Rapid transit ormass rapid transit (MRT) orheavy rail,[2][3] commonly referred to asmetro, is a type of high-capacitypublic transport that is generally built inurban areas. Agrade separated rapid transit line below ground surface through atunnel can be regionally called asubway,tube,metro orunderground.[4][5][6][7] They are sometimes grade-separated onelevated railways, in which case some are referred to asel trains – short for "elevated" – orskytrains. Rapid transit systems are usuallyelectricrailways, that unlikebuses ortrams operate on an exclusiveright-of-way, which cannot be accessed by pedestrians or other vehicles.[8]
Modern services on rapid transit systems are provided on designated lines betweenstations typically usingelectric multiple units onrailway tracks. Some systems useguided rubber tires, magnetic levitation (maglev), ormonorail. 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 samepublic transport authorities. Some rapid transit systems have at-grade intersections between a rapid transit line and a road or between two rapid transit lines.[9]
The termMetro is the most commonly used term for underground rapid transit systems used by non-native English speakers.[18] Rapid transit systems may be named after the medium by which passengers travel in busycentral business districts; the use oftunnels inspires names such assubway,[19]underground,[20]Untergrundbahn (U-Bahn) in German,[21] or theTunnelbana(T-bana) in Swedish.[22] The use ofviaducts inspires names such aselevated (L orel),skytrain,[23]overhead,overground orHochbahn 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 France, large cities, such asParis,Marseille andLyon, use the termmétro. Also the smaller cities ofLille andRennes have a light metro. Furthermore,Brussels in Belgium, andAmsterdam andRotterdam in the Netherlands also usemétro ormetro for their systems.
In Germany and Austria they rapid transit is known asU-Bahn, which are often supported byS-Bahn systems. In Germany,U-Bahn systems exist inBerlin,Hamburg,Munich,Nuremberg andFürth, while in Austria such a system exists inVienna. In addition, the small, car-free town ofSerfaus in the Austrian state ofTyrol also features a shortU-Bahn line. There are noU-Bahn systems in theGerman-speaking part of Switzerland, but the city ofLausanne has its own, smallmétro system. In Zurich, Switzerland's largest city, a project for aU-Bahn network was stopped by a referendum in the 1970s and instead itsS-Bahn system was developed further. OtherCentral European countries also have metro lines, for example in the cities ofBudapest (Hungary), where it is calledmetró,Prague (Czech Republic) andWarsaw (Poland) – the latter two systems also use the termmetro.
InNorthern Europe, rapid transit systems are calledmetro inCopenhagen (Denmark) andHelsinki (Finland), while they are refferd to asT-bane (tunnelbane) inOslo (Norway) andtunnelbana inStockholm (Sweden).
Various terms are used for rapid transit systems aroundNorth America. The termmetro is primarily used to describe non-English systems, such as theMexico City Metro and theMontreal Metro, although the term is still often used in English as well, as is the case forLos Angeles Metro Rail and theWashington Metro, among others. The term "subway" is more commoly used to describe rail rapid transit in English, despite few systems being known by the term. Systems known for their elevated character are often referred to as "the El", "the L", or as a "skytrain," with examples including theChicago "L" andVancouver Sky Train. Metro is also used as a shortened reference to ametropolitan area, with some systems referencing this in their names, with the REM (Réseau express métropolitain) andMetra (Metropolitan Rail) suburban rail in Chicago (despite the latter not being rapid transit at all).Boston's subway system is known locally as "The T". InAtlanta, theMetropolitan Atlanta Rapid Transit Authority goes by the acronym "MARTA." In theSan Francisco Bay Area, residents refer toBay Area Rapid Transit by its acronym "BART".[24][25]
TheNew 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 orL (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 twoNorth American systems that are primarily called "subways".
In general rapid transit is a synonym for "metro" type transit, though sometimes rapid transit is defined to include "metro", commuter trains andgrade-separated light rail.[33] Also high-capacity bus-based transit systems can have features similar to "metro" systems.[34]
The opening of London's steam-hauledMetropolitan Railway in 1863 marked the beginning of rapid transit. Initial experiences with steam engines, despite ventilation, were unpleasant. Experiments withpneumatic railways failed in their extended adoption by cities.
