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
Line C (Buenos Aires Underground) Line C (Buenos Aires Underground) Line C of the Buenos Aires Underground, that runs from Retiro to Constitución terminus, opened on 9 November 1934, and it has a length of . It runs under such streets as Lima Sur, Bernardo de Irigoyen, Carlos Pellegrini, Esmeralda, la Plaza San Martín and Avenida Ramos Mejia. It not only connects to every other line on the system (with the exception of Line H, which will be connected at a later date), but its termini at Retiro and Constitución also connect it to some of the most important commuter rail networks in Buenos Aires,