You seem to to know the right people at the moment Paulus - I hesitate to say anything on this subject as my mode of transport to Avebury is the number 49 bus - but how about a 20 mile an hour speed limit through the village and similar speed restrictions on the stretch of road by WKLB and Silbury Hill (I don't know what the current speed limit is along there).
The very first time I ever visited (back in the last century) was on a pagan's day out organised by some people at Scoob Books (at that time located by the British Museum) - I wasn't pagan but there was a spare seat going on the coach. I didn't quite get as far as the long-barrow as, thinking I was in the middle of the country-side, I came within a hair's breath of being flattened by a speeding car. Quickly scurried back to the safety of the pub - little knowing at the time how much life would change and that I would be living relatively close to Avebury in the future.
The bloody traffic still moves way too fast given there are so many walking around people in the area.