## Facts

- N. Fiorito Co., Inc. performed a highway improvement project near Vancouver, Washington, using dump trucks that crossed old Highway 99 to reach an on-ramp and dump area.
- Lawrence Derheim drove south on Interstate 5 and entered an off-ramp behind the defendant’s dump truck at a lawful speed.
- The parties disputed whether “Truck Crossing” warning signs were posted near the crossing area; an “End of Construction” sign faced southbound traffic near the underpass.
- As Derheim overtook the dump truck on old Highway 99, the truck made a left turn across lanes toward the on-ramp, and Derheim’s vehicle struck the truck’s left front.
- The dump truck’s left turn violated traffic rules; Derheim did not wear a seat belt and suffered significant injuries.
- In the trial court, the defendant sought to amend its answer and present expert testimony contending that seat belt use would have prevented or lessened Derheim’s injuries.
- The trial court excluded the proposed “seat belt defense” evidence and theories, and the jury returned a verdict for Derheim.

## Issues

1. Whether a plaintiff’s failure to wear a seat belt is admissible as contributory negligence to bar or reduce recovery in a negligence action.
2. Whether a plaintiff’s failure to wear a seat belt may reduce damages under the doctrine of avoidable consequences (mitigation of damages).

## Decision

- The Washington Supreme Court affirmed the judgment for the plaintiff.
- The court held that seat belt nonuse did not bar or reduce recovery as contributory negligence.
- The court held that seat belt nonuse could not reduce damages under avoidable consequences (mitigation).
- The court rejected characterizing seat belt nonuse as assumption of risk that would limit recovery.

## Legal Principles

- Contributory negligence concerns conduct that helps cause the accident; pre-accident seat belt nonuse, standing alone, does not contribute to the occurrence of the collision.
- The avoidable consequences (mitigation) doctrine generally addresses a plaintiff’s post-tort conduct; it does not apply to pre-accident decisions such as not wearing a seat belt.
- A plaintiff’s general failure to use an available safety device is not, without more, a legal assumption of the risk of injuries proximately caused by another’s negligent driving.
- Courts may consider policy and administrability when assessing new affirmative defenses; permitting seat belt defenses can shift trials toward competing expert disputes over safety-device effectiveness and injury causation.

## Conclusion

The court refused to allow the “seat belt defense” in negligence actions under then-existing Washington law, holding that a plaintiff’s failure to wear a seat belt neither constitutes contributory negligence nor supports a mitigation-based reduction of damages, and it does not operate as assumption of risk.


Derheim v. N. Fiorito Co., 80 Wash. 2d 161, 492 P.2d 1030 (Wash. 1972)