stops and long walking distances between outside access points. Bus or tram feeder systems transport people to rapid transit stops.


Lines

Each rapid transit system consists of one or more ''lines'', or circuits. Each line is serviced by at least one specific route with trains stopping at all or some of the line's stations. Most systems operate several routes, and distinguish them by colors, names, numbering, or a combination thereof. Some lines may share track with each other for a portion of their route or operate solely on their own right-of-way. Often a line running through the city center forks into two or more branches in the suburbs, allowing a higher service frequency in the center. This arrangement is used by many systems, such as the
Copenhagen Metro The Copenhagen Metro ( da, Københavns Metro, ) is a 24/7 rapid transit system in Copenhagen, Denmark, serving the municipalities of Copenhagen, Frederiksberg, and Tårnby. The original system opened in October 2002, serving nine stations ...
, the
Milan Metro The Milan Metro ( it, Metropolitana di Milano) is the rapid transit system serving Milan, Italy, operated by Azienda Trasporti Milanesi. The network consists of 5 lines, identified by different numbers and colours, with a total network length ...
, the
Oslo Metro The Oslo Metro ( no, Oslo T-bane or or simply ) is the rapid transit system of Oslo, Norway, operated by Sporveien T-banen on contract from the transit authority Ruter. The network consists of five lines that all run through the city centre, w ...
and the
New York City Subway The New York City Subway is a rapid transit system owned by the government of New York City and leased to the New York City Transit Authority, an affiliate agency of the state-run Metropolitan Transportation Authority (MTA). Opened on October ...
. Alternatively, there may be a single central terminal (often shared with the central railway station), or multiple interchange stations between lines in the city center, for instance in the Prague Metro. The
London Underground The London Underground (also known simply as the Underground or by its nickname the Tube) is a rapid transit system serving Greater London and some parts of the adjacent counties of Buckinghamshire, Essex and Hertfordshire in England. The ...
and
Paris Métro The Paris Métro (french: Métro de Paris ; short for Métropolitain ) is a rapid transit system in the Paris metropolitan area, France. A symbol of the city, it is known for its density within the capital's territorial limits, uniform architec ...
are densely built systems with a matrix of crisscrossing lines throughout the cities. The
Chicago 'L' (''City in a Garden''); I Will , image_map = , map_caption = Interactive Map of Chicago , coordinates = , coordinates_footnotes = , subdivision_type = Country , subdivision_name ...
has most of its lines converging on The Loop, the main business, financial, and cultural area. Some systems have a circular line around the city center connecting to radially arranged outward lines, such as the
Moscow Metro The Moscow Metro) is a metro system serving the Russian capital of Moscow as well as the neighbouring cities of Krasnogorsk, Reutov, Lyubertsy and Kotelniki in Moscow Oblast. Opened in 1935 with one line and 13 stations, it was the first ...
's Koltsevaya Line and
Beijing Subway The Beijing Subway is the rapid transit system of Beijing Municipality that consists of 25 lines including 20 rapid transit lines, two airport rail links, one maglev line and 2 light rail lines, and 463 stations. The rail network extends ...
's Line 10. The capacity of a line is obtained by multiplying the car capacity, the train length, and the service frequency. Heavy rapid transit trains might have six to twelve cars, while lighter systems may use four or fewer. Cars have a capacity of 100 to 150 passengers, varying with the
seated to standing ratio In urban public transport, provision is made for standing passengers, often called straphangers or standees, to rationalize operation and to provide extra capacity during rush hour. Occurrence On crowded rapid transit urban lines, while most tr ...
—more standing gives higher capacity. The minimum time interval between trains is shorter for rapid transit than for mainline railways owing to the use of Communications based train control: the minimum headway can reach 90 seconds, but many systems typically use 120 seconds to allow for recovery from delays. Typical capacity lines allow 1,200 people per train, giving 36,000 passengers per hour per direction. However, much higher capacities are attained in
East Asia East Asia is the eastern region of Asia, which is defined in both geographical and ethno-cultural terms. The modern states of East Asia include China, Japan, Mongolia, North Korea, South Korea, and Taiwan. China, North Korea, South Korea ...
with ranges of 75,000 to 85,000 people per hour achieved by
MTR Corporation MTR Corporation Limited is a majority government-owned public transport operator and property developer in Hong Kong which operates the Mass Transit Railway, the most popular public transport network in Hong Kong. It is listed on the Hon ...
's urban lines in Hong Kong.


Network topologies

Rapid transit
topologies In mathematics, topology (from the Greek words , and ) is concerned with the properties of a geometric object that are preserved under continuous deformations, such as stretching, twisting, crumpling, and bending; that is, without closing ho ...
are determined by a large number of factors, including geographical barriers, existing or expected travel patterns, construction costs, politics, and historical constraints. A transit system is expected to serve an ''area'' of land with a set of ''lines'', which consist of shapes summarized as "I", "L", "U", "S", and "O" shapes or loops. Geographical barriers may cause chokepoints where transit lines must converge (for example, to cross a body of water), which are potential congestion sites but also offer an opportunity for transfers between lines. Ring lines provide good coverage, connect between the radial lines and serve tangential trips that would otherwise need to cross the typically congested core of the network. A rough grid pattern can offer a wide variety of routes while still maintaining reasonable speed and frequency of service. A study of the 15 world largest subway systems suggested a universal shape composed of a dense core with branches radiating from it.


Passenger information

Rapid transit operators have often built up strong
brand A brand is a name, term, design, symbol or any other feature that distinguishes one seller's good or service from those of other sellers. Brands are used in business, marketing, and advertising for recognition and, importantly, to create an ...
s, often focused on easy recognition—to allow quick identification even in the vast array of signage found in large cities—combined with the desire to communicate speed, safety, and authority. In many cities, there is a single corporate image for the entire transit authority, but the rapid transit uses its own logo that fits into the profile. A transit map is a topological map or schematic
diagram A diagram is a symbolic representation of information using visualization techniques. Diagrams have been used since prehistoric times on walls of caves, but became more prevalent during the Enlightenment. Sometimes, the technique uses a three ...
used to show the routes and stations in a
public transport Public transport (also known as public transportation, public transit, mass transit, or simply transit) is a system of transport for passengers by group travel systems available for use by the general public unlike private transport, typi ...
system. The main components are
color-coded A color code is a system for displaying information by using different colors. The earliest examples of color codes in use are for long-distance communication by use of flags, as in semaphore communication. The United Kingdom adopted a color c ...
lines to indicate each line or service, with named icons to indicate stations. Maps may show only rapid transit or also include other modes of public transport.Ovenden, 2007: 9 Transit maps can be found in transit vehicles, on platforms, elsewhere in stations, and in printed
timetables A schedule or a timetable, as a basic time-management tool, consists of a list of times at which possible tasks, events, or actions are intended to take place, or of a sequence of events in the chronological order in which such things are ...
. Maps help users understand the interconnections between different parts of the system; for example, they show the interchange stations where passengers can transfer between lines. Unlike conventional maps, transit maps are usually not geographically accurate, but emphasize the
topological In mathematics, topology (from the Greek words , and ) is concerned with the properties of a geometric object that are preserved under continuous deformations, such as stretching, twisting, crumpling, and bending; that is, without closing ...
connections among the different stations. The graphic presentation may use straight lines and fixed angles, and often a fixed minimum distance between stations, to simplify the display of the transit network. Often this has the effect of compressing the distance between stations in the outer area of the system, and expanding distances between those close to the center. Some systems assign unique
alphanumeric code Alphanumericals or alphanumeric characters are a combination of alphabetical and numerical characters. More specifically, they are the collection of Latin letters and Arabic digits. An alphanumeric code is an identifier made of alphanumeric ch ...
s to each of their stations to help commuters identify them, which briefly encodes information about the line it is on, and its position on the line.Ström, 1998: 58 For example, on the
Singapore MRT The Mass Rapid Transit system, locally known by the initialism MRT, is a rapid transit system in Singapore and the island country's principal mode of railway transportation. The system commenced operations in November 1987 after two decades of ...
,
Changi Airport MRT station Changi Airport MRT station is an underground Mass Rapid Transit (MRT) station serving Changi Airport and its supplementary structure Jewel in Changi, Singapore. It is the terminus of the Changi Airport branch of the East West line (EWL). The ...
has the alphanumeric code CG2, indicating its position as the 2nd station on the Changi Airport branch of the East West Line. Interchange stations would have at least two codes, for example,
Raffles Place MRT station Raffles Place MRT station is an underground Mass Rapid Transit (MRT) interchange station on the North South Line (NSL) and East West Line (EWL) in Singapore. Located in the Downtown Core, the station is underneath Raffles Place, the centre o ...
has two codes, NS26 and EW14, the 26th station on the North South Line and the 14th station on the East West Line. Seoul Metro is another example that utilizes a code for its stations. But unlike that of Singapore's MRT, it is mostly numbers. Based on the line number, for example Sinyongsan station, coded as station 429. As it is on Line 4, the first number of the station code is 4. The last 2 numbers will be the station number on that line. Interchange stations can have multiple codes. Like City Hall station in Seoul which is served by Line 1 and Line 2. It has a code of 132 and 201 respectively. The Line 2 is a circle line and the first stop is City Hall, therefore, City Hall has the station code of 201. For lines without a number like Bundang line it will have an alphanumeric code. Lines without a number that are operated by KORAIL will start with the letter 'K'. With widespread use of the
Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, p ...
and
cell phone A mobile phone, cellular phone, cell phone, cellphone, handphone, hand phone or pocket phone, sometimes shortened to simply mobile, cell, or just phone, is a portable telephone that can make and receive telephone call, calls over a radio freq ...
s globally, transit operators now use these technologies to present information to their users. In addition to online maps and timetables, some transit operators now offer real-time information which allows passengers to know when the next vehicle will arrive, and expected travel times. The standardized
GTFS GTFS, which stands for General Transit Feed Specification or (originally) Google Transit Feed Specification, defines a common format for public transportation schedules and associated geographic information. GTFS contains only static or schedul ...
data format for transit information allows many third-party software developers to produce web and smartphone app programs which give passengers customized updates regarding specific transit lines and stations of interest.


