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
Suicide on the London Underground rushes on overhead". A study of 58 cases showed that the presence of a suicide pit halved the number of deaths. Another safety mechanism are platform edge doors (PEDs), which separate the train from the passengers. These are installed exclusively at the below-ground stations of the Jubilee Line Extension. PEDs are expensive to install and can fail to open, adding a potential reliability problem to train services. Alison Wertheimer wrote in 2001 that there were 100–150 suicides annually on the Underground. The annual number of suicides in the 1940s was 25, increasing to 100 by the 1980s, which, according to