In 1890, theCity & South London Railway was the first electric-traction rapid transit railway, which was also fully underground.[35] Prior to opening, the line was to be called the "City and South London Subway", thus introducing the term Subway into railway terminology.[36] Both railways, alongside others, were eventually merged intoLondon Underground. The 1893Liverpool Overhead Railway was designed to use electric traction from the outset.[37]
The technology quickly spread to othercities 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,Boston andNew York City all converted or purpose-designed and built electric rail services.[38]
Advancements in technology have allowed new automated services. Hybrid solutions have also evolved, such astram-train andpremetro, which incorporate some of the features of rapid transit systems.[35] 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 andsuburbs tended tospread out.[39] Since the 1970s, the viability of underground train systems in Australian cities, particularlySydney andMelbourne, has been reconsidered and proposed as a solution to over-capacity. Melbourne hadtunnels and stations developed in the 1970s and opened in 1980. Thefirst line of theSydney Metro was opened in 2019.[40]
Since the 1960s, many new systems have been introduced inEurope,Asia andLatin America.[21] 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 arapid transit system.[41][42]
Milan Metro is the largest rapid transit system in Italy in terms of length, number of stations and ridership; and the eighth longest inEurope.[43]
Rapid transit is used for local transport incities,agglomerations, andmetropolitan areas to transport large numbers of people often short distances at highfrequency.[8][44] The extent of the rapid transit system varies greatly between cities, with several transport strategies.[7]
Some systems may extend only to the limits of the inner city, or to its inner ring ofsuburbs with trains making frequent station stops. The outer suburbs may then be reached by a separatecommuter 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.[6]
Rapid transit systems may be supplemented by other systems such astrolleybuses, regularbuses,trams, 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.[45]
Each rapid transit system consists of one or morelines, 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 theCopenhagen Metro,[49] theMilan Metro, theOslo Metro, theIstanbul Metro and theNew York City Subway.[50]
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 thePrague Metro.[51] TheLondon Underground[52] andParis Métro[53] are densely built systems with a matrix of crisscrossing lines throughout the cities. TheChicago 'L' has most of its lines converging onThe 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 theMoscow Metro'sKoltsevaya Line andBeijing Subway'sLine 10.
The capacity of a line is obtained by multiplying the car capacity, the train length, and theservice 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 theseated 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 ofcommunications-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 36,000passengers per hour per direction. However, much higher capacities are attained inEast Asia with ranges of 75,000 to 85,000 people per hour achieved byMTR Corporation's urban lines in Hong Kong.[54][55][56]
Rapid transittopologies 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 anarea of land with a set oflines, 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.[57]
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.[57] A study of the 15 world largest subway systems suggested a universal shape composed of a dense core with branches radiating from it.[58]
Rapid transit operators have often built up strongbrands, 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.[59] In many cities, there is a singlecorporate image for the entire transit authority, but the rapid transit uses its own logo that fits into the profile.
TheShenzhen Metro uses large LCD information displays to show the current location, upcoming stops and diagrams of the next station.
Atransit map is atopological map orschematicdiagram used to show the routes and stations in apublic transport system. The main components arecolor-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.[60] Transit maps can be found in transit vehicles, onplatforms, elsewhere in stations, and in printedtimetables. Maps help users understand the interconnections between different parts of the system; for example, they show theinterchange stations where passengers can transfer between lines. Unlike conventional maps, transit maps are usually not geographically accurate, but emphasize thetopological 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.[60]
Some systems assign uniquealphanumeric codes 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.[61] For example, on theSingapore 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 two 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 theInternet andcell phones 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 standardizedGTFS 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.
Mexico City Metro uses a uniquepictogram for each station. Originally intended to help make the network map "readable" by illiterate people, this system has since become an "icon" of the system.
Compared to other modes of transport, rapid transit has a goodsafety record, with few accidents. Rail transport is subject to strictsafety regulations, with requirements for procedure and maintenance to minimize risk.Head-on collisions are rare due to use of double track, and low operating speeds reduce the occurrence and severity ofrear-end collisions andderailments.Fire is more of a danger underground, such as theKing'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.[62][63]
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 fromsecurity problems:petty crimes, such aspickpocketing and baggage theft, and more seriousviolent crimes, as well as sexual assaults on tightly packed trains and platforms.[64][65] Security measures includevideo surveillance,security guards, andconductors. In some countries a specializedtransit police may be established. These security measures are normally integrated with measures to protect revenue by checking that passengers are not travelling without paying.[66]
Some subway systems, such as theBeijing 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 toterrorism with many casualties, such as the 1995Tokyo subway sarin gas attack[67] and the 2005 "7/7" terrorist bombings on the London Underground.