Safety and security

Compared to other modes of transport, rapid transit has a good
safety Safety is the state of being "safe", the condition of being protected from harm or other danger. Safety can also refer to the control of recognized hazards in order to achieve an acceptable level of risk. Meanings There are two slightly di ...
record, with few accidents. Rail transport is subject to strict
safety regulations Occupational safety and health (OSH), also commonly referred to as occupational health and safety (OHS), occupational health, or occupational safety, is a multidisciplinary field concerned with the safety, health, and welfare of people at wor ...
, with requirements for procedure and maintenance to minimize risk.
Head-on collision A head-on collision is a traffic collision where the front ends of two vehicles such as cars, trains, ships or planes hit each other when travelling in opposite directions, as opposed to a side collision or rear-end collision. Rail transpor ...
s are rare due to use of double track, and low operating speeds reduce the occurrence and severity of
rear-end collision A rear-end collision (often called simply rear-end or in the UK a shunt) occurs when a vehicle crashes into the one in front of it. Common factors contributing to rear-end collisions include driver inattention or distraction, tailgating, panic ...
s and
derailment In rail transport, a derailment occurs when a rail vehicle such as a train comes off its rails. Although many derailments are minor, all result in temporary disruption of the proper operation of the railway system and they are a potentially ...
s.
Fire Fire is the rapid oxidation of a material (the fuel) in the exothermic chemical process of combustion, releasing heat, light, and various reaction products. At a certain point in the combustion reaction, called the ignition point, flames ...
is more of a danger underground, such as the
King's Cross fire The King's Cross fire was a 1987 fire in a London Underground station with 31 fatalities, after a fire under a wooden escalator suddenly spread into the underground ticket hall in a flashover. The fire began at approximately 19:30 on 18 Novembe ...
in London in November 1987, which killed 31 people. Systems are generally built to allow evacuation of trains at many places throughout the system. High platforms (usually over 1 meter / 3 feet) are a safety risk, as people falling onto the tracks have trouble climbing back.
Platform screen doors Platform screen doors (PSDs), also known as platform edge doors (PEDs), are used at some train, rapid transit and people mover stations to separate the platform from train tracks, as well as on some bus rapid transit, tram and light rail sys ...
are used on some systems to eliminate this danger. Rapid transit facilities are public spaces and may suffer from
security" \n\n\nsecurity.txt is a proposed standard for websites' security information that is meant to allow security researchers to easily report security vulnerabilities. The standard prescribes a text file called \"security.txt\" in the well known locat ...
problems:
petty crime A summary offence or petty offence is a violation in some common law jurisdictions that can be proceeded against summarily, without the right to a jury trial and/or indictment (required for an indictable offence). Canada In Canada, summary offenc ...
s, such as
pickpocketing Pickpocketing is a form of larceny that involves the stealing of money or other valuables from the person or a victim's pocket without them noticing the theft at the time. It may involve considerable dexterity and a knack for misdirection. A ...
and baggage theft, and more serious
violent crime A violent crime, violent felony, crime of violence or crime of a violent nature is a crime in which an offender or perpetrator uses or threatens to use harmful force upon a victim. This entails both crimes in which the violent act is the objecti ...
s, as well as sexual assaults on tightly packed trains and platforms. Security measures include
video surveillance Closed-circuit television (CCTV), also known as video surveillance, is the use of video cameras to transmit a signal to a specific place, on a limited set of monitors. It differs from broadcast television in that the signal is not openly tr ...
,
security guard A security guard (also known as a security inspector, security officer, or protective agent) is a person employed by a government or private party to protect the employing party's assets (property, people, equipment, money, etc.) from a variety ...
s, and conductors. In some countries a specialized
transit police Transit police (also known as transport police, railway police, railroad police and several other terms) are specialized police agencies employed either by a common carrier (a transit district, railway, railroad, bus line, or any other mass tr ...
may be established. These security measures are normally integrated with measures to protect revenue by checking that passengers are not travelling without paying. Some subway systems, such as the
Beijing Subway The Beijing Subway is the rapid transit system of Beijing Municipality that consists of 25 lines including 20 rapid transit lines, two airport rail links, one maglev line and 2 light rail lines, and 463 stations. The rail network extends ...
, which is ranked by Worldwide Rapid Transit Data as the "World's Safest Rapid Transit Network" in 2015, incorporate airport-style security checkpoints at every station. Rapid transit systems have been subject to
terrorism Terrorism, in its broadest sense, is the use of criminal violence to provoke a state of terror or fear, mostly with the intention to achieve political or religious aims. The term is used in this regard primarily to refer to intentional violen ...
with many casualties, such as the 1995 Tokyo subway sarin gas attack and the 2005 " 7/7" terrorist bombings on the London Underground.


Added features

Some rapid transport trains have extra features such as wall sockets, cellular reception (typically using leaky feeder in tunnels and DAS antennas in stations), as well as
Wi-Fi Wi-Fi () is a family of wireless network protocols, based on the IEEE 802.11 family of standards, which are commonly used for local area networking of devices and Internet access, allowing nearby digital devices to exchange data by radio waves ...
connectivity. The first metro system in the world to enable full mobile phone reception in underground stations and tunnels was Singapore's Mass Rapid Transit (MRT) system which launched its first underground mobile phone network (using AMPS) in 1989. Nowadays, many metro systems, such as the Hong Kong Mass Transit Railway (MTR) and the Berlin U-Bahn, provide mobile data connections in their tunnels for various network operators.


Infrastructure

The
technology Technology is the application of knowledge to reach practical goals in a specifiable and reproducible way. The word ''technology'' may also mean the product of such an endeavor. The use of technology is widely prevalent in medicine, scien ...
used for public, mass rapid transit has undergone significant changes in the years since the
Metropolitan Railway The Metropolitan Railway (also known as the Met) was a passenger and goods railway that served London from 1863 to 1933, its main line heading north-west from the capital's financial heart in the City to what were to become the Middlesex su ...
opened publicly in London in 1863. High capacity
Monorail A monorail (from "mono", meaning "one", and " rail") is a railway in which the track consists of a single rail or a beam. Colloquially, the term "monorail" is often used to describe any form of elevated rail or people mover. More accurat ...
s with larger and longer trains can be classified as rapid transit systems. Such monorail systems recently started operating in
Chongqing Chongqing ( or ; ; Sichuanese pronunciation: , Standard Mandarin pronunciation: ), alternately romanized as Chungking (), is a municipality in Southwest China. The official abbreviation of the city, "" (), was approved by the State Co ...
and
São Paulo São Paulo (, ; Portuguese for ' Saint Paul') is the most populous city in Brazil, and is the capital of the state of São Paulo, the most populous and wealthiest Brazilian state, located in the country's Southeast Region. Listed by the GaW ...
.
Light metro A medium-capacity system (MCS), also known as light rapid transit or light metro, is a rail transport system with a capacity greater than light rail, but less than typical heavy-rail rapid transit. MCS’s trains are usually 1-4 cars, or 1 lig ...
is a subclass of rapid transit that has the speed and grade separation of a "full metro" but is designed for smaller passenger numbers. It often has smaller loading gauges, lighter train cars and smaller consists of typically two to four cars. Light metros are typically used as feeder lines into the main rapid transit system. For instance, the Wenhu Line of the
Taipei Metro Taipei Mass Rapid Transit (MRT), branded as Metro Taipei, is a rapid transit system serving the areas of Taipei and New Taipei in Taiwan, operated by the government-owned Taipei Rapid Transit Corporation, which also operates the Maokong Gondo ...
serves many relatively sparse neighbourhoods and feeds into and complements the high capacity metro lines. Some systems have been built from scratch, others are reclaimed from former commuter rail or suburban tramway systems that have been upgraded, and often supplemented with an underground or elevated downtown section. At grade alignments with a dedicated
right-of-way Right of way is the legal right, established by grant from a landowner or long usage (i.e. by prescription), to pass along a specific route through property belonging to another. A similar ''right of access'' also exists on land held by a gov ...
are typically used only outside dense areas, since they create a physical barrier in the urban fabric that hinders the flow of people and vehicles across their path and have a larger physical footprint. This method of construction is the cheapest as long as land values are low. It is often used for new systems in areas that are planned to fill up with buildings after the line is built.


