Editing Piccadilly line (section)

===Depots and sidings===
[[File:Northfields Depot (18036366511).jpg|thumb|Northfields Depot, with an [[London Underground S7 and S8 Stock|S stock]] train]]
The line has two depots, at [[Cockfosters tube station|Cockfosters]] and [[Northfields Depot|Northfields]]. The former site is near [[Trent Park]], and was the preferred site over [[Oakwood tube station|Oakwood]], which was smaller,{{sfn|Horne|2007|p=66}} and its only access point was south of the station. Subsequently, Oakwood was built with an island platform, with its intended three-track terminus layout moved to Cockfosters.{{sfn|Horne|2007|p=72}} Light maintenance and cleaning of trains is done here, with the latter site, being the main depot, having train maintenance facilities.{{sfn|Horne|2007|p=127}} Northfields depot is also double-ended, with access from just west of [[Boston Manor tube station|Boston Manor station]]{{sfn|Horne|2007|p=50}} and Northfields station. For it to be built, the latter station had to be rebuilt nearer to [[South Ealing tube station|South Ealing station]].{{sfn|Horne|2007|p=55}} The depot was opened earlier than the Hounslow extension, on 4 July 1932, and fully electrified two months later.{{sfn|Horne|2007|p=57}}<ref name=cartomap/>{{refn|When opened, some District line trains were stabled here.{{sfn|Horne|2007|p=57}}|group=note}}

Single [[Siding (rail)|sidings]] are placed at Rayners Lane, Oakwood, Down Street (Hyde Park Corner), and Wood Green. Arnos Grove, Acton Town, South Harrow, Uxbridge, Hammersmith and Heathrow Terminal 5 have more than one siding for reversing trains or storing them.<ref name=cartomap/> Four [[Crossover (rail)|crossovers]] were built for the initial line opening in 1906,{{sfn|Horne|2007|p=27}} [[Hounslow Central tube station|Hounslow Central]] on 3 March 1923,{{sfn|Horne|2007|p=46}} and double crossovers at South Harrow were added in the 1930s.{{sfn|Horne|2007|p=57}}

Crossovers with other lines are present on the Piccadilly line. A connecting tunnel from the northbound Piccadilly line at King's Cross St Pancras to the northbound [[Northern line]] Bank branch was constructed in 1927.{{sfn|Horne|2007|p=98}}{{refn|It was built to facilitate rolling stock transfers between lines and to reach [[Acton depot|Acton works]].{{sfn|Horne|2007|p=98}}|group=note}} At Finsbury Park, a set of crossovers in the south were retained where trains can cross over onto the Victoria line.{{sfn|Horne|2007|p=114}}

[[Lillie Bridge Depot|Lillie Bridge]] was the main depot when the Piccadilly line was initially opened. Trains entering service on the line had to reverse and enter the District line tracks first via [[West Kensington tube station|West Kensington]].{{sfn|Horne|2007|p=26}}{{sfn|Follenfant|1974|p=130}} When the Piccadilly and District line tracks were realigned in the 1930s, access points into the depot had to be altered.{{sfn|Horne|2007|p=54}}{{sfn|Follenfant|1974|p=131}} When the line was extended to Northfields and Cockfosters in 1933, all trains except seven{{refn|This figure excluded trains serving the Aldwych branch which were also parked at the depot.{{sfn|Horne|2007|p=57}}|group=note}} were stabled at the newer depot.{{sfn|Horne|2007|p=57}} Once the Cockfosters depot was opened, Lillie Bridge was converted to a maintenance depot, where it housed only engineers' and materials trains.{{sfn|Horne|2007|p=90}}{{sfn|Follenfant|1974|p=130}}