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
History of the London Underground of London and especially the Blitz led to the use of many tube stations as air-raid shelters, with 175,000 people arriving every night in August 1940. Six stations were breached by a direct hit, and in March 1943, 173 people died in a crowd crush accident at the unfinished Bethnal Green station. In the 1940s a depot built for the Northern line extension and an unfinished stretch of the Central line extension, the underground section between Newbury Park and Leytonstone, was turned into aircraft factory. The closed Brompton Road station was used as an anti-aircraft control room. The closed Down