View source for Rapid transit

{{short description|High-capacity public transport commonly found in urban areas}}
{{other uses|Rapid transit (disambiguation)}}
{{Redirect|Mass rapid transit}}
{{Original research|date=April 2022}}
[[File:London Underground 1992 Stock at Theydon Bois by tompagenet.jpg|250px|thumb|The [[London Underground]] is the world's first and oldest rapid transit system.]]
[[File:R160 E enters 42nd Street.jpg|250px|thumb|The [[New York City Subway]] is the world's largest single-operator rapid transit system by number of [[metro station]]s, at 472.]]
[[File:Metro in the World.svg|250px|thumb|Metro in the world:<ref>[http://www.urbanrail.net www.urbanrail.net]</ref><br />
{{Color|#000080|Metro in one city}}<br />
{{Color|#FF0000|Metro in two or more cities}}<br />
{{Color|#FF8040|Metro under construction}}<br />
{{Color|#804000|Planned metro}}<br />
{{Color|#CDC3CC|No metro}}
]]

'''Rapid transit''' or '''mass rapid transit''' ('''MRT'''), also known as '''heavy rail''' or '''metro''', is a type of high-capacity [[public transport]] that is generally built in [[urban area]]s. A rapid transit system that primarily or traditionally runs below the surface may be called a '''subway''', '''tube''', or '''underground'''.<ref name="miriamwebster">{{cite web|url=http://www.merriam-webster.com/dictionary/rapid%20transit|title=Rapid transit|publisher=[[Merriam-Webster]]|access-date=2013-07-31|archive-url=https://web.archive.org/web/20130720025558/http://www.merriam-webster.com/dictionary/rapid%20transit|archive-date=2013-07-20|url-status=live}}</ref><ref name="IUTPMetro">{{cite web|url=http://ftp.uitfp.org/ftproot/euroteam/YVA/URP_Fundamental_Requirements_EN.pdf|title=Recommended basic reference for developing a minimum set of standards for voluntary use in the field of urban rail, according to mandate M/486|author=UITP|year=2011|access-date=2014-02-16|archive-url= https://web.archive.org/web/20140222133945/http://ftp.uitp.org/ftproot/euroteam/YVA/URP_Fundamental_Requirements_EN.pdf|archive-date=2014-02-22|url-status=dead}}</ref><ref name=aptaglossary>{{cite web|url=http://www.apta.com/resources/reportsandpublications/Documents/Transit_Glossary_1994.pdf|title=Glossary of Transit Terminology|publisher=[[American Public Transportation Association]]|access-date=2013-07-31|archive-url=https://web.archive.org/web/20130512230056/http://www.apta.com/resources/reportsandpublications/Documents/Transit_Glossary_1994.pdf|archive-date=2013-05-12|url-status=live}}</ref><ref name="mrt">{{cite journal |title=Mass rapid transit systems for cities in the developing world |year=2003 |url=https://www.tandfonline.com/doi/pdf/10.1080/0144164032000083095 |publisher=Taylor & Francis Online |doi=10.1080/0144164032000083095 |access-date=2 April 2023 |last1=Fouracre |first1=Phil |last2=Dunkerley |first2=Christian |last3=Gardner |first3=Geoff |journal=Transport Reviews |volume=23 |issue=3 |pages=299–310 |s2cid=154931412 |url-access=subscription }}</ref> Unlike [[bus]]es or [[tram]]s, rapid transit systems are [[railway]]s, usually [[electric railway|electric]], that operate on an exclusive [[right-of-way (transportation)|right-of-way]], which cannot be accessed by pedestrians or other vehicles.<ref name="Britannica">{{cite web|url=http://www.britannica.com/EBchecked/topic/491506/rapid-transit|title=Rapid Transit|publisher=[[Encyclopædia Britannica]]|access-date=2014-11-28|archive-url=https://web.archive.org/web/20141017033402/http://www.britannica.com/EBchecked/topic/491506/rapid-transit|archive-date=2014-10-17|url-status=live}}</ref> They are often [[grade-separated]] in [[tunnel]]s or on [[elevated railway]]s.

Modern services on rapid transit systems are provided on designated lines between [[metro station|stations]] typically using [[electric multiple unit]]s on [[railway track]]s. Some systems use guided rubber tires, magnetic levitation (''[[maglev]]''), or [[monorail]]. 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 [[transit authority|public transport authorities]]. Some rapid transit systems have at-grade intersections between a rapid transit line and a road or between two rapid transit lines.<ref name="UrbanRail.net">{{cite web|url=http://www.urbanrail.net/am/chic/chicago.htm|title=Chicago|access-date=2015-04-24|archive-url=https://web.archive.org/web/20150416074705/http://www.urbanrail.net/am/chic/chicago.htm|archive-date=2015-04-16|url-status=live}}</ref>

The world's first rapid transit system was the partially underground [[Metropolitan Railway]] which opened in 1863 using [[steam locomotive]]s, and now forms part of the [[London Underground]].<ref name=150Anniv>{{Cite book |url=http://www.tfl.gov.uk/corporate/modesoftransport/londonunderground/1604.aspx |title=London Underground: History|author=Transport for London |isbn=978-0-904711-30-1 |access-date=2013-01-02 |archive-url=https://web.archive.org/web/20130116190701/http://www.tfl.gov.uk/corporate/modesoftransport/londonunderground/1604.aspx |archive-date=2013-01-16 |url-status=dead|year=1981|publisher=Capital Transport }}</ref> In 1868, New York opened the elevated [[IRT Ninth Avenue Line|West Side and Yonkers Patent Railway]], initially a cable-hauled line using static [[steam engine]]s.

{{As of|2021}}, [[China]] has the largest number of [[List of metro systems|rapid transit systems in the world]]—40 in number,<ref>{{Cite web|date=2021-03-29|title=Luoyang and Ji'nan open metro lines|url=https://www.railjournal.com/regions/asia/luoyang-and-jinan-open-metro-lines/|access-date=2021-06-07|website=International Railway Journal|language=en}}</ref> running on over {{convert|4,500|km|abbr=on}} of track—and was responsible for most of the world's rapid-transit expansion in the 2010s.<ref>{{Cite news|url=https://www.itdp.org/2018/07/30/china-drives-rapid-transit-growth/|title=China's Metro Boom Continues to Drive Rapid Transit Growth – Institute for Transportation and Development Policy|date=2018-07-30|work=Institute for Transportation and Development Policy|access-date=2018-11-20|language=en-US|archive-url=https://web.archive.org/web/20181120095357/https://www.itdp.org/2018/07/30/china-drives-rapid-transit-growth/|archive-date=2018-11-20|url-status=live}}</ref><ref>{{Cite web|title = Metro Data|url = http://metro-data.info/|website = metro-data.info|access-date = 2018-09-28|archive-url = https://web.archive.org/web/20180929000328/http://metro-data.info/|archive-date = 2018-09-29|url-status = live}}</ref><ref>{{Cite news|url=https://www.itdp.org/2017/02/17/rapid-transit-trends/|title=Rapid Transit Trends Show Record Growth in 2016, with Huge Increases in China, Brazil – Institute for Transportation and Development Policy|date=2017-02-17|work=Institute for Transportation and Development Policy|access-date=2018-11-20|language=en-US|archive-url=https://web.archive.org/web/20181023020236/https://www.itdp.org/2017/02/17/rapid-transit-trends/|archive-date=2018-10-23|url-status=live}}</ref> The world's longest single-operator rapid transit system by [[Network length (transport)|route length]] is the [[Shanghai Metro]].<ref>{{cite magazine|url=http://www.railwaygazette.com/news/single-view/view/10/shanghai-now-the-worlds-longest-metro.html|title=Shanghai now the world's longest metro|magazine=[[Railway Gazette International]]|date=4 May 2010|access-date=2010-05-04|archive-url=https://web.archive.org/web/20100515130655/http://www.railwaygazette.com/news/single-view/view/10/shanghai-now-the-worlds-longest-metro.html|archive-date=15 May 2010|url-status=live}}</ref><ref>{{cite news |last=Smith |first=Stephen J. |url=http://nextcity.org/daily/entry/new-starts-shanghai-metro-worlds-longest-panama-canal-drama-japans-maglev |title=New Starts: Shanghai Metro World's Longest, Panama Canal Drama, Japan's Maglev |newspaper=Next City |date=6 January 2014 |access-date=2014-09-21 |archive-url=https://web.archive.org/web/20140925160200/http://nextcity.org/daily/entry/new-starts-shanghai-metro-worlds-longest-panama-canal-drama-japans-maglev |archive-date=25 September 2014 |url-status=live }}</ref> The world's largest single rapid transit service provider by number of stations (472 stations in total)<ref>{{cite web |url=http://web.mta.info/nyct/facts/ridership/ |title=Facts – Subway and Bus Ridership |publisher=[[Metropolitan Transportation Authority|Metropolitan Transportation Authority (MTA)]] |access-date=2014-09-21 |archive-url=https://web.archive.org/web/20140912073839/http://web.mta.info/nyct/facts/ridership/ |archive-date=2014-09-12 |url-status=live }}</ref> is the [[New York City Subway]]. The [[List of metro systems|busiest rapid transit systems in the world]] by annual ridership are the Shanghai Metro, [[Tokyo subway|Tokyo subway system]], [[Seoul Metro]] and the [[Moscow Metro]].

