Rapid transit


Rapid transit or mass rapid transit (MRT), also known as heavy rail, metro, subway, tube, , , metropolitana or underground, is a type of high-capacity generally found in s. Unlike es or s, rapid transit systems are s that operate on an exclusive , which cannot be accessed by pedestrians or other vehicles of any sort, and which is often in s or on s. Modern services on rapid transit systems are provided on designated lines between typically using s on s, although some systems use guided rubber tires, magnetic levitation ('), or . 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 . However, some rapid transit systems have at-grade intersections between a rapid transit line and a road or between two rapid transit lines. The world's first rapid transit system was the partially underground which opened as a conventional railway in 1863, and now forms part of the . In 1868, New York opened the elevated , initially a cable-hauled line using static s. , has the largest number of —40 in number, running on over 4,500 km of track—and is responsible for most of the world's rapid-transit expansion in the past decade. The world's longest single-operator rapid transit system by is the . The world's largest single rapid transit service provider by number of stations (472 stations in total) is the . The three by annual ridership are the , and the .


''Metro'' is the most common term for underground rapid transit systems used by non-native English speakers. Rapid transit systems may be named after the medium by which passengers travel in busy s; the use of s inspires names such as ''subway'', ''underground'', ''Untergrundbahn ()'' in German,White, 2002: 63 or the ''Tunnelbana (T-bana)'' in Swedish;Ovenden, 2007: 93 the use of s inspires names such as ''elevated'' (''L'' or ''el''), ''skytrain'',, 2007: 16 ''overhead'', ''overground'' or ''Hochbahn'' in German. One of these terms may apply to an entire system, even if a large part of the network (for example, in outer suburbs) runs at ground level. In most of , a ''subway'' is a ; the terms ''Underground'' and ''Tube'' are used for the London Underground, and the North East England , mostly overground, is known as the ''Metro''. In , however, the underground rapid transit system is known as the ''Subway''. Various terms are used for rapid transit systems around . The term ''metro'' is a shortened reference to a . Rapid transit systems such as the , , the , and the are generally called the ''Metro''. 's system that serves the entire metropolitan area is called ' (short for "Metropolitan Rail"), while its rapid transit system that serves the city is called the . However the is known locally as "The T". In , the term “El” is used for the which runs mostly on an elevated track, while the term “subway” applies to the which is almost entirely underground. The 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 refers specifically to the 14th Street–Canarsie Local line, and not other elevated trains. In most of and in , rapid transit systems are primarily known by the ''MRT''. The meaning however varies from one country to another. In , the acronym stands for ' or ''Integrated Mass ransitMode'' in English. In the , it stands for ', with also using the term ''subway'' being underground lines. In Singapore, it stands for '. In , it stands for ', and previously also used the ''Mass Rapid Transit'' name. In , there is a proposed MRT line which also stands for ''Mass Rapid Transit''. Outside of Southeast Asia, and have their own ''MRT'' systems which also stands for ''Mass Rapid Transit'' as with Singapore.


The opening of London's steam-hauled in 1863 marked the beginning of rapid transit. Initial experiences with steam engines, despite ventilation, were unpleasant. Experiments with s failed in their extended adoption by cities. Electric traction was more efficient, faster and cleaner than steam and the natural choice for trains running in tunnels and proved superior for elevated services. In 1890, the was the first electric-traction rapid transit railway, which was also fully underground.Ovenden, 2007: 7 Prior to opening, the line was to be called the "City and South London Subway", thus introducing the term Subway into railway terminology. Both railways, alongside others, were eventually merged into . The 1893 was designed to use electric traction from the outset. The technology quickly spread to other cities in Europe, the United States, Argentina, and Canada, with some railways being converted from steam and others being designed to be electric from the outset. , , and all converted or purpose-designed and built electric rail services. Advancements in technology have allowed new automated services. Hybrid solutions have also evolved, such as and , which incorporate some of the features of rapid transit systems. In response to cost, engineering considerations and topological challenges some cities have opted to construct tram systems, particularly those in Australia, where density in cities was low and s tended to . Since the 1970s, the viability of underground train systems in Australian cities, particularly and , has been reconsidered and proposed as a solution to over-capacity. The of , Australia's first rapid transit system, was opened in 2019. Since the 1960s, many new systems were introduced in , and . In the 21st century, most new expansions and systems are located in Asia, with China becoming the world's leader in metro expansion, operating some of the largest and busiest systems while possessing almost 60 cities that are operating, constructing or planning a .


