In the mountain west 80mph is the norm, and even then it is more of a suggestion, flow of traffic is closer to 90mph. Some states are posted 70mph on single-lan

In the mountain west 80mph is the norm, and even then it is more of a suggestion, flow of traffic is closer to 90mph. Some states are posted 70mph on single-lane county roads. Many practical logistics of living in those regions become infeasible at 50mph because people have schedules and finite amounts of time for travel. You are being unrealistic about the implications. When you live in the parts of the country that have 80mph limits, and I have, it is normal to spend 3-4 hours driving in a day. Things are very spread out and the distances are far, which is why the speed limits are so high. I've lived in towns where basic things like shopping were a 75 mile drive each way. Casually increasing those drive times by 75% is not a small thing and, frankly, no one would comply. You'll end up in exactly the situation you already have -- people in urban areas will drive slowly and people in more sparsely populated regions will drive as fast as is reasonably safe. The fact that these higher limits are largely in remote areas also has the implication that not that many people are driving that fast anyway, so it is unlikely to have much impact anyway. It would rightly generate considerable resentment with no meaningful impact on carbon emissions. All that aside, my car hits peak efficiency at around 70mph, as did my prior car. You can monitor this in many cars and I do. Drivetrains are optimized for typical highway speeds. It isn't the 1970s.