Boxer42 - the modus operandi for the Harrier Force (apart from 1 sqdn whose idea of a field deployment was to occupy the 3 & 4 Sqdn HAS sites at The Gut when they were out in the woods) was to operate from wooded areas close to the FEBA (Forward Edge of the Battle Area). In war they'd have used large buildings like supermarkets, industrial complexes etc. Harriers only needed a 1000 foot strip to take off from, motorways would be overkill.
On top of which, the autobahn were also the Main Supply Routes for NATO, with thousands of vehicles heading East to the Inner German Border, hopefully getting into position before they met the 3rd Soviet Shock Army coming West!