Rapid transit
The underground, subway or metro are common names for a form of mass transit public transport system, employing small trains where at least a portion of the rails are placed in tunnels dug beneath the surface of a city.
Underground trains are generally classed as a form of public transportation. An exception to this, perhaps, is a short, driverless, underground railway in London used exclusively to transport mail between sorting offices.
A bewildering flora of names have grown up that all refer to this kind of transportation, but by virtue of being the first in operation, the London Underground has given its name to this article about the phenomenon itself.
For a more comprehensive listing of other names of this kind of system in cities around the world, see the list of underground railway systems.
The underground trains usually stop at short intervals to let passengers on or off. The volume of passengers an underground train can carry is often quite high, and an underground system is often viewed as the backbone of a large city's public transportation system.
Traditionally, underground trains are driven by human drivers, but automated trains also exist, in, for example, London (the Victoria Line, Singapore, and Paris (Line 14 (Meteor) of the Metro). This is not a recent invention; 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 construction of an underground is an expensive project, often carried out over a number of years. Several modes of tunneling exist. One common method is to place the tracks directly beneath the city streets, upholding the roads by concrete pillars (parts of the New York Subway system are constructed in this manner, known as Cut-and-cover). Another usual way is to dig the tunnels (often with Tunnelling shield) beneath previously occupied subterranean space, through native bedrock, and seal the tunnels from leakage of ground water with concrete.
Underground systems use a variety of technologies. Most systems run on steel wheels and rails, although many modern systems use rubber tires and concrete rollways. (The Montreal metro was the first completely rubber-tired system.) Power may be supplied either with a third rail (New York) or overhead (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.
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.
Underground systems need constant investment from the public authority, to avoid disasters like King's Cross fire in London's underground.
History
The oldest subway tunnel in the world is the Atlantic Avenue Tunnel, built in 1844.
Boston has the the oldest subway system in the United States.
Alfred Beach's first New York Subway system used a pneumatic tube principle. It was only 300 feet long.
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The underground is sometimes a nickname for a resistance movement: "the underground" is also a common name for World War II resistance movements. By extension, the term was also applied to counter-cultural movement(s) many of which sprang up during the 1960s. In a similar sense, the Underground Railroad was an United States anti-slavery movement which helped slaves escape.
During the 1960s the term acquired a new nuance in that it referred to members of the counterculture, i.e. those people who did not necessarily conform to the mainstream of human experience such as e.g. hippies.