| The London Underground is an underground railway | | | | Passenger Transport Board (LPTB), a public |
| system - also known as a rapid transit system | | | | corporation that approximated in scope to the |
| (Tube). London is served by 12 Tube lines. It is the | | | | present-day TfL. |
| world's oldest underground system. The Underground | | | | During the 1930s and 1940s, several sections of |
| has 275 stations and runs over 253 miles (408 km) of | | | | main-line railway were converted into (surface) lines |
| line. | | | | of the Underground. The first real investment came |
| Since 2003, the Underground has been part of | | | | with the carefully planned Victoria line on a diagonal |
| Transport for London (TfL), which also administers | | | | northeast-southwest alignment beneath central |
| numerous other transport-related functions, including | | | | London, which opened in stages between 1968 and |
| the famous red double-decker buses. | | | | 1971. The Piccadilly line was extended to Heathrow |
| In the early 20th century, the presence of six | | | | Airport in 1977, and the Jubilee line was opened in |
| independent operators running different Underground | | | | 1979, taking over part of the Bakerloo line, with new |
| lines caused passengers substantial inconvenience; in | | | | tunnels between Baker Street and Charing Cross. In |
| many places passengers had to walk some distance | | | | 1999 the Jubilee was extended to Stratford in |
| above ground to change between lines. In 1933 the | | | | London's East End, including the completely |
| Combine and all the municipal and independent bus | | | | refurbished interchange station at Westminster, in |
| and tram undertakings were merged into the London | | | | several stages. |