SC Hwy. Dept. v. Barnwell Bros.

Background

A South Carolina law banned motor trucks and semi-trailer trucks wider than 90 inches or heavier than 20,000 pounds. Interstate truckers and shippers, joined by the Interstate Commerce Commission, sued to block enforcement, arguing the limits unreasonably burden interstate commerce. A three-judge federal trial court enjoined enforcement on many concrete highways, finding the rules would bar common interstate trucks and increase costs.

Reasoning

The Supreme Court reviewed whether the state limits unduly burden interstate commerce or violate the Fourteenth Amendment. The Court emphasized that states build and maintain local highways and may adopt safety and road‑preservation rules that apply equally to in‑state and out‑of‑state traffic when Congress has not acted. The Court examined the technical evidence — how weight is distributed, differences between gross and axle or wheel limits, road construction variations, and South Carolina’s own studies — and found a rational basis for the legislature’s choice. Because the law was non‑discriminatory and reasonably related to preserving highways and safety, the Court held the state regulation was within the legislature’s power.

Real world impact

The decision allows South Carolina to enforce its truck width and gross weight limits on the highways at issue and reverses the lower court’s injunction. Practically, interstate carriers must comply with the state’s size and weight rules on those roads unless Congress later sets a different national standard. The ruling recognizes room for varied state highway rules based on local road conditions and the legislature’s policy judgments.