Speed limits should be based on sound traffic engineering principles that give full consideration to the driving patterns of responsible motorists. With extremely rare exceptions, this should result in speed limits set at the 85th to 90th percentile speed of free-flowing traffic. If separate speed limits are set for different classes of vehicles or different time periods, the speed limits for those classes of vehicles or time periods shall also be set at the 85th or 90th percentile speed of those classes of vehicles or those identified time periods.

In those instances where 85th percentile speeds exceed 75 mph, serious consideration should be given to eliminating enumerated speed limits and posting advisory speed limits in those locations with design limitations that require slower speeds.