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 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