[steveosnyder]

Originally Posted by bomberjet

The bold statement is not quite correct, IMO. The road is not originally designed for a higher speed, then the speed limit lowered. The road is designed to 10 km/h higher than the posted speed limit is/will be, to allow for driver error. In both speed and direction.

Say for railway design, design speed is track speed. There is very little human involvement in controlling train direction. Ie: they are stuck on the track. Train speed is monitored and controlled much easier than a passenger vehicle. So for that application design and posted speed are the same due to the reduction of allowable error.

But the thing is TAC's code already take into account driver error when they make their 60km/h design speed codes and standards.