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) GER on 1 May 1903. The line has three junctions: The line has the shortest escalator on the London Underground system, at Stratford (previously at Chancery Lane), with a rise of and at Stratford and Greenford the only stations where escalators take passengers up to the trains. That at Greenford was the last escalator with wooden treads on the system until it was replaced in March 2014. They were exempt from fire regulations because they were outside the tunnel system. The line has the shallowest Tube platforms on the system, at Redbridge, just below the road, and the sharpest curve,