Editing London Underground (section)

===Railway===
As of 2021, the Underground serves 272 [[Underground station|stations]].<ref>{{Cite news|date=20 September 2021|title=Northern Line extension: Two new Tube stations open|language=en-GB|work=BBC News|url=https://www.bbc.com/news/uk-england-london-58621491|access-date=20 September 2021|archive-date=20 September 2021|archive-url=https://web.archive.org/web/20210920073208/https://www.bbc.com/news/uk-england-london-58621491|url-status=live}}</ref><ref>{{Cite news |last=Attwooll |first=Jolyon |url= https://www.telegraph.co.uk/travel/destinations/europe/united-kingdom/england/london/articles/London-Underground-150-fascinating-Tube-facts/ |archive-url= https://ghostarchive.org/archive/20220111/https://www.telegraph.co.uk/travel/destinations/europe/united-kingdom/england/london/articles/London-Underground-150-fascinating-Tube-facts/ |archive-date=11 January 2022 |url-access=subscription |url-status=live |title=150 London Underground facts (including the birth of Jerry Springer in East Finchley station) |date=25 January 2018 |work=The Telegraph |location= London |access-date=28 April 2020}}{{cbignore}}</ref> Sixteen stations (eight on each of the Metropolitan and Central lines) are outside the [[Greater London|London region]], with five of those beyond the [[M25 motorway|M25 London Orbital motorway]] ([[Amersham station|Amersham]], [[Chalfont & Latimer station|Chalfont & Latimer]], [[Chesham tube station|Chesham]], and [[Chorleywood station|Chorleywood]] on the Metropolitan line and [[Epping tube station|Epping]] on the Central).

Of the thirty-two [[London borough]]s, six ([[London Borough of Bexley|Bexley]], [[London Borough of Bromley|Bromley]], [[London Borough of Croydon|Croydon]], [[Royal Borough of Kingston upon Thames|Kingston]], [[London Borough of Lewisham|Lewisham]] and [[London Borough of Sutton|Sutton]]) are not served by the Underground network, while [[London Borough of Hackney|Hackney]] has [[Old Street tube station|Old Street]] (on the Northern line Bank branch) and [[Manor House tube station|Manor House]] (on the Piccadilly line) just inside its boundaries. Lewisham was served by the [[East London line]] (with stations at [[New Cross railway station|New Cross]] and [[New Cross Gate railway station|New Cross Gate]]) until 2010 when the line and the stations were transferred to the London Overground network.<ref>{{Cite news |url=http://news.bbc.co.uk/1/hi/england/london/8620188.stm |title=East London Line opens to public |date=27 April 2010 |newspaper=BBC |access-date=8 June 2016 |archive-date=18 April 2015 |archive-url=https://web.archive.org/web/20150418154822/http://news.bbc.co.uk/2/hi/uk_news/england/london/8620188.stm |url-status=live }}</ref>

{{wide image|London Underground with Greater London map.svg|980px|A geographic London Underground map showing the extent of the current network ([[Amersham station|Amersham]] and [[Chesham tube station|Chesham]] stations, top left, are beyond the extent of the map.)}}

London Underground's eleven lines total {{convert|402|km|mi}} in length,<ref name="Key Facts"/> making it the eleventh [[List of metro systems|longest metro system in the world]]. These are made up of the sub-surface network and the deep-tube lines.<ref name="Key Facts">{{cite web |url=http://www.tfl.gov.uk/corporate/about-tfl/what-we-do/london-underground/facts-and-figures |title=About TfL – What we do – London Underground – Facts & figures |publisher=Transport for London |access-date=17 June 2014 |archive-date=27 September 2014 |archive-url=https://web.archive.org/web/20140927002759/http://www.tfl.gov.uk/corporate/about-tfl/what-we-do/london-underground/facts-and-figures |url-status=live }}</ref>

The [[Circle line (London Underground)|Circle]], [[District line|District]], [[Hammersmith & City line|Hammersmith & City]], and [[Metropolitan line]]s form the sub-surface network, with [[cut-and-cover]] railway tunnels just below the surface and of a similar size to those on British main lines They converged on a bi-directional loop in central London, sharing tracks and stations with each other at various places along their respective routes.