==Terminology==
{{Train topics}}
{{Main|Passenger rail terminology}}
[[File:November 2007 Strikes France Crowded Platform.jpg|thumb|A crowded [[Paris Métro]] average station platform in 2007.]]
[[File:Sun Yat-sen University Station platform at old Line 2 in Guangzhou Metro.jpg|thumb|A station of the [[Guangzhou Metro]] in 2005.]]

The term ''Metro'' is the most commonly used term for underground rapid transit systems used by non-native English speakers.<ref>Fjellstrom&Wright, 2002: p.2</ref> Rapid transit systems may be named after the medium by which passengers travel in busy [[central business district]]s; the use of [[tunnel]]s inspires names such as ''subway'',<ref>{{cite book|title=The American Heritage Dictionary of the English Language|edition=Fourth|publisher=Houghton Mifflin Company|isbn=978-0-618-08230-8|author=Executive ed.: Joseph P. Pickert...|year=2000}}</ref> ''underground'',<ref>{{cite web|title=Definition of "Underground"|publisher=Chambers Reference Online|url=http://www.chambersharrap.co.uk/chambers/features/chref/chref.py/main?query=Underground&title=21st|access-date=2006-11-28|archive-url=https://web.archive.org/web/20070930015654/http://www.chambersharrap.co.uk/chambers/features/chref/chref.py/main?query=Underground&title=21st|archive-date=2007-09-30|url-status=live}}</ref> ''{{Lang|de|Untergrundbahn}} ([[Rapid-transit in Germany#U-Bahn|U-Bahn]])'' in German,<ref name=white63>White, 2002: 63</ref> or the ''Tunnelbana (T-bana)'' in Swedish.<ref name=ovenden93>Ovenden, 2007: 93</ref> The use of [[viaduct]]s inspires names such as ''elevated'' (''L'' or ''el''), ''skytrain'',<ref name=ovenden16>[[Mark Ovenden|Ovenden]], 2007: 16</ref> ''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 [[England, Wales and Scotland|Britain]], a ''subway'' is a [[pedestrian underpass]]. The terms ''Underground'' and ''Tube'' are used for the London Underground. The North East England [[Tyne and Wear Metro]], mostly overground, is known as the ''Metro''. In [[Scotland]], the [[Glasgow Subway]] underground rapid transit system is known as the ''Subway''.

Various terms are used for rapid transit systems around [[North America]]. The term ''metro'' is a shortened reference to a [[metropolitan area]]. Rapid transit systems such as the [[Washington Metro]], [[Los Angeles Metro Rail]], the [[Metrorail (Miami-Dade County)|Miami Metrorail]], and the [[Montreal Metro]] are generally called the ''Metro''. In [[Philadelphia]], 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]] which is almost entirely underground. [[Chicago]]'s [[commuter rail]] system that serves the entire metropolitan area is called ''[[Metra]]'' (short for '''Met'''ropolitan '''Ra'''il), while its rapid transit system that serves the city is called the [[Chicago "L"|"L"]]. [[Massachusetts Bay Transportation Authority|Boston's subway system]] is known locally as "The T". In the [[San Francisco Bay Area]], residents refer to [[Bay Area Rapid Transit]] by its acronym "BART".<ref>{{cite web |date=2013-11-03 |title=DC Metro System Fast Facts |url=http://edition.cnn.com/2013/11/03/us/dc-metro-system-fast-facts/ |url-status=live |archive-url=https://web.archive.org/web/20160124122948/http://edition.cnn.com/2013/11/03/us/dc-metro-system-fast-facts/ |archive-date=2016-01-24 |access-date=2015-07-20 |publisher=[[CNN.com|CNN]]}}</ref><ref>{{Cite web |title=Transportation Basics: How to Use BART |url=https://www.sftravel.com/article/transportation-basics-how-use-bart |access-date=2022-11-03 |website=San Francisco Travel |language=en}}</ref>

The [[New York City Subway]] 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)]] refers specifically to the 14th Street–Canarsie Local line, and not other elevated trains. Similarly, the Toronto Subway is referred to as "the subway", with some of its system also running above ground. These are the only two [[North America]]n systems that are called "subways".

In most of [[Southeast Asia]] and in [[Taiwan]], rapid transit systems are primarily known by the [[acronym]] ''MRT''. The meaning varies from one country to another. In [[Indonesia]], the acronym stands for ''[[Jakarta MRT|Moda Raya Terpadu]]'' or ''Integrated Mass [Transit] Mode'' in English.<ref>{{cite news|url=https://m.merdeka.com/jakarta/tarif-belum-diketok-warga-masih-bisa-nikmati-mrt-cuma-cuma-sampai-akhir-maret.html|title=Tarif Belum Diketok, Warga Masih Bisa Nikmati MRT Cuma-cuma Sampai Akhir Maret|newspaper=Merdeka.com|access-date=2017-12-22|language=id}}</ref> In the [[Philippines]], it stands for ''[[Manila Metro Rail Transit System|Metro Rail Transit]]''.<ref>{{cite web |url=http://dotcmrt3.gov.ph/about.php?route=7 |title=About Us – MRT3 Stations |publisher=Metro Rail Transit |access-date=2014-06-08 |url-status=dead |archive-url=https://web.archive.org/web/20130122003116/http://dotcmrt3.gov.ph/about.php?route=7 |archive-date=2013-01-22}}</ref>  [[Makati Intra-city Subway|Two]] underground [[Metro Manila Subway|lines]] use the term ''subway''. In [[Thailand]], it stands for ''[[MRT (Bangkok)|Metropolitan Rapid Transit]]'', previously using the ''Mass Rapid Transit'' name.<ref>{{cite web|url=https://bem.listedcompany.com/misc/presentation/20190311-bem-presentation-march-2019-02.pdf|title=BEM Investor presentation}}</ref> Outside of Southeast Asia, [[Kaohsiung]] and [[Taoyuan, Taiwan]] have their own ''MRT'' systems which stands for ''Mass Rapid Transit'', as with [[Singapore]].<ref>{{cite web|url=http://www2.dorts.gov.tw/news/newsletter/ns245/rp245_03.htm|script-title=zh:桃園都會區大眾捷運系統|publisher=Department of Rapid Transit Systems|language=zh|date=2008-07-01|access-date=2010-06-19|archive-date=2011-04-05|archive-url=https://web.archive.org/web/20110405183548/http://www2.dorts.gov.tw/news/newsletter/ns245/rp245_03.htm|url-status=dead}}</ref><ref>[http://www.kcg.gov.tw/~mtbu/html/promote/history.php KMRT History - Kaohsiung City Mass Rapid Transit Bureau official site (Traditional Chinese)] {{webarchive|url=https://web.archive.org/web/20140819082322/http://www.kcg.gov.tw/~mtbu/html/promote/history.php |date=2014-08-19 }}</ref><ref>{{cite book|last1=Seah C. M.|url=http://eservice.nlb.gov.sg/item_holding_s.aspx?bid=4183690|title=Southeast Asian Affairs.|date=1981|publisher=Singapore: Institute of Southeast Asian Studies|page=293}}</ref>

==History==
{{Main|History of rapid transit}}
[[File:Constructing the Metropolitan Railway.jpg|thumb|Initial construction stages of London's [[Metropolitan Railway]] at [[King's Cross St Pancras tube station|King's Cross St Pancras]] in 1861]]

The opening of London's steam-hauled [[Metropolitan Railway]] in 1863 marked the beginning of rapid transit. Initial experiences with steam engines, despite ventilation, were unpleasant. Experiments with [[pneumatic railway]]s failed in their extended adoption by cities.

In 1890, the [[City & South London Railway]] was the first electric-traction rapid transit railway, which was also fully underground.<ref name=Ovenden7>Ovenden, 2007: 7</ref> Prior to opening, the line was to be called the "City and South London Subway", thus introducing the term Subway into railway terminology.<ref>Emmerson, Andrew (2010). ''The London Underground''. London: Shire Publications Ltd. p. 13. {{ISBN|978-0-74780-790-2}}.</ref> Both railways, alongside others, were eventually merged into [[London Underground]]. The 1893 [[Liverpool Overhead Railway]] was designed to use electric traction from the outset.<ref>{{cite web |last=Bolger |first=Paul |title=Site Name: Liverpool Overhead Railway & Dingle Station |publisher=Subterranea Britannica |date=2004-11-22 |url=http://www.subbrit.org.uk/sb-sites/sites/l/liverpool_overhead_railway/index.shtml |access-date=2007-09-19 |archive-url=https://web.archive.org/web/20121122042759/http://www.subbrit.org.uk/sb-sites/sites/l/liverpool_overhead_railway/index.shtml |archive-date=2012-11-22 |url-status=live }}</ref>