Some rapid transport trains have extra features such as wall sockets, cellular reception, typically using aleaky feeder in tunnels andDAS antennas in stations, as well asWi-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 usingAMPS in 1989.[68] Many metro systems, such as the Hong KongMass Transit Railway (MTR) and the Berlin U-Bahn, provide mobile data connections in their tunnels for various network operators.
Thetechnology used for public, mass rapid transit has undergone significant changes in the years since theMetropolitan Railway opened publicly in London in 1863.[5][6]
High capacitymonorails with larger and longer trains can be classified as rapid transit systems.[citation needed] Such monorail systems recently started operating inChongqing andSão Paulo.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 asfeeder lines into the main rapid transit system.[69] For instance, theWenhu Line of theTaipei 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.[22] Ground-level alignments with a dedicatedright-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.[70]
Most rapid transit trains areelectric multiple units with lengths from three to over ten cars.[71] Crew sizes have decreased throughout history, with some modern systems now running completely unstaffed trains.[72] 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 athird rail or byoverhead wires. The whole London Underground network usesfourth rail and others use thelinear motor for propulsion.[73]
Some urban rail lines are built to aloading gauge as large as that ofmain-line railways; others are built to a smaller one and havetunnels that restrict the size and sometimes the shape of the train compartments. One example is most of theLondon Underground, which has acquired the informal term "tube train" due to the cylindrical shape of the trains used on thedeep tube lines.
Historically, rapid transit trains usedceiling fans and openable windows to provide fresh air andpiston-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 withair conditioning, such as theHudson and Manhattan Railroad K-series cars[74] from 1958, theNew York City SubwayR38 andR42 cars from the late-1960s, and theNagoya Municipal Subway 3000 series,Osaka Municipal Subway 10 series[75] andMTR M-Train EMUs 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 theMontreal Metro[76] (opened 1966) andSapporo 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 smallerloading 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.
Most rapid transit systems use conventionalstandard gaugerailway track. Since tracks in subway tunnels are not exposed torain,snow, or other forms ofprecipitation, they are often fixed directly to the floor rather than resting onballast, such as normal railway tracks.
An alternate technology, usingrubber tires on narrowconcrete or steelroll ways, was pioneered on certain lines of theParis Métro andMexico City Metro, and the first completely new system to use it was inMontreal, Canada. On most of these networks, additional horizontal wheels are required for guidance, and a conventional track is often provided in case offlat tires and forswitching. There are also some rubber-tired systems that use a centralguide rail, such as theSapporo Municipal Subway and theNeoVal system inRennes, France. Advocates of this system note that it is much quieter than conventional steel-wheeled trains, and allows for greaterinclines given the increasedtraction 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.[77]
For elevated lines, another alternative is themonorail, which can be built either asstraddle-beam monorails or as asuspended monorail. While monorails have never gained wide acceptance outside Japan, there are some such asChongqing Rail Transit's monorail lines which are widely used in a rapid transit setting.
Although trains on very early rapid transit systems like theMetropolitan Railway were powered usingsteam engines, either via cable haulage orsteam locomotives, nowadays virtually all metro trains useelectric power and are built to run asmultiple units. Power for the trains, referred to astraction power, is usually supplied via one of two forms: anoverhead line, suspended from poles or towers along the track or from structure or tunnel ceilings, or athird 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 ofoverhead wires.
The use of overhead wires allows higher power supplyvoltages to be used. Overhead wires are more likely to be used on metro systems without many tunnels, for example, theShanghai Metro. Overhead wires are employed on some systems that are predominantly underground, as inBarcelona,Fukuoka,Hong Kong,Madrid, andShijiazhuang. 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 asBlue Line inBoston.
At subterranean levels,tunnels move traffic away from street level, avoiding delays caused bytraffic 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 machines can be used to dig deep-bore tunnels that lie further down inbedrock.[35]
The construction of an underground metro is an expensiveproject and is often carried out over a number of years. There are several different methods of building underground lines.
