- This article talks about urban rail systems with certain characteristics, usually running mostly grade-separated with relatively high capacity. For a treatment of transit in cities in general, including terminology, see urban rail transit. For systems built to lower standards, usually with street-running and lower capacity, see light rail.
- For other meanings of terms that redirect here, see subway (disambiguation) and metro (disambiguation). For systems named Metro, see list of metro systems.
An urban heavy rail (metro, subway, elevated) system is a railroad system, usually in an urban area, that usually has high capacity, with large trains and total grade separation. In larger metropolitan areas the subway or metro system may extend only to the limits of the central city, or to its inner ring of suburbs, with the trains making relatively frequent station stops. The outer suburbs may then be reached by a separate regional rail network, which typically runs faster but less frequently and for higher prices.
Many suburban railways were first built to operate in one direction from a city-center terminus, but some have been extended across the city center, sometimes running in tunnel. By making multiple stops in the city, they can offer suburban passengers a choice of stations, and also provide useful transportation within the city. A notable example is the Paris RER system, where (in cooperation with the city's transit authority) several pairs of existing suburban lines running in opposite directions from the city have been extended in tunnel to join up and form new through routes across the city. They are provided with frequent service and, within the city, the same fares as the Métro are charged, providing an integrated network.
In some cases, such as the San Francisco Bay Area Rapid Transit (BART) and Washington Metrorail systems, the heavy rail system itself runs to the suburbs and effectively functions as a regional rail service as well. Where there are separate systems, the metro is typically a self-contained service with its own dedicated tracks and stations and technologically incompatible with other railway. Suburban rail services, on the other hand, often share tracks and stations with long-distance trains (historically they were usually operated by the same company, although this has become less common) and are subject to the same standards and regulations. There are exceptions; some London Underground lines share track with suburban rail services. In some cases metro lines have been extended by taking over existing regional rail lines, notably the Central and Northern Lines in London.
Elevated railways were a popular way to build mass transit systems in cities around the turn of the twentieth century, but they have fallen out of favor and many elevated lines were later demolished, being replaced by subways or buses. Some new elevated lines have been built in the late twentieth century, including monorails and the AirTrain JFK; these are typically seen as more futuristic, and often cast smaller shadows.
Importance, functions and metro station design
The volume of passengers a metro train can carry is often quite high, and a metro system is often viewed as the backbone of a large city's public transportation system.
In some cities, the urban rail system is so comprehensive and efficent that the majority of city residents go without an automobile. Paris and London arguably have the best subway systems in the world, while New York City's system is the only American city on the same level. Chicago and Boston follow New York distantly, while the rest of the cities in the United States only have partial or poorly used systems, such as Saint Louis or Detroit. In the Western Hemisphere, Mexico City also has a large system.
Most underground systems are for public transportation, but a few cities have built freight or postal lines. One example was the Post Office Railway, which transported mail underground between sorting offices in London from 1927 until it was "mothballed " in 2003. During the Cold War an important secondary function of some underground systems was to provide shelter in case of a nuclear attack. Another example was the Chicago Freight Subway, which had a dense grid of tunnels under downtown Chicago.
Urban rail systems have often been used to showcase economical, social, and technological achievements of a nation, especially in the Soviet Union and other socialist countries. With their marble walls, polished granite floors and splendid mosaics, the metro systems of Moscow and St. Petersburg are widely regarded as some of the most beautiful in the world. Modern metro stations in Russia are usually still built with the same emphasis on appearance. Similarly, the Independent Subway System in New York City was built to compete with the private and systems, and succeeded in running them out of business (in conjunction with other factors, such as fare limits).
Metro stations, more so than railway and bus stations, often have a characteristic artistic design which can identify each stop. Some have sculptures or frescos. For example, London's Baker Street station is adorned with tiles depicting Sherlock Holmes. Every metro station in Valencia, Spain has a different sculpture on the ticket-hall level. Alameda station is decorated with fragments of while tile, like the dominant style of the Ciutat de les Arts i les Ciències.
Some urban rail lines are built to the full size of main-line railways; others use smaller tunnels, restricting the size and sometimes the shape of the trains (in London the informal term tube train is commonly used). Some lines use light rail rolling stock, perhaps surface cars simply routed into a tunnel. In many cities, such as Boston, lines using different types of vehicles are organized into a single unified system (though often not connected by track).
Most metro trains are electric multiple units, with steel wheels running on two steel rails. Power is commonly supplied by means of a single live third rail (as in New York) at 600 to 750 volts, but some systems use two live rails (London) and thus eliminate the return current from the running rails. Overhead wires, allowing higher voltages, are more likely to be used on metro systems without much length in tunnel, as in Amsterdam ; but they also occur on some that are underground, as in (Madrid).
