What is the Tube?
Background - A Short Summary
The Tube, officially called the London Underground but mostly called "the Tube", is one of the major urban transportation systems in the world. This article is a short description of the London Underground, giving a flavour of the size and importance of the railway to London.
A link to a map of the system is in the right hand column. It's from the official website and it's a large file so it might take a while to download.
The System
The Official Map
Why "the Tube"?
The name comes from the small circular tunnels some of the lines have. The track for each direction runs in its own circular iron tube about 3.5m (12ft) in diameter.
The London Underground (official web site) is one of the world's largest urban rapid transit systems.
It has 11 lines and serves 269 stations, which provide services for up to twenty hours a day.
The system is operated by London Underground, part of the Transport for London (TfL) organisation.
London is one of the world's major capital cities. Greater London has an area of 618 square miles and a population of over 7 million.
Over a million people travel into central London each day for work and over 60% of these use the London Underground system.
Over the last fifteen years there has been a 70% increase in the demand for travel on the Underground so that, more than ever before, London relies upon the Underground system as part of the social and economic structure of the city.
On occasions, the number of passenger journeys exceeded 4 million a day. The central area of London is enclosed by the major main line railway termini and the Underground's Circle Line which connects them.
This area within the Circle Line forms the commercial heart of the capital.
The City, east of Holborn, is the financial district while the West End contains the principal shopping and entertainment areas.
Until the beginning of the twentieth century there was virtually no penetration of these areas by railways but then the various deep level Underground "tube" lines were opened and now there is a network of lines covering both the City and West End zones and connecting them with many of the suburbs.
The routes to the suburbs rise to the surface outside the central area of London and, in fact, more of the London Underground is in the open than in tunnel.
The greater London area is geographically divided into two halves by the River Thames which flows west to east across the city. In the north-south division which this causes, by far the greater proportion of the Underground system is located in the northern area.
Of the 268 stations served the system only 25 are located south of the Thames, due partly to old railway company politics and partly to the nature of the subsoil, which rendered tube construction difficult and expensive.
In contrast with the freight rich railway companies north of the river, the southern companies depended very much on local passenger traffic for revenue and provided a dense network of frequent services which were electrified almost entirely by 1930 and in some cases before 1914.
Two Sizes of Trains
This photo, taken some years ago, shows the two types of LU trains (tube and sub-surface) at Stamford Brook, District Line. The smaller tube train is on the Piccadilly Line while the Larger train is on the District Line. Photo by Brian Hardy.
One of the features of the London Underground is that it operates trains of two different sizes. This is because of the two tunnel sizes adopted over the long period of its development.
The differing sizes were due to the different methods of construction. The original method, used for the Circle Line and its extensions (now the Metropolitan and District Lines) is known as the "cut and cover" method.
A cutting is excavated along the line of route just deep enough to take a normal-sized train. When completed the tunnel is roofed over and the surface restored, often with a roadway.
Most of the resulting tunnels are wide enough to take two tracks, except at stations where they are further widened to take platforms and stairways.
Because of their proximity to the surface they are often referred to as "the surface" lines, even the sections which are underground. More correctly, they should be referred to as sub-surface lines.
The second type of tunnel is the deep level "tube" tunnel.
This method of construction was adopted to overcome the acute surface disruption caused by the cut and cover method and it took advantage of the blue clay upon which London is built.
Single track, circular tunnels of just under 3.4 m diameter (11 ft. 8½ ins.) were bored at a level deep enough to avoid conflicts with water mains, sewers and other underground services.
Tunnels bored since the 1930s are to a standard 12 ft diameter.
Tube station tunnels are generally 21 - 25 ft diameter.
The greater depth of these lines (an average of 20 metres) meant that lifts or escalators are provided for street access.
The technology of deep level tube construction was available quite early on in the development of railways but it had to await a practical means of propulsion without smoke and steam.
The trains in the tube tunnels are smaller than those used on the sub-surface lines.
The train floors are about 300 mm (1 foot) lower and the roof height is about 1 m lower than a sub-surface train. The train passenger capacities are also lower.
The name "tube" appeared early in the 20th century when the deep level lines first opened with their small diameter tunnels. It is now often used (incorrectly) by the general public to mean any Underground line.
"I'll take the Tube" is an expression commonly heard in London.
The sub surface lines are the Circle, District, Hammersmith & City and Metropolitan Lines. Only the others, the Bakerloo, Central, Jubilee, Northern, Piccadilly, Victoria and Waterloo & City Lines are true tube lines.
Offices and Facilities
The head office of London Underground Ltd. is at 55 Broadway, London SW1 0BH, in a large white stone building built over St James's Park station.
The building itself is an interesting architectural specimen finished in Portland stone and features external sculptures by Eric Aumonier, Henry Moore, Jacob Epstein, Eric Gill and others. It was built in 1929.
In addition to the head office there are a large number of other premises owned by LUL throughout its operating area.
These include 255 of the 275 stations served, 12 major train depots, the Railway Equipment Workshop at Acton, 115 electrical substations and many more installations like signal cabins and control rooms needed for maintaining and operating a large urban railway system.
The company manages a system employing some 13,000 staff in many different jobs, not just in the public eye on trains and stations but in the many behind-the-scenes activities like maintenance, planning, engineering and training.
With the partial privatisation of the system, some 7,000 other staff are employed by the PPP contractors (including the now defunct Metronet) who look after the infrastructure.
Last updated 6th August 2011 © Copyright Tubeprune 2001 - 2011.
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