Editing Piccadilly line (section)

==History==
{{for|detailed histories of the Great Northern, Piccadilly & Brompton Railway (GNP&BR), the Great Northern & Strand Railway (GN&SR), and the Brompton & Piccadilly Circus Railway (B&PCR)|Great Northern, Piccadilly and Brompton Railway}}
The Piccadilly line began as the Great Northern, Piccadilly & Brompton Railway (GNP&BR), one of several railways controlled by the [[Underground Electric Railways Company of London]] (UERL), whose chief director was [[Charles Yerkes|Charles Tyson Yerkes]],{{sfn|Horne|2007|p=15}} although he died before the first section of the line opened. It currently runs on tracks built by The GNP&BR, the [[District Railway]] (DR) and the Metropolitan Railway (Met), and received major extensions in the 1930s and 1970s.

The GNP&BR was formed from the merger of two earlier, but unbuilt,{{sfn|Horne|2007|pp=6,8}} tube-railway companies taken over in 1901 by Yerkes's consortium: the Great Northern & Strand Railway (GN&SR) and the Brompton & Piccadilly Circus Railway (B&PCR).{{sfn|Horne|2007|p=10}} The GN&SR's and B&PCR's separate routes were linked with an additional section between {{lus|Piccadilly Circus}} and {{lus|Holborn}}. A section of the DR's scheme for a deep-level tube line between {{lus|South Kensington}} and {{lus|Earl's Court}} was also added in order to complete the route.{{refn|The original [[District Railway]] tube line was to be from Earl's Court to [[Mansion House tube station|Mansion House]]. It was intended to be an express route from South Kensington to Mansion House, with an intermediate station at [[Embankment tube station|Embankment]].<ref name="Gazette_03">{{London Gazette |date=22 November 1896 |issue=26797 |pages=6764–6767}}</ref>{{sfn|Horne|2007|p=7}}|group=note}} This finalised route, between [[Finsbury Park station|Finsbury Park]] and [[Hammersmith tube station (District and Piccadilly lines)|Hammersmith]] stations, was formally opened on 15 December 1906.{{sfn|Wolmar|2005|p=181}} On 30 November 1907, the short branch from Holborn to the Strand (later renamed {{lus|Aldwych}}) opened; it had been planned as the last section of the GN&SR before the amalgamation with the B&PCR.{{sfn|Horne|2007|pp=9,13,19}}

Initial ridership growth was low due to high use of new electric [[trams]] and motor buses. Financial stability was an issue, and as a result the company heavily promoted their railways via a new management team. UERL also agreed with other independent railway companies such as the [[Central London Railway]] (CLR, now part of the [[Central line (London Underground)|Central line]]) to jointly advertise a combined network known as the Underground.{{sfn|Horne|2007|p=32}}{{sfn|Badsey-Ellis|2005|pp=282–283}} On 1 July 1910, the GNP&BR and the other UERL-owned tube railways (the [[Baker Street and Waterloo Railway]] and the [[Charing Cross, Euston and Hampstead Railway]]) were merged by an [[act of Parliament]]{{which|date=July 2024}}<ref name=merge>{{London Gazette |date=23 November 1909 |issue=28311 |pages=8816–8818}}</ref> to become the ''[[London Electric Railway]] Company'' (LER).{{refn|The merger was carried out by transferring the assets of the CCE&HR and the BS&WR to the GNP&BR and renaming the GNP&BR as the London Electric Railway.{{sfn|Horne|2007|p=33}}|group=note}} The Underground railways still suffered financial issues,{{sfn|Wolmar|2005|pp=259–262}} and to address this, the [[London Passenger Transport Board]] was established on 1 July 1933.{{sfn|Wolmar|2005|p=266}}<ref name="LPTA">{{London Gazette |date=9 December 1930 |issue=33668 |pages=7905–7907}}</ref>

There were significant station layout changes in the 1910s and 1920s. On 4 October 1911, Earl's Court had new escalators installed connecting the [[District line|District]] and Piccadilly lines. They were the first to be installed on the Underground.{{sfn|Horne|2007|p=33}}{{sfn|Wolmar|2005|p=182}} On 10 December 1928, a rebuilt Piccadilly Circus station, designed by [[Charles Holden]],<ref name="eh_1226877">{{NHLE|num=1226877|desc=Piccadilly Circus Underground Station Booking Hall Concourse and Bronzework to Pavement Subway Entrances|access-date=2 August 2020}}</ref> was opened. This included a new booking hall located below ground and eleven escalators, replacing the original lifts.{{sfn|Horne|2007|p=39}}{{refn|The old street level station building closed on 21 July 1929.{{sfn|Lee|1966|p=23}}{{sfn|Horne|2007|p=39}}|group=note}}

One of the shafts at [[Holloway Road tube station|Holloway Road station]] was used as an experiment for [[Escalator#Alternative designs|spiral escalators]], but never used.{{sfn|Horne|2007|p=23}} An experiment to encourage passengers to step on the escalator three at a time at [[Manor House tube station|Manor House station]] was trialled.{{sfn|Horne|2007|p=82}} It failed due to opposition and potential dangers pointed out by the public.{{sfn|Horne|2007|p=82}}

===Extension to Cockfosters===
[[File:Ventilation panel, Wood Green tube station - geograph.org.uk - 1401101.jpg|thumb|One of the ventilation panels at Wood Green station platforms]]

