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
London Underground well as many of London's bus and tram operators. Only the Metropolitan Railway, along with its subsidiaries the Great Northern & City Railway and the East London Railway, and the Waterloo & City Railway, by then owned by the main line London and South Western Railway, remained outside the Underground Group's control. A joint marketing agreement between most of the companies in the early years of the 20th century included maps, joint publicity, through ticketing and UD signs, incorporating the first bullseye symbol, outside stations in Central London. At time, the term Underground was selected from three other proposed names;