Editing Piccadilly line (section)

===Extension to Heathrow Airport===
[[File:LU1973 Refurbished Interior.jpg|thumb|upright=1.35|Inside a Piccadilly line car]]
To cater to the rapid growth of road traffic to [[Heathrow Airport]], several rail lines were considered to serve the airport. An average increment of 1 million passengers a year between 1953 and 1973, and rising issues with airline [[Coach (bus)|coach]] services from major terminals due to location, traffic congestion, larger aircraft capacity and increasing leisure travel further increased the need for public transport connections. Other than the Piccadilly line extension from [[Hounslow West tube station|Hounslow West]],{{refn|The four-tracking extension to [[Hounslow East tube station|Hounslow East]] from Northfields was considered in the 1940s to allow Heathrow express trains to run fast into central London. Another express rail link planned by LPTB would terminate at Hyde Park or Earl's Court, which would have costed £5–12&nbsp;million.{{sfn|Horne|2007|pp=117–118}}|group=note}} a [[Southern Railway (UK)|Southern Railway]] spur (section now transferred to part of [[South Western Railway (train operating company)|South Western Railway]]) from [[Feltham railway station|Feltham]] was also contemplated. These schemes were brought into parliamentary discussion in November 1966, and were approved with [[royal assent]] as the London Transport Act 1967 (c. xxxix) and British Railways Act 1967 (c. xxx) respectively on 27 July 1967.<ref>{{London Gazette |date=1 August 1967 |issue=44377 |pages=8450}}</ref> Partial government funding was obtained in April 1972 for the {{convert|3.5|mi|km|abbr=on}} Piccadilly line extension, and the estimated cost of construction was £12.3&nbsp;million.{{sfn|Horne|2007|pp=115–120}}

On 27 April 1971, a construction ceremony was launched by Sir [[Desmond Plummer]], leader of the [[Greater London Council]], by bulldozing "the first [[sod]]". Platforms at Hounslow West had to be relocated below-ground to the north of the existing for the new track alignment. The 1931 ticket hall was retained, with connections to the new platforms. A [[Tunnel#Cut-and-cover|cut-and-cover]] excavation method was used between Hounslow West and [[Hatton Cross tube station|Hatton Cross]], a new station on the extension. This 2-mile section had a shallow [[trench]] dug, with the tunnel walls supported by intersecting [[Deep foundation|concrete piles]]. The line had to cross the [[River Crane, London|River Crane]] just east of Hatton Cross; therefore it emerges briefly on a bridge, with the two portals having concrete retaining walls. Deep tube tunnels were bored from Hatton Cross to [[Heathrow Terminals 2 & 3 tube station|Heathrow Central]] (now Heathrow Terminals 2 & 3). On 19 July 1975, the line was extended to Hatton Cross.{{sfn|Day|Reed|2008|p=178}}{{refn|Several coach services were redirected to this station from Hounslow West.{{sfn|Horne|2007|p=121}}|group=note}} The Heathrow Central extension was inaugurated by [[Elizabeth II|the Queen]] around noon on 16 December 1977, with revenue services commencing at 3pm.{{sfn|Horne|2007|pp=120–121}}