While early plans to serve Wood Green (specifically [[Alexandra Palace railway station|Alexandra Palace]]) existed since the 1890s as part of the GN&SR,<ref name="Gazette_04">{{London Gazette |date=22 November 1898 |issue=27025 |pages=7040–7043}}</ref><ref name="Gazette_05">{{London Gazette |date=4 August 1899 |issue=27105 |pages=4833–4834}}</ref> this section to [[Finsbury Park station|Finsbury Park]] was later dropped from the GNP&BR proposal in 1902 when the GN&SR was merged with the B&PCR.{{sfn|Badsey-Ellis|2005|p=131}}{{sfn|Horne|2007|p=11}} In 1902, as part of an agreement for taking over the GN&SR, the [[Great Northern Railway (Great Britain)|Great Northern Railway]] (GNR) imposed a sanction<!--no suitable wikilink available--> on Yerkes to abandon the section north of Finsbury Park and they would construct the terminus below ground.{{sfn|Horne|2007|p=11}}{{sfn|Badsey-Ellis|2005|p=138}}{{sfn|Martin|2012|pp=182–183}}<ref name=hornsyhist1>{{cite web |url=https://hornseyhistorical.org.uk/piccadilly-line-extension-part-one/ |title=Part One |work=The Piccadilly Line Extension |last=Dean |first=Deadre |date=4 October 2019 |publisher=Hornsey Historical Society |access-date=5 August 2020 |url-status=live |archive-url=https://web.archive.org/web/20200806102029/https://hornseyhistorical.org.uk/piccadilly-line-extension-part-one/ |archive-date=6 August 2020}}</ref> Finsbury Park remained as an overcrowded terminus of the line, and was described as "intolerable". Many passengers arriving at both stations had to change onto buses, trams, and [[suburban rail]] services to complete their journeys further north.{{sfn|Horne|2007|p=91}}{{refn|The diagram in the reference shows bus or tram routes in the north which were in close proximity to Finsbury Park.|group=note}} The GNR attempted to address this issue by considering [[electrification]] several times, but to no avail due to shortage of funds. Meanwhile, the LER proposed an extension in 1920 but was [[wikt:overrule#Verb|overruled]] by the GNR, which was widely regarded as "unreasonable". In 1923, a petition by the Middlesex Federation of Ratepayers to [[repeal]] the 1902 act of Parliament{{which|date=July 2024}} emerged. It was reported that a "fierce exchange of arguments" occurred during a parliamentary session in March 1924 to request this change.<ref>{{cite web |url=https://hansard.parliament.uk/Commons/1924-03-05/debates/3693b732-edd8-43ac-b586-573bf88e0a0d/LondonAndNorthEasternRailwayBill(ByOrder) |title=London and North Eastern Railway Bill (By Order) |publisher=Hansard Parliament UK |date=15 March 1924 |access-date= 6 August 2020 |url-status=live |archive-url=https://web.archive.org/web/20200806101549/https://hansard.parliament.uk/Commons/1924-03-05/debates/3693b732-edd8-43ac-b586-573bf88e0a0d/LondonAndNorthEasternRailwayBill%28ByOrder%29 |archive-date=6 August 2020}}</ref><ref name=hornsyhist1/> [[Frank Pick]], as the new assistant managing director of the Underground, distributed photographs of the congestion at Finsbury Park to the press. All of this pressure finally prompted the government to initiate "The North and North-East London Traffic Inquiry", with initial reports only recommending a one-station extension to [[Manor House tube station|Manor House]]. The [[London and North Eastern Railway]] (LNER), being the successor of the GNR, was placed in the position of electrifying its own services or withdrawing its [[veto]] of an extension of the Piccadilly line. With funds still being insufficient to electrify the railway, the LNER reluctantly agreed to the latter.{{sfn|Martin|2012|pp=182–183}} An extension was highly likely at this stage, based on a study in October 1925 by the [[London and Home Counties Traffic Advisory Committee|London & Home Counties Traffic Advisory Committee]].{{sfn|Horne|2007|p=65}}{{sfn|Wolmar|2005|pp=227–231}}

