Just my observation, in my state the highway speed limit is 80 and people drive at right around 80, and drop down to 75 at night. Then, on a Texas road where it was 85, I was surprised to see most people still going about 80. And in a neighboring state where the speed limit is 70 for similar roads, people still drive right around 80. And once I drove through Chicago at night through a stretch where the speed limit was 45, and people were still going 75 - 80... not sure what the deal with 80 is, but it seems to be the sweet spot a lot of the time.