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
Central line (London Underground) interchange, it was ruled out on grounds of cost, the disruption it would cause to the Central line while being built and because the platforms would be too close to sidings at Liverpool Street and would not be developed until after Crossrail is fully operational. The developers of the "First Central" business park at Park Royal, west London, were planning a new station between North Acton and Hanger Lane. This would have served the business park and provided a walking distance interchange with Park Royal station on the Piccadilly line. This is not being actively pursued; London Underground has said