Bibb v. Navajo Freight Lines, Inc.

Background

An Illinois law adopted in 1957 required trucks and trailers to use a curved “contour” rear mudguard with detailed size, placement, and attachment rules. Several interstate trucking companies that interchange whole trailers challenged the law after a three-judge District Court found it would make straight mudflaps illegal in Illinois even though they are legal in most other States, impose high retrofit costs, and disrupt normal interstate trailer exchanges.

Reasoning

The Supreme Court considered whether the law’s burdens on interstate commerce outweighed Illinois’ stated safety goal. The Court relied on the District Court record showing the contour flap “possesses no advantages” in safety and may create hazards like brake-drum heat, being bumped while backing, or falling off. The Court emphasized that the law conflicts with an Arkansas rule requiring straight flaps, forces costly retrofits ($30 or more per vehicle and $4,500–$45,840 total for plaintiffs), and unduly hinders interline operations, so the statute could not be sustained.

Real world impact

The ruling frees interstate carriers from having to refit or swap mudguards when crossing state lines and preserves fast interline trailer exchanges used for perishables and sealed explosives. The decision notes the Interstate Commerce Commission declined to set flap standards, leaving states free to regulate — but here the Court found a single State’s unique design requirement placed too great a nationwide burden, so Illinois’ law was blocked.

Dissents or concurrances

Justice Harlan, joined by Justice Stewart, wrote a separate opinion agreeing with the judgment and highlighting the District Court findings that the contour mudflap offered no safety benefits and created hazards, reinforcing that those facts made the burden on interstate commerce unjustified.