Rapid transit is used in , , and s to transport large numbers of people often short distances at high . The extent of the rapid transit system varies greatly between cities, with several transport strategies. Some systems may extend only to the limits of the inner city, or to its inner ring of s with trains making frequent station stops. The outer suburbs may then be reached by a separate network where more widely spaced stations allow higher speeds. In some cases the differences between urban rapid transit and suburban systems are not clear. Rapid transit systems may be supplemented by other systems such as es, regular es, s, or . 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.


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 , the , the and the . 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 . The and are densely built systems with a matrix of crisscrossing lines throughout the cities. The has most of its lines converging on , 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 's and 's . The capacity of a line is obtained by multiplying the car capacity, the train length, and the . 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 —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 : 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 . However, much higher capacities are attained in with ranges of 75,000 to 85,000 people per hour achieved by 's urban lines in Hong Kong.

Network topologies

Rapid transit 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", "U", "S", and "O" shapes or loops. Geographical barriers may cause chokepoints where transit lines must converge (for example, to cross a body of water), which are potential congestion sites but also offer an opportunity for transfers between lines. Ring lines provide good coverage, connect between the radial lines and serve tangential trips that would otherwise need to cross the typically congested core of the network. A rough grid pattern can offer a wide variety of routes while still maintaining reasonable speed and frequency of service. A study of the 15 world largest subway systems suggested a universal shape composed of a dense core with branches radiating from it.

Passenger information

Rapid transit operators have often built up strong s, often focused on easy recognition—to allow quick identification even in the vast array of signage found in large cities—combined with the desire to communicate speed, safety, and authority. In many cities, there is a single for the entire transit authority, but the rapid transit uses its own logo that fits into the profile. A is a or used to show the routes and stations in a system. The main components are lines to indicate each line or service, with named icons to indicate stations. Maps may show only rapid transit or also include other modes of public transport.Ovenden, 2007: 9 Transit maps can be found in transit vehicles, on , elsewhere in stations, and in printed . Maps help users understand the interconnections between different parts of the system; for example, they show the stations where passengers can transfer between lines. Unlike conventional maps, transit maps are usually not geographically accurate, but emphasize the connections among the different stations. The graphic presentation may use straight lines and fixed angles, and often a fixed minimum distance between stations, to simplify the display of the transit network. Often this has the effect of compressing the distance between stations in the outer area of the system, and expanding distances between those close to the center. Some systems assign unique s to each of their stations to help commuters identify them, which briefly encodes information about the line it is on, and its position on the line.Ström, 1998: 58 For example, on the , has the alphanumeric code CG2, indicating its position as the 2nd station on the Changi Airport branch of the East West Line. Interchange stations would have at least two codes, for example, has two codes, NS26 and EW14, the 26th station on the North South Line and the 14th station on the East West Line. Seoul Metro is another example that utilizes a code for its stations. But unlike that of Singapore's MRT, it is mostly numbers. Based on the line number, for example Sinyongsan station, coded as station 429. As it is on Line 4, the first number of the station code is 4. The last 2 numbers will be the station number on that line. Interchange stations can have multiple codes. Like City Hall station in Seoul which is served by Line 1 and Line 2. It has a code of 132 and 201 respectively. The Line 2 is a circle line and the first stop is City Hall, therefore, City Hall has the station code of 201. For lines without a number like Bundang line it will have an alphanumeric code. Lines without a number that are operated by KORAIL will start with the letter 'K'. With widespread use of the and 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 data format for transit information allows many third-party software developers to produce web and smartphone app programs which give passengers customized updates regarding specific transit lines and stations of interest.

Safety and security

Compared to other modes of transport, rapid transit has a good record, with few accidents. Rail transport is subject to strict , with requirements for procedure and maintenance to minimize risk. s are rare due to use of double track, and low operating speeds reduce the occurrence and severity of s and s. is more of a danger underground, such as the in London in November 1987, which killed 31 people. Systems are generally built to allow evacuation of trains at many places throughout the system. (usually over 1 meter / 3 feet) are a safety risk, as people falling onto the tracks have trouble climbing back. are used on some systems to eliminate this danger. Rapid transit facilities are public spaces and may suffer from problems: s, such as and baggage theft, and more serious s, as well as sexual assaults on tightly packed trains and platforms. Security measures include , s, and . In some countries a specialized may be established. These security measures are normally integrated with measures to protect revenue by checking that passengers are not travelling without paying. Some subway systems, such as the , which is ranked by Worldwide Rapid Transit Data as the "World's Safest Rapid Transit Network" in 2015, incorporate airport-style security checkpoints at every station. Rapid transit systems have been subject to with many casualties, such as the 1995 and the 2005 "" terrorist bombings on the London Underground.

