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
East Rail line branches in the north at Sheung Shui to terminate at Lo Wu or Lok Ma Chau stations. Both are boundary crossing points into Shenzhen. All of the stations are at- grade or elevated before the opening of Shatin to Central Link which will provide underground track. The distance between Hung Hom and Lo Wu stations is . The total distance of the line (including the Lok Ma Chau Spur line) is approximately , making it the longest line in total distance within the system network. The line is coloured light blue on the MTR map. The same railway is used