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
London Underground persist to this day. "" has a single-player level named "Mind The Gap" where most of the level takes place between the dockyards and Westminster while the player and a team of SAS attempt to take down terrorists attempting to escape using the London Underground via a hijacked train. The game also features the multiplayer map "Underground", in which players are combating in a fictitious Underground station. The London Underground map serves as a playing field for the conceptual game of Mornington Crescent (which is named after a station on the Northern line) and the board game "The London Game".