South Carolina State Highway Department v. Barnwell Bros.

Background

A South Carolina law banned trucks wider than 90 inches and heavier than 20,000 pounds, treating semitrailers as a single unit. Trucking companies, interstate shippers, and the Interstate Commerce Commission challenged the law after a three‑judge federal court blocked enforcement of those limits on many state highways, concluding the limits unlawfully burdened interstate truck traffic.

Reasoning

The core question was whether the size and weight limits unconstitutionally burden interstate commerce. The Court said states may adopt non‑discriminatory rules to protect highway safety and preserve roads, especially when Congress has not regulated the matter. Judges should not substitute their own policy choices for the legislature’s if the law has a rational basis. The Court found evidence in the record—about road construction, axle and wheel stresses, and local highway conditions—sufficient to support South Carolina’s legislative judgment on gross weight and width limits and therefore reversed the order blocking enforcement.

Real world impact

Interstate truckers and shippers will face enforceable limits on many South Carolina routes and may need lighter or narrower equipment or alternate routing. State highway officials can enforce the limits as a safety and maintenance measure unless Congress or a future court decision changes the national standard. The ruling restores the State’s regulatory choice and reverses the prior court’s ban on enforcing these limits.