The correct solution here is road engineering so that the natural speed of the road is slower, rather than artificially slowing down traffic via a posted limit. This can be done by adding curves or thinning the road
Pennsylvania seems to have started pushing towards that in the middle of last year:
"On Aug. 5, the Superior Court of Pennsylvania held for the first time that Pennsylvania's Medical Marijuana Act (MMA) allows an employee to sue his or her employer for taking an adverse employment action based on the employee's status as a certified user of medical marijuana."[1]