The technology quickly spread to other [[List of metro systems in Europe|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]], [[Chicago]], [[Glasgow]] and [[New York City]] all converted or purpose-designed and built electric rail services.<ref>{{cite encyclopedia|url=http://www.britannica.com/eb/article-9070117/subway|title=Subway|encyclopedia=Encyclopædia Britannica online|access-date=2006-12-02|archive-url=https://web.archive.org/web/20061220144312/http://www.britannica.com/eb/article-9070117/subway|archive-date=2006-12-20|url-status=live}}</ref>

Advancements in technology have allowed new automated services. Hybrid solutions have also evolved, such as [[tram-train]] and [[premetro]], which incorporate some of the features of rapid transit systems.<ref name="Ovenden7" /> 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]]s tended to [[urban sprawl|spread out]].<ref name=pulling>{{cite web |url=http://www.railway-technology.com/features/feature1953/ |title=Light Rail – the Solution to Inner-City Chaos? |author=Pulling, Niel |publisher=Railway Technology |date=2008-05-22 |access-date=2008-08-18 |archive-url=https://web.archive.org/web/20120229165634/http://www.railway-technology.com/features/feature1953/ |archive-date=2012-02-29 |url-status=live }}</ref> Since the 1970s, the viability of underground train systems in Australian cities, particularly [[Sydney]] and [[Melbourne]], has been reconsidered and proposed as a solution to over-capacity. Melbourne had [[City Loop|tunnels and stations]] developed in the 1970s and opened in 1980. The [[Metro North West Line|first line]] of the [[Sydney Metro]] was opened in 2019.<ref>{{Cite web|date=2019-05-29|title=Australia's first metro system opened in Sydney|url=https://www.urban-transport-magazine.com/en/australias-first-metro-system-opened-in-sydney/|access-date=2021-04-03|website=Urban Transport Magazine|language=en-US}}</ref>

Since the 1960s, many new systems were introduced in [[Europe]], [[Asia]] and [[Latin America]].<ref name=white63 /> 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 [[Urban rail transit in China|rapid transit system]].<ref>{{Cite news|url=https://www.itdp.org/2017/02/17/rapid-transit-trends/|title=Rapid Transit Trends Show Record Growth in 2016, with Huge Increases in China, Brazil – Institute for Transportation and Development Policy|date=2017-02-17|work=Institute for Transportation and Development Policy|access-date=2018-09-01|language=en-US|archive-url=https://web.archive.org/web/20180805112927/https://www.itdp.org/2017/02/17/rapid-transit-trends/|archive-date=2018-08-05|url-status=live}}</ref><ref>{{Cite news|url=https://www.thetransportpolitic.com/2018/01/17/in-response-to-growth-chinese-cities-choose-metros/|title=In response to growth, Chinese cities choose metros|date=2018-01-17|work=The Transport Politic|access-date=2018-09-01|language=en-US|archive-url=https://web.archive.org/web/20180907234018/https://www.thetransportpolitic.com/2018/01/17/in-response-to-growth-chinese-cities-choose-metros/|archive-date=2018-09-07|url-status=live}}</ref>

==Operation==
Rapid transit is used for local transport in [[city|cities]], [[urban agglomeration|agglomerations]], and [[metropolitan area]]s to transport large numbers of people often short distances at high [[frequency]].<ref name="Britannica"/> The extent of the rapid transit system varies greatly between cities, with several transport strategies.<ref name="mrt"/>

Some systems may extend only to the limits of the inner city, or to its inner ring of [[suburb]]s with trains making frequent station stops. The outer suburbs may then be reached by a separate [[commuter rail]] network where more widely spaced stations allow higher speeds. In some cases the differences between urban rapid transit and suburban systems are not clear.<ref name="aptaglossary" />

Rapid transit systems may be supplemented by other systems such as [[trolleybus]]es, regular [[bus]]es, [[tram]]s, or commuter rail. 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.<ref>Cervero, 1998: 13</ref>

===Lines===
[[File:Ana rosa, São Paulo Metro, Line blue, Brazil.jpg|thumb|[[Ana Rosa (São Paulo Metro)|Ana Rosa station]] platform, [[Line 2 (São Paulo Metro)|line 2]] in [[São Paulo Metro]]]]
[[File:Delhi Metro - Magenta Line.jpg|thumb|The coaches of the [[Delhi Metro]] are color-coded to indicate different service lines.]]
[[File:Lauttasaaren metroasema 2.jpg|thumb|[[Helsinki Metro]] is the northernmost metro system in the world.<ref>{{Cite web |url=https://discoverhelsinki.fi/gettingaround/helsinki-metro/ |title=Helsinki Metro – Discover Helsinki |date=19 March 2019 |access-date=2020-07-04 |archive-date=2020-07-06 |archive-url=https://web.archive.org/web/20200706060219/https://discoverhelsinki.fi/gettingaround/helsinki-metro/ |url-status=live }}</ref><ref>{{Cite web |url=https://transportationhistory.org/2017/08/02/today-in-transportation-history-1982-the-northernmost-public-transportation-system/ |title=Today in Transportation History – 1982: The Northernmost Public Transportation System |date=2 August 2017 |access-date=2020-07-04 |archive-date=2020-07-05 |archive-url=https://web.archive.org/web/20200705215547/https://transportationhistory.org/2017/08/02/today-in-transportation-history-1982-the-northernmost-public-transportation-system/ |url-status=live }}</ref><ref>{{Cite web |url=https://www.myhelsinki.fi/en/see-and-do/neighbourhoods/8-charming-pictures-from-helsinkis-metro |title=8 charming pictures from Helsinki's metro |access-date=2020-07-04 |archive-date=2020-07-04 |archive-url=https://web.archive.org/web/20200704212905/https://www.myhelsinki.fi/en/see-and-do/neighbourhoods/8-charming-pictures-from-helsinkis-metro |url-status=live }}</ref>]]

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]],<ref>Ovenden, 2007: 84</ref> the [[Milan Metro]], the [[Oslo Metro]], the [[Istanbul Metro]] and the [[New York City Subway]].<ref>Ovenden, 2007: 32–35</ref>

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]].<ref>Ovenden, 2007: 95</ref> The [[London Underground]]<ref>Ovenden, 2007: 28–31</ref> and [[Paris Métro]]<ref>Ovenden, 2007: 36–39</ref> are densely built systems with a matrix of crisscrossing lines throughout the cities. The [[Chicago 'L']] has most of its lines converging on [[downtown Chicago|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]]'s [[Koltsevaya Line]] and [[Beijing Subway]]'s [[Line 10, Beijing Subway|Line 10]].

The capacity of a line is obtained by multiplying the car capacity, the train length, and the [[headway|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]]—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]] with ranges of 75,000 to 85,000 people per hour achieved by [[MTR Corporation]]'s urban lines in Hong Kong.<ref>{{Cite web|title=MTR > A Service of World-class Quality|url=https://www.mtr.com.hk/en/corporate/operations/detail_worldclass.html|access-date=2021-06-27|website=www.mtr.com.hk|language=en}}</ref><ref>{{Cite book|last=Runnacles|first=Timothy V.|title=Land-use/Transport Planning in Hong Kong: A Review of Principles and Practices|publisher=Routledge|year=2020|isbn=978-1138361959|editor-last=Dimitriou|editor-first=Harry T.|pages=107|editor-last2=Cook|editor-first2=Alison H.S}}</ref><ref>{{Cite book|last=White|first=Peter|title=Public Transport: Its Planning, Management, and Operation|publisher=Spon Press|year=2002|pages=65–66}}</ref>

====Network topologies====
{{Main|List of metro systems}}

Rapid transit [[topology|topologies]] 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.<ref name=Walker/>

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.<ref name=Walker>{{cite book|last1=Walker|first1=Jarret|title=Human transit : how clearer thinking about public transit can enrich our communities and our lives|date=2012|publisher=Island Press|location=Washington|isbn=978-1-59726-972-8}}</ref> A study of the 15 world largest subway systems suggested a universal shape composed of a dense core with branches radiating from it.<ref name="Roth">{{cite journal |last1=Roth |first1=C |last2=Kang |first2=SM |last3=Batty |first3=M |last4=Barthelemy |first4=M |title=A long-time limit for world subway networks |journal=Journal of the Royal Society Interface |date=16 May 2012 |volume=9 |issue=75 |pages=2540–2550 |doi=10.1098/rsif.2012.0259 |pmid=22593096 |pmc=3427522 }}</ref>

