Facts of the Case

An Iowa law restricted the length of vehicles traveling on its highways. Iowa justified the law as a reasonable use of its police power to assure safety on the state's roads.

Question

Did the law pose an unconstitutional burden on interstate commerce?

Conclusion

The Court held that the law violated the Commerce Clause for two reasons. First, Iowa could not prove that the vehicles it targeted posed potential danger to highway travelers. The safety interest was "illusory." Second, the law was "out of step with the laws of all other Midwestern and Western States" which did not have similar regulations. This placed significant burdens on the flow of interstate commerce