In one common method, known ascut-and-cover the citystreets 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 ofutilities commonly buried not far below street level – particularlypower andtelephone wiring,water andgas mains, andsewers. This relocation must be done carefully, as according to documentaries from the National Geographic Society, one of the causes of the April 1992explosions in Guadalajara was a mislocated water pipeline. The structures are typically made ofconcrete, perhaps with structural columns ofsteel. In the oldest systems,brick, andcast 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 calledbored tunneling. Here, construction starts with avertical shaft from which tunnels are horizontally dug, often with atunneling shield, thus avoiding almost any disturbance to existing streets, buildings, and utilities. But problems withground water are more likely, and tunneling through nativebedrock may requireblasting. The first city to extensively use deep tunneling wasLondon, where a thicksedimentary layer ofclay largely avoids both problems. The confined space in the tunnel also limits the machinery that can be used, but specializedtunnel-boring machines 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 installair 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 withair-conditioned trains.
The deepest metro system in the world was built inSt. Petersburg, Russia where in themarshland, stable soil starts more than 50 metres (160 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 100–120 metres (330–390 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:
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 theCity and South London Railway and has been used many times since, for example in Montreal or Nuremberg.
TheWest Island line, an extension of theMTR Island line serving western Hong Kong Island, opened in 2015, has two stations (Sai Ying Pun andHKU) situated over 100 metres (330 ft) below ground level, to serve passengers on theMid-levels. They have several entrances/exits equipped with high-speed lifts, instead ofescalators. These kinds of exits have existed in many London Underground stations and stations in former Soviet Union nations.
Elevated railways 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'sSkyTrain, London'sDocklands Light Railway,[78] theMiami Metrorail,Bangkok Skytrain,[79] andSkyline Honolulu.[80]
Stations function ashubs 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 eitherisland- orside platforms.[81] Underground stations, especially deep-level ones, increase the overall transport time: longescalator rides to the platforms mean that the stations can become bottlenecks if not adequately built. Some underground and elevated stations are integrated into vastunderground orskyway networks respectively, that connect to nearby commercial buildings.[82] In suburbs, there may be a "park and ride" connected to the station.[83]
To allow easy access to the trains, theplatform height allows step-free access between platform and train. If the station complies withaccessibility standards, it allows both disabled people and those with wheeled baggage easy access to the trains,[84] though if the track is curved there can be agap between the train and platform. Some stations useplatform screen doors to increase safety by preventing people falling onto the tracks, as well as reducing ventilation costs.
A giantnautilus in redmarble on the wall on Moscow Metro
Particularly in the formerSoviet Union and other Eastern European countries, but to an increasing extent elsewhere, the stations were built with splendid decorations such asmarble walls, polishedgranite floors and mosaics—thus exposing the public to art in their everyday life, outside galleries and museums. Moscow Metro's wall claddingcontains many fossils, fromcorals toammonoids andnautiluses. The systems inMoscow,St. Petersburg,Tashkent andKyiv are widely regarded as some of the most beautiful in the world.[85] Several other cities such as London,[86]Stockholm,Montreal,Lisbon,Naples andLos 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.[87] It may be possible to profit by attracting more passengers by spending relatively small amounts on grandarchitecture, art,cleanliness,accessibility,lighting and a feeling ofsafety.[88]
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" or "guard") to operate the doors or gates, as well as a driver (also called the "engineer" or "motorman"). The introduction of powered doors around 1920 permitted crew sizes to be reduced, and trains in many cities are now operated bya 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,mirrors orclosed-circuit TV monitors are often provided for that purpose.
A replacement system for human drivers became available in the 1960s, with the advancement ofcomputerized technologies forautomatic 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 therailway platform at the next station, while taking into account the information that a human driver would obtain fromlineside orcab signals. The first metro line to use this technology in its entirety was London'sVictoria 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'sBART network.
A variant of ATO, "driverless train operation" (DTO) or technically "GoA 3", is seen on some systems, as in London'sDocklands 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 mostelevators do. When the initially increasing costs forautomation began to decrease, this became a financially attractive option for the operators.
At the same time, countervailing arguments stated that in anemergency 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 anevacuation if needed, or call for the correctemergency 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 theScarborough 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 onlight metro lines. One of the first such systems was theVAL (véhicule automatique léger or "automated light vehicle"), first used in 1983 on theLille Metro in France. Additional VAL lines have been built in other cities such asToulouse, France, andTurin, Italy. Another system that uses unstaffed trains isBombardier'sInnovia Metro, originally developed by theUrban Transportation Development Corporation as theIntermediate Capacity Transit System (ICTS). It was later used on theSkyTrain in Vancouver and theKelana Jaya Line in Kuala Lumpur, both of which carry no crew members.