Trains

Most rapid transit trains are electric multiple units with lengths from three to over ten cars.White, 2002: 64 Crew sizes have decreased throughout history, with some modern systems now running completely unstaffed trains. Other trains continue to have drivers, even if their only role in normal operation is to open and close the doors of the trains at stations. Power is commonly delivered by a
third rail A third rail, also known as a live rail, electric rail or conductor rail, is a method of providing electric power to a railway locomotive or train, through a semi-continuous rigid conductor placed alongside or between the rails of a railway ...
or by
overhead wires An overhead line or overhead wire is an electrical cable that is used to transmit electrical energy to electric locomotives, trolleybuses or trams. It is known variously as: * Overhead catenary * Overhead contact system (OCS) * Overhead equipment ...
. The whole London Underground network uses
fourth rail A railway electrification system supplies electric power to railway trains and trams without an on-board prime mover or local fuel supply. Electric railways use either electric locomotives (hauling passengers or freight in separate cars ...
and others use the
linear motor A linear motor is an electric motor that has had its stator and rotor "unrolled", thus, instead of producing a torque (rotation), it produces a linear force along its length. However, linear motors are not necessarily straight. Characteristica ...
for propulsion. Some urban rail lines are built to a
loading gauge A loading gauge is a diagram or physical structure that defines the maximum height and width dimensions in railway vehicles and their loads. Their purpose is to ensure that rail vehicles can pass safely through tunnels and under bridges, and ke ...
as large as that of main-line railways; others are built to a smaller one and have
tunnel A tunnel is an underground passageway, dug through surrounding soil, earth or rock, and enclosed except for the entrance and exit, commonly at each end. A pipeline is not a tunnel, though some recent tunnels have used immersed tube cons ...
s that restrict the size and sometimes the shape of the train compartments. One example is most of the
London Underground The London Underground (also known simply as the Underground or by its nickname the Tube) is a rapid transit system serving Greater London and some parts of the adjacent counties of Buckinghamshire, Essex and Hertfordshire in England. The ...
, which has acquired the informal term "tube train" due to the cylindrical shape of the trains used on the deep tube lines. In many cities, metro networks consist of lines operating different sizes and types of vehicles. Although these sub networks are not often connected by track, in cases when it is necessary, rolling stock with a smaller
loading gauge A loading gauge is a diagram or physical structure that defines the maximum height and width dimensions in railway vehicles and their loads. Their purpose is to ensure that rail vehicles can pass safely through tunnels and under bridges, and ke ...
from one sub network may be transported along other lines that use larger trains. On some networks such operations are part of normal services.


Tracks

Most rapid transit systems use conventional
standard gauge A standard-gauge railway is a railway with a track gauge of . The standard gauge is also called Stephenson gauge (after George Stephenson), International gauge, UIC gauge, uniform gauge, normal gauge and European gauge in Europe, and SGR in E ...
railway track A railway track (British English and UIC terminology) or railroad track (American English), also known as permanent way or simply track, is the structure on a railway or railroad consisting of the rails, fasteners, railroad ties (sleeper ...
. Since tracks in subway tunnels are not exposed to
rain Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water f ...
,
snow Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water throughou ...
, or other forms of
precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
, they are often fixed directly to the floor rather than resting on
ballast Ballast is material that is used to provide stability to a vehicle or structure. Ballast, other than cargo, may be placed in a vehicle, often a ship or the gondola of a balloon or airship, to provide stability. A compartment within a boat, ship ...
, such as normal railway tracks. An alternate technology, using
rubber tires A tire (American English) or tyre (British English) is a ring-shaped component that surrounds a wheel's rim to transfer a vehicle's load from the axle through the wheel to the ground and to provide traction on the surface over which t ...
on narrow
concrete Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wid ...
or steel
roll way A roll way or running pad is the pad placed on a concrete slab or on the ties on the outside of the conventional track along both running rails of a rubber-tyred metro or along the unconventional track of a tram. The rubber-tyred wheels roll d ...
s, was pioneered on certain lines of the
Paris Métro The Paris Métro (french: Métro de Paris ; short for Métropolitain ) is a rapid transit system in the Paris metropolitan area, France. A symbol of the city, it is known for its density within the capital's territorial limits, uniform architec ...
and Mexico City Metro, and the first completely new system to use it was in
Montreal Montreal ( ; officially Montréal, ) is the second-most populous city in Canada and most populous city in the Canadian province of Quebec. Founded in 1642 as '' Ville-Marie'', or "City of Mary", it is named after Mount Royal, the triple- ...
, Canada. On most of these networks, additional horizontal wheels are required for guidance, and a conventional track is often provided in case of
flat tire A flat tire (British English: flat tyre) is a deflated pneumatic tyre, which can cause the rim of the wheel to ride on the tire tread or the ground potentially resulting in loss of control of the vehicle or irreparable damage to the tire. The mo ...
s and for switching. There are also some rubber-tired systems that use a central
guide rail A guide rail is a device or mechanism to direct products, vehicles or other objects through a channel, conveyor, roadway or rail system. Several types of guide rails exist and may be associated with: * Factory or production line conveyors * Pow ...
, such as the Sapporo Municipal Subway and the NeoVal system in
Rennes Rennes (; br, Roazhon ; Gallo: ''Resnn''; ) is a city in the east of Brittany in northwestern France at the confluence of the Ille and the Vilaine. Rennes is the prefecture of the region of Brittany, as well as the Ille-et-Vilaine departme ...
, France. Advocates of this system note that it is much quieter than conventional steel-wheeled trains, and allows for greater inclines given the increased traction of the rubber tires. However, they have higher maintenance costs and are less energy efficient. They also lose traction when weather conditions are wet or icy, preventing above-ground use of the Montréal Metro and limiting it on the Sapporo Municipal Subway, but not rubber-tired systems in other cities. Some cities with steep hills incorporate
mountain railway A mountain railway is a railway that operates in a mountainous region. It may operate through the mountains by following mountain valleys and tunneling beneath mountain passes, or it may climb a mountain to provide transport to and from the ...
technologies in their metros. One of the lines of the
Lyon Metro The Lyon Metro (french: Métro de Lyon) is a rapid transit system serving Lyon Metropolis, France. First opened in 1974, it currently consists of four lines, serving 40 stations and comprising of route. Part of the Transports en Commun Lyonnai ...
includes a section of rack (cog) railway, while the
Carmelit The Carmelit ( he, כַּרְמְלִית Arabic: كرمليت) is an underground funicular railway in Haifa, Israel. Construction started in 1956 and ended in 1959. It is the oldest underground transit system in the Middle East and currently th ...
, in Haifa, is an underground
funicular A funicular (, , ) is a type of cable railway system that connects points along a railway track laid on a steep slope. The system is characterized by two counterbalanced carriages (also called cars or trains) permanently attached to opposite ...
. For elevated lines, another alternative is the
monorail A monorail (from "mono", meaning "one", and " rail") is a railway in which the track consists of a single rail or a beam. Colloquially, the term "monorail" is often used to describe any form of elevated rail or people mover. More accurat ...
, which can be built either as straddle-beam monorails or as a suspended monorail. While monorails have never gained wide acceptance outside Japan, there are some such as
Chongqing Rail Transit The Chongqing Rail Transit (branded as CRT; also known as Chongqing Metro) is the rapid transit system in the city of Chongqing, China. In operation since 2005, it serves the transportation needs of the city's main business and entertainment d ...
's monorail lines which are widely used in a rapid transit setting.


Motive power

Although trains on very early rapid transit systems like the
Metropolitan Railway The Metropolitan Railway (also known as the Met) was a passenger and goods railway that served London from 1863 to 1933, its main line heading north-west from the capital's financial heart in the City to what were to become the Middlesex su ...
were powered using
steam engine A steam engine is a heat engine that performs mechanical work using steam as its working fluid. The steam engine uses the force produced by steam pressure to push a piston back and forth inside a cylinder. This pushing force can be ...
s, either via cable haulage or
steam locomotive A steam locomotive is a locomotive that provides the force to move itself and other vehicles by means of the expansion of steam. It is fuelled by burning combustible material (usually coal, oil or, rarely, wood) to heat water in the loco ...
s, nowadays virtually all metro trains use
electric power Electric power is the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second. Standard prefixes apply to watts as with other SI units: thousands, millions and billions ...
and are built to run as
multiple unit A multiple-unit train or simply multiple unit (MU) is a self-propelled train composed of one or more carriages joined together, which when coupled to another multiple unit can be controlled by a single driver, with multiple-unit train cont ...
s. Power for the trains, referred to as traction power, is usually supplied via one of two forms: an
overhead line An overhead line or overhead wire is an electrical cable that is used to transmit electrical energy to electric locomotives, trolleybuses or trams. It is known variously as: * Overhead catenary * Overhead contact system (OCS) * Overhead equipm ...
, suspended from poles or towers along the track or from structure or tunnel ceilings, or a
third rail A third rail, also known as a live rail, electric rail or conductor rail, is a method of providing electric power to a railway locomotive or train, through a semi-continuous rigid conductor placed alongside or between the rails of a railway ...
mounted at track level and contacted by a sliding "
pickup shoe Electric current collectors are used by trolleybuses, trams, electric locomotives or EMUs to carry electrical power from overhead lines, electrical third rails, or ground-level power supplies to the electrical equipment of the vehicles. Those for ...
". The practice of sending power through rails on the ground is mainly due to the limited overhead clearance of tunnels, which physically prevents the use of
overhead wires An overhead line or overhead wire is an electrical cable that is used to transmit electrical energy to electric locomotives, trolleybuses or trams. It is known variously as: * Overhead catenary * Overhead contact system (OCS) * Overhead equipment ...
. The use of overhead wires allows higher power supply
voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to ...
s to be used. Although overhead wires are more likely to be used on metro systems without many tunnels, an example of which is the
Shanghai Metro The Shanghai Metro (; Shanghainese: ''Zaon6he5 Di6thiq7'') is a rapid transit system in Shanghai, operating urban and suburban transit services to 14 of its 16 municipal districts and to Kunshan, Jiangsu Province. Served as a part of Shang ...
, overhead wires are employed on some systems that are predominantly underground, as in
Barcelona Barcelona ( , , ) is a city on the coast of northeastern Spain. It is the capital and largest city of the autonomous community of Catalonia, as well as the second most populous municipality of Spain. With a population of 1.6 million within c ...
,
Fukuoka is the sixth-largest city in Japan, the second-largest port city after Yokohama, and the capital city of Fukuoka Prefecture, Japan. The city is built along the shores of Hakata Bay, and has been a center of international commerce since anc ...
,
Hong Kong Hong Kong ( (US) or (UK); , ), officially the Hong Kong Special Administrative Region of the People's Republic of China (abbr. Hong Kong SAR or HKSAR), is a List of cities in China, city and Special administrative regions of China, special ...
,
Madrid Madrid ( , ) is the capital and most populous city of Spain. The city has almost 3.4 million inhabitants and a metropolitan area population of approximately 6.7 million. It is the second-largest city in the European Union (EU), and ...
, and
Shijiazhuang Shijiazhuang (; ; Mandarin: ), formerly known as Shimen and romanized as Shihkiachwang, is the capital and most populous city of China’s North China's Hebei Province. Administratively a prefecture-level city, it is about southwest of Beijin ...
. Both overhead wire and third-rail systems usually use the running rails as the return conductor, but some systems use a separate fourth rail for this purpose. There are transit lines that make use of both rail and overhead power, with vehicles able to switch between the two such as Blue Line in
Boston Boston (), officially the City of Boston, is the state capital and most populous city of the Commonwealth of Massachusetts, as well as the cultural and financial center of the New England region of the United States. It is the 24th- mo ...
.


