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
London Rail Rail Silverlink franchise in 2007. It has since taken on more services through a former London Underground line and over other network rail lines. London Rail lets a concession to operate the Overground. Operation is contracted to Arriva Rail London (owned by Arriva UK Trains) until 2024. London Trams is responsible only for the Croydon Tram known as Tramlink. Tramlink was set up in 2000 by a private finance initiative. It was bought by TfL in 2008 and is operated on its behalf by FirstGroup. London Trams has been working on proposals for other tram schemes in west and central