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 London line extension station closed permanently to facilitate work on the extension, with services from Whitechapel being replaced by buses. The rest of the East London line closed on 22 December 2007, with rail replacement buses linking the stations north and south of the Thames (but not crossing the river due to height restrictions in the Rotherhithe Tunnel). On 5 September 2006 it was announced that the line would transfer from London Underground to London Overground, branded with a version of the Underground roundel with red replaced by orange, the colour used on Tube maps for the East London Line. Three major new