Tunnels

Underground
tunnel A tunnel is an underground passageway, dug through surrounding soil, earth or rock, and enclosed except for the entrance and exit, commonly at each end. A pipeline is not a tunnel, though some recent tunnels have used immersed tube cons ...
s move traffic away from street level, avoiding delays caused by
traffic congestion Traffic congestion is a condition in transport that is characterized by slower speeds, longer trip times, and increased vehicular queueing. Traffic congestion on urban road networks has increased substantially since the 1950s. When traffic de ...
and leaving more land available for buildings and other uses. In areas of high land prices and dense land use, tunnels may be the only economic route for mass transportation.
Cut-and-cover A tunnel is an underground passageway, dug through surrounding soil, earth or rock, and enclosed except for the entrance and exit, commonly at each end. A pipeline is not a tunnel, though some recent tunnels have used immersed tube cons ...
tunnels are constructed by digging up city streets, which are then rebuilt over the tunnel; alternatively,
tunnel-boring machine A tunnel boring machine (TBM), also known as a "mole", is a machine used to excavate tunnels with a circular cross section through a variety of soil and rock strata. They may also be used for microtunneling. They can be designed to bore thro ...
s can be used to dig deep-bore tunnels that lie further down in
bedrock In geology, bedrock is solid rock that lies under loose material ( regolith) within the crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface material. An exposed portion of be ...
. The construction of an underground metro is an expensive
project A project is any undertaking, carried out individually or collaboratively and possibly involving research or design, that is carefully planned to achieve a particular goal. An alternative view sees a project managerially as a sequence of even ...
and is often carried out over a number of years. There are several different methods of building underground lines. In one common method, known as
cut-and-cover A tunnel is an underground passageway, dug through surrounding soil, earth or rock, and enclosed except for the entrance and exit, commonly at each end. A pipeline is not a tunnel, though some recent tunnels have used immersed tube cons ...
the city
street A street is a public thoroughfare in a built environment. It is a public parcel of land adjoining buildings in an urban context, on which people may freely assemble, interact, and move about. A street can be as simple as a level patch of di ...
s are excavated and a tunnel structure strong enough to support the road above is built in the trench, which is then filled in and the roadway rebuilt. This method often involves extensive relocation of
utilities A public utility company (usually just utility) is an organization that maintains the infrastructure for a public service (often also providing a service using that infrastructure). Public utilities are subject to forms of public control and ...
commonly buried not far below street level – particularly
power Power most often refers to: * Power (physics), meaning "rate of doing work" ** Engine power, the power put out by an engine ** Electric power * Power (social and political), the ability to influence people or events ** Abusive power Power may a ...
and
telephone A telephone is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most efficiently the human voice, into e ...
wiring,
water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...
and gas mains, and sewers. This relocation must be done carefully, as according to documentaries from the National Geographic Society, one of the causes of the April 22, 1992, explosions in Guadalajara was a mislocated water pipeline. The structures are typically made of
concrete Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wid ...
, perhaps with structural columns of
steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistan ...
; in the oldest systems,
brick A brick is a type of block used to build walls, pavements and other elements in masonry construction. Properly, the term ''brick'' denotes a block composed of dried clay, but is now also used informally to denote other chemically cured cons ...
, and
cast iron Cast iron is a class of iron– carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impuri ...
were used. Cut-and-cover construction can take so long that it is often necessary to build a temporary roadbed while construction is going on underneath, in order to avoid closing main streets for long periods of time. Another usual type of tunneling method is called bored tunneling. Here, construction starts with a vertical shaft from which tunnels are horizontally dug, often with a
tunneling shield A tunnelling shield is a protective structure used during the excavation of large, man-made tunnels. When excavating through ground that is soft, liquid, or otherwise unstable, there is a potential health and safety hazard to workers and the proj ...
, thus avoiding almost any disturbance to existing streets, buildings, and utilities. But problems with
ground water Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidate ...
are more likely, and tunneling through native
bedrock In geology, bedrock is solid rock that lies under loose material ( regolith) within the crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface material. An exposed portion of be ...
may require blasting. The first city to extensively use deep tunneling was
London London is the capital and List of urban areas in the United Kingdom, largest city of England and the United Kingdom, with a population of just under 9 million. It stands on the River Thames in south-east England at the head of a estuary dow ...
, where a thick
sedimentary Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...
layer of
clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay pa ...
largely avoids both problems. The confined space in the tunnel also limits the machinery that can be used, but specialized
tunnel-boring machine A tunnel boring machine (TBM), also known as a "mole", is a machine used to excavate tunnels with a circular cross section through a variety of soil and rock strata. They may also be used for microtunneling. They can be designed to bore thro ...
s are now available to overcome this challenge. One disadvantage with this, however, is that the cost of tunneling is much higher than building cut-and-cover systems, at-grade or elevated. Early tunneling machines could not make tunnels large enough for conventional railway equipment, necessitating special low, round trains, such as are still used by most of the London Underground, which cannot install
air conditioning Air conditioning, often abbreviated as A/C or AC, is the process of removing heat from an enclosed space to achieve a more comfortable interior environment (sometimes referred to as 'comfort cooling') and in some cases also strictly controlling ...
on most of its lines because the amount of empty space between the trains and tunnel walls is so small. Other lines were built with cut-and-cover and have since been equipped with air-conditioned trains. The deepest metro system in the world was built in
St. Petersburg Saint Petersburg ( rus, links=no, Санкт-Петербург, a=Ru-Sankt Peterburg Leningrad Petrograd Piter.ogg, r=Sankt-Peterburg, p=ˈsankt pʲɪtʲɪrˈburk), formerly known as Petrograd (1914–1924) and later Leningrad (1924–1991), i ...
, Russia where in the
marshland A marsh is a wetland that is dominated by herbaceous rather than woody plant species.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p Marshes can often be found at ...
, stable soil starts more than deep. Above that level, the soil mostly consists of water-bearing finely dispersed sand. Because of this, only three stations out of nearly 60 are built near ground level and three more above the ground. Some stations and tunnels lie as deep as below the surface. However, the location of the world's deepest station is not clear. Usually, the vertical distance between the ground level and the rail is used to represent the depth. Among the possible candidates are: * Deepest stations in
Saint Petersburg Metro The Saint Petersburg Metro (russian: links=no, Петербургский метрополитен, Peterburgskiy metropoliten) is a rapid transit system in Saint Petersburg, Russia. Construction began in early 1941, but was put on hold due to Wor ...
, Russia: ** '' Admiralteyskaya'' (''The Admiralty'', , opened 2011, probably the best candidate) ** '' Komendantsky Prospekt'' (''The Commandant Avenue'', , opened 2005) ** '' Chernyshevskaya'' (''
Chernyshevsky Nikolay Gavrilovich Chernyshevsky ( – ) was a Russian literary and social critic, journalist, novelist, democrat, and socialist philosopher, often identified as a utopian socialist and leading theoretician of Russian nihilism. He was ...
'', , opened 1958) ** '' Ploshad Lenina'' (''
Lenin Vladimir Ilyich Ulyanov. ( 1870 – 21 January 1924), better known as Vladimir Lenin,. was a Russian revolutionary, politician, and political theorist. He served as the first and founding head of government of Soviet Russia from 1917 to 1 ...
Square'', , opened 1958) * '' Arsenalna'' station in Kyiv Metro, Ukraine (, opened 1960, built under a hill) *''
Hongtudi station Hongtudi is an interchange station on Line 6 and Line 10 of Chongqing Rail Transit in Chongqing Municipality, China. It is located in the Jiangbei District. The lowest level being 94 meters below ground makes it one of the world's deepest ...
'' in
Chongqing Metro The Chongqing Rail Transit (branded as CRT; also known as Chongqing Metro) is the rapid transit system in the city of Chongqing, China. In operation since 2005, it serves the transportation needs of the city's main business and entertainment ...
, China (, opened in 2016) *''Liyuchi station'' in
Chongqing Metro The Chongqing Rail Transit (branded as CRT; also known as Chongqing Metro) is the rapid transit system in the city of Chongqing, China. In operation since 2005, it serves the transportation needs of the city's main business and entertainment ...
, China (, opened in 2017) * '' Park Pobedy'' station in
Moscow Moscow ( , US chiefly ; rus, links=no, Москва, r=Moskva, p=mɐskˈva, a=Москва.ogg) is the capital and largest city of Russia. The city stands on the Moskva River in Central Russia, with a population estimated at 13.0 million ...
(~, opened 2005, built under a hill) * ''Puhung'' station in
Pyongyang Metro The Pyongyang Metro () is the rapid transit system in the North Korean capital Pyongyang. It consists of two lines: the Chollima Line, which runs north from Puhŭng Station on the banks of the Taedong River to Pulgŭnbyŏl Station, and the Hyŏksi ...
, North Korea (which doubles as a nuclear shelter) * '' Washington Park''
MAX Light Rail The Metropolitan Area Express (MAX) is a light rail system serving the Portland metropolitan area in the U.S. state of Oregon. Owned and operated by TriMet, it consists of five color-designated lines that altogether connect the six sectio ...
station in Portland, Oregon (built under a hill), 260 feet (80 m) One advantage of deep tunnels is that they can dip in a basin-like profile between stations, without incurring the significant extra costs associated with digging near ground level. This technique, also referred to as putting stations "on humps", allows gravity to assist the trains as they accelerate from one station and brake at the next. It was used as early as 1890 on parts of the
City and South London Railway The City and South London Railway (C&SLR) was the first successful deep-level underground "tube" railway in the world, and the first major railway to use electric traction. The railway was originally intended for cable-hauled trains, but owing ...
and has been used many times since, particularly in Montreal. The
West Island line The Extension of Island line to Western District (previously known as West Island line) is a three- station western extension of the Hong Kong MTR's Island line. Construction of the line began on 10 August 2009, and the two westernmost stations ...
, an extension of the MTR Island line serving western Hong Kong Island, opened in 2015, has two stations (
Sai Ying Pun Sai Ying Pun is an area in Western District, on Hong Kong Island, in Hong Kong. It is administratively part of the Central and Western District. Etymology In Cantonese, ''Sai'' () means "west" and ''Ying Pun'' () means "camp", especially a ...
and
HKU The University of Hong Kong (HKU) (Chinese: 香港大學) is a public research university in Hong Kong. Founded in 1887 as the Hong Kong College of Medicine for Chinese, it is the oldest tertiary institution in Hong Kong. HKU was also the fi ...
) situated over below ground level, to serve passengers on the
Mid-levels Mid-Levels is an affluent residential area on Hong Kong Island in Hong Kong. It is located between Victoria Peak and Central. Residents are predominantly more affluent Hong Kong locals and expatriate professionals. The Mid-Levels is furth ...
. They have several entrances/exits equipped with high-speed lifts, instead of
escalators An escalator is a moving staircase which carries people between floors of a building or structure. It consists of a Electric motor, motor-driven chain of individually linked steps on a track which cycle on a pair of tracks which keep the st ...
. These kinds of exits have existed in many London Underground stations and stations in former Soviet Union nations.


