Throughput is mostly independent of road as distances between cars increase more than you can speed up to compensate (you reaction time stays the same or get's

Throughput is mostly independent of road as distances between cars increase more than you can speed up to compensate (you reaction time stays the same or get's worse). Type of road can make a difference, obviously dirt makes the distance requirements worse. If people also exit/enter the road it's even worse. I was assuming an ideal road though with everyone sticking to the same speed. Cross lane movement and speed difference in traffic also places limits and slower speeds limit both of those afaik.