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 ticketing ticket has been resold can be a difficult and time-consuming process. In an attempt to reduce the numbers of Travelcards being used by more than one person, an experiment took place at Brixton station in 2002. A box was provided at the station exit into which passengers were encouraged to deposit Travelcards that were no longer required, and for each ticket deposited London Underground made a small donation to local charities for the homeless. London Underground ticket machines in all stations support the following 17 languages: English, Spanish, French, German, Italian, Japanese, Arabic, Bengali, Chinese, Greek, Gujarati, Hindi, Polish, Punjabi,