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 station closed permanently to facilitate work on the extension, with services from Whitechapel being replaced by buses. The rest of the East London line closed on 22 December 2007, with rail replacement buses linking the stations north and south of the Thames (but not crossing the river due to height restrictions in the Rotherhithe Tunnel). On 5 September 2006 it was announced that the line would transfer from London Underground to London Overground, branded with a version of the Underground roundel with red replaced by orange, the colour used on Tube maps for the East London Line. Three major new