Piccadilly line

The Piccadilly line is a deep-level London Underground line which runs between the west and the north of London with 53 stations on the line. The line serves Heathrow Airport, and some of its stations are near tourist attractions in Central London such as King's Cross, Piccadilly Circus and Buckingham Palace. It has two western branches which split at Acton Town, with the main one towards Heathrow Airport terminals and the other northern branch towards Uxbridge. The District and Metropolitan lines share some sections of track with the Piccadilly line. The line is printed in dark blue (officially "Corporate Blue", Pantone 072) on the Tube map. It is the sixth-busiest line on the Underground network, with nearly 218 million passenger journeys in 2019.

The first section, between Finsbury Park and Hammersmith, was opened in 1906 as the Great Northern, Piccadilly and Brompton Railway (GNP&BR). The station tunnels and buildings were designed by Leslie Green, featuring ox-blood terracotta facades with semi-circular windows on the first floor. When Underground Electric Railways of London (UERL) took over the line, it was renamed the Piccadilly line. Subsequent extensions were made to Cockfosters, Hounslow West and Uxbridge in the early 1930s, when many existing stations on the Uxbridge and Hounslow branches were rebuilt to designs by Charles Holden of the Adams, Holden & Pearson architectural practice. These were generally rectangular, with brick bases and large tiled windows, topped with a concrete slab roof. The western extensions took over certain existing District line services, which were fully withdrawn in 1964.