## Facts

- Arizona enacted a 1912 statute limiting passenger trains to 14 cars and freight trains to 70 cars, imposing monetary penalties for violations.
- In 1940 Arizona sued Southern Pacific Company to collect penalties for operating trains exceeding both limits within the state.
- Southern Pacific admitted operating over-length trains but challenged the statute as unconstitutional and inconsistent with federal rail legislation.
- After trial and factual findings, the state trial court held the statute unconstitutional as a burden on interstate commerce.
- The Arizona Supreme Court reversed, treating the statute as a valid safety measure under state police power despite adverse effects on interstate train operations.
- The record showed nearly all rail traffic in Arizona was interstate, and compliance required operational changes affecting trains beyond Arizona.
- The trial court found the law required operation of about 30% more trains, increasing costs by roughly $1,000,000 annually for Southern Pacific, with uncertain or negative safety effects due to more train movements and switching.

## Issues

1. Whether federal rail statutes displaced state authority to regulate train length as a safety measure.
2. If not displaced, whether Arizona’s train-length limits imposed an undue burden on interstate commerce in violation of the Commerce Clause.

## Decision

- The Supreme Court held that the cited federal statutes did not, by themselves, displace state power to regulate train length as a safety measure.
- The Supreme Court nonetheless held Arizona’s train-limit law unconstitutional as applied to interstate trains because it imposed a substantial burden on interstate commerce not justified by the asserted safety benefits.
- The Court credited the trial court’s unchallenged factual findings showing significant operational disruption and cost increases.
- The Court concluded that any safety gain was unproven and that increased train frequency could increase overall accident risk.
- Judgment was for Southern Pacific; the statute could not be enforced against interstate train operations on these facts.
- Justice Rutledge concurred in the judgment; Justices Black and Douglas dissented, favoring greater deference to the state’s safety judgment.

## Legal Principles

- Congressional regulation of interstate commerce does not displace state safety measures absent a clearly manifested purpose to do so, or a direct conflict with federal law or policy.
- Even in the absence of federal preemption, the Commerce Clause limits state laws that materially obstruct interstate commerce.
- For facially non-discriminatory state safety regulations affecting interstate commerce, courts weigh the nature and extent of the interstate burden against the law’s demonstrated local benefits.
- Where regulation of a national transportation system calls for uniform operational standards, substantial state-by-state interference may be unconstitutional when local benefits are weak or speculative.

## Conclusion

The Court upheld state authority to legislate for rail safety absent clear federal displacement, but struck down Arizona’s train-length limits because their heavy operational and economic burdens on interstate rail traffic outweighed the statute’s unproven safety justification.


S. Pac. Co. v. Arizona ex rel. Sullivan, 325 U.S. 761 (1945)