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
London Underground engineering stock London Underground engineering stock Over the years, London Underground has acquired various types of engineering stock to help with the construction of new lines and maintenance of existing lines. Some of these wagons were inherited from its predecessors, many were built new and some were acquired second-hand from the main-line railways. Several types of specialist wagons have been used, which are described below. London Underground uses a numbering system comprising the wagon number prefixed with a letter which designates the wagon's type. These are summarised below. London Underground has used various designs of brake van. They were used for the