{{Infobox UK legislation
| short_title           = London Electric Metropolitan District Central London and City and South London Railway Companies Act 1930
| type                  = Act
| parliament            = Parliament of the United Kingdom
| long_title            = 
| year                  = 1930
| citation              = [[20 & 21 Geo. 5]]. c. lxxxviii
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| introduced_lords      = 
| territorial_extent    = 
| royal_assent          = 4 June 1930
| commencement          = 
| expiry_date           = 
| repeal_date           = 
| amends                = 
| replaces              = 
| amendments            = 
| repealing_legislation = 
| related_legislation   = 
| status                = 
| legislation_history   = 
| theyworkforyou        = 
| millbankhansard       = 
| original_text         = https://www.legislation.gov.uk/ukla/Geo5/20-21/88/pdfs/ukla_19300088_en.pdf
| revised_text          = 
| use_new_UK-LEG        = 
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| collapsed             = yes
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Pick, together with the Underground board, began working on the extension proposal. Much pressure was also received from a few districts such as [[Tottenham]] and [[Harringay]], but it was decided that the optimal route would be the midpoint of the GNR and the [[Lea Valley lines|Hertford Line]].{{refn|An interchange at Manor House was provided instead for connecting trams to [[Edmonton, London|Edmonton]], Tottenham and [[London Borough of Enfield|Enfield]] East.{{sfn|Horne|2007|p=65}}|group=note}} This was backed by the committee, and parliamentary approval for the extension was obtained on 4 June 1930, under the '''{{visible anchor|London Electric Metropolitan District Central London and City and South London Railway Companies Act 1930}}''' ([[20 & 21 Geo. 5]]. c. lxxxviii).<ref>{{London Gazette |date=6 June 1930 |issue=33613 |pages=3561}}</ref><ref name=hornsyhist2>{{cite web |url=https://hornseyhistorical.org.uk/piccadilly-line-extension-part-two/ |title=Part Two |work=The Piccadilly Line Extension |last=Dean |first=Deadre |date=18 January 2020 |publisher=Hornsey Historical Society |access-date=5 August 2020 |url-status=live |archive-url=https://web.archive.org/web/20200806101853/https://hornseyhistorical.org.uk/piccadilly-line-extension-part-two/ |archive-date=6 August 2020}}</ref>{{refn|LNER continued to oppose the decision, and promised to electrify the line if the extension was rejected.{{sfn|Horne|2007|p=66}}<ref name=hornsyhist1/>|group=note}} Funding was obtained from legislation under the Development (Loan Guarantees and Grants) Act 1929 ([[20 & 21 Geo. 5]]. c. 7) instead of the [[Trade Facilities Act]]. The extension would pass through [[Manor House, London|Manor House]], [[Wood Green]] and [[Southgate, London|Southgate]], ending at Enfield West (now [[Oakwood tube station|Oakwood]]);{{sfn|Horne|2007|pp=65–66}}{{refn|It was intended for the station to be named East Barnet, but was quickly renamed before opening. Alternative suggestions were Merryhills and Oakwood. The station was gradually renamed, to Enfield West (Oakwood) on 3 May 1934, and to its present name on 1 September 1946.{{sfn|Horne|2007|pp=68,73}}{{sfn|Harris|2006|p=53}}|group=note}} based on the absence of property development along the line. In November 1929, the projected terminus was shifted further north to [[Cockfosters tube station|Cockfosters]] to accommodate a larger depot. It was estimated that ridership on the extension, which would cost £4.4&nbsp;million, would be 36 million passengers a year.{{sfn|Horne|2007|p=66}} In addition to Enfield West, stations were designated at [[Southgate tube station|Southgate]], [[Arnos Grove tube station|Arnos Grove]], [[Bounds Green tube station|Bounds Green]], [[Wood Green tube station|Wood Green]], [[Turnpike Lane tube station|Turnpike Lane]], and Manor House. Bounds Green station was almost cancelled in order to improve journey times.{{sfn|Horne|2007|p=70}} A more expensive provision was rejected, which included construction of a third track between Finsbury Park and Wood Green. Furthermore, since journey speed was a primary consideration in decision-making for the extension, the pencilled-in and much lobbied-for additional station near the corner of Green Lanes and St. Ann's Road in [[Harringay]] was dropped.{{sfn|Horne|2007|pp=68–70}}<ref name=hornsyhist2/>

Tunnel rings, cabling and [[concrete]] were produced in Northern England, while unemployed industrial workers there helped in the construction of the extension. Construction of the extension started quickly, with the boring of the twin tube tunnels between Arnos Grove and Finsbury Park proceeding at the rate of a mile per month. Twenty-two tunnelling shields were used for the tunnels,{{sfn|Martin|2012|pp=181–182}} and tunnel diameters were slightly larger than the old section, at {{convert|12|ft|m|abbr=on}}. Sharp curves were also avoided to promote higher average speeds on the extension. Platforms {{convert|400|ft|m|abbr=on}} long were originally planned for each station to fit 8-car trains, but were cut short to {{convert|385|ft|m|abbr=on}} when built. Some stations were also built with wider platform tunnels to cater to expected high patronage. To connect with buses and trams, interchange stations were provided with exits which led passengers directly to the bus terminal or tram stop from the subsurface ticket hall. The exits were purposed to improve connections which avoided chaotic passenger flow such as at Finsbury Park. Wood Green was an exception due to engineering difficulties, with the ticket hall at street level instead. Ventilation shafts were provided at Finsbury Park Tennis Courts, Colina Road and Nightingale Road, supplementing the existing fans within the stations. Provisions for future branch lines to [[Enfield, London|Enfield]] and Tottenham were made at Wood Green and Manor House respectively, both to have reversing sidings. This had since changed, with only a reversing siding built at Wood Green and no provision for the branch line. Arnos Grove was built to have four platforms facing three tracks for trains to reverse regularly, with seven stabling sidings instead of one reversing siding and two platforms.{{sfn|Horne|2007|pp=69,74–75,86}}<ref>{{cite web |url=https://www.google.com/maps/place/Arnos+Grove/@51.61645,-0.13304,17z/data=!3m1!4b1!4m2!3m1!1s0x48761973b6a2cc5f:0x3f182b0278779adc |title=Arnos Grove tube station |website=Google Maps |access-date=5 August 2020}}</ref><ref name=cartomap>{{cite map |url=http://cartometro.com/documents/CartoMetroLondon.v3.9.pdf?r=cmf |format=PDF |title=Greater London Transport Tracks Map |work=CartoMetro London Edition |version=3.9 |last=Jarrier |first=Franklin |url-status=live |archive-url=https://web.archive.org/web/20200823123452/http://cartometro.com/documents/CartoMetroLondon.v3.9.pdf?r=cmf |archive-date=23 August 2020 |access-date=23 August 2020}}</ref>

