The problem is that the majority of drivers (about two thirds, I understand), have got into the habit of driving well above the legal speed limits ....
Wessex Water are currently renewing a main on the quite heavily used B road between Gillingham and the A303. It's a typical 60 mph 2-lane country road.
They have traffic lights protecting the road works themselves, which take up one lane, and have imposed a 30 mph speed limit, fair enough, but at either end of the works, there is a HUGE - and I mean huge - run-off before the 30 mph zone ends and you're back to normal line speed. Going through the traffic lights today, all the cars in front of me accelerated away from the road works and must have been doing 40-50 while still technically in the 30 mph limit. I'm totally paranoid about mobile traffic cameras and stuck to 30, not exactly endearing myself to the people behind.
My point is this - there is absolutely no need whatsoever for Wessex Water / the Local Authority to impose such a lengthy 30 mph limit either side of these works. And we see that all the time down here, including with fixed speed 30/40/50 mph limits. This is something that needs addressing alongside all the measures imposed to curb speeding.