{{gallery|width=125|title=|height=125
|File:Diameter-line.png|[[Line (geometry)|Line]], e.g. [[Algiers Metro|Algiers]], [[Almaty Metro|Almaty]], [[Baltimore Metro Subway|Baltimore]], [[Red Line (Cleveland)|Cleveland]], [[Dhaka Metro|Dhaka]], [[Gwangju Metro|Gwangju]], [[Helsinki Metro|Helsinki]], [[Astram Line|Hiroshima]], [[Skyline (Honolulu)|Honolulu]], [[Izmir Metro|Izmir]], [[Jakarta MRT|Jakarta]], [[Kazan Metro|Kazan]], [[Lima Metro|Lima]],  [[LRT Line 2| Manila]], [[Maracaibo Metro|Maracaibo]], [[Metrorail (Miami-Dade County)|Miami]], [[Navi Mumbai Metro]], [[Quito Metro|Quito]], [[Sydney Metro|Sydney]], [[Valencia Metro (Venezuela)|Valencia (Venezuela)]], [[Yekaterinburg Metro|Yekaterinburg]]
|File:Cross-system.png|Cross, e.g. [[Metropolitan Atlanta Rapid Transit Authority|Atlanta]], [[Namma Metro|Bangalore]], [[Incheon Metro|Incheon]], [[Kaohsiung Mass Rapid Transit|Kaohsiung]], [[Kyoto Municipal Subway|Kyoto]], [[Metrorrey|Monterrey]], [[Nagpur Metro|Nagpur]], [[Nizhny Novgorod Metro|Nizhny Novgorod]], [[Panama Metro|Panama City]], [[SEPTA|Philadelphia (SEPTA)]],  [[Pyongyang Metro|Pyongyang]], [[Rotterdam Metro|Rotterdam]], [[Sendai Subway|Sendai]], [[Warsaw Metro|Warsaw]]
|File:X-system.png|X-shaped, e.g. [[Amsterdam Metro|Amsterdam]], [[Brussels Metro|Brussels]], [[Bay Area Rapid Transit|San Francisco Bay Area]], [[Stockholm Metro|Stockholm]], [[Thessaloniki Metro|Thessaloniki]]
|File:Air-bladder-system.png|Two crossing paths (air bladder), e.g. [[Cairo Metro|Cairo]], [[Chennai Metro|Chennai]], [[Lille Metro|Lille]], [[Marseille Metro|Marseille]], [[Montreal Metro|Montreal]], [[Nanchang Metro|Nanchang]], [[Nuremberg U-Bahn|Nuremberg]], [[Rotterdam Metro|Rotterdam]], [[Toronto subway|Toronto]]
|File:Secant-system.png|[[Secant line|Secant]], e.g. [[Athens Metro|Athens]], [[Budapest Metro|Budapest]], [[Busan Metro|Busan]], [[Guadalajara light rail system|Guadalajara]], [[Kharkiv Metro|Kharkiv]], [[Hyderabad Metro|Hyderabad]], [[Lisbon Metro|Lisbon]], [[Milan Metro|Milan]], [[Munich U-Bahn|Munich]], Philadelphia (including [[PATCO Speedline|PATCO]]), [[Prague Metro|Prague]], [[Rome Metro|Rome]], [[São Paulo Metro|São Paulo]], [[Tashkent Metro|Tashkent]]
|File:Radial-system.png|Radial, e.g. [[MBTA subway|Boston]], [[Budapest Metro|Budapest]], [[Buenos Aires Underground|Buenos Aires]], [[Chicago "L"|Chicago]], [[Daegu Metro|Daegu]], [[Kyiv Metro|Kyiv]], [[Los Angeles Metro Rail|Los Angeles]], [[Sapporo Municipal Subway|Sapporo]], [[Tehran Metro|Tehran]], [[DC Metro|Washington DC]]
|File:Circle-system.png|Circle, e.g. [[Detroit_People_Mover|Detroit]], [[Glasgow Subway|Glasgow]]
|File:Circle-radial-system.png|Circle-radial, e.g. [[MRT (Bangkok)|Bangkok]], [[Beijing Subway|Beijing]], [[Bucharest Metro|Bucharest]], [[Chengdu Metro|Chengdu]], [[Chongqing Rail Transit|Chongqing]], [[Copenhagen Metro|Copenhagen]], [[Delhi Metro|Delhi]], [[Hamburg U-Bahn|Hamburg]], [[London Underground|London]], [[Madrid Metro|Madrid]], [[Moscow Metro|Moscow]], [[Nagoya Municipal Subway|Nagoya]], [[Paris Métro|Paris]],  [[Shanghai Metro|Shanghai]], [[Mass Rapid Transit (Singapore)|Singapore]], [[Tokyo subway|Tokyo]], [[Zhengzhou Metro|Zhengzhou]]
|File:Intermeshed-system.png|Complex grid, e.g. [[Barcelona Metro|Barcelona]], [[Berlin U-Bahn|Berlin]], [[Guangzhou Metro|Guangzhou]], [[Hangzhou Metro|Hangzhou]], [[MTR|Hong Kong]], [[Mexico City Metro|Mexico City]], [[Milan Metro|Milan]], [[Mumbai Metro|Mumbai]], [[Nanjing Metro|Nanjing]], [[New York City Subway|New York]], [[Osaka Metro|Osaka]], [[Seoul Metropolitan Subway|Seoul]], [[Shenzhen Metro|Shenzhen]], [[Taipei Metro|Taipei]], [[Tianjin Metro|Tianjin]], [[Vienna U-Bahn|Vienna]], [[Wuhan Metro|Wuhan]]
|File:Loop extended.png|Extended loop, e.g. [[Naples Metro|Naples]], [[Tyne and Wear Metro|Newcastle]], [[Mass Rapid Transit (Singapore)|Singapore]], [[Sofia Metro|Sofia]]
}}

===Passenger information===
[[File:Tokyo metro 1000 series lcd display 01.png|thumb|The [[Tokyo Metro]] uses large LCD information display to show the current location, upcoming stops, and advertisements in several languages ([[Japanese language|Japanese]], [[English language|English]], [[Simplified Chinese characters|Simplified Chinese]], [[Korean language|Korean]]).]]
Rapid transit operators have often built up strong [[brand]]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.<ref>Ovenden, 2007: 107</ref> 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.

[[File:深圳地铁11号线中车长客车第二代报站显示.jpg|thumb|The [[Shenzhen Metro]] uses large LCD information displays to show the current location, upcoming stops and diagrams of the next station.]]
A [[transit map]] is a [[topological map]] or [[schematic]] [[diagram]] used to show the routes and stations in a [[public transport]] system. The main components are [[Color-coding|color-coded]] 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.<ref name=ovenden9>Ovenden, 2007: 9</ref> Transit maps can be found in transit vehicles, on [[railway platform|platforms]], elsewhere in stations, and in printed [[public transport timetable|timetables]]. Maps help users understand the interconnections between different parts of the system; for example, they show the [[Interchange station|interchange]] stations where passengers can transfer between lines. Unlike conventional maps, transit maps are usually not geographically accurate, but emphasize the [[topology|topological]] 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.<ref name=ovenden9 />

Some systems assign unique [[alphanumeric code]]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.<ref name=strom58>Ström, 1998: 58</ref> For example, on the [[Singapore MRT]], [[Changi Airport MRT station]] has the alphanumeric code CG2, indicating its position as the 2nd station on the Changi Airport branch of the East West Line. Interchange stations have at least two codes, for example, [[Raffles Place MRT station]] has two codes, NS26 and EW14, the 26th station on the North South Line and the 14th station on the East West Line.

The Seoul Metro is another example that utilizes a code for its stations. Unlike that of Singapore's MRT, it is mostly numbers. Based on the line number, for example Sinyongsan station, is coded as station 429. Being on Line 4, the first number of the station code is 4. The last 2 numbers are 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]] and [[cell phone]]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 [[General Transit Feed Specification|GTFS]] 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===
{{see also|Classification of railway accidents}}
[[File:2000년대 초반 서울소방 소방공무원(소방관) 활동 사진 부활절 안전근무-1.jpg|thumb|[[Seoul Metropolitan Fire and Disaster Management Headquarters|Seoul Fire Services]] personnel participating in a firefighting exercise on [[Seoul Subway Line 6]] in March 2001.]]
[[File:Xinyi Line Platform 2, Daan Station 20131124a.jpg|thumb|[[Platform-edge doors]] are used for safety at [[Daan Station]] on [[Tamsui-Xinyi Line|the Red Line (Tamsui-Xinyi Line)]], [[Taipei Metro]], [[Taiwan]].]]
[[File:Chennai Underground metrostation with India's first Platform Screen Doors.jpg|thumb|Full-height enclosed [[platform screen doors]] installed in an underground station of the [[Chennai Metro]]]]

Compared to other modes of transport, rapid transit has a good [[safety]] record, with few accidents. Rail transport is subject to strict [[safety|safety regulations]], with requirements for procedure and maintenance to minimize risk. [[Head-on collision]]s are rare due to use of double track, and low operating speeds reduce the occurrence and severity of [[rear-end collision]]s and [[derailment]]s. [[Fire]] is more of a danger underground, such as the [[King's Cross fire]] in London in November 1987, which killed 31 people. Systems are generally built to allow evacuation of trains at many places throughout the system.<ref>{{cite web| url=http://hazmat.dot.gov/riskmgmt/riskcompare.htm| title=A Comparison of Risk: Accidental Deaths – United States – 1999–2003| author=Office of Hazardous Materials Safety| publisher=US Department of Transportation| access-date=2007-09-10 |archive-url = https://web.archive.org/web/20070907235322/http://hazmat.dot.gov/riskmgmt/riskcompare.htm |archive-date = 7 September 2007}}</ref><ref>{{cite web| url=http://www.rail-reg.gov.uk/| title=Office of Rail Regulation| publisher=UK Health & Safety Executive| access-date=2007-09-10| archive-url=https://web.archive.org/web/20140127201437/http://www.rail-reg.gov.uk/| archive-date=2014-01-27| url-status=live}}</ref>

[[railway platform height|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]] are used on some systems to eliminate this danger.

