London Underground at +420 V, giving a potential difference of 630 V. On the sections of line shared with mainline trains, such as the District line from East Putney to Wimbledon and Gunnersbury to Richmond, and the Bakerloo line north of Queen's Park, the centre rail is bonded to the running rails. The average speed on the Underground is 20.5 mph. Outside the tunnels of central London, many lines' trains tend to travel at over 40 mph in the suburban and countryside areas. The Metropolitan line can reach speeds of 62 mph. The London Underground was used by 1.379 billion passengers in
Romford–Upminster line Romford–Upminster line The Romford–Upminster line is a railway branch line in Greater London that connects , on the Great Eastern Main Line, to , on the London, Tilbury and Southend Line and London Underground. The route is in length and there is one intermediate station at . The line is part of Network Rail Strategic Route 7, SRS 07.09, and is classified as a rural line. The line is single-track throughout, electrified at 25 kV AC, has a loading gauge of W6, and a maximum speed of . As of May 2015 services are operated by London Overground, with two