When were exemptions from the 25 mile per hour speed limit put i

Avalon - When were exemptions from the 25 mile per hour speed limit put into effect for pickup trucks (and trucks in general)? Trucks roar up and down Dune Drive at 50 mph, and go unnoticed. Let a passenger car exceed 30 mph and tickets are a flying. This seems especially true if the pick up truck is a construction worker.