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
Romford–Upminster line Romford–Upminster line The Romford–Upminster line is a railway branch line in Greater London that connects , on the Great Eastern Main Line, to , on the London, Tilbury and Southend Line and London Underground. The route is in length and there is one intermediate station at . The line is part of Network Rail Strategic Route 7, SRS 07.09, and is classified as a rural line. The line is single-track throughout, electrified at 25 kV AC, has a loading gauge of W6, and a maximum speed of . As of May 2015 services are operated by London Overground, with two