Almost every speed limit is too low (2017)

The choice of the 85th percentile speed is a data-driven conclusion—as noted lieutenant Megge and speed limit resources like the Michigan State Police’s guide—that has been established by the consistent findings of years of traffic studies. One member pointed us to a 1992 report by the US Department of Transportation on the “Effects of Raising and Lowering Speed Limits,” which, beside making the same arguments described above, noted that the majority of highway agencies set speed limits below the 85th percentile, leading over 50% of motorists to drive “in technical violation of the speed limit laws.” Why speed limits are low
If you peruse the websites of state’s departments of transportation, you’ll often find a very technocratic explanation of the 85th percentile principle.

Source: qz.com