Most of the tunnelling works were completed by October 1931, with the Wood Green and Bounds Green station tunnels done by the end of the year.<ref name=hornsyhist2/> The first phase of the extension to Arnos Grove opened on 19 September 1932, without ceremony. The line was further extended to Enfield West on 13 March 1933 and finally to Cockfosters on 31 July 1933, again without ceremonies.{{sfn|Wolmar|2005|pp=227–231}}{{sfn|Rose|1999}} The total length of the extension was {{convert|12.3|km|mi|abbr=on|order=flip}}.<ref name=culgcalculations/> Free tickets were distributed to residents on the first days of service on each extension. Initial ridership was 25&nbsp;million at the end of 1933, which sharply increased to 70&nbsp;million by 1951.{{sfn|Horne|2007|p=100}} Despite there being no official opening ceremonies, [[Edward VIII|the Prince of Wales]] visited the extension on 14 February 1933.{{sfn|Horne|2007|pp=90–92}}{{refn|He travelled from Piccadilly Circus to Wood Green, and back to [[Hyde Park Corner tube station|Hyde Park Corner]] for inspection.{{sfn|Horne|2007|p=92}}|group=note}}

===Westward extensions===
The [[Hounslow West tube station|Hounslow West]] (then Hounslow Barracks) extension of the Piccadilly line, together with the [[Uxbridge]] extension, aimed to improve services on the [[District line]] which at the time were serving both branches from [[Acton Town tube station|Acton Town]] (then Mill Hill Park).{{sfn|Horne|2007|p=42}}{{refn|The Hounslow & Metropolitan Railway originally opened a shuttle service between Mill Hill Park and [[Hounslow Town tube station|Hounslow Town]] on 1 May 1883, with a single-track branch to Hounslow Barracks which opened on 21 July 1884. The route to Hounslow Town eventually closed on 2 May 1909. The District Railway took over the branches in 1903.{{sfn|Horne|2007|pp=42,46}}|group=note}} The Uxbridge extension followed along existing routes on the DR and Met. The DR opened a spur from [[Ealing Common tube station|Ealing Common]] to [[South Harrow tube station|South Harrow]] in June 1903. The Met opened its extension to Uxbridge in July 1904.{{sfn|Horne|2007|pp=42–45}} Through trains of the DR were eventually extended to Uxbridge on 1 March 1910, henceforth sharing tracks with the Met between [[Rayners Lane tube station|Rayners Lane]] and Uxbridge.{{sfn|Horne|2007|pp=44–45}}{{refn|The Ealing & South Harrow Railway (E&SHR) was approved in 1894 and completed in 1899 after approximately a two-year construction period. Insufficient funds from the DR delayed its opening. On the other hand, the [[Harrow & Uxbridge Railway]] (H&UR) was proposed in 1896 and authorised a year later.{{sfn|Simpson|2003|p=97}} The Met offered to fund the line, with conditions to take over the Rayners Lane to [[Uxbridge tube station|Uxbridge]] section of the H&UR. Agreement was reached in 1899, with the Met also constructing the connection from South Harrow to Rayners Lane, whilst allowing up to three trains an hour from the DR between South Harrow and Uxbridge.{{sfn|Horne|2003|p=26}} Construction began in 1901, and the Met opened its extension to Uxbridge on 4 July 1904.{{sfn|Horne|2007|pp=42–45}}|group=note}}

