Grand Pa told me about when Tn instituted speed limits, in 1955. Up til then it was reasonable and safe or some such, outside of town limits.
They theory was adopted to set speed limits at 85% of what the average speed was in an area. Porch Sitters didn't like cars whizzing by at 40 or 55 or 65. They relished the days not long before when cars usually drove 15 mph to 30 moh because roads were not that good and cars not that powerful The reason he said was the small town and other Law saw a way to make some money to pay for police and fire. the 85%rule is ridiculous. Reason says you set the speed limit at what the average speed is plus a bit more, unless you are a control freak and also want to use human nature and want to make money writing tickets.
Case in point of the ridiculous logic used is when they inflicted the national 55mh speed limit. It had been 75 in Tn on Interstates and 65 on State Roads.
If you drove 90, or 15 over the 75 mph limit it was considered reckless driving.
When it was 55 if you drove 15mph over the 55 limit or 70 mph it was labeled reckless driving. That defies logic and reason. Reasonable and prudent should be the rule,and ticket issued to persons driving 10 mph under in the left lane and other regulations to harmonize traffic flow.