London Underground
The London Underground is a rapid transit system that provides passenger services in and around London, and the neighbouring counties of Essex, Buckinghamshire and Hertfordshire.
London Underground is named after the deep bore tunnels in which some of the London Underground trains operate, however around 55% of London Underground track is above ground.
London Underground is also colloquially known as the "tube" due to the tube like appearance of the London Underground tunnels, and may also be referred to as the subway or metro (after the first ever rapid transport system, the Metropolitan line) in other countries. London Underground is managed by Transport for London (Tfl) as is the London Overground.
London Underground operates on a network of eleven colour coded lines across London and its suburbs, ranging from the longest: The red London Underground Central line which covers a total of 74km from Epping Forest in Essex all the way to Ealing Broadway to the London Underground's smallest line the light blue Waterloo and City line calling at only two stations.
Two of the London Underground's most popular lines include the Yellow Circle Line which calls at more mainline London termini than any other station and the Black London Underground Northern line which runs north to south from High Barnet and Edgware to Morden.