The viaduct from Studland Road Junction west of Hammersmith to [[Turnham Green tube station|Turnham Green]] was quadrupled on 3 November 1911. The [[London and South Western Railway]] (L&SWR) used the northern pair of tracks while the District Railway used the southern pair.{{sfn|Horne|2007|pp=46–47}} The LER proposed an extension in November 1912 to [[Richmond station (London)|Richmond]] due to available capacity to the west and the fact that passenger interchanges were large at Hammersmith. It would connect with the L&SWR tracks at Turnham Green.<ref>{{London Gazette |date=22 November 1912|issue=28665|pages=8798–8801}}</ref> It was approved as the [[London Electric Railway Act 1913]] ([[3 & 4 Geo. 5]]. c. xcvii) on 15 August 1913,<ref>{{London Gazette|date=19 August 1913|issue=28747|pages=5929–5931}}</ref> but [[World War I]] resulted in no works done on the extension.{{sfn|Horne|2006|p=56}} A parliamentary report of 1919 recommended through running to Richmond and [[Ealing]].{{sfn|Barker|Robbins|1974|p=252}} The Richmond extension plan was revived in 1922 by [[Albert Stanley, 1st Baron Ashfield|Lord Ashfield]], the Underground's chairman. It was decided that the Piccadilly line extension was favourable over the CLR's as it was cheaper and had more capacity available.{{sfn|Horne|2007|pp=48–49}}{{refn|The CLR also had its Richmond extension proposal passed on the same day as the LER's. Nothing was done either.{{sfn|Horne|2007|p=48}} The L&SWR section ceased operation in 1916 and its ownership was transferred to the [[Southern (Govia Thameslink Railway)|Southern Railway]] in 1923.{{sfn|Horne|2006|p=55}} The CLR, by the 1920s, had capacity constraints due to increased patronage from Ealing and congestion in the central section.{{sfn|Horne|2007|pp=48–49}}|group=note}} By 1925, the [[District line]] was running out of capacity west of Hammersmith, where services were headed to South Harrow, Hounslow Barracks, Richmond and [[Ealing Broadway station|Ealing Broadway]]. Demand was also low on the South Harrow branch because of infrequent services and competition among other rail lines in the vicinity of each station. This prompted the Piccadilly line extension to be an express service between Hammersmith and Acton Town, with the future [[Heathrow Airport]] extension safeguarded in 40 years' time.{{sfn|Horne|2007|p=51}} The Piccadilly line would run on the inner pair of tracks, and the District line on the outer.{{sfn|Barker|Robbins|1974|p=252}} Permission was granted to quadruple tracks to Acton Town in 1926 in conjunction with permit renewal for the extension. The Richmond extension never happened, but provisions allocated would allow this option to be revisited later.{{sfn|Horne|2007|pp=51,52}} Extensions would instead be to Hounslow Barracks and South Harrow, taking over DR services to the latter, with an estimated cost of £2.3&nbsp;million.{{sfn|Horne|2007|pp=50–51,66}}{{refn|The District line instead focused on running trains to Richmond, Ealing Broadway and [[Wimbledon station|Wimbledon]], with the South Harrow to Uxbridge and Acton Town to [[South Acton railway station (England)|South Acton]] shuttles to remain. In October 1930, provision was also made to have rush hour DR services to South Harrow.{{sfn|Horne|2006|pp=52,56}}|group=note}} In 1930, unsuccessful negotiations were made between LER and the Met to extend Piccadilly line trains to Rayners Lane for passengers to change trains.{{sfn|Horne|2007|p=58}}

In 1929, quadrupling was to extend to [[Northfields tube station|Northfields]] for express trains to terminate there. This work was completed on 18 December 1932. Overall works for the extension began in 1931, approximately a year after permission was granted and funded under the Development (Loan Guarantees and Grants) Act 1929 ([[20 & 21 Geo. 5]]. c. 7). The Studland Road Junction area was partially rebuilt, with some of the old viaducts retained to date. The junctions diverging to Richmond were reconfigured at Turnham Green. Reversing facilities were initially designated at the latter, but these were not built.{{sfn|Horne|2007|p=52}} Trial runs of Piccadilly line trains began on 27 June 1932. On 4 July 1932, services were extended to South Harrow, which replaced DR services. Northfields services were introduced on 9 January 1933, and on 13 March, were extended to Hounslow West. On 1 July 1933, the [[London Passenger Transport Board]] (LPTB) was formed, which included the Met, the DR and LER.{{sfn|Wolmar|2005|p=266}} The board decided that there was sufficient demand to run through trains to Uxbridge due to rapidly developing suburbs along the line. The extension of Piccadilly line trains to Uxbridge began on 23 October 1933, but with many trains still reversing at South Harrow. By then, most Piccadilly line trains continued beyond Hammersmith, and District line trains to Hounslow were reduced to off-peak shuttles to Acton Town. An enhanced off-peak Piccadilly line service was introduced on 29 April 1935, cutting off-peak District line services down to the Acton Town–[[South Acton railway station (England)|South Acton]] shuttle.{{sfn|Horne|2006|p=60}} South Harrow short trips proved to be an inconvenience. The solution was to move reversing facilities to Rayners Lane. A new reversing siding was built there in 1935, which allowed some peak hour trains to terminate beginning in May 1936. Regular reversals were fully implemented in October 1943.{{sfn|Horne|2007|pp=54,57–58}} Peak-hour District line trains to Hounslow were fully withdrawn on 9 October 1964.{{sfn|Horne|2006|p=88}}

