South Dakota Supreme Court Establishes Federal Trucking Regulations as Standard of Care

Hoy Law wins landmark ruling that reshapes how truck accident cases will be litigated and settled statewide.

Published on Mar. 6, 2026

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The South Dakota Supreme Court's February 4, 2026 decision in Hamer v. Duffy establishes that violations of Federal Motor Carrier Safety Regulations (FMCSRs) can constitute negligence per se under state law. This ruling, secured by Hoy Law, will have significant implications for how truck accident cases are litigated and settled in South Dakota going forward.

Why it matters

The decision means that any violation of federal trucking safety regulations, such as those covering hours of service, hazardous condition driving, vehicle maintenance, and driver qualifications, can now support a negligence per se claim when the violation causes injury. This shifts the focus of trials from whether a truck driver acted 'reasonably' to whether the driver broke a specific safety rule, giving plaintiffs concrete regulatory violations to point to. It also changes settlement dynamics, as trucking companies in South Dakota now face direct accountability when their drivers violate federal safety rules.

The details

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. At trial, the court excluded Hamer's expert witnesses, blocked his attempt to raise federal trucking regulations, and refused to instruct the jury on those standards. Without that testimony or the federal regulatory framework, the jury found both drivers negligent but awarded Hamer nothing under South Dakota's contributory negligence standard. Hoy Law appealed, and the Supreme Court unanimously reversed on three grounds: 1) the FMCSRs establish the standard of care for commercial truck drivers, and unexcused violations constitute negligence per se; 2) the trial court abused its discretion in excluding the expert witnesses; and 3) the jury should have been instructed on the regulation prohibiting operating a commercial vehicle while impaired by fatigue.

  • The South Dakota Supreme Court issued its decision on February 4, 2026.
  • The original collision occurred in April 2019.

The players

Hoy Law

A law firm in Sioux Falls, South Dakota that represented Justin and Kim Hamer and secured the landmark ruling.

Justin Hamer

The driver of the pickup truck that was struck in the April 2019 collision.

Paul Duffy

The driver of the commercial truck that struck the Hamer's pickup.

Cornerstone Poured Foundations

The employer of Paul Duffy, the commercial truck driver.

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What’s next

The case will now go back to the trial court for a new trial where the Hamers' full case can finally reach a jury.

The takeaway

This landmark ruling in South Dakota will have far-reaching implications, shifting the focus of truck accident cases from whether a driver acted 'reasonably' to whether they violated specific federal safety regulations. Trucking companies in the state now face direct accountability when their drivers break these rules, changing the dynamics of both litigation and settlement negotiations.