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
Art on the Underground Art on the Underground Art on the Underground, previously called "Platform for Art", is a visual arts showcase sponsored by London Underground, the rapid transit system for London, England. London Underground's associations with visual art began in 1908 when its then Publicity Officer Frank Pick began commissioning leading artists to work on poster campaigns for the rapidly expanding network. The company's distinctive corporate image, including official Underground roundel and iconic tube map designed by Harry Beck are also considered major contributions to visual art, and several of the network's stations have been decorated with artistic tiling or murals depicting local