===Modernisation, World War II and Victoria line===
In conjunction with the new extensions, several stations were considered for closure to increase overall line speeds. [[Down Street tube station|Down Street]] closed on 21 May 1932, [[Brompton Road tube station|Brompton Road]] on 29 July 1934, and [[York Road tube station|York Road]] on 17 September 1932.{{sfn|Rose|1999}}{{sfn|Lee|1966|p=22}} All three stations were lightly used. Down Street and Brompton Road were replaced, respectively, by relocated entrances at [[Hyde Park Corner tube station|Hyde Park Corner]] and [[Knightsbridge tube station|Knightsbridge]]. Knightsbridge's new below-ground ticket hall required stairwells from the entrance, one of which took over part of the Barclays Bank branch there. Both of the latter two stations retained their existing platforms, but the access from the surface was reconstructed with their entrances closer to the closed stations. These new entrances were provided with escalators, which replaced the lifts, improving passenger circulation. The Aldwych branch was deemed unprofitable. In 1929, an extension to [[Waterloo tube station|Waterloo]] was approved, costed at £750,000, but no progress was made on its construction. Dover Street (now [[Green Park tube station|Green Park]]), [[Leicester Square tube station|Leicester Square]] and [[Holborn tube station|Holborn]] stations received new sets of escalators, the latter having four in a single shaft. These were completed in the early 1930s.{{sfn|Badsey-Ellis|2016|p=212}}<ref>{{cite web |url=http://www.architecture.com/LibraryDrawingsAndPhotographs/Exhibitionsandloans/VARIBAArchitecturePartnershipexhibitions/UndergroundJourneys/Holdenesque/LeicesterSquare.aspx |title=Underground Journeys: Leicester Square |publisher=[[Royal Institute of British Architects]] |archive-url=https://web.archive.org/web/20110707160725/http://www.architecture.com/LibraryDrawingsAndPhotographs/Exhibitionsandloans/VARIBAArchitecturePartnershipexhibitions/UndergroundJourneys/Holdenesque/LeicesterSquare.aspx |archive-date=7 July 2011 |url-status=dead |df=dmy-all |access-date=11 August 2020}}</ref><ref>{{cite web |url=https://www.flickr.com/photos/36844288@N00/4490232964 |title=Architectural Plan and Elevation |publisher=London Passenger Transport Board |year=1933 |access-date=11 August 2020 |url-status=live |archive-url=https://web.archive.org/web/20200811131255/https://www.flickr.com/photos/36844288@N00/4490232964 |archive-date=11 August 2020}}</ref> As part of the 1935–40 [[New Works Programme]], Earl's Court was largely reconstructed at street level. At [[King's Cross St Pancras tube station|King's Cross St Pancras]], the Piccadilly and Northern lines were finally connected via new escalators, albeit with construction delayed due to financial difficulties.{{sfn|Day|Reed|2010|p=131}}{{refn|The four escalators led passengers down from the ticket hall to the new Central line concourse, and a further three to the Piccadilly line concourse.{{sfn|Horne|2007|p=96}}|group=note}} As a result, [[Russell Square tube station|Russell Square]] station retained its lifts.{{sfn|Horne|2007|pp=92–96}}

To prepare for the [[Second World War]], several stations had [[blast wall]]s added. Others, such as Green Park, Knightsbridge and King's Cross St Pancras, had floodgates installed. The line was also involved in the evacuation of 200,000 children, by transporting them towards both ends of the line, then transferring them to main line trains to continue their journeys to different country distribution hubs.{{sfn|Horne|2007|pp=103–106}} Some underground stations were fitted with [[bunk bed]]s, toilets and first aid facilities, and [[sewerage]]. The disused Down Street was converted to an underground [[bunker]] for government use.{{sfn|Connor|2006|p=33}} Other stations such as Holborn and Earl's Court also had essential wartime uses. The former had the Aldwych branch platforms as the wartime engineering quarters whilst the branch service was temporarily closed.{{sfn|Connor|2001|pp=98–99}} The latter produced [[Torpedo Data Computer]]s at the transfer concourse between the District and Piccadilly lines.{{sfn|Horne|2007|pp=103–106}} Aldwych station was used as storage for [[British Museum]] exhibits.{{sfn|Connor|2001|pp=98–99}} On 13 October 1940, a bomb explosion caused the westbound platform tunnel at Bounds Green station to collapse, killing nineteen shelterers. Train services were suspended for two months.{{sfn|Horne|2007|p=105}}<ref name=blitz>{{cite web |url=http://www.bowesandbounds.org/profiles/blogs/bounds-green-and-the-blitz |last=Richard |first=McKeever |title=Bounds Green and the Blitz |publisher=Bowes and Bounds Connected |date=7 September 2010 |access-date=13 November 2020 |archive-date=9 May 2015 |url-status=live |archive-url=https://web.archive.org/web/20150509120225/http://www.bowesandbounds.org/profiles/blogs/bounds-green-and-the-blitz}}</ref>

[[File:Finsbury Park station Platform Changes.png|thumb|upright=1.35|Reconfiguration of tunnels and platforms at Finsbury Park]]

In preparation for the [[Victoria line]], [[cross-platform interchange]] was to be provided at a few stations, which included Finsbury Park on the Piccadilly line.{{sfn|HMSO|1959|p=13}} This meant that the Piccadilly line had to be realigned there, and the [[Northern City line]] platforms, being parallel to the existing Piccadilly line platforms, were to be transferred to the pair of lines. The Northern City line would be redirected to the surface platforms. The westbound Piccadilly line track would be rerouted onto one of these platforms, with the southbound Victoria line using the other. The northbound Victoria line would reuse the old westbound Piccadilly line platform and a part of the old tunnels, with the Piccadilly line diversion tunnels spanning {{convert|3150|ft|m|abbr=on}}.{{sfn|Horne|2007|p=113}}

Construction of the diversion began in October 1964, with the Northern City line having a temporary closure.{{sfn|Day|Reed|2010|p=163}} At the northern junction, step plate [[Junction (rail)|junctions]] were built to divert the existing line when the new tunnels were complete. They were fitted into the original Northern City line tunnels which had a greater tunnel diameter until two running tunnels were able to merge. The old and unused running tunnel was disconnected and blocked off when the junction tunnel was near its completion. Alteration of temporary [[Points (rail)|points]] junctions and shifting of signals completed the diversion tunnels. In the south, the Piccadilly would be diverted to descend sharply under the northbound Victoria line tunnel, and then ascending to the original level which had a difference of {{convert|5|ft|m|abbr=on}} approximately {{convert|200|ft|m|abbr=on}} north of [[Arsenal tube station|Arsenal station]]. The old westbound tunnel had to be supported on a [[Trestle support|trestle]] for works to be done. The trestle and old tracks were entirely removed once the diversion was ready for switchover. New tracks were laid at a rapid rate; it was done in about thirteen hours on 3 October 1965.{{sfn|Horne|2007|p=113}} Both lines were connected via junctions south of Finsbury Park for stock movement and engineering trains. It was intended for Green Park to have cross-platform interchange, but was deemed impossible due to the lines crossing at right angles. The Victoria line opened on 1 September 1968 from [[Walthamstow Central tube station|Walthamstow Central]] to [[Highbury & Islington station|Highbury & Islington]] via Finsbury Park, and on 7 March 1969 to [[Warren Street tube station|Warren Street]] via King's Cross St Pancras,{{sfn|Day|Reed|2010|p=166}} providing relief to the Piccadilly line.{{sfn|Horne|2007|p=114}}

