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
Central line (London Underground) by escalators. The Central London Railway was absorbed into the Underground Group on 1 January 1913. In 1911, the Great Western Railway won permission for a line from Ealing Broadway to a station near to the CLR's Shepherd's Bush station, with a connection to the West London Railway, and agreement to connect the line to the Central London Railway and for the CLR to run trains to Ealing Broadway. Construction of the extension from the CLR to Ealing Broadway started in 1912 but opening was delayed by World War I. The CLR purchased new rolling stock for the extension, which