Silverstone Circuit is best known as the home of the British Grand Prix, which it first hosted in 1948. The 1950 British Grand Prix at Silverstone was the first race in the newly-created Formula One World Championship. The race rotated between Silverstone, Aintree and Brands Hatch from 1955 to 1986, but relocated permanently to Silverstone in 1987. Half the circuit is in Northamptonshire and half is in Buckinghamshire, roughly equidistant from Milton Keynes, Northampton and Oxford. It is built on the site of a World War II bomber base, RAF Silverstone, which opened in 1943. The airfield's three runways, in classic WWII triangle format, lie within the outline of the present track. During the Grand Prix, the airfield becomes the busiest in the UK, complete with its own air traffic control. In recent years Silverstone has been criticised for its deteriorating facilities. Silverstone has, in the past, been criticised for traffic jams on race day. When the race was moved to an April date in 2000, rainy conditions turned car parks into mud baths, causing chaos for spectators trying to park.