Yerkes soon had control of the District Railway and established the Underground Electric Railways Company of London (UERL) in 1902 to finance and operate three tube lines, the Baker Street and Waterloo Railway (Bakerloo), the Charing Cross, Euston and Hampstead Railway (Hampstead) and the Great Northern, Piccadilly and Brompton Railway, (Piccadilly), which all opened between 1906 and 1907.[41][42] When the "Bakerloo" was so named in July 1906, The Railway Magazine called it an undignified "gutter title".[42] By 1907 the District and Metropolitan Railways had electrified the underground sections of their lines.[43]
A joint marketing agreement between most of the companies in the early years of the 20th century included maps, joint publicity, through ticketing and UNDERGROUND signs, incorporating the first bullseye symbol,[37] outside stations in Central London.[46] At the time, the term Underground was selected from three other proposed names; 'Tube' and 'Electric' were both officially rejected.[37] Ironically, the term Tube was later adopted alongside the Underground. The Bakerloo line was extended north to Queen's Park to join a new electric line from Euston to Watford, but the First World War delayed construction and trains reached Watford Junction in 1917. During air raids in 1915 people used the tube stations as shelters.[47] An extension of the Central line west to Ealing was also delayed by the war and was completed in 1920.[48] After the war, government-backed financial guarantees were used to expand the network and the tunnels of the City and South London and Hampstead railways were linked at Euston and Kennington;[49] the combined service was not named the Northern line until later.[50] The Metropolitan promoted housing estates near the railway with the "Metro-land" brand and nine housing estates were built near stations on the line. Electrification was extended north from Harrow to Rickmansworth, and branches opened from Rickmansworth to Watford in 1925 and from Wembley Park to Stanmore in 1932.[51][52] The Piccadilly line was extended north to Cockfosters and took over District line branches to Harrow (later Uxbridge) and Hounslow.[53]
In 1933, most of London's underground railways, tramway and bus services were merged to form the London Passenger Transport Board, which used the London Transport brand.[54] The Waterloo & City Railway, which was by then in the ownership of the main line Southern Railway, remained with its existing owners.[55] In the same year that the London Passenger Transport Board was formed, Harry Beck's diagrammatic tube map first appeared.[56]
During the war many tube stations were used as air-raid shelters.[62] They were not always a guarantee of safety however; on 11 January 1941 during the London Blitz, a bomb penetrated the booking hall of Bank Station, the blast from which killed 111 people, many of whom were sleeping in passage ways and on platforms.[63] On 3 March 1943, a test of the air-raid warning sirens, together with the firing of a new type of anti-aircraft rocket, resulted in a crush of people attempting to take shelter in Bethnal Green Underground station. A total of 173 people, including 62 children, died, making this both the worst civilian disaster in Britain during the Second World War, and the largest loss of life in a single incident on the London Underground network.[64]
On 28 February 1975, a southbound train on the Northern City Line failed to stop at its Moorgate terminus and crashed into the wall at the end of the tunnel, in the Moorgate tube crash. There were 43 deaths and 74 injuries, the greatest loss of life during peacetime on the London Underground.[74] In 1976 the Northern City Line was taken over by British Rail and linked up with the main line railway at Finsbury Park, a transfer that had already been planned prior to the accident.[75]
In 1979 another new tube, the Jubilee line, named in honour of Queen Elizabeth's Silver Jubilee, took over the Stanmore branch from the Bakerloo line, linking it to a newly constructed line between Baker Street and Charing Cross stations.[76] Under the control of the GLC, London Transport introduced a system of fare zones for buses and underground trains that cut the average fare in 1981. Fares increased following a legal challenge but the fare zones were retained, and in the mid-1980s the Travelcard and the Capitalcard were introduced.[77]
On 18 November 1987, fire broke out in an escalator at King's Cross St Pancras tube station. The resulting fire cost the lives of 31 people and injured a further 100. London Underground was strongly criticised in the aftermath for its attitude to fires underground, and publication of the report into the fire led to the resignation of senior management of both London Underground and London Regional Transport.[80] Following the fire, substantial improvements to safety on the Tube were implemented - including the banning of smoking, removal of wooden escalators, installation of CCTV and fire detectors, as well as comprehensive radio coverage for the emergency services.[81]
London Underground's eleven lines total 402 kilometres (250 mi) in length,[1] making it the seventh longest metro system in the world. These are made up of the sub-surface network and the deep-tube lines.[1] The Circle, District, Hammersmith & City, and Metropolitan lines form the sub-surface network, with railway tunnels just below the surface and of a similar size to those on British main lines, converging on a bi-directional loop around zone 1. The four sub-surface lines share tracks and stations with each other at various places along their respective routes. The Bakerloo, Central, Jubilee, Northern, Piccadilly, Victoria and Waterloo & City lines are deep-level tubes, with smaller trains that run in circular tunnels (tubes) with a diameter of about 11 feet 8 inches (3.56 m), with one tube for each direction. The seven deep-level lines have the exclusive use of tracks and stations along their routes with the exception of the Piccadilly line, which shares track with the District line between Acton Town and Hanger Lane Junction and with the Metropolitan line between Rayners Lane and Uxbridge; and the Bakerloo line, which shares track with London Overground's Watford DC Line for its above-ground section north of Queen's Park.[107]
Fifty-five per cent of the system runs on the surface. There are 20 miles (32 km) of cut-and-cover tunnel and 93 miles (150 km) of tube tunnel.[1] Many of the central London underground stations on deep-level tube routes are higher than the running lines to assist deceleration when arriving and acceleration when departing.[108] Trains generally run on the left-hand track. In some places, the tunnels are above each other (for example, the Central line east of St Paul's station), or the running tunnels are on the right (for example on the Victoria line between Warren Street and King's Cross St. Pancras, to allow cross-platform interchange with the Northern line at Euston).[107][109]
London Underground trains come in two sizes, larger sub-surface trains and smaller deep-tube trains.[126] Since the early 1960s all passenger trains have been electric multiple units with sliding doors[127] and a train last ran with a guard in 2000.[128] All lines use fixed-length trains with between six and eight cars, except for the Waterloo & City line that uses four cars.[129] New trains are designed for maximum number of standing passengers and for speed of access to the cars and have regenerative braking and public address systems.[130] Since 1999 all new stock has had to comply with accessibility regulations that require such things as access and room for wheelchairs, and the size and location of door controls. All underground trains are required to comply with The Rail Vehicle Accessibility (Non Interoperable Rail System) Regulations 2010 (RVAR 2010) by 2020.[131]
Stock on sub-surface lines is identified by a letter (such as S Stock, used on the Metropolitan line), while tube stock is identified by the year of intended introduction[132] (for example, 1996 Stock, used on the Jubilee line).
When the Bakerloo line opened in 1906, it was advertised with a maximum temperature of 60 F (16 C), but over time the tube tunnels have warmed up.[164] In 1938 approval was given for a ventilation improvement programme, and a refrigeration unit was installed in a lift shaft at Tottenham Court Road.[164] Temperatures of 117 F (47 C) were reported in the 2006 European heat wave.[165] It was claimed in 2002 that, if animals were being transported, temperatures on the Tube would break European Commission animal welfare laws.[166] A 2000 study reported that air quality was seventy-three times worse than at street level, with a passenger inhaling the same mass of particulates during a twenty-minute journey on the Northern line as when smoking a cigarette.[167][168] The main purpose of the London Underground's ventilation fans is to extract hot air from the tunnels,[164] and fans across the network are being refurbished, although complaints of noise from local residents preclude their use at full power at night.[169]
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