In the 1944 case of Southern Pacific Co. v. Arizona Ex Rel. Sullivan, Attorney General, the U.S Supreme Court ruled that an Arizona state law limiting train lengths was unconstitutional because it placed an undue burden on interstate commerce. The law in question limited trains to a maximum length of 14 cars for safety reasons but caused significant operational inefficiencies for railroads like Southern Pacific Company which had to split longer trains into shorter ones at the Arizona border and then reassemble them after crossing the state. In its decision, the court applied what is known as "Dormant Commerce Clause" jurisprudence - interpreting from Article I Section 8 Clause 3 of US Constitution (the Commerce Clause) that states cannot pass laws excessively interfering with or burdening interstate commerce even when Congress has not explicitly legislated on such matters.

In the dissenting opinion for Southern Pacific Co. v. Arizona ex rel. Sullivan, Justice Frank Murphy argued that the majority's decision to strike down an Arizona law limiting train lengths was a misuse of judicial power and encroached upon states' rights to regulate their own commerce for public safety reasons. He contended that there was no clear evidence proving that longer trains were safer or more efficient than shorter ones, as claimed by the railroad company and accepted by the court majority. Instead, he believed this issue should be left up to individual states who are better equipped to assess local conditions and needs rather than being dictated by federal courts based on speculative arguments about interstate commerce efficiency.