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 saw an end to years of speculation about its future. There is only one intermediate station, at Emerson Park. At the connection west of the station to the main line was severed in 1968. The branch has just one signal, on approach to Romford. There were plans to link the line from platform six at Upminster to the reception tracks of the London Underground depot there. This would have allowed the transfer of London Underground D78 Stock units onto the main line to be hauled away by diesel locomotive for refurbishment at the Ilford depot. These plans were scrapped when