I remeber a few years ago a mate telling me that one, if you wanted to avoid setection you had to be going in excess of 160mph, then they got a picture of your shadow, 150 and you might be ok, 160 and you're fine.
yeah I thought, urban myth, 'till he said to one of my other mates "but don't try doing it on the road past your work or you'll leave the floor on that little bump"
Yeap, I think he had tried it.