Consolidated Freightways Corp. (Consolidated) (plaintiff) was a trucking company with routes that included shipping goods through Iowa. Consolidated used both semi (one trailer) and twin (two trailers) trucks in its operations. Consolidated preferred to use 65-foot-long twin trucks because they could transport more goods at once. An Iowa state law, however, prohibited the use of most trucks longer than 55 feet within the state’s borders. Consolidated could either use other trailer options, detach its trailers at the Iowa border, or divert its trucks around the state. Consolidated was not satisfied with these options and filed suit against Kassel (defendant), the state official responsible for enforcement of the Iowa statute, in federal district court on the ground that the Iowa state law unconstitutionally burdened interstate commerce. Iowa defended its law on the ground that it was necessary for highway safety. The district court concluded that there was no difference in safety between a semi and a twin truck and held the Iowa law unconstitutional. The court of appeals affirmed, and the United States Supreme Court granted certiorari.