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
History of the London Underground half of the 19th century, London had grown greatly and the development of a commuting population arriving by train each day led to traffic congestion with carts, cabs and omnibuses filling the roads. By 1850 there were seven railway termini located around the urban centre of London and the concept of an underground railway linking the City of London with these stations was first proposed in the 1830s. Charles Pearson, Solicitor to the City of London, was a leading promoter of several schemes, and he contributed to the creation of the City Terminus Company to build such a railway from