Circle line (London Underground) with the other London Underground sub-surface lines: the Hammersmith & City line from Hammersmith to just before Aldgate; the Metropolitan line from Baker Street to Aldgate; and the District line from Tower Hill station to Edgware Road station. The line is electrified with a four-rail DC system: a central conductor rail is energised at and a rail outside the running rail at , giving a potential difference of . The running rails are not electrified. Much of the double track railway from the Hammersmith terminus to Westbourne Park station is on a high brick viaduct. East of Westbourne Park the
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,