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 with a few stations to the south of River Thames. The only London Underground stations in Zones 7 to 9 are on the Metropolitan line beyond Moor Park, outside Greater London. Some stations are in two zones, and the cheapest fare applies. Paper tickets, the contactless Oyster cards, contactless debit or credit cards and Apple Pay and Android Pay smartphones and watches can be used for travel. Single and return tickets are available in either format, but Travelcards (season tickets) for longer than a day are available only on Oyster cards. TfL introduced the Oyster card in 2003; this is