Rapid transit facilities are public spaces and may suffer from [[security]] problems: [[petty crime]]s, such as [[pickpocketing]] and baggage theft, and more serious [[violent crime]]s, as well as sexual assaults on tightly packed trains and platforms.<ref>{{cite web|url=http://metro.co.uk/2017/04/30/sexual-assault-on-public-transport-is-an-increasing-problem-heres-why-we-need-to-speak-out-6593306/|title=Why we need to talk about sexual assault on public transport|date=30 April 2017|access-date=6 January 2018|archive-url=https://web.archive.org/web/20180106174449/http://metro.co.uk/2017/04/30/sexual-assault-on-public-transport-is-an-increasing-problem-heres-why-we-need-to-speak-out-6593306/|archive-date=6 January 2018|url-status=live}}</ref><ref>{{cite web|url=http://fortune.com/2016/06/22/sex-crimes-subway/|title=Sexual Harassment on the New York Subway Has Increased More Than 50% This Year|access-date=2018-01-06|archive-url=https://web.archive.org/web/20180106174334/http://fortune.com/2016/06/22/sex-crimes-subway/|archive-date=2018-01-06|url-status=live}}</ref> Security measures include [[video surveillance]], [[security guard]]s, and [[conductor (transportation)|conductors]]. In some countries a specialized [[transit police]] may be established. These security measures are normally integrated with measures to protect revenue by checking that passengers are not travelling without paying.<ref>Needle et al., 1997: 10–13</ref>

Some subway systems, such as the [[Beijing Subway]], which is ranked by Worldwide Rapid Transit Data as the "World's Safest Rapid Transit Network" in 2015, incorporates airport-style security checkpoints at every station. Rapid transit systems have been subject to [[terrorism]] with many casualties, such as the 1995 [[Tokyo subway sarin gas attack]]<ref>{{cite news |url=http://www.elmundo.es/documentos/2006/04/11/auto_11m.html |title=El auto de procesamiento por el 11-M |newspaper=El Mundo |language=es |access-date=2008-09-08 |archive-url=https://web.archive.org/web/20081220195300/http://www.elmundo.es/documentos/2006/04/11/auto_11m.html |archive-date=2008-12-20 |url-status=live }}</ref> and the 2005 "[[7/7]]" terrorist bombings on the London Underground.

=== Added features ===
[[File:Wi-Fi and mobile phone antenna inside New York City subway.jpg|thumb|[[Distributed antenna system|DAS antennas]], such as this one installed by [[Transit Wireless]] in a [[New York City Subway|NYC Subway]] station, are commonly used to provide cellular reception in metro stations.]]
Some rapid transport trains have extra features such as wall sockets, cellular reception, typically using a [[leaky feeder]] in tunnels and [[Distributed antenna system|DAS antennas]] in stations, as well as [[Wi-Fi]] 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 [[Advanced Mobile Phone System|AMPS]] in 1989.<ref>{{cite web|url=https://graphics.straitstimes.com/STI/STIMEDIA/Interactives/2015/10/35-years-of-ict/supercharging-singapore/the-1980s.html|title=Supercharging Singapore|website=The Straits Times|date=10 October 2015 }}</ref> 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==
[[File:Metro Turin Italy Tunnel.JPG|thumb|Inside a tunnel on the [[Turin Metro]], the interlocking tunnel lining segments placed by a [[tunnel boring machine]] can be clearly seen.]]
[[File:Hamburg Hochbahn - Bruecke am Stintfang.jpg|thumb|[[Landungsbrücken station]] in Hamburg is an example where the [[Hamburg U-Bahn|U-Bahn]] is on the surface while the [[S-Bahn]] station is on a lower level.]]

The [[technology]] used for public, mass rapid transit has undergone significant changes in the years since the [[Metropolitan Railway]] opened publicly in London in 1863.<ref name="IUTPMetro"/><ref name=aptaglossary/>

High capacity [[Monorail]]s with larger and longer trains can be classified as rapid transit systems.{{citation needed|date=December 2017}} Such monorail systems recently started operating in [[Chongqing Rail Transit|Chongqing]] and [[São Paulo Metro|São Paulo]]. [[Medium-capacity rail transport system|Light metro]] 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 line (network)|feeder lines]] into the main rapid transit system.<ref>White, 2002: 64–65</ref> For instance, the [[Wenhu Line]] of the [[Taipei Metro]] 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.<ref name="ovenden93" /> Ground-level alignments with a dedicated [[Right-of-way (transportation)|right-of-way]] 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.<ref name="kjenstad46" />

===Trains===
{{See also|Loading gauge}}

Most rapid transit trains are [[electric multiple units]] with lengths from three to over ten cars.<ref name="White, 2002: 64">White, 2002: 64</ref> Crew sizes have decreased throughout history, with some modern systems now running completely unstaffed trains.<ref>{{cite web |url=http://www.railway-technology.com/projects/toulouse/ |title=Toulouse Metro, France |author=Railway Technology |access-date=2008-08-20 |archive-url=https://web.archive.org/web/20080926060841/http://www.railway-technology.com/projects/toulouse/ |archive-date=2008-09-26 |url-status=live }}</ref> 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]] or by [[overhead wires]]. The whole London Underground network uses [[fourth rail]] and others use the [[linear motor]] for propulsion.<ref>{{cite journal |title= Review on rail corrugation studies |author1=Sato, Yoshihiko |author2=Matsumoto, Akira |author3=Knothe, Klaus  |name-list-style=amp |journal=[[Wear (journal)|Wear]] |issue=1–2 |volume=253  |year=2002 |doi=10.1016/S0043-1648(02)00092-3 |pages=130–139}}</ref>

Some urban rail lines are built to a [[loading gauge]] as large as that of [[heavy rail|main-line railways]]; others are built to a smaller one and have [[tunnel]]s that restrict the size and sometimes the shape of the train compartments. One example is most of the [[London Underground]], which has acquired the informal term "tube train" due to the cylindrical shape of the trains used on the [[London Underground infrastructure#Subsurface versus deep-level tube lines|deep tube lines]].

Historically, rapid transit trains used [[ceiling fan]]s and openable windows to provide fresh air and [[Piston effect|piston-effect]] wind cooling to riders. From the 1950s to the 1990s (and in most of Europe until the 2000s), many rapid transit trains from that era were also fitted with forced-air ventilation systems in carriage ceiling units for passenger comfort. Early rapid transit rolling stock fitted with [[air conditioning]], such as the [[PATH (rail system)|Hudson and Manhattan Railroad]] K-series cars<ref>{{cite web | url=https://hoboken.pastperfectonline.com/archive/45CDC2F1-59A0-4758-8193-365369441079 | title=Hudson and Manhattan Railroad. Full issue of Electric Railroads, No. 27, Aug. 1959. Published by Electric Railroaders Assn., N.Y., N.Y. - Serial &#124; Hoboken Historical Museum }}</ref> from 1958, the [[New York City Subway]] [[R38 (New York City Subway car)|R38]] and [[R42 (New York City Subway car)|R42]] cars from the late-1960s, and the [[Nagoya Municipal Subway 3000 series]], [[Osaka Municipal Subway 10 series]]<ref>{{Cite web |last=Tsuchiya |first=Takeyuki |date=7 July 2022 |title=昔の地下鉄は暑かった？車両「冷房化」の意外な歴史 |trans-title=Was it hot in the old subway? Surprising history of vehicle "cooling" |url=https://mainichi.jp/premier/business/articles/20220706/biz/00m/020/014000c |url-access=subscription |archive-url=https://web.archive.org/web/20220706195540/https://mainichi.jp/premier/business/articles/20220706/biz/00m/020/014000c |archive-date=6 July 2022 |access-date=15 August 2022 |website=Mainichi Shimbun |language=ja}}</ref> and [[MTR Metro Cammell EMU (DC)|MTR M-Train EMU]]s from the 1970s, were generally only made possible largely due to the relatively generous loading gauges of these systems and also adequate open-air sections to dissipate hot air from these air conditioning units. Especially in some rapid transit systems such as the [[Montreal Metro]]<ref>{{cite web|url=http://ruefrontenac.com/nouvelles-generales/92-transport/27088-stm-metro-nouvelles|title=Métro et autobus: chaud débat sur la climatisation|date=January 27, 2009|publisher=Ruefrontenac.com|language=fr|access-date=March 10, 2011}}</ref> (opened 1966) and [[Sapporo Municipal Subway]] (opened 1971), their entirely enclosed nature due to their use of rubber-tyred technology to cope with heavy snowfall experienced by both cities in winter precludes any air-conditioning retrofits of rolling stock due to the risk of heating the tunnels to temperatures that would be too hot for passengers and for train operations.

In many cities, metro networks consist of lines operating different sizes and types of vehicles. Although these sub-networks may not often be connected by track, in cases when it is necessary, rolling stock with a smaller [[loading gauge]] 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===
{{See also|Railway gauge}}

Most rapid transit systems use conventional [[standard gauge]] [[railway track]]. Since tracks in subway tunnels are not exposed to [[rain]], [[snow]], or other forms of [[precipitation]], they are often fixed directly to the floor rather than resting on [[track ballast|ballast]], such as normal railway tracks.

