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 bring the total of step-free stations to over 100. In mid-2012 London Underground, in partnership with Virgin Media, tried out Wi-Fi hot spots in many stations, but not in the tunnels, that allowed passengers free internet access. The free trial proved successful and was extended to the end of 2012 whereupon it switched to a service freely available to subscribers to Virgin Media and others, or as a paid-for service. It is not currently possible to use mobile phones underground using native 2G, 3G or 4G networks, and a project to extend coverage before the 2012 Olympics was abandoned because