Bibb v. Navajo Freight Lines

The Court normally upheld state safety regulations. However, the safety advantages of contoured mudguards were too inconclusive to justify the "great burden" they imposed on interstate motor carriers. Hence the Illinois law was unconstitutional under the "commerce clause."

Under an Illinois law effective 8 July 1957, all trucks and trailers operating in that state had to be equipped with contoured rear-fender mudguards. Navajo Freight Lines and other interstate trucking companies challenged the law's constitutionality. When it was overturned by the district court, Illinois appealed to the Supreme Court. (Bibb lent his name to the case as state director of public safety.)