Added features

Some rapid transport trains have extra features such as wall sockets, cellular reception (typically using in tunnels and in stations), as well as 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 ) in 1989. Nowadays, many metro systems, such as the Hong Kong Mass Transit Railway (MTR) and the Berlin U-Bahn, provide mobile data connections in their tunnels for various network operators.


The used for public, mass rapid transit has undergone significant changes in the years since the opened publicly in London in 1863. High capacity s with larger and longer trains can be classified as rapid transit systems. Such monorail systems recently started operating in and . 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 into the main rapid transit system. For instance, the of the serves many relatively sparse neighbourhoods and feeds into and complements the high capacity metro lines. Some systems have been built from scratch, others are reclaimed from former commuter rail or suburban tramway systems that have been upgraded, and often supplemented with an underground or elevated downtown section. At grade alignments with a dedicated 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.


Most rapid transit trains are with lengths from three to over ten cars.White, 2002: 64 Crew sizes have decreased throughout history, with some modern systems now running completely unstaffed trains. Other trains continue to have drivers, even if their only role in normal operation is to open and close the doors of the trains at stations. Power is commonly delivered by a or by . The whole London Underground network uses and others use the for propulsion. Some urban rail lines are built to a as large as that of ; others are built to smaller and have s that restrict the size and sometimes the shape of the train compartments. One example is the which has acquired the informal term "tube train" due to its cylindrical cabin shape. In many cities, metro networks consist of lines operating different sizes and types of vehicles. Although these sub networks are not often connected by track, in cases when it is necessary, rolling stock with a smaller from one sub network may be transported along other lines that use larger trains.


Most rapid transit systems use conventional . Since tracks in subway tunnels are not exposed to , , or other forms of , they are often fixed directly to the floor rather than resting on , such as normal railway tracks. An alternate technology, using on narrow or steel s, was pioneered on certain lines of the and , and the first completely new system to use it was in , Canada. On most of these networks, additional horizontal wheels are required for guidance, and a conventional track is often provided in case of s and for . There are also some rubber-tired systems that use a central , such as the and the system in , France. Advocates of this system note that it is much quieter than conventional steel-wheeled trains, and allows for greater given the increased of the rubber tires. However, they have higher maintenance costs and are less energy efficient. They also lose traction when weather conditions are wet or icy, preventing above-ground use of the Montréal Metro and limiting it on the Sapporo Municipal Subway, but not rubber-tired systems in other cities. Some cities with steep hills incorporate technologies in their metros. One of the lines of the includes a section of , while the , in Haifa, is an underground . For elevated lines, another alternative is the , which can be built either as or as a . While monorails have never gained wide acceptance outside Japan, there are some such as 's monorail lines which are widely used in a rapid transit setting.

Motive power

Although initially the trains of what is now the were drawn by s, virtually all metro trains, both now and historically, use and are built to run as s. Power for the trains, referred to as , usually takes one of two forms: an , suspended from poles or towers along the track or from structure or tunnel ceilings, or a mounted at track level and contacted by a sliding "". 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 . The use of overhead wires allows higher power supply s to be used. Although overhead wires are more likely to be used on metro systems without many tunnels, an example of which is the , overhead wires are employed on some systems that are predominantly underground, as in , , , , and . Both overhead wire and third-rail systems usually use the running rails as the return conductor, but some systems use a separate fourth rail for this purpose. There are transit lines that make use of both rail and overhead power, with vehicles able to switch between the two such as in .


