In so many ways these are ineffective, expensive and dangerous and if anybody in a traffic department had back problems they would never go for this idea, even if there were many other pluses (which there aren't). In council offices people would be out of a job if they didn't think up another (expensive) scheme to add to the rest. The result is speed bumps and a growing accretion of signs which confuse and distract. At Village Way, Rayners Lane I counted 32 metal posts defacing what was once a lovely mock Tudor road. Get rid of the bumps and the clutter.
Why does this idea matter?
It will save time, cost and people's backs.