The [[Bakerloo line|Bakerloo]], [[Central line (London Underground)|Central]], [[Jubilee line|Jubilee]], [[Northern line|Northern]], [[Piccadilly line|Piccadilly]], [[Victoria line|Victoria]] and [[Waterloo & City line]]s are deep-level tubes, with smaller trains that run in circular tunnels (''tubes'') with a diameter of about {{convert|11|ft|8|in}}, with one tube for each direction. The seven deep-level lines have the exclusive use of tracks and stations along their routes with the exceptions of the Piccadilly line, which shares track with the District line, between Acton Town and Hanger Lane Junction, and with the Metropolitan line, between Rayners Lane and Uxbridge; and the Bakerloo line, which shares track with [[London Overground]]'s [[Watford DC Line]] for its above-ground section north of Queen's Park.<ref name="map">{{cite web |url=http://cartometro.com/cartes/metro-london/ |archive-url=https://web.archive.org/web/20200728161716/http://cartometro.com/cartes/metro-london/ |url-status=dead |archive-date=28 July 2020 |title=Detailed London Transport Map |access-date=1 December 2012 |work=cartometro.com }}</ref>

Fifty-five per cent of the system runs on the surface. There are {{convert|20|mi}} of sub-surface tunnels and {{convert|93|mi}} of tube tunnels.<ref name="Key Facts" /> Many of the central London Underground stations on deep-level tube routes are higher than the running lines to assist deceleration when arriving and acceleration when departing.{{sfnp|Croome|Jackson|1993|pp=26, 33, 38, 81}} Trains generally run on the left-hand track. In some places, the tunnels are above each other (for example, the Central line east of St Paul's station); or trains run on the right (for example on the Victoria line between Warren Street and King's Cross St. Pancras, to allow [[cross-platform interchange]] with the Northern line at [[Euston tube station|Euston]]).<ref name="map" />{{sfnp|Croome|Jackson|1993|pp=327–328}}

The lines are electrified with a four-rail DC system: a conductor rail between the rails is energised at {{Val|-210|u=V}} and a rail outside the running rails at {{Val|+420|u=V}}, giving a potential difference of {{Val|630|u=V}}. On the sections of line shared with mainline trains, such as the District line from East Putney to Wimbledon and Gunnersbury to Richmond, and the Bakerloo line north of Queen's Park, the centre rail is bonded to the running rails.<ref name="Martin2012">{{cite book |author=Martin, Andrew |title=Underground, Overground: A Passenger's History of the Tube |url=https://books.google.com/books?id=vh3n5WD_YqsC&pg=PT137 |access-date=7 December 2012 |date=26 April 2012 |publisher=Profile Books |isbn=978-1-84765-807-4 |pages=137–138 |location=London |archive-date=19 January 2023 |archive-url=https://web.archive.org/web/20230119080910/https://books.google.com/books?id=vh3n5WD_YqsC&pg=PT137 |url-status=live }}</ref>

The average speed on the Underground is {{convert|20.5|mph|km/h|abbr=on}}.<ref name="150 tube facts" /> Outside the tunnels of central London, many lines' trains tend to travel at over {{convert|40|mph|km/h|abbr=on}} in the suburban and countryside areas. The Metropolitan line can reach speeds of {{convert|62|mph|km/h|abbr=on}}.<ref>{{Cite web|url=https://citymonitor.ai/transport/which-london-underground-line-fastest-3322|title=Which London Underground line is the fastest?|date=18 September 2017|access-date=21 April 2021|archive-date=15 May 2021|archive-url=https://web.archive.org/web/20210515160549/https://citymonitor.ai/transport/which-london-underground-line-fastest-3322|url-status=live}}</ref>