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
Wimbledon, London Queen's Road and Wimbledon Bridge. The architects were Bradshaw Gass & Hope. By the 1930s, residential expansion had peaked in Wimbledon and the new focus for local growth had moved to neighbouring Morden, which had remained rural until the arrival of the Underground at Morden station in 1926. Wimbledon station was rebuilt by the Southern Railway with a simple Portland stone facade for the opening of a new railway branch line from Wimbledon to Sutton in 1930. Damage to housing stock in Wimbledon and other parts of London during the Second World War led to a final major building phase,