Central line (London Underground) that the transport benefits of a Park Royal station on the Central line are not sufficiently high to justify the costs of construction. Central line (London Underground) The Central line is a London Underground line that runs through central London, from , Essex, in the north-east to and in the west. Coloured red on the Tube map, the line serves 49 stations over , which makes it the longest Tube line. It is also one of only two lines on the Underground network to cross the Greater London boundary, the other being the Metropolitan line. One of London's deep-level railways,
London Overground than a solid single line, to distinguish it from the colour-coded Underground lines. The London Overground also uses a variant of the TfL roundel. TfL denotes its different transport modes such as London Underground or London Buses with variants of the roundel device using a range of colours, and the London Overground version consists of an orange ring with a blue bar. The roundel has its origins in a 1933 design by the London Passenger Transport Board and has spawned many variations. Unlike other National Rail stations, London Overground stations which are not served by another National Rail operator now