Facts of the Case

The Illinois legislature adopted a law requiring all trucks and trailers traveling on the state's highways to operate with contour mudguards. The legislators believed that this specific type of mudguard would protect motorists by preventing trucks from throwing debris into the windshields of passing or trailing vehicles.

Question

Did a law which required a specific type of rear mudguard on trucks and trailers operated on Illinois's state highways conflict with the Commerce Clause of the Constitution?

Conclusion

Yes. The Court held that the Illinois requirement did place an unconstitutional burden on interstate commerce. While arguing that safety measures "carry a strong presumption of validity when challenged," Justice Douglas nevertheless affirmed that if the effect of such measures are "slight or problematical" then the interests of commerce should prevail. Since the Illinois law was unlike the requirements of almost all of the other states in the nation, the Court found that it did place a great burden on the interstate transport of goods.