===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>

===Aldwych branch closure===
{{for|detailed explanation of the Aldwych branch|Aldwych tube station}}
Plans to extend the Aldwych branch south to Waterloo were revived several times during the station's life. The extension was considered in 1919 and 1948, but no progress towards constructing the link was made.{{sfn|Connor|2001|pp=98–99}}

In the years after the Second World War, a series of preliminary plans for relieving congestion on the London Underground had considered various east–west routes through the Aldwych area, although other priorities meant that these were never proceeded with. In March 1965, a [[British Railways Board|British Rail]] and [[London Transport Board|London Transport]] joint planning committee published "A Railway Plan for London", which proposed a new tube railway, the [[Fleet line]] (later renamed the [[Jubilee line]]), to join the [[Bakerloo line]] at {{stl|London Underground|Baker Street}} then run via Aldwych and into the City of London before heading into south-east London. An interchange was proposed at Aldwych and a second recommendation of the report was the revival of the link from Aldwych to Waterloo.{{sfn|Horne|2000|pp=31–33}}<ref name="railarch">{{cite book |url=https://www.railwaysarchive.co.uk/documents/BRLT_RailwayPlanForLondon1965.pdf |title=A Railway Plan for London |date=March 1965 |author=[[British Railways Board]]/[[London Transport Board]] |page=23 |access-date=31 October 2020 |url-status=live |archive-date=30 August 2020 |archive-url=https://web.archive.org/web/20200830122021/https://www.railwaysarchive.co.uk/documents/BRLT_RailwayPlanForLondon1965.pdf}}</ref> London Transport had already sought parliamentary approval to construct tunnels from Aldwych to Waterloo in November 1964,<ref name="notices">{{cite journal |date=3 December 1964 |title=Parliamentary Notices |journal=[[The Times]] |issue=56185 |pages=2 |url=http://infotrac.galegroup.com/itw/infomark/322/785/116929157w16/purl=rc1_TTDA_0_CS33777539&dyn=17!xrn_1_0_CS33777539&hst_1 |archive-url=https://web.archive.org/web/20120927174941/http://infotrac.galegroup.com/itw/infomark/322/785/116929157w16/purl%3Drc1_TTDA_0_CS33777539%26dyn%3D17%21xrn_1_0_CS33777539%26hst_1 |archive-date=27 September 2012 |url-status=live |url-access=subscription}}</ref> and in August 1965, parliamentary powers were granted. Detailed planning took place, although public spending cuts led to postponement of the scheme in 1967 before [[Invitation to tender|tender]]s were invited.{{sfn|Connor|2001|p=99}}

With the Aldwych branch receiving no extensions, it remained a lightly used shuttle service from Holborn. The branch was considered for closure many times, but it survived.{{sfn|Connor|2001|pp=98–,99}} Saturday services were fully withdrawn on 5 August 1962, leaving the line with a peak hour only shuttle on weekdays.{{sfn|Horne|2007|p=134}} In 1993, The original 1907 lifts, which now failed to meet the safety standards at the time, required replacement at a cost of over £3&nbsp;million. As a result, in August 1993, a public inquiry was held for closure of the short branch line. On 30 September 1994, the branch was closed to traffic.{{refn|The [[Epping tube station|Epping]] to [[Ongar railway station|Ongar]] section of the [[Central line (London Underground)|Central line]] also closed on 30 September.{{sfn|Rose|1999}}|name=note4|group=note}} The disused station is now used for commercial filming and as a training facility, with the line retaining its link to the rest of the Piccadilly line.{{sfn|Horne|2007|pp=134–135}}

===Notable incidents and events===
====King's Cross fire====
{{main article|King's Cross fire}}

[[File:Memorial plaque with clock, King's Cross St. Pancras tube station, London.jpg|thumb|Memorial plaque of the [[King's Cross fire]] erected at the station]]

