The state of Iowa had a statute limiting to 55 feet the length of trucks on its highways. This made it illegal for commonly used doubletrailer trucks 65 feet long to use Iowa highways. The shippers had to either use shorter trucks or go around the state. Iowa justified the regulation on the basis of safety on the highways, and because the bigger trucks caused more damage to its highways. Was this regulation constitutional? [Kassel v. Consolidated Freightways Corp., 450 U.S. 662 (1981)]