Here's an interesting point...
the 85th percentile rule is accepted by road traffic experts world wide as valid.
It states, that the 85th percentile of traffic speed down a road is the safe speed for that road - if it's dangerous people will slow down - if it's not people will go faster irrespective of a posted limit.
The speed (sorry saftey) camera guidlines for locating the camera state that a camera can only be located where the 85th percentile exceeds the speedlimit (apart from roadworks - I totally agree in roadworks camera should be present tea break or not).
i.e. only put a camera where the majority of road users think it's safe to brake the speed limit.
So speed cameras are therefore not put where the 85th percentile (normal drivers) think that it's dangerous and the dangerous 15th percentile are actually causing a larger hazard than they would otherwise, but rather where normal safe traffic flow encourages a driver to break the speed limit...
Simon.