[mitthrowaway2]

Vehicles can all synchronize speed independently based on a well-tuned control law while observing only the distance to the vehicle in front of them. So looking out the window is sufficient for that, if the drivers are not terrible.

If driving at the speed limit on a winding road is unsafe, the speed limit is probably too high for that road. But in practice, it's complex, winding roads that cause people to drive at reasonable speeds, rather than numbers posted on signs.