Southern Railway Co. v. United States

Southern Railway Company v. United States, 222 U.S. 20 (1911), was a decision by the United States Supreme Court which held that under the Commerce Clause, the U.S. Congress can regulate safety on intrastate rail traffic because there is a close and substantial connection to interstate traffic.
Background.
Congress required all train cars to be equipped with couplers as a safety measure. Southern Railway argued that the requirement applied only to train cars crossing state lines, not to train cars that operated inside one state.
The Safety Appliance Act of March 2, 1893, 27 Stat. 531, c. 196:
Decision.
The Commerce Clause is plenary to protect persons and property moving in interstate commerce from all danger. No matter the source or destination, Congress may require all vehicles moving on lanes of interstate commerce to be so equipped with safety devices to avoid danger to persons and property in interstate commerce.