@Iceman 10112 wrote:
They could if they were on signposts?
Arrows certainly do work when they are on signposts, or even better on gantry signs above the carriageway although I imagine that that would be expensive.
With regard to the B&Q roundabout I suspect that local drivers have become accustomed to tackling it in a particular way and are now loathe to change their ways to conform with the signs. I don’t think the system was broken before, so why change it?