Elevated railways

Elevated railway An elevated railway or elevated train (also known as an el train for short) is a rapid transit railway with the tracks above street level on a viaduct or other elevated structure (usually constructed from steel, cast iron, concrete, or bricks ...
s are a cheaper and easier way to build an exclusive right-of-way without digging expensive tunnels or creating barriers. In addition to street level railways they may also be the only other feasible alternative due to considerations such as a high water table close to the city surface that raises the cost of, or even precludes underground railways (e.g.
Miami Miami ( ), officially the City of Miami, known as "the 305", "The Magic City", and "Gateway to the Americas", is a coastal metropolis and the county seat of Miami-Dade County in South Florida, United States. With a population of 442,241 at ...
). Elevated guideways were popular around the beginning of the 20th century, but fell out of favor; they came back into fashion in the last quarter of the century—often in combination with driverless systems, for instance Vancouver's SkyTrain, London's
Docklands Light Railway The Docklands Light Railway (DLR) is an automated light metro system serving the redeveloped Docklands area of London, England and provides a direct connection between London's two major financial districts, Canary Wharf and the City of Lo ...
, the Miami Metrorail, and the
Bangkok Skytrain The Bangkok Mass Transit System, commonly known as the BTS Skytrain ( th, รถไฟฟ้าบีทีเอส '' TS'), is an elevated rapid transit system in Bangkok, Thailand. It is operated by Bangkok Mass Transit System PCL (BTSC), ...
.


Stations

Stations function as hubs to allow passengers to board and disembark from trains. They are also payment checkpoints and allow passengers to transfer between modes of transport, for instance to buses or other trains. Access is provided via either island- or
side platform A side platform (also known as a marginal platform or a single-face platform) is a platform positioned to the side of one or more railway tracks or guideways at a railway station, tram stop, or transitway. A station having dual side platfo ...
s. Underground stations, especially deep-level ones, increase the overall transport time: long
escalator An escalator is a moving staircase which carries people between floors of a building or structure. It consists of a motor-driven chain of individually linked steps on a track which cycle on a pair of tracks which keep the step tread horizo ...
rides to the platforms mean that the stations can become bottlenecks if not adequately built. Some underground and elevated stations are integrated into vast underground or
skyway A skyway, skybridge, skywalk, or sky walkway is an elevated type of pedway connecting two or more buildings in an urban area, or connecting elevated points within mountainous recreational zones. Urban skyways very often take the form of enclo ...
networks respectively, that connect to nearby commercial buildings. In suburbs, there may be a "
park and ride A park and ride, also known as incentive parking or a commuter lot, is a parking lot with public transport connections that allows commuters and other people heading to city centres to leave their vehicles and transfer to a bus, rail system ( ...
" connected to the station. To allow easy access to the trains, the
platform height Railway platform height is the built height – ''above top of rail (ATR)'' – of passenger platforms at stations. A connected term is ''train floor height'', which refers to the ATR height of the floor of rail vehicles. Worldwide, there are m ...
allows step-free access between platform and train. If the station complies with
accessibility Accessibility is the design of products, devices, services, vehicles, or environments so as to be usable by people with disabilities. The concept of accessible design and practice of accessible development ensures both "direct access" (i. ...
standards, it allows both disabled people and those with wheeled baggage easy access to the trains, though if the track is curved there can be a gap between the train and platform. Some stations use
platform screen doors Platform screen doors (PSDs), also known as platform edge doors (PEDs), are used at some train, rapid transit and people mover stations to separate the platform from train tracks, as well as on some bus rapid transit, tram and light rail sys ...
to increase safety by preventing people falling onto the tracks, as well as reducing ventilation costs. The deepest station in the world is Arsenalna station in
Kyiv, Ukraine Kyiv, also spelled Kiev, is the capital and most populous city of Ukraine. It is in north-central Ukraine along the Dnieper River. As of 1 January 2021, its population was 2,962,180, making Kyiv the seventh-most populous city in Europe. Kyi ...
(105.5 m). Particularly in the former
Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen nationa ...
and other Eastern European countries, but to an increasing extent elsewhere, the stations were built with splendid decorations such as
marble Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or dolomite. Marble is typically not foliated (layered), although there are exceptions. In geology, the term ''marble'' refers to metamorphose ...
walls, polished
granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies un ...
floors and mosaics—thus exposing the public to art in their everyday life, outside galleries and museums. The systems in
Moscow Moscow ( , US chiefly ; rus, links=no, Москва, r=Moskva, p=mɐskˈva, a=Москва.ogg) is the capital and largest city of Russia. The city stands on the Moskva River in Central Russia, with a population estimated at 13.0 million ...
,
St. Petersburg Saint Petersburg ( rus, links=no, Санкт-Петербург, a=Ru-Sankt Peterburg Leningrad Petrograd Piter.ogg, r=Sankt-Peterburg, p=ˈsankt pʲɪtʲɪrˈburk), formerly known as Petrograd (1914–1924) and later Leningrad (1924–1991), i ...
,
Tashkent Tashkent (, uz, Toshkent, Тошкент/, ) (from russian: Ташкент), or Toshkent (; ), also historically known as Chach is the capital and largest city of Uzbekistan. It is the most populous city in Central Asia, with a population of 2 ...
and
Kyiv Kyiv, also spelled Kiev, is the capital and most populous city of Ukraine. It is in north-central Ukraine along the Dnieper River. As of 1 January 2021, its population was 2,962,180, making Kyiv the seventh-most populous city in Europe. Ky ...
are widely regarded as some of the most beautiful in the world. Several other cities such as London,
Stockholm Stockholm () is the capital and largest city of Sweden as well as the largest urban area in Scandinavia. Approximately 980,000 people live in the municipality, with 1.6 million in the urban area, and 2.4 million in the metropo ...
,
Montreal Montreal ( ; officially Montréal, ) is the second-most populous city in Canada and most populous city in the Canadian province of Quebec. Founded in 1642 as '' Ville-Marie'', or "City of Mary", it is named after Mount Royal, the triple- ...
,
Lisbon Lisbon (; pt, Lisboa ) is the capital and largest city of Portugal, with an estimated population of 544,851 within its administrative limits in an area of 100.05 km2. Lisbon's urban area extends beyond the city's administrative limits w ...
,
Naples Naples (; it, Napoli ; nap, Napule ), from grc, Νεάπολις, Neápolis, lit=new city. is the regional capital of Campania and the third-largest city of Italy, after Rome and Milan, with a population of 909,048 within the city's adm ...
and
Los Angeles Los Angeles ( ; es, Los Ángeles, link=no , ), often referred to by its initials L.A., is the largest city in the state of California and the second most populous city in the United States after New York City, as well as one of the world ...
have also focused on art, which may range from decorative wall claddings, to large, flamboyant artistic schemes integrated with station architecture, to displays of ancient artifacts recovered during station construction. It may be possible to profit by attracting more passengers by spending relatively small amounts on grand
architecture Architecture is the art and technique of designing and building, as distinguished from the skills associated with construction. It is both the process and the product of sketching, conceiving, planning, designing, and constructing buildings ...
, art, cleanliness,
accessibility Accessibility is the design of products, devices, services, vehicles, or environments so as to be usable by people with disabilities. The concept of accessible design and practice of accessible development ensures both "direct access" (i. ...
,
lighting Lighting or illumination is the deliberate use of light to achieve practical or aesthetic effects. Lighting includes the use of both artificial light sources like lamps and light fixtures, as well as natural illumination by capturing dayl ...
and a feeling of
safety Safety is the state of being "safe", the condition of being protected from harm or other danger. Safety can also refer to the control of recognized hazards in order to achieve an acceptable level of risk. Meanings There are two slightly di ...
.


