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) Ilford carriage depot. The extension transferred to London Underground management in 1949, when Epping began to be served by Central line trains. The single line to Ongar was served by a steam autotrain operated by British Rail (BR) until 1957, when the line was electrified. BR trains accessed the line via a link from Temple Mills East to Leyton. The Central line stations east of Stratford kept their goods service for a time, being worked from Temple Mills, with the Hainault loop stations served via Woodford. The BR line south of Newbury Park closed in 1956 and Hainault loop stations