Older systems generally use DC power rather than AC, even though this requires large rectifiers for the power supply. DC motors were formerly more efficient for railway applications, and once a DC system is in place, converting it to AC is generally considered too large a project to contemplate.
An alternative technology using rubber tires on narrow concrete or steel rollways was pioneered on the Paris Metro, and the first complete system to use it was in Montreal. Additional horizontal wheels are required for guidance, and a conventional track is often provided in case of flat tires and for switching.
Some cities with steep hills have underground lines using mountain railway technologies. The Lyon Metro includes a section of rack (cog) railway, while the Carmelit in Haifa is an underground funicular.
For elevated lines, still another alternative is the monorail. Supported monorails, with a single rail below the train, include the Tokyo Monorail; the Schwebebahn in Wuppertal is a suspended monorail, where the train body hangs below the wheels and rail.
Drivers and automation
Traditionally, metro trains are driven by human drivers, but automated trains also exist, for example, in London (the Victoria Line), Singapore, and Paris. This is not a recent innovation; operation of trains on the Victoria Line has been automatic since its opening in 1968. In common with most systems, however, an operator is still carried in a cab at the front of the train.
The VAL (véhicule automatique léger, i.e. "automated light vehicle") of Lille, France, inaugurated in 1983, was the first driverless underground system in the world, with no operator carried in the cab at the front of the train. It was followed by another VAL metro system in Toulouse, France, in 1993 (one line at the moment, second to be opened in 2007). Other driverless lines include the Vancouver SkyTrain (1985), London's Docklands Light Railway (1987), and line 14 (Meteor) of the Paris Metro, opened in 1998. Singapore's North East MRT Line (2003) claims to be the world's first fully automated underground urban heavy rail line.
- See also People mover.
The construction of an underground metro is an expensive project, 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 streets are excavated and a tunnel structure strong enough to support the road above is built at the trench, which is then filled in and the roadway rebuilt. This method (used for most of the underground parts of the São Paulo metro, for example) often involves extensive relocation of the utilities commonly buried not far below city streets – particularly power and telephone wiring, water and gas mains, and sewers. 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; in Toronto, a temporary surface on Yonge Street supported cars and streetcar tracks for several years while the Yonge subway was built.
Some American cities, like Cincinnati and Rochester, were initially built around canals. When the railways replaced canals, they were able to bury a subway in the disused canal's trench, without rerouting other utilities, or acquiring a right of way piecemeal.
Another usual way is to start with a vertical shaft and then dig the tunnels horizontally from there, often with a tunnelling shield, thus avoiding almost any disturbance to existing streets, buildings, and utilities. But problems with ground water are more likely, and tunnelling through native bedrock may require 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 specialised tunnel-boring machines are now available to overcome this challenge. One disadvantage with this, however, is that the cost of tunnelling is much higher than building systems cut-and-cover, at-grade or elevated. Early tunnelling machines could not make tunnels large enough for conventional railway equipment, necessitating special low, round trains, such as are still used by most of the London Underground, which cannot install air conditioning on most of its lines because the amount of empty space between the trains and tunnel walls is so small.
The deepest metro system in the world was built in St. Petersburg, Russia. In this city, built in the marshland, stable soil starts more than 50 metres 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 the ground level and three more above the ground. Some stations and tunnels lie as deep as 100-120 meters below the surface. However, the location of the world's deepest station is not as 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 St. Petersburg, Russia:
- Admiraltejskaya (The Admiralty, 102 meters, still in construction, probably the best candidate)
Komendantskij Prospekt (The Commandant Avenue, 78 meters, launched 2005)
Chernishevskaya (Chernyshevsky , 74 meters, launched 1958)
Ploshad Lenina (Lenin Square, 72 meters, launched 1958)
Arsenalnaya station in Kiev, Ukraine (built under a hill)
Park Pobedy station in Moscow Metro (built under a hill)
Puhung station in Pyongyang, North Korea (the Pyongyang metro doubles as a nuclear shelter)
Washington Park station on Metropolitan Area Express 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 significant extra costs due to having to dig deeper. 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.
In 1850 the Long Island Rail Road bricked over the Atlantic Avenue Tunnel (which had been an open cut), carrying its line for about 2750 feet (850 m) under the streets of Brooklyn (now part of New York City). Although sometimes called the "world's oldest subway tunnel", this had no stations and was used for long-distance as well as suburban trains. Today is would be categorized as a regional rail line.
The first real underground line in the sense discussed here was the Metropolitan Railway in London, which opened in 1863, using the era's most advanced propulsive technology: steam locomotives, designed to condense their exhaust steam when in the tunnels. It was an immediate success and many extensions followed; the Metropolitan eventually became an important part of the London Underground system. Steam operations underground lasted until 1905.
