Cynically, I say alot of these lower speed limits are being lowered because the roads are so poor and it is easier and cheaper to downgrade the limit than surfacing them to a proper standard. Also of course I think even the most niaive of people knows that everyone speeds at sometime but most won't exceed the limit by much so if you want people doing 50 you set it at 40.
40 On rural roads sounds a bit excessive - the A350 now appears to have a 40mph speed limit, set not by the government but road captains who drive at 40-45