Crew size and automation

In the early days of underground railways, at least two staff members were needed to operated each train: one or more attendants (also called " conductor" or "guard") to operate the doors or gates, as well as a driver (also called the "
engineer Engineers, as practitioners of engineering, are professionals who Invention, invent, design, analyze, build and test machines, complex systems, structures, gadgets and materials to fulfill functional objectives and requirements while considerin ...
" or "motorman"). The introduction of powered doors around 1920 permitted crew sizes to be reduced, and trains in many cities are now operated by a single person. Where the operator would not be able to see the whole side of the train to tell whether the doors can be safely closed,
mirror A mirror or looking glass is an object that reflects an image. Light that bounces off a mirror will show an image of whatever is in front of it, when focused through the lens of the eye or a camera. Mirrors reverse the direction of the im ...
s or
closed-circuit TV Closed-circuit television (CCTV), also known as video surveillance, is the use of video cameras to transmit a signal to a specific place, on a limited set of monitors. It differs from broadcast television in that the signal is not openly tr ...
monitors are often provided for that purpose. A replacement system for human drivers became available in the 1960s, with the advancement of
computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations ( computation) automatically. Modern digital electronic computers can perform generic sets of operations known as programs. These prog ...
ized technologies for
automatic train control Automatic train control (ATC) is a general class of train protection systems for railways that involves a speed control mechanism in response to external inputs. For example, a system could effect an emergency brake application if the driver d ...
and, later, automatic train operation (ATO). ATO could start a train, accelerate to the correct speed, and stop automatically in the correct position at the
railway platform A railway platform is an area alongside a railway track providing convenient access to trains. Almost all stations have some form of platform, with larger stations having multiple platforms. The world's longest station platform is at Hubbali ...
at the next station, while taking into account the information that a human driver would obtain from lineside or cab signals. The first metro line to use this technology in its entirety was London's
Victoria line The Victoria line is a London Underground line that runs between in south London and in the north-east, via the West End. It is printed in light blue on the Tube map and is one of the only two lines on the network to run completely underg ...
, opened in 1968. In normal operation, a crew member sits in the driver's position at the front, but is only responsible for closing the doors at each station. By pressing two "start" buttons the train would then move automatically to the next station. This style of "semi-automatic train operation" (STO), known technically as " Grade of Automation (GoA) 2", has become widespread, especially on newly built lines like the San Francisco Bay Area's
BART Bart is a masculine given name, usually a diminutive of Bartholomew, sometimes of Barton, Bartolomeo, etc. Bart is a Dutch and Ashkenazi Jewish surname, and derives from the name ''Bartholomäus'', a German form of the biblical name ''Bartho ...
network. A variant of ATO, "driverless train operation" (DTO) or technically "GoA 3", is seen on some systems, as in London's
Docklands Light Railway The Docklands Light Railway (DLR) is an automated light metro system serving the redeveloped Docklands area of London, England and provides a direct connection between London's two major financial districts, Canary Wharf and the City of Lo ...
, which opened in 1987. Here, a "passenger service agent" (formerly called "train captain") would ride with the passengers rather than sit at the front as a driver would, but would have the same responsibilities as a driver in a GoA 2 system. This technology could allow trains to operate completely automatically with no crew, just as most
elevator An elevator or lift is a cable-assisted, hydraulic cylinder-assisted, or roller-track assisted machine that vertically transports people or freight between floors, levels, or decks of a building, vessel, or other structure. They ...
s do. When the initially increasing costs for
automation Automation describes a wide range of technologies that reduce human intervention in processes, namely by predetermining decision criteria, subprocess relationships, and related actions, as well as embodying those predeterminations in machines ...
began to decrease, this became a financially attractive option for employers. At the same time, countervailing arguments stated that in an
emergency An emergency is an urgent, unexpected, and usually dangerous situation that poses an immediate risk to health, life, property, or environment and requires immediate action. Most emergencies require urgent intervention to prevent a worsening ...
situation, a crew member on board the train would have possibly been able to prevent the emergency in the first place, drive a partially failed train to the next station, assist with an evacuation if needed, or call for the correct
emergency services Emergency services and rescue services are organizations that ensure public safety and health by addressing and resolving different emergencies. Some of these agencies exist solely for addressing certain types of emergencies, while others deal w ...
and help direct them to the location where the emergency occurred. In some cities, the same reasons are used to justify a crew of two rather than one; one person drives from the front of the train, while the other operates the doors from a position farther back, and is more conveniently able to assist passengers in the rear cars. An example of the presence of a driver purely due to union opposition is the
Scarborough RT Line 3 Scarborough (originally known as the Scarborough RT or SRT) is a light rapid transit line that is part of the Toronto subway system in Toronto, Ontario, Canada. The line runs entirely within the suburban district of Scarborough, encompas ...
line in Toronto. Completely unstaffed trains, or "unattended train operation" (UTO) or technically "GoA 4", are more accepted on newer systems where there are no existing crews to be displaced, and especially on
light metro A medium-capacity system (MCS), also known as light rapid transit or light metro, is a rail transport system with a capacity greater than light rail, but less than typical heavy-rail rapid transit. MCS’s trains are usually 1-4 cars, or 1 lig ...
lines. One of the first such systems was the
VAL Val may refer to: Val-a Film * ''Val'' (film), an American documentary about Val Kilmer, directed by Leo Scott and Ting Poo Military equipment * Aichi D3A, a Japanese World War II dive bomber codenamed "Val" by the Allies * AS Val, a Sov ...
(''véhicule automatique léger'' or "automated light vehicle"), first used in 1983 on the
Lille Metro The Lille Metro (french: Métro de Lille) is a driverless light metro system located in Lille, France. It was opened on 25 April 1983 and was the first to use the VAL (french: véhicule automatique léger, en, light automated vehicle) sys ...
in France. Additional VAL lines have been built in other cities such as
Toulouse Toulouse ( , ; oc, Tolosa ) is the prefecture of the French department of Haute-Garonne and of the larger region of Occitania. The city is on the banks of the River Garonne, from the Mediterranean Sea, from the Atlantic Ocean and fr ...
, France, and
Turin Turin ( , Piedmontese language, Piedmontese: ; it, Torino ) is a city and an important business and cultural centre in Northern Italy. It is the capital city of Piedmont and of the Metropolitan City of Turin, and was the first Italian capital ...
, Italy. Another system that uses unstaffed trains is Bombardier's
Innovia Metro Innovia Metro is an automated rapid transit system manufactured by Alstom. Innovia Metro systems run on conventional metal rails and pull power from a third rail, but are powered by a linear induction motor that provides traction by pulling on ...
, originally developed by the
Urban Transportation Development Corporation The Urban Transportation Development Corporation Ltd. (UTDC) was a Crown corporation owned by the Government of Ontario, Canada. It was established in the 1970s as a way to enter what was then expected to be a burgeoning market in advanced l ...
as the Intermediate Capacity Transit System (ICTS). It was later used on the SkyTrain in Vancouver and the
Kelana Jaya Line The LRT Kelana Jaya Line is a medium-capacity light rapid transit (LRT) line and the first fully automated and driverless rail system in the Klang Valley, Malaysia. It forms a part of the Klang Valley Integrated Transit System in and around ...
in Kuala Lumpur, both which carries no crew members. Systems that use automatic trains also commonly employ full-height
platform screen doors Platform screen doors (PSDs), also known as platform edge doors (PEDs), are used at some train, rapid transit and people mover stations to separate the platform from train tracks, as well as on some bus rapid transit, tram and light rail sys ...
or half-height
automatic platform gate Automatic may refer to: Music Bands * Automatic (band), Australian rock band * Automatic (American band), American rock band * The Automatic, a Welsh alternative rock band Albums * ''Automatic'' (Jack Bruce album), a 1983 electronic rock ...
s in order to improve safety and ensure passenger confidence, but this is not universal, as networks like
Nuremberg Nuremberg ( ; german: link=no, Nürnberg ; in the local East Franconian dialect: ''Nämberch'' ) is the second-largest city of the German state of Bavaria after its capital Munich, and its 518,370 (2019) inhabitants make it the 14th-largest ...
do not, using
infrared sensors Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
instead to detect obstacles on the track. Conversely, some lines which retain drivers or manual train operation nevertheless use PSDs, notably London's
Jubilee Line Extension The Jubilee Line Extension (JLE) is the extension of the London Underground Jubilee line from to through south and east London. An eastward extension of the line was first proposed in the 1970s. As part of the development of London Docklands, ...
. The first network to install PSDs on an already operational system was Hong Kong's MTR, followed by the Singapore MRT. As for larger trains, the
Paris Métro The Paris Métro (french: Métro de Paris ; short for Métropolitain ) is a rapid transit system in the Paris metropolitan area, France. A symbol of the city, it is known for its density within the capital's territorial limits, uniform architec ...
has human drivers on most lines but runs automated trains on its newest line, Line 14, which opened in 1998. The older Line 1 was subsequently converted to unattended operation by 2012, and it is expected that Line 4 will follow by 2023. The
North East MRT line The North East MRT line (NEL) is a high-capacity Mass Rapid Transit (MRT) line in Singapore. Operated by SBS Transit, it is the shortest MRT line at . The line runs from HarbourFront station in southern Singapore to Punggol station in the n ...
in Singapore, which opened in 2003, is the world's first fully automated underground urban heavy-rail line. The MTR
Disneyland Resort line The Disneyland Resort line is a heavy rail MTR line connecting Sunny Bay to the Hong Kong Disneyland Resort, coloured pink on the network diagram. It is the seventh line of the former MTR network before the merger of MTR and KCR, and the w ...
is also automated, along with trains on the
South Island line The South Island line, identified by light green on the MTR route map, is a rapid transit line of Hong Kong's MTR metro system. This line connects the HK business district from Admiralty station to the Southern District of Hong Kong Island ...
.