An alternate technology, using [[rubber-tired metro|rubber tires]] on narrow [[concrete]] or steel [[roll way]]s, was pioneered on certain lines of the [[Paris Métro]] and [[Mexico City Metro]], and the first completely new system to use it was in [[Montreal Metro|Montreal]], 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]]s and for [[railroad switch|switching]]. There are also some rubber-tired systems that use a central [[guide rail]], such as the [[Sapporo Municipal Subway]] and the [[NeoVal]] system in [[Rennes Metro|Rennes]], France. Advocates of this system note that it is much quieter than conventional steel-wheeled trains, and allows for greater [[slope|inclines]] given the increased [[Traction (engineering)|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.<ref>{{cite book|url=http://www.stm.info/English/en-bref/a-notrefierte.pdf |title=The Montreal Métro, a source of pride |author=Société de transport de Montréal |isbn=978-2-921969-08-6 |page=6 |url-status=dead |archive-url=https://web.archive.org/web/20070930211539/http://www.stm.info/English/en-bref/a-notrefierte.pdf |archive-date=September 30, 2007 |year=2002 |publisher=Société de transport de Montréal }}</ref>

Some cities with steep hills incorporate [[mountain railway]] technologies in their metros. One of the lines of the [[Lyon Metro Line C|Lyon Metro]] includes a section of [[Rack railway|rack (cog) railway]], while the [[Carmelit]], in Haifa, is an underground [[funicular]].

For elevated lines, another alternative is the [[monorail]], which can be built either as [[straddle beam monorail|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]]'s monorail lines which are widely used in a rapid transit setting.

===Motive power===
{{See also|Railway electrification system}}

Although trains on very early rapid transit systems like the [[Metropolitan Railway]] were powered using [[steam engine]]s, either via cable haulage or [[steam locomotive]]s, nowadays virtually all metro trains use [[electric motor|electric power]] and are built to run as [[multiple unit]]s. Power for the trains, referred to as [[Traction power network|traction power]], is usually supplied via one of two forms: an [[overhead line]], suspended from poles or towers along the track or from structure or tunnel ceilings, or a [[third rail]] mounted at track level and contacted by a sliding "[[pickup shoe]]". 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 lines|overhead wires]].

The use of overhead wires allows higher power supply [[voltage]]s to be used. Overhead wires are more likely to be used on metro systems without many tunnels, for example, the [[Shanghai Metro]]. Overhead wires are employed on some systems that are predominantly underground, as in [[Barcelona metro|Barcelona]], [[Fukuoka Subway|Fukuoka]], [[MTR|Hong Kong]], [[Madrid Metro|Madrid]], and [[Shijiazhuang Metro|Shijiazhuang]]. Both overhead wire and third-rail systems usually use the running rails as the return conductor. 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 (MBTA)|Blue Line]] in [[Boston]].

===Tunnels===
[[File:Metro Prague Construction Works Prosek.jpg|right|thumb|Constructing a subway station ''[[Prosek (Prague Metro)|Prosek]]'' in [[Prague]]]]

At subterranean levels, [[tunnel]]s move traffic away from street level, avoiding delays caused by [[traffic congestion]] 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]] tunnels are constructed by digging up city streets, which are then rebuilt over the tunnel. Alternatively, [[tunnel-boring machine]]s can be used to dig deep-bore tunnels that lie further down in [[bedrock]].<ref name="Ovenden7" />

The construction of an underground metro is an expensive [[project]] 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]] the city [[street]]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]] commonly buried not far below street level&nbsp;– particularly [[electric power|power]] and [[telephone]] wiring, [[drinking water|water]] and [[natural gas|gas]] mains, and [[sanitary sewer|sewers]]. This relocation must be done carefully, as according to documentaries from the National Geographic Society, one of the causes of the April 1992 [[1992 explosion in Guadalajara|explosions in Guadalajara]] was a mislocated water pipeline. The structures are typically made of [[concrete]], perhaps with structural columns of [[steel]]. In the oldest systems, [[brick]], and [[cast iron]] 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 tunneling method is called [[bored tunnel]]ing. Here, construction starts with a [[Shaft (civil engineering)|vertical shaft]] from which tunnels are horizontally dug, often with a [[tunnelling shield|tunneling shield]], thus avoiding almost any disturbance to existing streets, buildings, and utilities. But problems with [[ground water]] are more likely, and tunneling through native [[bedrock]] may require [[Rock blasting|blasting]]. The first city to extensively use deep tunneling was [[London]], where a thick [[sedimentary]] layer of [[clay]] largely avoids both problems. The confined space in the tunnel also limits the machinery that can be used, but specialized [[tunnel-boring machine]]s are now available to overcome this challenge.

A disadvantage with this, 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. It cannot install [[air conditioning]] 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 [[London Underground S7 and S8 Stock|air-conditioned trains]].

The deepest metro system in the world was built in [[Saint Petersburg Metro|St. Petersburg]], Russia where in the [[marshland]], stable soil starts more than {{Convert|50|m|ft}} 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 {{Convert|100|-|120|m|ft}} below the surface.  Usually, the vertical distance between the ground level and the rail is used to represent the depth. Among the possible candidates are:
[[File:Metro SPB Line5 Sportivnaya Upper Hall.jpg|right|thumb|The ''[[Sportivnaya (Saint Petersburg Metro)|Sportivnaya]]'' station of the [[Saint Petersburg Metro]] has two levels.]]
* Deepest stations:
* ''[[Arsenalna]]'' station in [[Kyiv Metro]], Ukraine ({{Convert|105.5|m|ft}}, opened 1960, built under a hill)
* ''[[Admiralteyskaya (Saint Petersburg Metro)|Admiralteyskaya]]'' (''The Admiralty'', {{Convert|102|m|ft}}, opened 2011, probably the best candidate)
*''[[Hongtudi station]]'' in [[Chongqing Rail Transit|Chongqing Metro]], China ({{Convert|94|m|ft|abbr=}}, opened in 2016)
*''Liyuchi station'' in [[Chongqing Rail Transit|Chongqing Metro]], China ({{Convert|76|m|ft|abbr=}}, opened in 2017)
* ''[[Park Pobedy (Moscow Metro)|Park Pobedy]]'' station in [[Moscow Metro|Moscow]] (~{{Convert|80|m|ft}}, opened 2005, built under a hill)
* ''Puhung'' station in [[Pyongyang Metro]], North Korea (which doubles as a [[Nuclear fallout shelter|nuclear shelter]])
* ''[[Washington Park MAX Station|Washington Park]]'' [[MAX Light Rail]] station in Portland, Oregon, US(built under a hill), 260 feet (80 m)

An 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]] and has been used many times since, particularly in Montreal.

The [[Extension of Island line to Western District|West Island line]], an extension of the [[Island line (MTR)|MTR Island line]] serving western Hong Kong Island, opened in 2015, has two stations ([[Sai Ying Pun station|Sai Ying Pun]] and [[HKU station|HKU]]) situated over {{Convert|100|m|ft}} below ground level, to serve passengers on the [[Mid-levels]]. They have several entrances/exits equipped with high-speed lifts, instead of [[escalators]]. These kinds of exits have existed in many London Underground stations and stations in former Soviet Union nations.

===Elevated railways===
[[Elevated railway]]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]]). 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 [[Vancouver SkyTrain|SkyTrain]], London's [[Docklands Light Railway]],<ref>{{cite web |url=http://www.tfl.gov.uk/dlr/about/facts.shtml |title= Docklands Light Railway – About DLR |access-date=2006-12-04 |archive-url = https://web.archive.org/web/20061027170620/http://www.tfl.gov.uk/dlr/about/facts.shtml |archive-date = 27 October 2006}}</ref> the [[Miami Metrorail]], [[Bangkok Skytrain]],<ref>{{cite web |url=http://www.bts.co.th/en/btstrain.asp |title= Bangkok Mass Transit System Company Limited – BTS SkyTrain|access-date=2006-12-04 |archive-url=https://web.archive.org/web/20061119024422/http://www.bts.co.th/en/btstrain.asp <!--Added by H3llBot--> |archive-date=2006-11-19 }}</ref> and [[Skyline (Honolulu)|Skyline Honolulu]].<ref>{{cite web |url=https://www.honolulu.gov/transportation/divisions/mobility/rail-operations.html |title=Skyline Rail Operations |date=9 January 2024 |publisher=City and County of Honolulu |access-date=17 January 2024}}</ref>

===Stations===
{{Main|Metro station}}
[[File:Getafe Central interior.JPG|thumb|upright|The [[Getafe Central (Madrid Metro)|Getafe Central]] station on Line 12 of [[Madrid Metro]] has several levels.]]

