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 prior to the accident. In 1979 another new tube, the Jubilee line, named in honour of Queen Elizabeth's Silver Jubilee, took over the Stanmore branch from the Bakerloo line, linking it to a newly constructed tube between Baker Street and Charing Cross stations. Under the control of the GLC, London Transport introduced a system of fare zones for buses and underground trains that cut the average fare in 1981. Fares increased following a legal challenge but the fare zones were retained, and in the mid-1980s the Travelcard and the Capitalcard were introduced. In 1984 control of London Buses and the