The first elevated railway in the world was the Ninth Avenue Elevated in New York City, opened in 1868 as a cable car and later converted for steam and then electric operation. Elevated railways were seen as a cheaper alternative to subways, but were often seen as dirty, ugly and dangerous.
In 1870 short single-track lines opened in both New York and London using alternative technologies, neither of which was a success. In New York, Alfred Beach built a 95 m tunnel (with a single station and a dead end at the other end) to demonstrate pneumatic train operation; this operated until 1873, after which the tunnel became a rifle range and was then abandoned. In London, the Tower Subway provided a crossing under the River Thames using a tiny cable car for the 410 m journey; the line closed in a matter of months and the tunnel was given over to pedestrians, later becoming a utility conduit.
The first deep-level underground line (other than the Tower Subway) was the City and South London Railway, which opened in 1890. Steam operation being considered ridiculous in view of the limited ventilation so far underground, cable traction was chosen; but during construction the management decided to try electric locomotives instead, and so the C&SLR became the first underground electric railway. It too is now part of the London Underground.
The first line of the Chicago 'L' opened in 1892; most of Chicago's system is still elevated, but a few subways have been built, the first opening in 1943.
The first underground railway in continental Europe was completed in Budapest in 1896, after only two years of construction, from Vörösmarty tér (the city centre) to Városliget and the local zoo. This line, now part of the Budapest Metro, stretched 3.7 km (2.3 mi). The 10.4 km (6.5 mi) Glasgow Subway in Scotland opened the same year and used cable haulage, until it was electrified in 1935.
The first line of the Paris Metro opened in 1900. Its full name was the Chemin de Fer Métropolitain, a direct translation into French of London's Metropolitan Railway. The name was shortened to métro, and this word has since been borrowed by many other languages.
Boston has the oldest subway tunnel in the United States, part of the Green Line downtown, dating from 1897. The original construction was a short four-track tunnel downtown, with only two stations, built to take light rail cars from outlying areas off the streets. Later subways in Boston carried full-size trains; the Green Line still operates with light rail equipment. In 1901, heavy rail trains began to use the tunnel as part of the original configuration of the Main Line Elevated , the first elevated railway in Boston.
The New York City Subway, which has become the world's largest (by some measures), did not open its first section until 1904, but this was a fully separate four-track line, stretching 9 miles (14.5 km) from City Hall to 145th Street . Extensions were soon built, reaching the Bronx and Brooklyn; this is now part of the IRT system. Subway trains now run on right-of-way first used in 1863, and converted R44 cars run on the 1860 Staten Island Railway.
In 1907, the first line in Philadelphia, now part of the Market-Frankford Line, began running on both elevated and underground structures.
The oldest subway in the Southern Hemisphere opened in 1913 in Buenos Aires, Argentina, which is also the oldest one in Latin America and the whole Spanish-speaking world . The system is now known as el subte.
On 1923 the Mancomunitat de Catalunya opened the Barcelona Metro.
Asia's oldest subway line is Tokyo's Ginza Line, opened in 1927. Now there are 12 subway lines running on about 150 miles of track. Other major Japanese cities also have subway systems, including Yokohama, Osaka, Nagoya, Sapporo, Kobe, Kyoto, Fukuoka, and Sendai.
The Toronto Subway (1954) used the first aluminum subway car (which was at the time also the longest car in the world), which reduced weight and therefore operating costs.
In Brazil, the first underground opened in 1974 in São Paulo, and now carries some 4 million passengers on an average week day as part of the São Paulo Metro. Part of it consists of converted older railways; some of its stations actually date from the 1880s. Underground lines have been built also in Rio de Janeiro, Belo Horizonte, Recife, Porto Alegre and Brasília.
The Washington Metro in Washington, DC opened in 1976, as part of changing attitudes towards transportation in the United States, leading to subway systems in many systems that had done without.
In 1979, Hong Kong's subway line, now called MTR, began operations. It currently has six lines, including four that run underneath Victoria Harbor.
Recent developments include new elevated lines such as AirTrain JFK in New York City and Hudson-Bergen Light Rail across the Hudson River in New Jersey. These are often seen as futuristic, and are compared favorably to old-style els.
Many older subway systems were originally constructed by private enterprise, either independently as in London, or under a government franchise as in Paris. Later, direct government control and ownership became the norm, although in recent years, this trend has been reversed to some extent.
Whatever its original financing, any metro system requires ongoing expenditure to maintain and replace its trains, tracks, tunnels, and other infrastructure. An underfinanced system will become unreliable and unpleasant to use, and eventually unsafe, and thus will lose public support.
In the United States, the lack of metro, subway, or rapid transit systems except in a few of the larger cities has been attributed to the influence of the automotive industry and oil refining companies, which essentially used automobiles, buses, and advocacy of public road-funding to compete effectively against existing streetcar and trolley systems. These went into decline early in the twentieth century as the public chose personal over public transportation.