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 Borough of Havering Romford, Gidea Park and Harold Wood. There is also a branch line from Romford to Upminster which is currently operated by London Overground. There are proposals for transport improvements in the south of the borough where the population is expected to rise. With the introduction of Crossrail there will be an increased service from Romford to both Central London and Reading. In March 2011, the main forms of transport that residents used to travel to work were: driving a car or van, 31.8% of all residents aged 16–74; train, 6.3%; underground, metro, light rail, tram, 6.3%; bus, minibus or coach,