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
Urban rail in the United Kingdom Line, via tunnels through central London, with a branch to . It is the largest construction project in Europe. Crossrail will start a full service in 2018, taking over suburban services operated by Abellio Greater Anglia to Shenfield, Heathrow Connect to Heathrow Airport and First Great Western to Reading. Once opened, Crossrail will be one of three partially underground suburban rail networks in the United Kingdom as the network cannot be classed as a Metro system like the London Underground or the Glasgow Subway. The Merseyrail and Glasgow commuter rail networks also have below ground stations. Crossrail 2 is a