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 engineering stock London Underground engineering stock Over the years, London Underground has acquired various types of engineering stock to help with the construction of new lines and maintenance of existing lines. Some of these wagons were inherited from its predecessors, many were built new and some were acquired second-hand from the main-line railways. Several types of specialist wagons have been used, which are described below. London Underground uses a numbering system comprising the wagon number prefixed with a letter which designates the wagon's type. These are summarised below. London Underground has used various designs of brake van. They were used for the