London Underground ticketing destinations and most interchange stations are in zone 1, meaning that most journeys over similar distances will cost the same. A few stations in the north east of the network, on the Central line, outside Greater London (in the Epping Forest district) are in zones 4, 5 and 6. In the north west of the network, on the Metropolitan line, zones 7, 8 and 9 (formerly A - D) cover stations outside Greater London including Amersham and Chesham in the Chiltern district of Buckinghamshire. Unlike the lower numbered zones, these ancillary areas do not encircle the capital. Some stations are
M25 motorway unofficial, and illegal, motor racing. At the end of the 1980s, before the advent of speed enforcement devices, owners of supercars would meet at night at service stations such as South Mimms and conduct time trials. Times below 1 hour were achieved - an average speed of over 117 mph (188 km/h), which included coming to a halt at the Dartford Tunnel road user charge payment booths. Data from driver location signs provide carriageway identifier information. The numbers on the signs are kilometres from a point near the River Thames, east of London, when travelling clockwise on the motorway. The