- This page refers to urban rail mass transit systems. For other uses see metro (disambiguation)
Stations of the metro in Athens, Greece double as museums with displays of antiquities found in excavations of its tunnels in the historic city. A Metro is a form of mass transit public transport system employing trains. In many cases, at least a portion of the rails are placed in tunnels dug beneath the surface of a city in which case the system may be called the Underground or the subway.
If the tracks are elevated above the ground it may be called the elevated train, the El-train, The El or The L, e.g. the Chicago L, or Light Railway, e.g. the Docklands Light Railway.
Definition and nomenclature
 Ancient Greece-themed Sportivnaya station, St. Petersburg, Russia. The word "sportivnaya" means "sporty" or "athletic". One definition of a "true" metro system is as follows:
- an urban, electric mass transit system
- totally independent from other traffic
- with high service frequency.
Those who prefer the American term "subway" or the British "underground"
would additionally specify that at least the most important, central parts
of the system must be located below street level; those who prefer "metro"
tend to view this as a less important characteristic and are pleased to
include systems that are entirely elevated or at grade. In some cities
"subway" refers to the entire system, in others only to the portions that actually are underground.
For a more comprehensive listing of other names of this kind of system in cities around the world, see the list of metro systems. Germanic languages
generally use names meaning "underground railway", while many others use
"metro".
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 suburban, commuter,
or regional rail network. Suburban trains typically achieve a higher
average speed by having stops more widely spaced, but may
operate less frequently, sometimes only in rush hours.
Sometimes for political reasons they are operated by a separate authority
that tends not to cooperate with the city's transit authority.
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 suburban lines running in opposite directions from the city have been linked into through routes across the city. They are provided with frequent service and, within the city, the same fares as the Metro are charged, providing an integrated network. In German-speaking countries such a system is called an S-Bahn.
In some cases, such as the San Francisco Bay Area Rapid Transit (BART) and Washington Metrorail systems, the metro 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.
Importance and functions
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.
Most underground systems are for public transportation, but a few cities
have built freight (Chicago Freight Subway) 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.
Metro 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.
Metro trains
Some metro 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 trams
simply routed into a tunnel. In many cities, such as
Boston, lines using
different types of vehicles are organized into a single unified system.
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. However, in common with most systems, 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 the VAL metro system of Toulouse, France, in 1993 (one line at the moment, second to be opened in 2007). Other driverless lines now include the line 14 (Meteor) of the Paris Metro, opened in 1998. The Docklands Light Railway (1987) in London, whilst for the most part not underground, is also driverless. Singapore's North East MRT Line (2003) claims to be the world's first fully automated heavy rail line. See also People mover.
Subway construction
The construction of an underground is an expensive project, often carried out over a number of years. Several modes of tunneling exist. 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. Some American cities, like Cincinnati and Rochester, were initially built around canals. And when the railways replaced canals, they were able to bury a subway in the disused canal's trench, without rerouting other utilities, or aquiring 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 specialized
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.
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 meters deep. Above that level the soil mostly consists of water-bearing finely dispersed sand. Because of this, only 3 stations out of nearly 60 are built near the ground level and 3 more above the ground. Many stations lie as deep as 100 meters below the surface. However, the location of the world's deepest station is not as clear. Among the possible candidates are:
- Admiraltejskaya, Proletarskaya and Komendantskij Prospekt stations in St. Petersburg (currently not operational)
- 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)
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.
History
 Helsinki metro, the northernmost metro system in the world, began operating in 1982. In 1844 the Long Island Rail Road opened the Atlantic Avenue Tunnel, carrying its line for about 500 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.
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 working underground lasted until 1905.
In 1870 short single-track lines opened in both New York and London using alternative technologies. 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 and the first important electric railway of any kind. It too is now part of the London Underground.
The first underground railway in continental Europe was completed in Budapest in 1896, after only two years of construction between Vörösmarty tér in the city centre and Széchenyi fürdő as the first electric underground (Földalatti) line on the European mainland. The Glasgow Subway opened the same year and did use 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 of London's
Metropolitan Railway. The name was shortened to métro in French, and this word was borrowed by many other languages.
Boston has the oldest subway system in the United States, the Green Line, dating from 1897. Later lines carried full-size trains rather
than trams. The New York Subway, which became the world's largest (by some measures), did not open its first section until 1904.
The oldest underground railway 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. UrbanRail (http://www.urbanrail.net/am/buen/buenos-aires.htm)
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, Kyoto, Kobe, Fukuoka, and Sendai.
The Toronto subway (1954) was the first to replace street transit routes. Toronto also developed the aluminum subway car, which reduced 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. 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.
In 1979, Hong Kong's subway line, now called MTR, began operations. It currently has six lines, including four that run underneath Victoria Harbor.
Finance
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 this trend has reversed
to some extent in recent years.
Whatever is original financing, any metro system requires ongoing
expenditure to maintain its trains and tracks replace them when they
wear out, as well as other infrastructure such as the tunnels of an
underground system. An underfinanced system will become unreliable and
unpleasant to use, and eventually unsafe, and thus will lose public support.
See also
External links
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