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 Underground battery-electric locomotives Victoria line ATP equipment which was designed by Metronet BCV on behalf of Transplant, the operator of the fleet. This system was installed during 2007 at Ruislip Depot. It is compatible with the new Distance-to-Go Radio (DTG-R) ATP system which has been implemented on the Victoria line by Westinghouse Rail Systems. The locomotives are, since the start of London Underground's PPP scheme, in the ownership of TransPlant. The locomotives are usually stabled at Lillie Bridge Depot or Ruislip depot. The traditional use of these locomotives has been to haul trains using power from the rails until they reach the area