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
Urban rail in the United Kingdom Line, via tunnels through central London, with a branch to . It is the largest construction project in Europe. Crossrail will start a full service in 2018, taking over suburban services operated by Abellio Greater Anglia to Shenfield, Heathrow Connect to Heathrow Airport and First Great Western to Reading. Once opened, Crossrail will be one of three partially underground suburban rail networks in the United Kingdom as the network cannot be classed as a Metro system like the London Underground or the Glasgow Subway. The Merseyrail and Glasgow commuter rail networks also have below ground stations. Crossrail 2 is a