...On certain stretches of interstate freeways and state highways, speed limits are posted for passenger cars and trucks. The word “trucks” on signs giving notice to maximum speed limits means vehicles over 10,000 pounds and all vehicles in combination. This restriction applies to all vehicles towing a trailer regardless of the size of vehicle or trailer (RCW 46.61.410). Fines for speeding are based on miles per hour over the posted speed limit....