Richard Fairhurst wrote:I see your point thirdcrank, but I think that ship has sailed. Many drivers treat NSL as a target speed too. I don't see that installing 30 roundels in place of NSL roundels would cause that sort of driver to speed up: they already drive as fast as they can.
mjr's allusion to technology is interesting, though. Already, satnavs/Google Maps/etc. know about speed limits and use it in route choice. If a road has a 20mph limit, that makes it less likely that a satnav will choose it (because the overall speed will be slower), thereby reducing rat-running. Looking into the future, that will surely be even more important as self-driving cars come into use. (And it may not be that far in the future: there was an interesting paper in the US last month about self-driving cars being feasible on rural roads even without detailed lane mapping databases.)
The idea of reducing speed limits on certain lanes to stop satnavs choosing them is very interesting. I can't see why that wouldn't work.