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
Attacks on the London Underground in London. On 7 July 2005, bombs exploded on Underground trains between Aldgate and Liverpool Street stations, Russell Square and King's Cross St. Pancras stations and Edgware Road and Paddington stations. A double-decker bus at Tavistock Square was also destroyed. The bombs were detonated by four homegrown terrorist suicide bombers. The explosions killed 52 people and resulted in over 700 injuries. Four more attacks, unconnected with those on 7 July, were attempted on 21 July 2005 at Shepherd's Bush Market, Warren Street and Oval stations, as well as on a bus in Bethnal Green. In these incidents, each bomb detonator