There's a good photo on Pastscape showing just how close the circle is to the road, and only a very thin layer of trees protecting it...
Yes, and if you click on the Read more about this photograph link, and then on the magnifying glass, you'll get a pretty good close-up of both the circle and the King Stone (on the left). There's someone crossing over the road between the circle and the King Stone; trying to do that with more heavy and fast moving vehicles coming at you isn't going to be much fun. http://pastscape.english-heritage.org.uk/hob.aspx?hob_id=332813