Stations function as [[transport hub|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 platform|island-]] or [[side platform]]s.<ref>Uslan et al., 1990: 71</ref> Underground stations, especially deep-level ones, increase the overall transport time: long [[escalator]] 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 city|underground]] or [[skyway]] networks respectively, that connect to nearby commercial buildings.<ref>Cervero, 1998: 8</ref> In suburbs, there may be a "[[park and ride]]" connected to the station.<ref>Cervero, 1998: 226</ref>

To allow easy access to the trains, the [[railway platform height|platform height]] allows step-free access between platform and train. If the station complies with [[accessibility]] standards, it allows both disabled people and those with wheeled baggage easy access to the trains,<ref>{{cite journal |title=Dual-Mode Traction Power Distribution for Light Rail Transit: A Design Option |author= Boorse, Jack W. |journal=Transportation Research Record |volume=1677 |year=1999 |pages=67–72 |doi=10.3141/1677-09 |s2cid= 110192749 }}</ref> though if the track is curved there can be a [[Platform gap|gap between the train and platform]]. Some stations use [[platform screen doors]] to increase safety by preventing people falling onto the tracks, as well as reducing ventilation costs.

Particularly in the former [[Soviet Union]] and other Eastern European countries, but to an increasing extent elsewhere, the stations were built with splendid decorations such as [[marble]] walls, polished [[granite]] floors and mosaics—thus exposing the public to art in their everyday life, outside galleries and museums. The systems in [[Moscow Metro|Moscow]], [[Saint Petersburg Metro|St. Petersburg]], [[Tashkent Metro|Tashkent]] and [[Kyiv Metro|Kyiv]] are widely regarded as some of the most beautiful in the world.<ref name="mb art">{{cite web |url=http://mic-ro.com/metro/metroart.html |title=Metro Arts and Architecture |publisher=Metro Bits |access-date=2006-12-04 |archive-url=https://web.archive.org/web/20061202064053/http://mic-ro.com/metro/metroart.html |archive-date=2006-12-02 |url-status=live }}</ref> Several other cities such as London,<ref>{{cite web|url=https://art.tfl.gov.uk|title=Art on the Underground}}</ref> [[Stockholm Metro|Stockholm]], [[Montreal Metro|Montreal]], [[Lisbon Metro|Lisbon]], [[Naples Metro|Naples]] and [[Los Angeles County Metropolitan Transportation Authority|Los Angeles]] 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.<ref>{{cite web|url=http://www.sl.se/templates/Page.aspx?id=1669 |author=Storstockholms Lokaltrafik |author-link=Storstockholms Lokaltrafik |title=Konståkning i världens längsta konstutställning |access-date=2008-08-20 |language=sv |url-status=dead |archive-url=https://web.archive.org/web/20071013204448/http://sl.se/templates/Page.aspx?id=1669 |archive-date=October 13, 2007 }}</ref> It may be possible to profit by attracting more passengers by spending relatively small amounts on grand [[architecture]], art, [[cleanliness]], [[accessibility]], [[lighting]] and a feeling of [[safety]].<ref>{{cite web |url=http://www.apta.com/research/info/online/documents/10ways.pdf |title=10 Ways to Enhance Your Community: Unleash the Power of Public Transportation |access-date=2006-12-04 |archive-url = https://web.archive.org/web/20061017031905/http://www.apta.com/research/info/online/documents/10ways.pdf |archive-date = 17 October 2006}}</ref>

==Crew size and automation==
[[File:Cab of C851E set 7093-7094.jpg|thumb|[[Alstom Metropolis C751C|Trains]] on the [[North East MRT line]] in [[Mass Rapid Transit (Singapore)|Singapore]] are fully automated and are not operated by any driver.]]
In the early days of underground railways, at least two staff members were needed to operate each train: one or more attendants (also called "[[Conductor (rail)|conductor]]" or "guard") to operate the doors or gates, as well as a driver (also called the "[[railroad engineer|engineer]]" or "motorman"). The introduction of powered doors around 1920 permitted crew sizes to be reduced, and trains in many cities are now operated by [[One Person Train Operation|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]]s or [[Closed-circuit television|closed-circuit TV]] monitors are often provided for that purpose.
[[Image:Praha metro novy vlak kabina.jpg|thumb|[[Prague Metro]], [[Metro M1 (Prague)|M1]] driver panel]]

A replacement system for human drivers became available in the 1960s, with the advancement of [[computer]]ized technologies for [[automatic train control]] 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]] at the next station, while taking into account the information that a human driver would obtain from [[railway signal|lineside]] or [[cab signaling|cab signals]]. The first metro line to use this technology in its entirety was London's [[Victoria line]], 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 [[Bay Area Rapid Transit|BART]] 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]], 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]]s do. When the initially increasing costs for [[automation]] began to decrease, this became a financially attractive option for the operators.

At the same time, countervailing arguments stated that in an [[emergency]] 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 [[emergency evacuation|evacuation]] if needed, or call for the correct [[emergency services]] 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 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]] lines. One of the first such systems was the [[Véhicule Automatique Léger|VAL]] (''véhicule automatique léger'' or "automated light vehicle"), first used in 1983 on the [[Lille Metro]] in France. Additional VAL lines have been built in other cities such as [[Toulouse Metro|Toulouse]], France, and [[Turin Metro|Turin]], Italy. Another system that uses unstaffed trains is [[Bombardier Transportation|Bombardier's]] [[Bombardier Innovia Metro|Innovia Metro]], originally developed by the [[Urban Transportation Development Corporation]] as the [[Bombardier Innovia Metro|Intermediate Capacity Transit System]] (ICTS). It was later used on the [[Vancouver SkyTrain|SkyTrain]] in Vancouver and the [[Kelana Jaya Line]] in Kuala Lumpur, both which carries no crew members. 
[[File:CastleHillMetroStation.jpg|thumb|Platform screen doors at Castle Hill Station on the [[Sydney Metro]]]]

Systems that use automatic trains also commonly employ full-height [[platform screen doors]] or half-height [[automatic platform gate]]s in order to improve safety and ensure passenger confidence, but this is not universal, as networks like [[Nuremberg U-Bahn|Nuremberg]] do not, using [[infrared sensors]] 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 first network to install PSDs on an already operational system was [[MTR|Hong Kong's MTR]], followed by the Singapore MRT.

As for larger trains, the [[Paris Métro]] has human drivers on most lines but runs automated trains on its newest line, [[Paris Métro Line 14|Line 14]], which opened in 1998. The older [[Paris Métro Line 1|Line 1]] was subsequently converted to unattended operation by 2012, and it is expected that [[Paris Métro Line 4|Line 4]] will follow by 2023.<ref>{{cite news |last1=Chicheportiche |first1=Olivier |title=Métro parisien: l'automatisation de la ligne 4 prendra du retard |url=https://www.bfmtv.com/economie/entreprises/transports/metro-parisien-l-automatisation-de-la-ligne-4-prendra-du-retard_AN-202111150320.html |access-date=14 February 2022 |publisher=BFM Business |date=November 15, 2021}}</ref> The [[North East MRT line]] in Singapore, which opened in 2003, is the world's first fully automated underground urban heavy-rail line. The MTR [[Disneyland Resort line]] is also automated, along with trains on the [[South Island line]].
{{clear right}}

==Modal tradeoffs and interconnections==
{{Main|Urban rail transit}}
[[File:Stratford x pltfm.jpg|thumb|[[Stratford station|Stratford Station]] in London is shared by [[London Underground]] trains (left) and main line rail services (right), as well as the [[Docklands Light Railway]] (not shown).]]

Since the 1980s, [[tram]]s have incorporated several features of rapid transit: [[light rail]] systems (trams) run on their own [[Right-of-way (transportation)|rights-of-way]], thus avoiding [[Traffic congestion|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.<ref name=pulling />

A [[premetro]] 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]]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]].<ref name="White, 2002: 64"/>

Suburban [[commuter rail]] 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]]s, Jakarta's [[KRL Commuterline]], [[Chennai Suburban Railway|Chennai Suburban]], [[Commuter rail in Australia|Australian suburban networks]], Danish [[S-train|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]], [[Shanghai Metro]], [[MetroSur]] of the [[Madrid Metro]], [[Taipei Metro]], [[Rapid Rail|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]], [[Bay Area Rapid Transit]], [[Los Teques Metro]] and [[Seoul Subway Line 7]], etc.) serving bi- and multi-nucleus [[urban agglomeration|agglomerations]].

Some cities have opted for two tiers of urban railways: an urban rapid transit system (such as the [[Paris Métro]], [[Berlin U-Bahn]], [[London Underground]], [[Sydney Metro]], [[Tokyo subway]], [[Jakarta MRT]] and [[SEPTA#Rapid transit|Philadelphia Subway]]) and a suburban system (such as their counterparts [[Réseau Express Régional|RER]], [[Berlin S-Bahn|S-Bahn]], [[Crossrail]] & [[London Overground]], [[Sydney Trains]], [[East Japan Railway Company|JR Urban Lines]], [[KRL Commuterline]] and [[SEPTA Regional Rail|Regional Rail]] respectively). Such systems are known variously as [[S-train]]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.<ref name="white6364">White, 2002: 63–64</ref><ref>Cervero, 1998: 21</ref>

In some cases, such as the [[London Underground]] and the [[London Overground]], suburban and rapid transit systems even run on the exact same track along some sections. [[California]]'s [[BART]], [[Federal District (Brazil)|Federal District]]'s [[Federal District Metro (Brazil)|Metrô-DF]] and [[Washington, D.C.|Washington]]'s [[Washington Metro|Metrorail]] 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 [[Through train|interline]] with intervals dropping to typical rapid transit headways.

