The London Underground is a rapid transit system serving Greater London and some parts of the adjacent home counties of Buckinghamshire, Essex and Hertfordshire in England.
The nickname "Tube" comes from the circular tube-like tunnels through which the small profile trains travel. (Deep level Northern line London Underground 1995 Stock train)
A sub-surface Metropolitan line train (S8 Stock) at Farringdon
The Metropolitan Railway opened in 1863 using GWR broad-gauge locomotives.
Passengers wait to board a tube train in 1906.
Rapid transit or mass rapid transit (MRT), also known as metro, is a type of high-capacity public transport that is generally built in urban areas. A rapid transit system that primarily or traditionally runs below the surface may be called a subway, tube, or underground. Unlike buses or trams, rapid transit systems are railways, usually electric, that operate on an exclusive right-of-way, which cannot be accessed by pedestrians or other vehicles. They are often grade-separated in tunnels or on elevated railways.
The London Underground is the world's first and oldest rapid transit system.
The New York City Subway is the world's largest single-operator rapid transit system by number of metro stations, at 472.
A crowded Paris Métro average station platform in 2007
A station of the Guangzhou Metro in 2005