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
Guadalajara light rail system the large numbers of users of the rail system, there are plans to extend Line 2 to the west and to build a third line. Line 1 runs underground in the city center, but runs "at grade" north and south of the city center, and its surface sections include several level crossings, protected by crossing gates. The station platforms accommodate trains composed of no more than two cars. Line 2 is entirely underground except for a non-passenger section at its east end, connecting the last station to the maintenance facility. Its stations are long enough to accommodate trains of up