The Central line is a London Underground line that crosses London from Ealing and Ruislip in the west to Stratford in East London before heading north-east to Epping in Essex, outside Greater London and the M25, London's orbital motorway. Coloured red on the tube map, the line serves 49 stations, 20 of which are below ground, in 46 miles (74 km). It is the longest tube line. It is also one of only two lines on the network to cross the Greater London boundary, the other being the Metropolitan line.