Like trying to steer a boat through winter chop with a fogged windshield and a slow reaction time, operating under the influence means being in control of a vehicle, vessel, or other equipment while alcohol, drugs, or another intoxicating substance has impaired safe judgment, coordination, or alertness. In legal use, it usually points to driving or otherwise operating something while intoxicated, whether the substance is illegal, prescribed, or over-the-counter. The exact label can vary by state - DUI, OWI, or a similar charge - but the core idea is the same: impaired operation that creates a danger to others.

In practice, the issue often turns on more than a bad breath test. Police and prosecutors may rely on driving behavior, field sobriety tests, chemical testing, and officer observations. In Washington, RCW 46.61.502 makes it a DUI to drive with a blood alcohol concentration of 0.08 or higher, a THC concentration of 5.00 nanograms per milliliter of whole blood or higher, or while affected by intoxicants to a degree that makes safe driving impossible.

For an injury claim, proof that someone was operating under the influence can strongly support negligence and help show fault. If a drunk or drug-impaired driver caused a crash on a flooded road near Puget Sound or anywhere else in Washington, that evidence can increase the value of damages, including pain and suffering, because Washington does not cap non-economic damages.