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
Romford–Upminster line the refurbishment work was transferred to Wakefield in Yorkshire and the transfer was done by road. The point-work which was half installed is still visible from the eastern end of platform five at Upminster. The line is entirely within Travelcard Zone 6. Services are currently operated by London Overground, which replaced the previous operator, Abellio Greater Anglia, in May 2015. Trains are typically formed by a Class 315 or Class 317. As of December 2015, the service pattern on the route is one train every 30 minutes between approximately 6:15 am and 10 pm Mondays to Saturdays, and approximately 8:30