London Underground
The London Underground is a rapid transit system serving Greater London and some parts of the adjacent counties of Buckinghamshire, Essex and Hertfordshire in England. The Underground has its origins in the Metropolitan Railway, the world's first underground passenger railway. Opened on 10 January 1863, it is now part of the Circle, District, Hammersmith & City and Metropolitan lines. The first line to operate underground electric traction trains, the City & South London Railway in 1890, is now part of the Northern line. The network has expanded to 11 lines, and in 2020/21 was used for 296 million passenger journeys, making it one of the world's busiest metro systems. The 11 lines collectively handle up to 5 million passenger journeys a day and serve 272 stations. The system's first tunnels were built just below the ground, using the cut-and-cover method; later, smaller, roughly circular tunnels—which gave rise to its nickname, the Tube—were dug through at a deeper level.