Underground s move traffic away from street level, avoiding delays caused by 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. tunnels are constructed by digging up city streets, which are then rebuilt over the tunnel; alternatively, s can be used to dig deep-bore tunnels that lie further down in . The construction of an underground metro is an expensive 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 the city 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 commonly buried not far below street level – particularly and wiring, and mains, and . This relocation must be done carefully, as according to documentaries from the National Geographic Society, one of the causes of the April 22, 1992, was a mislocated water pipeline. The structures are typically made of , perhaps with structural columns of ; in the oldest systems, , and were used. Cut-and-cover construction can take so long that it is often necessary to build a temporary roadbed while construction is going on underneath, in order to avoid closing main streets for long periods of time. Another usual type of tunneling method is called . Here, construction starts with a from which tunnels are horizontally dug, often with a , thus avoiding almost any disturbance to existing streets, buildings, and utilities. But problems with are more likely, and tunneling through native may require . The first city to extensively use deep tunneling was , where a thick layer of largely avoids both problems. The confined space in the tunnel also limits the machinery that can be used, but specialized s are now available to overcome this challenge. One disadvantage with this, however, is that the cost of tunneling is much higher than building cut-and-cover systems, at-grade or elevated. Early tunneling machines could not make tunnels large enough for conventional railway equipment, necessitating special low, round trains, such as are still used by most of the London Underground, which cannot install 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 . The deepest metro system in the world was built in , Russia where in the , stable soil starts more than deep. Above that level, the soil mostly consists of water-bearing finely dispersed sand. Because of this, only three stations out of nearly 60 are built near ground level and three more above the ground. Some stations and tunnels lie as deep as below the surface. However, the location of the world's deepest station is not clear. Usually, the vertical distance between the ground level and the rail is used to represent the depth. Among the possible candidates are: * Deepest stations in , Russia: ** ' (''The Admiralty'', , opened 2011, probably the best candidate) ** ' (''The Commandant Avenue'', , opened 2005) ** ' (', , opened 1958) ** ' ('' Square'', , opened 1958) * ' station in , Ukraine (, opened 1960, built under a hill) *' in , China (, opened in 2016) *''Liyuchi station'' in , China (, opened in 2017) * ' station in (~, opened 2005, built under a hill) * ''Puhung'' station in , North Korea (which doubles as a ) * ' station in Portland, Oregon (built under a hill), 260 feet (80 m) One advantage of deep tunnels is that they can dip in a basin-like profile between stations, without incurring the significant extra costs associated with digging near ground level. This technique, also referred to as putting stations "on humps", allows gravity to assist the trains as they accelerate from one station and brake at the next. It was used as early as 1890 on parts of the and has been used many times since, particularly in Montreal. The , an extension of the serving western Hong Kong Island, opened in 2015, has two stations ( and ) situated over below ground level, to serve passengers on the . They have several entrances/exits equipped with high-speed lifts, instead of . These kinds of exits have existed in many London Underground stations and other stations in former Soviet Union nations.

Elevated railways

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. ). 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 , London's , the , and the .


Stations function as 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 or s. Underground stations, especially deep-level ones, increase the overall transport time: long rides to the platforms mean that the stations can become bottlenecks if not adequately built. Some underground and elevated stations are integrated into vast or networks respectively, that connect to nearby commercial buildings. In suburbs, there may be a "" connected to the station. To allow easy access to the trains, the allows step-free access between platform and train. If the station complies with standards, it allows both disabled people and those with wheeled baggage easy access to the trains, though if the track is curved there can be a . Some stations use to increase safety by preventing people falling onto the tracks, as well as reducing ventilation costs. The deepest station in the world is in (105.5 m). Particularly in the former and other Eastern European countries, but to an increasing extent elsewhere, the stations were built with splendid decorations such as walls, polished floors and mosaics—thus exposing the public to art in their everyday life, outside galleries and museums. The systems in , , and are widely regarded as some of the most beautiful in the world. Several other cities such as , , , and have also focused on art, which may range from decorative wall claddings, to large, flamboyant artistic schemes integrated with station architecture, to displays of ancient artifacts recovered during station construction. It may be possible to profit by attracting more passengers by spending relatively small amounts on grand , art, , , and a feeling of .

