All but one lane were closed on Interstate 5 northbound in Seattle, south of I-90, where two cars rolled over.
Rick Johnson, Washington State Patrol Trooper, said on Twitter that the crash was caused by a driver in custody, with DUI cited as a factor.
The backup has extended miles, he said. All lanes have been reopened since then.
Johnson said the driver who caused the collision was driving an SUV when it changed lanes, hit a smaller car, and swept a third vehicle aside. Both the SUV and the first car hit rolled over. The passenger in the SUV suffered serious injuries and the driver of the car, an elderly woman, suffered non-life-threatening injuries, Johnson said.
Because of the injuries, police are processing the scene as an attack, Johnson said.
Johnson first tweeted about the crash just before 11 a.m. on Wednesday.
The left three lanes reopened around 12:15 p.m. and all lanes reopened around 12:40 p.m., but Johnson said people should avoid the area anyway.
Here are pictures from the scene on I-5. Vehicles are run over on both sides of the motorway. This too is blocked for a while, as WSP investigates. I will update with a reopening time when the detectives arrive. pic.twitter.com/bHZFmbbPlA
– Soldier Rick Johnson (@ wspd2pio) January 20, 2021