Modal tradeoffs and interconnections

Since the 1980s,
tram A tram (called a streetcar or trolley in North America) is a rail vehicle that travels on tramway tracks on public urban streets; some include segments on segregated right-of-way. The tramlines or networks operated as public transport ...
s have incorporated several features of rapid transit: light rail systems (trams) run on their own
rights-of-way Right of way is the legal right, established by grant from a landowner or long usage (i.e. by prescription), to pass along a specific route through property belonging to another. A similar ''right of access'' also exists on land held by a gov ...
, thus avoiding congestion; they remain on the same level as buses and cars. Some light rail systems have elevated or underground sections. Both new and upgraded tram systems allow faster speed and higher capacity, and are a cheap alternative to construction of rapid transit, especially in smaller cities. A
premetro A premetro is a tramway or light railway which includes segments built to rapid transit standards, generally as part of a process of conversion to a metro-standards railway usually by the construction of tunnels in the central city area. Hist ...
design means that an underground rapid transit system is built in the city center, but only a light rail or tram system in the suburbs. Conversely, other cities have opted to build a full metro in the suburbs, but run trams in city streets to save the cost of expensive tunnels. In North America,
interurban The Interurban (or radial railway in Europe and Canada) is a type of electric railway, with streetcar-like electric self-propelled rail cars which run within and between cities or towns. They were very prevalent in North America between 1900 ...
s were constructed as street-running suburban trams, without the grade-separation of rapid transit. Premetros also allow a gradual upgrade of existing tramways to rapid transit, thus spreading the investment costs over time. They are most common in Germany with the name
Stadtbahn ' (; German for "city railway"; plural ') is a German word referring to various types of urban rail transport. One type of transport originated in the 19th century, firstly in Berlin and followed by Vienna, where rail routes were created that co ...
. Suburban
commuter rail Commuter rail, or suburban rail, is a passenger rail transport service that primarily operates within a metropolitan area, connecting commuters to a central city from adjacent suburbs or commuter towns. Generally commuter rail systems are con ...
is a heavy rail system that operates at a lower frequency than urban rapid transit, with higher average speeds, often only serving one station in each village and town. Commuter rail systems of some cities (such as German
S-Bahn The S-Bahn is the name of hybrid urban-suburban rail systems serving a metropolitan region in German-speaking countries. Some of the larger S-Bahn systems provide service similar to rapid transit systems, while smaller ones often resemble c ...
s, Jakarta's
KRL Commuterline KRL Commuterline, or commonly known as Commuterline, is a commuter rail system for Greater Jakarta in Indonesia. It was previously known as KRL Jabodetabek. It is operated by PT KAI Commuter Indonesia (KAI Commuter/KCI), a subsidiary of the ...
, Chennai Suburban, Australian suburban networks, Danish S-tog etc.) can be seen as the substitute for the city's rapid transit system providing frequent mass transit within city. In contrast, the mainly urban rapid transit systems in some cities (such as the
Dubai Metro The Dubai Metro is a rapid transit rail network in the city of Dubai, United Arab Emirates. It is currently operated by the French company Keolis. The Red Line and Green Line are operational, with a major 15 km (9.3 mi) extension to the Red L ...
,
Shanghai Metro The Shanghai Metro (; Shanghainese: ''Zaon6he5 Di6thiq7'') is a rapid transit system in Shanghai, operating urban and suburban transit services to 14 of its 16 municipal districts and to Kunshan, Jiangsu Province. Served as a part of Shang ...
,
MetroSur Line 12, also known as MetroSur (Spanish for ''MetroSouth''), is a line of the Madrid Metro inaugurated on 11 April 2003. Line 12 is a circle line that is not in the city of Madrid, but links five suburban towns south of Madrid, serving around on ...
of the
Madrid Metro The Madrid Metro ( Spanish: ''Metro de Madrid'') is a rapid transit system serving the city of Madrid, capital of Spain. The system is the 14th longest rapid transit system in the world, with a total length of 293 km (182 mi). Its gr ...
,
Taipei Metro Taipei Mass Rapid Transit (MRT), branded as Metro Taipei, is a rapid transit system serving the areas of Taipei and New Taipei in Taiwan, operated by the government-owned Taipei Rapid Transit Corporation, which also operates the Maokong Gondo ...
, Kuala Lumpur Rapid Transit etc.) have lines that fan out to reach the outer suburbs. With some other urban or "near urban" rapid transit systems (
Guangfo Metro The Guangfo Metro or Guangfo line is a intercity metro line that connects the Chinese cities Foshan and Guangzhou. As of December 2018, the line is currently long and has 25 stations, which are all underground. History The line was expected ...
,
Bay Area Rapid Transit Bay Area Rapid Transit (BART) is a rapid transit system serving the San Francisco Bay Area in California. BART serves 50 stations along six routes on of rapid transit lines, including a spur line in eastern Contra Costa County which u ...
, Los Teques Metro and
Seoul Subway Line 7 Seoul Subway Line 7 of the Seoul Metropolitan Subway was built from 1990 to 1996 (Jangam- Konkuk Univ.) and was completed on August 1, 2000 (central section 17 km. Konkuk University to Sinpung); the western section between Sinpung and O ...
, etc.) serving bi- and multi-nucleus agglomerations. Some cities have opted for two tiers of urban railways: an urban rapid transit system (such as the
Paris Métro The Paris Métro (french: Métro de Paris ; short for Métropolitain ) is a rapid transit system in the Paris metropolitan area, France. A symbol of the city, it is known for its density within the capital's territorial limits, uniform architec ...
,
Berlin U-Bahn The Berlin U-Bahn (; short for , "underground railway") is a rapid transit system in Berlin, the capital and largest city of Germany, and a major part of the city's public transport system. Together with the S-Bahn, a network of suburban tra ...
,
London Underground The London Underground (also known simply as the Underground or by its nickname the Tube) is a rapid transit system serving Greater London and some parts of the adjacent counties of Buckinghamshire, Essex and Hertfordshire in England. The ...
,
Sydney Metro The Sydney Metro is a fully automated rapid transit system serving the city of Sydney, New South Wales, Australia. Currently consisting of one line that opened on 26 May 2019, it runs from Tallawong to Chatswood and consists of 13 stat ...
, Tokyo subway,
Jakarta MRT The Jakarta Mass Rapid Transit ( id, Moda Raya Terpadu ''Jakarta'') or Jakarta MRT (, stylized as ''mrt jakarta'') is a rapid transit system in Jakarta, the capital city of Indonesia. The system is operated by PT Mass Rapid Transit Jakarta (Per ...
and Philadelphia Subway) and a suburban system (such as their counterparts RER,
S-Bahn The S-Bahn is the name of hybrid urban-suburban rail systems serving a metropolitan region in German-speaking countries. Some of the larger S-Bahn systems provide service similar to rapid transit systems, while smaller ones often resemble c ...
, future
Crossrail Crossrail is a railway construction project mainly in central London. Its aim is to provide a high-frequency hybrid commuter rail and rapid transit system crossing the capital from suburbs on the west to east, by connecting two major railway l ...
&
London Overground London Overground (also known simply as the Overground) is a suburban rail network serving London and its environs. Established in 2007 to take over Silverlink Metro routes, (via archive.org). it now serves a large part of Greater London as w ...
,
Sydney Trains Sydney Trains is the operator of the suburban passenger rail network serving the city of Sydney, New South Wales, Australia. The network is a hybrid urban-suburban rail system with a central underground core that covers over of track and 170 ...
, JR Urban Lines,
KRL Commuterline KRL Commuterline, or commonly known as Commuterline, is a commuter rail system for Greater Jakarta in Indonesia. It was previously known as KRL Jabodetabek. It is operated by PT KAI Commuter Indonesia (KAI Commuter/KCI), a subsidiary of the ...
and
Regional Rail Regional rail, also known as local trains and stopping trains, are passenger rail services that operate between towns and cities. These trains operate with more stops over shorter distances than inter-city rail, but fewer stops and faster serv ...
respectively). Such systems are known variously as
S-train The S-Bahn is the name of hybrid urban-suburban rail systems serving a metropolitan region in German-speaking countries. Some of the larger S-Bahn systems provide service similar to rapid transit systems, while smaller ones often resemble c ...
s, suburban service, or (sometimes) regional rail. The suburban systems may have their own purpose built trackage, run at similar "rapid transit-like" frequencies, and (in many countries) are operated by the national railway company. In some cities these suburban services run through tunnels in the city center and have direct transfers to the rapid transit system, on the same or adjoining platforms.White, 2002: 63–64 In some cases, such as the
London Underground The London Underground (also known simply as the Underground or by its nickname the Tube) is a rapid transit system serving Greater London and some parts of the adjacent counties of Buckinghamshire, Essex and Hertfordshire in England. The ...
and the
London Overground London Overground (also known simply as the Overground) is a suburban rail network serving London and its environs. Established in 2007 to take over Silverlink Metro routes, (via archive.org). it now serves a large part of Greater London as w ...
, suburban and rapid transit systems even run on the exact same track along some sections.
California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...
's
BART Bart is a masculine given name, usually a diminutive of Bartholomew, sometimes of Barton, Bartolomeo, etc. Bart is a Dutch and Ashkenazi Jewish surname, and derives from the name ''Bartholomäus'', a German form of the biblical name ''Bartho ...
,
Federal District A federal district is a type of administrative division of a federation, usually under the direct control of a federal government and organized sometimes with a single municipal body. Federal districts often include capital districts, and they ...
's Metrô-DF and
Washington Washington commonly refers to: * Washington (state), United States * Washington, D.C., the capital of the United States ** A metonym for the federal government of the United States ** Washington metropolitan area, the metropolitan area centered o ...
's
Metrorail METRORail is the light rail system in Houston, Texas (United States). In , the system had a ridership of , or about per weekday as of . METRORail ranks as the second most-traveled light rail system in the Southern United States and the 12th ...
system is an example of a hybrid of the two: in the suburbs the lines function like a commuter rail line, with longer intervals and longer distance between stations; in the downtown areas, the stations become closer together and many lines interline with intervals dropping to typical rapid transit headways.


