[smeej]

Roads do a surprisingly good job of making clear how fast is safe to drive on them. I'm sure there must be places where people think, "Oh wow, going with the flow of the rest of these drivers feels really unsafe," but much more common is the experience where people are comfortably driving 10-20mph over the speed limit and there is no higher incidence of accidents there than anywhere else.

I think in general setting a speed limit to try to regulate speed for the sake of safety is one of the least effective ways to bring about the desired change.