==Costs, benefits, and impacts==
{{Main|Transport planning}}
[[File:Docklands Light Railway 121 (6175977501).jpg|thumb|The [[Docklands Light Railway]] in London allows for dense land use, while retaining a high capacity.]]
{{As of|2018|March}}, 212 cities have built rapid transit systems.<ref>{{cite web |url=http://mic-ro.com/metro/table.html |title=World Metro Database |publisher=Metro Bits |access-date=2013-11-17 |archive-url=https://web.archive.org/web/20100923072945/http://mic-ro.com/metro/table.html |archive-date=2010-09-23 |url-status=live }}</ref> The [[capital cost]] is high, as is the risk of [[cost overrun]] and benefit shortfall; [[public financing]] is normally required. Rapid transit is sometimes seen as an alternative to an extensive [[road transport]] system with many [[motorway]]s;<ref name=bb258>Banister and Berechman, 2000: 258</ref> the rapid transit system allows higher capacity with less land use, less environmental impact, and a lower cost.<ref>Cervero, 1998: 26</ref><ref name="mrt"/> A 2023 study found that rapid transit systems lead to a massive reduction in {{CO2}} emissions.<ref>{{Cite journal |last1=Dasgupta |first1=Susmita |last2=Lall |first2=Somik |last3=Wheeler |first3=David |date=2023 |title=Subways and {{CO2}} emissions: A global analysis with satellite data |url=https://www.sciencedirect.com/science/article/pii/S0048969723023124 |journal=Science of the Total Environment |language=en |volume=883 |pages=163691 |doi=10.1016/j.scitotenv.2023.163691 |pmid=37100143 |bibcode=2023ScTEn.883p3691D |s2cid=258327571 |issn=0048-9697|url-access=subscription }}</ref>

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]]s often depress nearby residential [[land value]]s, but proximity to a rapid transit station often triggers commercial and residential growth, with large [[transit oriented development]] office and housing blocks being constructed.<ref name=bb258 /><ref>European Conference of Ministers of Transport, 2003: 187</ref> Also, an efficient transit system can decrease the economic welfare loss caused by the increase of [[population density]] in a metropolis.<ref name="Rémy Prud'homme">{{cite journal |last=Prud'homme|first=Rémy |title=Public transport congestion costs: The case of the Paris subway |journal=Transport Policy |doi=10.1016/j.tranpol.2011.11.002 |volume=21 |pages=101–109|year=2012 }}</ref>

Rapid transit systems have high [[fixed cost]]s. Most systems are publicly owned, by either local governments, [[transit authority|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]]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]], allowing for [[Free transfer (public transit)|free transfers]] between modes. Almost all transit systems operate at a deficit, requiring [[transit fare|fare revenue]], [[advertising]] and [[subsidy|government funding]] to cover costs.

The [[farebox recovery ratio]], a ratio of ticket income to operating costs, is often used to assess operational profitability, with some systems including Hong Kong's [[MTR Corporation]],<ref name=mtrresult>{{cite web |url=http://www.mtr.com.hk/eng/corporate/file_rep/PR-08-075-E.pdf |title=Announcement of Unaudited Results for the Six Months Ended 30 June 2008 |author=MTR Corporation |author-link=MTR Corporation |date=2008-08-05 |access-date=2008-08-21 |archive-url=https://web.archive.org/web/20080909221821/http://www.mtr.com.hk/eng/corporate/file_rep/PR-08-075-E.pdf |archive-date=9 September 2008 |url-status=live }}</ref> and [[Taipei Rapid Transit System|Taipei]]<ref>{{cite web|title=Taipei Rapid Transit Corporation '08 Annual Report|url=http://english.trtc.com.tw/public/Attachment/9112716543575.pdf|publisher=Taipei Rapid Transit Corporation|page=96|access-date=2010-07-06|archive-url=https://web.archive.org/web/20111225183011/http://english.trtc.com.tw/public/Attachment/9112716543575.pdf|archive-date=2011-12-25|url-status=live}}</ref> achieving recovery ratios of well over 100%. This ignores both heavy capital costs incurred in building the system, which are often funded with [[soft loan]]s<ref>{{cite web |url=http://cfusrug.org/articles/financing_strat.php |title=:: Center for Urban Studies and Research |access-date=2010-11-11 |url-status=dead |archive-url=https://web.archive.org/web/20110725153952/http://cfusrug.org/articles/financing_strat.php |archive-date=2011-07-25 }}</ref> and whose [[loan servicing|servicing]] is excluded from calculations of profitability, as well as ancillary revenue such as income from [[real estate]] portfolios.<ref name=mtrresult /> 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,<ref name=kjenstad46>Kjenstad, 1994: 46</ref> a process known as [[value capture]].

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.<ref>{{cite web |last1=Booth |first1=Geoffrey |last2=Leonard |first2=Bruce |last3=Pawlukiewicz |first3=Michael |title=Ten Principles for Reinventing America's Suburban Business Districts |url=https://americas.uli.org/wp-content/uploads/2012/07/TP_BusinessDistricts.ashx_.pdf |website=ULI Americas |publisher=Urban Land Institute |access-date=2021-07-26}}</ref>

==See also==
{{portal|Transport|Trains|Buses}}
* [[List of metro systems]]
* [[Bus rapid transit]]
* [[Megaproject]]
* [[Personal rapid transit]]
* [[Rapid transit track gauge]]

== References ==

=== Citations ===
{{Reflist}}

=== Sources ===
{{refbegin}}
* {{cite book |title=Transport Investment and Economic Development |author1=Banister, David |author2=Berechman, Joseph  |name-list-style=amp |url = https://books.google.com/books?id=g1UClQCOdE4C |year=2000 |publisher=Routledge |isbn=978-0-419-25590-1 }}
* Bobrick, Benson (1981). ''Labyrinths of Iron'': ''a''[''n''] ''History of the World's Subways''. New York: Newsweek Books. {{ISBN|0-88225-299-2}}.
* {{cite book |title = The Transit Metropolis |last=Cervero |first = Robert |author-link=Robert Cervero |url = https://books.google.com/books?id=bLs3H_IWr3wC |year=1998 |publisher=Island Press |isbn=978-1-55963-591-2 }}
* {{cite book |title = Safe & Sustainable Transport |author=European Conference of Ministers of Transport |url = https://books.google.com/books?id=I-Ny0W7XN6QC |year=2003 |publisher=OECD Publishing |location=Paris |isbn=978-92-821-1303-5 }}
* {{cite web |url = https://3gozaa3xxbpb499ejp30lxc8-wpengine.netdna-ssl.com/wp-content/uploads/2014/07/Sustainable-Transport-Mass-Transit-Options.pdf |title=Mass Transit Options |work=Sustainable Transport: A Sourcebook for Policy-Makers in Developing Cities |author1=Fjellstrom, K. |author2=Wright, L. |publisher=[[Deutsche Gesellschaft für Technische Zusammenarbeit]] |year=2002 |access-date=2009-07-09 }}
* {{cite book |title = På skinner i Bymarka |author=Kjenstad, Rune |year=1994 |publisher=Baneforlaget |location=Oslo |language=no |isbn=978-82-91448-01-5 }}
* {{cite book |title = Transit Maps of the World |author=Ovenden, Mark |year=2007 |publisher=Penguin |location=London |isbn=978-0-14-311265-5 |author-link=Mark Ovenden }}
* {{cite book |title=Improving Transit Security |author1=Needle, Jerome A. |author2=Transportation Security Board |author3=Cobb, Renée M. |name-list-style=amp |year=1997 |url = https://books.google.com/books?id=WfBt0kzz524C |publisher=Transportation Security Board |isbn=978-0-309-06013-4 }}
* {{cite book |title=Metro Art |author=Ström, Marianne |year=1998 |url = https://books.google.com/books?id=cOkxz36ITdoC |publisher=ACR Edition |isbn=978-2-86770-068-2 }}
* {{cite book |title = Public Transport: Its Planning, Management, and Operation |author=White, Peter |year=2002 |publisher=Taylor & Francis |url = https://books.google.com/books?id=d1oZxyjPDF4C |isbn=978-0-415-25772-5 }}
* {{cite book |title = Access to Mass Transit for Blind and Visually Impaired Travelers |author=Uslan, Mark |author2=American Foundation for the Blind |author2-link=American Foundation for the Blind |author3=Peck, Alec |author4=Wiener, William |author5=Stern, Arlene |name-list-style=amp |year=1990 |publisher=American Foundation for the Blind |isbn=978-0-89128-166-5 }}
* {{cite book|title=The American Heritage Dictionary of the English Language|edition=4th|publisher=Houghton Mifflin Company|isbn=978-0-618-08230-8|editor=Joseph P. Pickert |display-editors=etal |year=2000}}
{{refend}}

== External links ==
{{Commons category|Rapid transit}}
* [http://urbanrail.net/ UrbanRail]

; Databases
* [http://metro-data.info/ Metro-Data.info] ({{Webarchive|url=https://web.archive.org/web/20180929000328/http://metro-data.info/ |date=2018-09-29 }}) – database of metro systems around the world

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