In the 1970s, planning was already underway for a [[Heathrow Terminal 4|fourth terminal]] for the airport, and its location was to be to the southeast of the existing terminals. As the Piccadilly line's route to the existing terminals was out of place, a loop track was adopted as the best method to serve the new terminal. The westbound track between Hatton Cross and Heathrow Central would be retained for emergency services. Approval for [[Heathrow Airport Holdings|British Airport Authority]] (BAA) to construct the fourth terminal was granted in 1979.<ref name=":03">{{Cite news |last=Cobley |first=Jim |date=28 March 1986 |title=Royals "Fly the Tube" as Heathrow plugs in |work=LRT News |pages=4–5}}</ref> Permissions for constructing for the loop was approved and received royal assent under the London Transport Act 1981 (c. xxxii) on 30 October 1981.<ref>{{London Gazette |date=5 November 1981 |issue=48785 |pages=14033}}</ref> The [[station box]] would be built by BAA as part of the £200 million construction cost of the new terminal. By 1982, construction of the fourth terminal building was behind schedule, and in July 1982 the location of [[Heathrow Terminal 4 tube station|the station]] was moved from below the terminal building to a nearby car park. Construction of the {{convert|2.5|mi|km|abbr=on}} extension began on 9 February 1983, with an estimated cost of £24.6&nbsp;million. Tunnelling for the loop was completed in seventeen months. It was expected that the extension would open with the new terminal. However, the terminal opening was delayed, with the loop service completed and commissioned on 4 November 1985.<ref name=":02">{{Cite news |last=Cobley |first=Jim |date=28 March 1986 |title=Royals "Fly the Tube" as Heathrow plugs in |work=LRT News |pages=4–5}}</ref> The terminal and station were finally opened a few months later on 1 April 1986, by the [[Charles, Prince of Wales|Prince]] and [[Diana, Princess of Wales|Princess of Wales]]. Regular traffic began twelve days later with trains serving Terminal 4 via a one-way loop to Terminals 1,2,3.{{sfn|Horne|2007|pp=125–126}} The station only has a single platform, the only one with this configuration on the Piccadilly line.<ref name=cartomap/>

[[Heathrow Terminal 5 station|Terminal 5]] required another extension, funded by BAA. However, its proposed alignment caused an issue: it was reported that London Underground was unhappy with the terminal's location on the site of the old [[Perry Oaks]] sludge works which was originally intended for Terminal 4.{{sfn|Horne|2007|p=138}} It was now impossible for all three terminals to be served on the same route, and the final solution was to have twin tunnels serving Terminal 5 from Terminals 1,2,3. From 7 January 2005 until 17 September 2006, the loop via Terminal 4 was closed to allow this connection to be built. Terminals 1,2,3 became a temporary terminus; shuttle buses served Terminal 4 from the Hatton Cross bus station.{{sfn|Horne|2007|pp=137–138}} Part of the junction between the through and loop tracks needed to be rebuilt. The Terminal 5 project team shut down two [[Hangar|aircraft stand]]s from Terminal 3 so that an access shaft could be constructed. The new junction was then built into a concrete box which connected all the underground tunnels.<ref>{{cite press release |url=https://tfl.gov.uk/info-for/media/press-releases/2006/september/tube-one-step-closer-for-heathrow-terminal-5 |title=Tube One Step Closer for Heathrow Terminal 5 |date=14 September 2006 |access-date=17 August 2020 |publisher=[[Transport for London]] |url-status=live |archive-url=https://web.archive.org/web/20200817145027/https://tfl.gov.uk/info-for/media/press-releases/2006/september/tube-one-step-closer-for-heathrow-terminal-5 |archive-date=17 August 2020}}</ref> The station and terminal were opened on 27 March 2008, splitting westbound Piccadilly line services into two: one via the Terminal 4 loop, another direct to Terminal 5.<ref name=heathrowt5pressrelease>{{cite press release |url=https://tfl.gov.uk/info-for/media/press-releases/2008/march/first-piccadilly-line-passengers-travel-to-heathrow-terminal-5 |title=First Piccadilly Line Passengers Travel to Heathrow Terminal 5 |date=27 March 2008 |access-date=17 August 2020 |publisher=[[Transport for London]] |url-status=live |archive-url=https://web.archive.org/web/20200817150229/https://tfl.gov.uk/info-for/media/press-releases/2008/march/first-piccadilly-line-passengers-travel-to-heathrow-terminal-5 |archive-date=17 August 2020}}</ref><ref name=culgpiccadilly>{{cite web |url=http://www.davros.org/rail/culg/piccadilly.html |title=Piccadilly Line |work=Clive's Underground Line Guides |last=Feather |first=Clive |date=8 May 2020 |access-date=17 August 2020 |url-status=live |archive-url=https://web.archive.org/web/20200726113358/http://www.davros.org/rail/culg/piccadilly.html |archive-date=26 July 2020}}</ref>