London Underground at +420 V, giving a potential difference of 630 V. On the sections of line shared with mainline trains, such as the District line from East Putney to Wimbledon and Gunnersbury to Richmond, and the Bakerloo line north of Queen's Park, the centre rail is bonded to the running rails. The average speed on the Underground is 20.5 mph. Outside the tunnels of central London, many lines' trains tend to travel at over 40 mph in the suburban and countryside areas. The Metropolitan line can reach speeds of 62 mph. The London Underground was used by 1.379 billion passengers in
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