London Underground with smaller trains that run in two circular tunnels ("tubes") with a diameter about . These lines have the exclusive use of a pair of tracks, except for 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 services north of Queen's Park. Fifty-five per cent of the system runs on the surface. There are of cut-and-cover tunnel and of tube tunnel. Many of the central London underground stations on deep-level tube routes
Attacks on the London Underground in London. On 7 July 2005, bombs exploded on Underground trains between Aldgate and Liverpool Street stations, Russell Square and King's Cross St. Pancras stations and Edgware Road and Paddington stations. A double-decker bus at Tavistock Square was also destroyed. The bombs were detonated by four homegrown terrorist suicide bombers. The explosions killed 52 people and resulted in over 700 injuries. Four more attacks, unconnected with those on 7 July, were attempted on 21 July 2005 at Shepherd's Bush Market, Warren Street and Oval stations, as well as on a bus in Bethnal Green. In these incidents, each bomb detonator