An airfield would be nice - you could have a track like Thruxton (or bigger), the track itself and then the runways. Thruxton has three runways, the longest is 1.34 km long and is 50m wide. I know it's not Heathrow size (4km or so long, 85 or so wide) but large airports don't get closed for racing, St Pete, which holds IRL, is smaller than Thruxton.