People mostly drive at what feels like a safe speed for the road, regardless of speed limit. Lowering the speed limit significantly below that speed makes roads much more dangerous
This works on the east coast, but massive states like Montana and Texas have 80 mph highways for a reason. Low population density + no trains. You can drive for 3-4 hours at 80 mph between major cities. Many do well north of 80 though.
Between this or running across an infinite lane stroad, I'd pick the stroad. Although I'd prefer to step away from cars as a common method of transportation altogether.