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 infrastructure lines share all their stations and most of the track with other lines. The Bakerloo, Central, Jubilee, Northern, Piccadilly, Victoria and Waterloo & City lines are deep-level tubes, with smaller trains that run in two circular tunnels with a diameter of about , lined with cast-iron or precast concrete rings, which were bored using a tunnelling shield. It is these that were the "tube" lines, although since the 1950s the term "tube" has come to be used to refer to the whole London Underground system. Many of the central London deep-tube line stations, such as those on the Central and