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
East London line extension East London line extension The East London line extension (ELLX) project was a British railway engineering project in London, managed by Transport for London. The project involved extending the East London Line (formerly part of the London Underground network) and making it part of the mainline London Overground network. This was done by re-opening sections of disused railway line and by converting track electrified by the third-rail system, signalling, lineside signage and communication systems, etc. to mainline standards. New rolling stock was introduced and four new stations built along the route, with a fifth scheduled to be added in the