Another obstacle to conversion of existing lines to fully automated operation is that the conversion may necessitate a shutdown of operations. Furthermore, where several lines share the same infrastructure, it may be necessary to share tracks between automated and human-operated trains at least for a transitory period. The Nuremberg U-Bahn converted the existingU2 to fully automated (GoA4) in early 2010 without a single day of service disruption. Before that it had run in mixed operation with the newly opened fully driverlessU3 from 2008. Nuremberg U-Bahn was the first system in the world to undertake such a transition with mixed operation and without service disruption. While this demonstrates that those technological hurdles can be overcome, the project was severely delayed, missing the target of being in operation in time for the2006 FIFA World Cup and the hoped for international orders for the system of automation employed in Nuremberg never materialized.
Platform screen doors at Castle Hill Station on theSydney Metro
Systems that use automatic trains also commonly employ full-heightplatform screen doors or half-heightautomatic platform gates in order to improve safety and ensure passenger confidence, but this is not universal, as networks likeNuremberg do not, usinginfrared sensors instead to detect obstacles on the track. Conversely, some lines which retain drivers or manual train operation nevertheless use PSDs, notably London'sJubilee Line Extension. The first network to install PSDs on an already operational system wasHong Kong's MTR, followed by the Singapore MRT.
As for larger trains, theParis Métro has human drivers on most lines but runs automated trains on its newest line,Line 14, which opened in 1998. The olderLine 1 was subsequently converted to unattended operation by 2012, andLine 4 in 2023. TheNorth East MRT line in Singapore, which opened in 2003, is the world's first fully automated underground urban heavy-rail line. The MTRDisneyland Resort line is also automated, along with trains on theSouth Island line.
Since the 1980s,trams have incorporated several features of rapid transit:light rail systems (trams) run on their ownrights-of-way, thus avoidingcongestion; 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.[39]
Apremetro 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,interurbans were constructed asstreet-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 nameStadtbahn.[71]
Some cities have opted for two tiers of urban railways: an urban rapid transit system (such as theParis Métro,Berlin U-Bahn,London Underground,Sydney Metro,Tokyo subway,Jakarta MRT andPhiladelphia Subway) and a suburban system (such as their counterpartsRER,S-Bahn,Crossrail &London Overground,Sydney Trains,JR Urban Lines,KRL Commuterline andRegional Rail respectively). Such systems are known variously asS-trains, 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.[89][90]
In some cases, such as theLondon Underground and theLondon Overground, suburban and rapid transit systems even run on the exact same track along some sections.California'sBART,Federal District'sMetrô-DF andWashington'sMetrorail 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 linesinterline with intervals dropping to typical rapid transit headways.
TheDocklands Light Railway in London allows for dense land use, while retaining a high capacity.
As of March 2018[update], 212 cities have built rapid transit systems.[91] Thecapital cost is high, as is the risk ofcost overrun and benefit shortfall;public financing is normally required. Rapid transit is sometimes seen as an alternative to an extensiveroad transport system with manymotorways;[92] the rapid transit system allows higher capacity with less land use, less environmental impact, and a lower cost.[93][7] A 2023 study found that rapid transit systems lead to a massive reduction in CO2 emissions.[94]
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.Motorways often depress nearby residentialland values, but proximity to a rapid transit station often triggers commercial and residential growth, with largetransit oriented development office and housing blocks being constructed.[92][95] Also, an efficient transit system can decrease the economic welfare loss caused by the increase ofpopulation density in a metropolis.[96]
Rapid transit systems have highfixed costs. 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 forroads. The transit systems may be operated by the owner or by a private company through apublic service obligation. The owners of the systems often also own the connecting bus or rail systems, or are members of the localtransport association, allowing forfree transfers between modes. Almost all transit systems operate at a deficit, requiringfare revenue,advertising andgovernment funding to cover costs.
Thefarebox recovery ratio, a ratio of ticket income to operating costs, is often used to assess operational profitability, with some systems including Hong Kong'sMTR Corporation,[97] andTaipei[98] achieving recovery ratios of well over 100%. This ignores both heavy capital costs incurred in building the system, which are often funded withsoft loans[99] and whoseservicing is excluded from calculations of profitability, as well as ancillary revenue such as income fromreal estate portfolios.[97] 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,[70] a process known asvalue capture.
Urbanland-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.[100]
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