The Central line is a London Underground line that runs through central London, from Ealing and Ruislip in the west to Epping, Essex in the north-east. Coloured red on the tube map, the line serves 49 stations, 20 of which are below ground, in . It is the longest tube line. It is also one of only two lines on the London Underground network to cross the Greater London boundary, the other being the Metropolitan. One of London's deep-level tube railways, the trains are smaller than those on British main lines.