Costs, benefits, and impacts

, 212 cities have built rapid transit systems. The
capital cost Capital costs are fixed, one-time expenses incurred on the purchase of land, buildings, construction, and equipment used in the production of goods or in the rendering of services. In other words, it is the total cost needed to bring a projec ...
is high, as is the risk of
cost overrun A cost overrun, also known as a cost increase or budget overrun, involves unexpected incurred costs. When these costs are in excess of budgeted amounts due to a value engineering underestimation of the actual cost during budgeting, they are known ...
and benefit shortfall;
public financing Public finance is the study of the role of the government in the economy. It is the branch of economics that assesses the government revenue and government expenditure of the public authorities and the adjustment of one or the other to achie ...
is normally required. Rapid transit is sometimes seen as an alternative to an extensive
road transport Road transport or road transportation is a type of transport using roads. Transport on roads can be roughly grouped into the transportation of goods and transportation of people. In many countries licensing requirements and safety regulations ...
system with many
motorway A controlled-access highway is a type of highway that has been designed for high-speed vehicular traffic, with all traffic flow—ingress and egress—regulated. Common English terms are freeway, motorway and expressway. Other similar terms ...
s;Banister and Berechman, 2000: 258 the rapid transit system allows higher capacity with less land use, less environmental impact, and a lower cost. Elevated or underground systems in city centers allow the transport of people without occupying expensive land, and permit the city to develop compactly without physical barriers.
Motorway A controlled-access highway is a type of highway that has been designed for high-speed vehicular traffic, with all traffic flow—ingress and egress—regulated. Common English terms are freeway, motorway and expressway. Other similar terms ...
s often depress nearby residential
land value Real estate appraisal, property valuation or land valuation is the process of developing an opinion of value for real property (usually market value). Real estate transactions often require appraisals because they occur infrequently and every prop ...
s, but proximity to a rapid transit station often triggers commercial and residential growth, with large
transit oriented development In urban planning, transit-oriented development (TOD) is a type of urban development that maximizes the amount of residential, business and leisure space within walking distance of public transport. It promotes a symbiotic relationship between ...
office and housing blocks being constructed. Also, an efficient transit system can decrease the economic welfare loss caused by the increase of
population density Population density (in agriculture: standing stock or plant density) is a measurement of population per unit land area. It is mostly applied to humans, but sometimes to other living organisms too. It is a key geographical term.Matt RosenberPopu ...
in a metropolis. Rapid transit systems have high
fixed cost In accounting and economics, 'fixed costs', also known as indirect costs or overhead costs, are business expenses that are not dependent on the level of goods or services produced by the business. They tend to be recurring, such as interest or r ...
s. Most systems are publicly owned, by either local governments, transit authorities or national governments. Capital investments are often partially or completely financed by taxation, rather than by passenger fares, but must often compete with funding for
road A road is a linear way for the conveyance of traffic that mostly has an improved surface for use by vehicles (motorized and non-motorized) and pedestrians. Unlike streets, the main function of roads is transportation. There are many types o ...
s. The transit systems may be operated by the owner or by a private company through a public service obligation. The owners of the systems often also own the connecting bus or rail systems, or are members of the local
transport association A transit district or transit authority is a government agency or a public-benefit corporation created for the purpose of providing public transportation within a specific region. A transit district may operate bus, rail or other types of tr ...
, allowing for free transfers between modes. Almost all transit systems operate at a deficit, requiring fare revenue,
advertising Advertising is the practice and techniques employed to bring attention to a product or service. Advertising aims to put a product or service in the spotlight in hopes of drawing it attention from consumers. It is typically used to promote a ...
and
subsidies A subsidy or government incentive is a form of financial aid or support extended to an economic sector (business, or individual) generally with the aim of promoting economic and social policy. Although commonly extended from the government, the ter ...
to cover costs. The
farebox recovery ratio The farebox recovery ratio (also called fare recovery ratio, fare recovery rate or other terms) of a passenger transportation system is the fraction of operating expenses which are met by the fares paid by passengers. It is computed by dividing ...
, a ratio of ticket income to operating costs, is often used to assess operational profitability, with some systems including Hong Kong's
MTR Corporation MTR Corporation Limited is a majority government-owned public transport operator and property developer in Hong Kong which operates the Mass Transit Railway, the most popular public transport network in Hong Kong. It is listed on the Hon ...
, and
Taipei Taipei (), officially Taipei City, is the capital and a special municipality of the Republic of China (Taiwan). Located in Northern Taiwan, Taipei City is an enclave of the municipality of New Taipei City that sits about southwest of the ...
achieving recovery ratios of well over 100%. This ignores both heavy capital costs incurred in building the system, which are often subsidized with
soft loan A soft loan is a loan with a below-market rate of interest. This is also known as ''soft financing''. Sometimes soft loans provide other concessions to borrowers, such as long repayment periods or interest holidays. Soft loans are usually provi ...
s and whose servicing is excluded from calculations of profitability, as well as ancillary revenue such as income from
real estate Real estate is property consisting of land and the buildings on it, along with its natural resources such as crops, minerals or water; immovable property of this nature; an interest vested in this (also) an item of real property, (more genera ...
portfolios. Some systems, particularly Hong Kong's, extensions are partly financed by the sale of land whose value has appreciated by the new access the extension has brought to the area,Kjenstad, 1994: 46 a process known as
value capture Value capture is a type of public financing that recovers some or all of the value that public infrastructure generates for private landowners. In many countries, the public sector is responsible for the infrastructure required to support urban dev ...
. Urban land-use planning policies are essential for the success of rapid transit systems, particularly as mass transit is not feasible in low-density communities. Transportation planners estimate that to support rapid rail services, there must be a residential housing density of twelve dwelling units per acre.


See also

*
List of metro systems This list of metro systems includes electrified rapid transit train systems worldwide. In some parts of the world, metro systems are referred to as subways, U-Bahn or undergrounds. , 205 cities in 61 countries have a metro system. The Londo ...
*
Bus rapid transit Bus rapid transit (BRT), also called a busway or transitway, is a bus-based public transport system designed to have much more capacity, reliability and other quality features than a conventional bus system. Typically, a BRT system includes ...
*
Megaproject A megaproject is an extremely large-scale investment project. According to the ''Oxford Handbook of Megaproject Management'', "Megaprojects are large-scale, complex ventures that typically cost $1 billion or more, take many years to develop and ...
*
Personal rapid transit Personal rapid transit (PRT), also referred to as podcars or guided/railed taxis, is a public transport mode featuring small low-capacity automated vehicles operating on a network of specially built guideways. PRT is a type of automated guideway ...
* Rapid transit track gauge


References


Citations


Sources

* * Bobrick, Benson (1981). ''Labyrinths of Iron'': ''a'' 'n''''History of the World's Subways''. New York: Newsweek Books. . * * * * * * * * * *


External links


UrbanRail
; Databases
metro data
Database of metro systems around the world {{Authority control Passenger rail transport Articles containing video clips 1863 introductions