Comment Re: ...not that you should be speeding on public r (Score 1) 167
If you set it to "85th percentile of observed traffic" you are selecting 15% to be targets of fines. Why 15 and not 20, or 10?
States with "reasonable and prudent" rather than "explicit speed limits" do a more logically consistent job here. Reasonable and prudent is what we're really looking for - everyone choose a speed that is safe for the conditions of the road, the vehicle, and the surrounding traffic.
The problem is that it's difficult to fine people for that, because it is partly subjective and different for every driver and weather conditions. It's much easier to set an explicit speed limit and then measure speeds. Explicit speed limits exist for the convenience of the courts, with safety of the road users as a distant secondary objective.
If you want to improve safety, then look into "traffic calming" measures. In particular those that cause drivers to perceive higher risk (and research into conditions where drivers falsely perceive lower risk). Even just drawing the lines narrower on a wide street can have an effect. If you design the road right, drivers will naturally choose the right speed for the environment without any need for a road nanny.