In the 1970's (height of motorway & dual carriage way building?) quite a few old RAF stations in Lincolnshire had the old runways dug up, crushed and used for road base. I knew a farmer who effectively got paid for having his tillable acreage increased! Perhaps there was a similar arrangement up here (parts of the A9?).
...but they commented the runways had gone and crops were growing where they used to be. Strange that as every other disused airfield I have seen still has the runways present as the cost and effort of removing them must be immense.