SIOUX FALLS, S.D. - Tennsun -- The South Dakota Supreme Court's February 4, 2026 decision in Hamer v. Duffy, 2026 S.D. 4, establishes that violations of Federal Motor Carrier Safety Regulations can constitute negligence per se under state law, reshaping how truck accident cases will be litigated and settled statewide. Hoy Law of Sioux Falls represented Justin and Kim Hamer and secured the landmark ruling.

The case arose from an April 2019 collision at a malfunctioning traffic signal near the Interstate 29 interchange in Lincoln County. Justin Hamer, driving a pickup, was struck by a commercial truck operated by Paul Duffy of Cornerstone Poured Foundations. With no independent witnesses and both drivers claiming right of way, the case went to trial, but not before pretrial rulings stripped it down to almost nothing.

The trial court excluded both of Hamer's expert witnesses, blocked his attempt to raise federal trucking regulations, and refused to instruct the jury on those standards. One expert would have testified about Duffy's fatigue from working 13-hour days on fragmented sleep. An accident reconstructionist had calculated Duffy had nearly five seconds to react to Hamer's vehicle. Without that testimony or any federal regulatory framework, the jury found both drivers negligent but awarded Hamer nothing under South Dakota's contributory negligence standard.

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Hoy Law appealed, and the Supreme Court unanimously reversed on three grounds. First, it held that the FMCSRs, adopted into state law under SDCL 49-28A-3, establish the standard of care for commercial truck drivers, and that unexcused violations constitute negligence per se. The Court rejected the defense argument that these regulations don't create a private cause of action. Second, the Court found the trial court abused its discretion in excluding both experts, noting their testimony provided specialized knowledge beyond what any layperson could bring. The Court also observed that defense counsel argued the very issues in closing that the excluded experts would have addressed. Third, the Court ruled the jury should have been instructed on 49 C.F.R. § 392.3, which prohibits operating a commercial vehicle while impaired by fatigue.

The implications reach beyond this case. The FMCSRs cover hours of service, hazardous condition driving, vehicle maintenance, and driver qualifications. Any of those can now support a negligence per se claim when a violation causes injury, shifting the trial question from whether a truck driver acted "reasonably" to whether the driver broke a specific safety rule. It also changes settlement dynamics, giving plaintiffs concrete regulatory violations to point to. Because employers are liable for employees' negligent acts on the job, trucking companies in South Dakota face direct accountability when drivers violate federal safety rules.

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Thanks to Hoy Law taking this case to the state's highest court, the Hamers will get a new trial where their full case can finally reach a jury.