 The original GNP & BR route was extended at both ends in the early 1930s. In the north, a new route was constructed to Wood Green, Southgate and Cockfosters. In the west, the extension from Hammersmith approved in 1913 was finally carried out. The extension paralleled the District line's route to Acton and Hounslow, and took over the District line's route to Uxbridge. In 1977, the Hounslow branch was extended to Heathrow Airport. The Strand branch was closed in 1994. Today, the GNP & BR's tunnels form the core of the Piccadilly line's 73.97-kilometre (45.96 mi) route.
