Southern Pacific Co. v. Arizona

In Southern Pacific Co. v. Arizona (1945), the U.S. Supreme Court addressed the extent of state power to regulate interstate commerce. The case involved an Arizona law that limited the length of trains operating within the state. The Court ruled that this law unduly burdened interstate commerce, even in the absence of conflicting federal legislation.

The Court established a three-part test to determine the validity of state laws affecting interstate commerce:
1. The law must not discriminate against or excessively interfere with interstate commerce.
2. The commerce regulated should not require uniform national regulation.
3. The state's interest in regulation must not be outweighed by the federal government's interest.1

This decision affirmed the principle of the "dormant" commerce clause, which implies a prohibition against state laws that interfere with or discriminate against interstate commerce. The Southern Pacific Railroad was a major rail system in the western United States, playing a significant role in the nation's transportation network.12