Arcturus posted a superb photo a few day ago of a coach/bus speeding into Avebury with the Swindon Stone in foreground of the photo. This was in fact the skilful use of a photographic technique which is explained in the comments box - there is a 30 mile speed limit going into Avebury and buses always slow down. However, it did kick off an interesting discussion which mainly took place in the comments box under the photo (17 comments in all).
Arcturus' Photos (scroll down to Avebury Stone Circle)
I was wondering if there are any other famous sites that have roads either running through them or close by where it is actually dangerous to try and visit by foot. The one that comes instantly to mind is the A4 which has to be crossed if you visit Swallowhead Spring or West Kennet Long Barrow by foot from Avebury - a dangerous and fast road through a World Heritage Site with no concessions to visitors at all.