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The London Underground is a public transport network, composed of electrified railways (that is, a metro system) that run underground in tunnels in central London and above ground in the city's suburbs. The oldest metropolitan underground network in the world, first operating in 1863, the London Underground is usually referred to as either simply "the Underground" by Londoners, or (more familiarly) as "the Tube".

1 Background

Passengers wait for trains at the northbound platform at Baker Street. Note the brown signage indicating the Bakerloo Line.

Since 2003, the Tube has been part of Transport for London (TfL), which also schedules and lets contracts for the famous red double-decker buses. Previously London Transport was the holding company for London Underground.

There are currently 275 open stations and over 253 miles ( 408 km) of active lines, with three million passenger journeys made each day (927 million journeys made 1999-2000; there are a number of stations and tunnels now closedSt Mary's (Whitechapel Road) tube station shortly after its closure in 1938 Closed tube stations These stations of the London Underground and its predecessor companies (such as the Metropolitan Railway, the City and South London Railway and Underground El).

Lines on the Underground can be classified into two types: sub-surface and deep level. The sub-surface lines were dug by the cut-and-cover method, with the tracks running about 5 metres below the surface. Trains on the sub-surface lines have the same loading gaugeA loading gauge is the envelope or contoured shape within which all railway vehicles, engines, coaches and trucks must fit. It is dictated by the size of tunnels, height of bridges and shape and height of platforms. It varies between different countries a as British mainline trains. The deep-level or "tube" lines, bored using a tunnelling shieldA tunnelling shield is a protective structure used in the excavation of tunnels through soil that is too soft or fluid to remain stable during the time it takes to line the tunnel with a support structure of concrete or steel. In effect, the shield serves, run about 20 metres below the surface (although this varies considerably), with each track running in a separate tunnel lined with cast-iron rings. These tunnels can have a diameter as small as 3.56m (11ft 8.25in) and the loading gauge is thus considerably smaller than on the sub-surface lines, though standard gaugeAs railways developed and expanded one of the key issues to be decided was that of the rail gauge (the distance between the two rails of the track) which should be used. The eventual result was the adoption throughout a large part of the world of a standa track is used. Lines of both types usually emerge onto the surface outside the central area, the exceptions being the Victoria LineThe Victoria Line is a line of the London Underground, coloured light blue on the Tube map. It is a deep-level line running from the south-west to the north-east of London. It was built in the 1960s to relieve congestion on other lines, in particular the which is in tunnel for its entire length save for a maintenance depot, and the Waterloo & City LineThe Waterloo & City Line is a short underground metro line in London, formally opened on 11 July 1898. It has only two stations, Waterloo and Bank (formerly called "City" hence the name of the line), between which it passes under the River Thames. It exis which, being very short, has no non-central part and no surface line.



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