On 18 November 1987, the large [[King's Cross fire]] broke out, the incident being near the Northern/Piccadilly line escalators which killed 31 people.{{sfn|Horne|2007|p=132}}{{sfn|Day|Reed|2010|p=191}} As a result, wooden escalators were replaced at all Underground stations.<ref>{{cite hansard | house = House of Commons | url = https://api.parliament.uk/historic-hansard/commons/1989/apr/12/kings-cross-fire-fennell-report#S6CV0150P0_19890412_HOC_145 | title = King's Cross Fire (Fennell Report) | date = 12 April 1989 | column_start = 915 | column_end = 917 | speaker = [[Paul Channon]] | access-date = 17 August 2020 | archive-url = https://web.archive.org/web/20121227101227/http://hansard.millbanksystems.com/commons/1989/apr/12/kings-cross-fire-fennell-report#S6CV0150P0_19890412_HOC_145 | archive-date = 27 December 2012 | url-status = live }}</ref><ref>{{cite news |url= https://www.telegraph.co.uk/news/obituaries/law-obituaries/8618848/Sir-Desmond-Fennell.html |work=The Daily Telegraph |location= London |title=Sir Desmond Fennell |date=5 July 2011 |access-date=17 August 2020 |archive-url= https://web.archive.org/web/20180613050755/https://www.telegraph.co.uk/news/obituaries/law-obituaries/8618848/Sir-Desmond-Fennell.html |archive-date=13 June 2018 |url-status=live }}</ref>{{refn|All except the two at [[Greenford station]] were replaced. These have since been decommissioned on 20 March 2014,<ref>{{cite news|url=http://www.london24.com/news/transport/tube_s_only_wooden_escalator_to_carry_last_passengers_1_3419976 |title=Tube's only wooden escalator to carry last passengers |last=Mann |first=Sebastian |date=11 March 2014 |publisher=London 24 |access-date=17 August 2020 |url-status=dead |archive-url=https://web.archive.org/web/20141029143253/http://www.london24.com/news/transport/tube_s_only_wooden_escalator_to_carry_last_passengers_1_3419976 |archive-date=29 October 2014 }}</ref><ref>Fact 121 in the reference. {{cite news |url= https://www.telegraph.co.uk/travel/destinations/europe/united-kingdom/england/london/articles/London-Underground-150-fascinating-Tube-facts/ |title=London Underground: 150 Fascinating Tube Facts |last=Attwooll |first=Jolyon |date=9 January 2017 |access-date=17 August 2020 |url-status=live |work=The Telegraph |location= London |archive-url= https://web.archive.org/web/20200817173309/https://www.telegraph.co.uk/travel/destinations/europe/united-kingdom/england/london/articles/London-Underground-150-fascinating-Tube-facts/ |archive-date=17 August 2020}}</ref> being replaced with an [[Inclined elevator|inclined lift]] and an up metal escalator the following year.<ref>{{cite press release |url=https://tfl.gov.uk/info-for/media/press-releases/2015/october/uk-first-as-incline-lift-opens-at-greenford-tube-station |title=Incline lift at Greenford Tube Station is UK First |publisher=[[Transport for London]] |date=20 October 2015 |access-date=17 August 2020 |url-status=live |archive-url= https://web.archive.org/web/20200817181048/https://tfl.gov.uk/info-for/media/press-releases/2015/october/uk-first-as-incline-lift-opens-at-greenford-tube-station |archive-date=17 August 2020}}</ref>|group=note}} The Piccadilly line platforms remained open, but with the escalators to the ticket hall closed for repairs. Access was temporarily via the Victoria line or [[Kings Cross Midland City|Midland City platforms]]. New escalators were fully installed on 27 February 1989.{{sfn|Croome|Jackson|1993|pp=259,262}}

====7 July 2005 London bombings====
{{main article|7 July 2005 London bombings}}
On 7 July 2005, a Piccadilly line train was attacked by [[Suicide attack|suicide bomber]] [[Germaine Lindsay]] in the [[7 July 2005 London bombings|day's London bombings]].<ref>{{cite news |url=http://news.bbc.co.uk/2/hi/uk_news/politics/4689739.stm |title=Image of Bombers' Deadly Journey |publisher=[[BBC News]] |date=17 July 2005 |access-date=17 August 2020 |url-status=live |archive-url=https://web.archive.org/web/20200817152016/http://news.bbc.co.uk/2/hi/uk_news/politics/4689739.stm |archive-date=17 August 2020}}</ref> The blast occurred at 08:50 [[British Summer Time|BST]] while the train was between King's Cross St Pancras and Russell Square. It was part of a co-ordinated [[Islamic terrorism|Islamist terrorist attack]] on London's transport network, and was synchronised with three other attacks: two on the [[Circle line (London Underground)|Circle line]] and one on a bus at [[Tavistock Square]]. The Piccadilly line bomb led to the largest number of fatalities, with 26 people reported killed. Owing to it being a deep-level line, evacuation of station users and access for the emergency services proved difficult.<ref name="north-diary">{{cite news |url=http://news.bbc.co.uk/2/hi/uk_news/4670099.stm |title=Coming together as a city |access-date=17 August 2020 |date=15 July 2005 |last=North |first=Rachel |publisher=[[BBC News]] |url-status=live |archive-url=https://web.archive.org/web/20200817153435/http://news.bbc.co.uk/2/hi/uk_news/4670099.stm |archive-date=17 August 2020}}</ref> Shuttle services were introduced between Hyde Park Corner and the Heathrow loop, between Acton Town and Rayners Lane, and between Arnos Grove and Cockfosters. Full service was restored on 4 August, four weeks after the bombing.{{sfn|Horne|2007|p=132}}<ref name=culgpiccadilly />

====100-year celebration====
On 15 December 2006, a 100-year celebration of the Piccadilly line was launched. A birthday card was revealed by [[Tim O'Toole (businessman)|Tim O'Toole]], then London Underground Managing Director at [[Leicester Square tube station|Leicester Square station]].{{sfn|Horne|2007|p=140}}