Also, crossing the road to the King Stone'd be a problem, not to mention fucking the 'ritual landscape'....
You're right Moth. I can't see that the road could be widened towards the circle without cutting down some or all of the trees, and that would not only destroy the ambience of the circle it would bringing the road perilously close to the stones. Widening on the other side of the road would bring it closer to the King Stone - not good either :-( 