3 Metro trains

Greenbelt station, end of the Green line on the Washington MetroThe Washington Metro is the public transportation system of Washington DC and adjoining regions of Maryland and Virginia. It is owned and operated by the Washington Metropolitan Area Transit Authority (WMATA), a multijurisdictional agency funded by the Di

Some metro systems 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), or use light rail rolling stock. The trains usually stop at frequent intervals to let passengers on or off.

4 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.

5 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.

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 moslty 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.

Underground systems use a variety of technologies. Most systems run on steel wheels and rails, although a number of modern systems use rubber tires and concrete rollways. (The Montreal metro was the first completely rubber-tired metro system.) Power is usually supplied either by means of a single third rail ( New York), but some systems use two live rails ( London) or overhead lines ( Madrid). Systems may be underground, at grade, elevated, or a mix as in the Paris metro. Some systems use light rail; other cities' systems are hybrids wherein a tramway moves underground in the city centre.

Due to the complexity of construction and operations, underground systems need constant investment from the public authority, to avoid disasters like King's Cross fire in London's Underground.

6 History

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 condensing steam locomotives as no better motive power was available. 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 was the City and South London Railway, which opened in 1890. Steam operation being considered ridiculous, 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.

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 fürdo as the first electric underground (Földalatti) line on the European mainland.

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. 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.

thumb Helsinki metro, the northernmost metro system in the world, began operating in 1982.

The oldest underground in Latin America opened in 1913 in Buenos Aires, Argentina. UrbanRail

The Toronto subway (1953) 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.

Asia's oldest subway line is Tokyo's Ginza Line, opened in 1927.

7 See also

• List of metro systems
• metro station
• U-Bahn
• advanced light rapid transit
• monorail
• Metrophile (A person with a devoted interest in these systems) .

8 External links

• UrbanRail.Net (formerly called metroPlanet) – descriptions of all metro systems in the world, each with a schematic map showing all stations.
• Metropla.net
• Comparison of world subway systems at the same scale.
• "Mind the Gap".
• Memoirs of a subway musician This musician played in the subway stations of NYC, Paris, Prague & Rome.

Metro Rail transport

<Hide>