The problem is that posting a lower limit doesn't really stop most people from driving faster. Then, some people will obey the speed limit and they become hazar

The problem is that posting a lower limit doesn't really stop most people from driving faster. Then, some people will obey the speed limit and they become hazards. Other people might believe the posted speed limit tells you about the speed you can expect cars to go on the road. It doesn't. The main safety increase I can see is with respect to commercial trucking. Not all vehicles have the same acceleration and braking ability. But the fact that people just ignore the speed limit is a hard problem. So, yes, as far as is practical, that's the idea. We just post the speed people are driving at.