What is Piccadilly line?
{{Infobox rail line | name = Piccadilly line | logo = Piccadilly line flag box.png | logo_width = 250px | logo_alt = | image = RUSSELL SQUARE-14 020909 CPS (3998135457).jpg | image_width = | image_alt = | caption = A Piccadilly line train at {{lus|Russell Square}} | type = [[Rapid transit]] | system = [[London Underground]] | mapcolour = Dark blue | mapcolourlink = Tube map | stations = 53 | ridership2 = 210.169 million (2011/12)<ref>{{cite web|url=http://www.tfl.gov.uk/assets/downloads/Performance_Data_Store_P2_2012-13_Issued(1).xlsm|title = LU Performance Data Almanac|publisher=[[Transport for London]]|year=2011–2012|accessdate =1 August 2012 |url-status = dead|archive-url=https://web.archive.org/web/20120803065342/http://www.tfl.gov.uk/assets/downloads/Performance_Data_Store_P2_2012-13_Issued(1).xlsm |archive-date=2012-08-03}}</ref> passenger journeys | open = 15 December 1906 | lastextension = 2008 | character = Deep Tube | depot = Cockfosters<br /> Northfields | stock = [[London Underground 1973 Stock|1973 Stock]] | linelength = {{convert|71|km|mi||abbr=on}} | tracklength = | gauge = {{RailGauge|4ft8.5in|allk=on}} | website = [http://www.tfl.gov.uk/ tfl.gov.uk] | map_name = [[Transport for London]] rail&nbsp;lines | map = {{London rail lines}} | map_state = collapsed }} The '''Piccadilly line''' is a line of the [[London Underground]]. It is coloured dark blue on the [[Tube map]]. It is the fifth busiest