Speed limits (in North America) are simply the 85th percentile speed of drivers on a specific type of road. The onus should be on the civil engineer who designed the road to make it physically impossible to go 150 in the first place - e.g. narrow/curved lanes, speed bumps, concrete bollards, trees on the sides, etc. If roads are actually designed properly, then speed limit laws are unnecessary because drivers will naturally slow down to avoid damaging their vehicle or themselves.