Crew size and automation

In the early days of underground railways, at least two staff members were needed to operated each train: one or more attendants (also called "" or "guard") to operate the doors or gates, as well as a driver (also called the "" or "motorman"). The introduction of powered doors around 1920 permitted crew sizes to be reduced, and trains in many cities are now operated by . Where the operator would not be able to see the whole side of the train to tell whether the doors can be safely closed, s or monitors are often provided for that purpose. A replacement system for human drivers became available in the 1960s, with the advancement of ized technologies for and, later, (ATO). ATO could start a train, accelerate to the correct speed, and stop automatically in the correct position at the at the next station, while taking into account the information that a human driver would obtain from or . The first metro line to use this technology in its entirety was London's , 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 network in the San Francisco Bay Area. A variant of ATO, "driverless train operation" (DTO) or technically "GoA 3", is seen on some systems, as in London's , 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 s do. When the initially increasing costs for began to decrease, this became a financially attractive option for employers. At the same time, countervailing arguments stated that in an 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 if needed, or call for the correct 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 line in Toronto. Completely unmanned 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 lines. One of the first such systems was the (''véhicule automatique léger'' or "automated light vehicle"), first used in 1983 on the in France. Additional VAL lines have been built in other cities such as , France, and , Italy. Another system that uses unmanned trains is , originally developed by the as the (ICTS). It was later used on the in Vancouver, British Columbia, which carries no crew members, and the in Kuala Lumpur, Malaysia. Systems that use automatic trains also commonly employ full-height or half-height s in order to improve safety and ensure passenger confidence, but this is not universal, as networks like do not, using instead to detect obstacles on the track. Conversely, some lines which retain drivers or manual train operation nevertheless use PSDs, notably London's . The first network to install PSDs on an already operational system was , followed by the Singapore MRT. As for larger trains, the has human drivers on most lines but runs automated trains on its newest line, , which opened in 1998. The older was subsequently converted to unattended operation by 2012, and it is expected that will follow by 2019. The in Singapore, which opened in 2003, is the world's first fully automated underground urban heavy-rail line. The MTR is also automated, along with trains on the .

Modal tradeoffs and interconnections

Since the 1980s, s have incorporated several features of rapid transit: systems (trams) run on their own , thus avoiding ; they remain on the same level as buses and cars. Some light rail systems have elevated or underground sections. Both new and upgraded tram systems allow faster speed and higher capacity, and are a cheap alternative to construction of rapid transit, especially in smaller cities. A 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, s were constructed as 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 . Suburban 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, Jakarta's , , , Danish 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 , , of the , , etc.) have lines that fan out to reach the outer suburbs. With some other urban or "near urban" rapid transit systems (, , and , etc.) serving bi- and multi-nucleus . Some cities have opted for two tiers of urban railways: an urban rapid transit system (such as the , , , , , and ) and a suburban system (such as their counterparts , , future & , , , and respectively). Such systems are known variously as s, suburban service, or (sometimes) regional rail. The suburban systems may have their own purpose built trackage, run at similar "rapid transit-like" frequencies, and (in many countries) are operated by the national railway company. In some cities these suburban services run through tunnels in the city center and have direct transfers to the rapid transit system, on the same or adjoining platforms.White, 2002: 63–64 's , 's and 's 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 with intervals dropping to typical rapid transit headways.

Costs, benefits, and impacts

, 212 cities have built rapid transit systems. The is high, as is the risk of and benefit shortfall; is normally required. Rapid transit is sometimes seen as an alternative to an extensive system with many s;Banister and Berechman, 2000: 258 the rapid transit system allows higher capacity with less land use, less environmental impact, and a lower cost. Elevated or underground systems in city centers allow the transport of people without occupying expensive land, and permit the city to develop compactly without physical barriers. s often depress nearby residential s, but proximity to a rapid transit station often triggers commercial and residential growth, with large office and housing blocks being constructed. Also, an efficient transit system can decrease the economic welfare loss caused by the increase of in a metropolis. Rapid transit systems have high s. Most systems are publicly owned, by either local governments, 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 s. The transit systems may be operated by the owner or by a private company through a . The owners of the systems often also own the connecting bus or rail systems, or are members of the local , allowing for between modes. Almost all transit systems operate at a deficit, requiring , and to cover costs. The , a ratio of ticket income to operating costs, is often used to assess operational profitability, with some systems including Hong Kong's , and achieving recovery ratios of well over 100%. This ignores both heavy capital costs incurred in building the system, which are often subsidized with s and whose is excluded from calculations of profitability, as well as ancillary revenue such as income from portfolios. Some systems, particularly Hong Kong's, extensions are partly financed by the sale of land whose value has appreciated by the new access the extension has brought to the area,Kjenstad, 1994: 46 a process known as . Urban land-use planning policies are essential for the success of rapid transit systems, particularly as mass transit is not feasible in low-density communities. Transportation planners estimate that to support rapid rail services, there must be a residential housing density of twelve dwelling units per acre.

See also

* * * * * *




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

External links

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