Investigators are trying to determine what caused a Port Townsend woman to lose control of her station wagon and cross the median, triggering the collision Monday.
The woman, Jan S. Wheeland, 50, was pronounced dead at the scene, the State Patrol reported.
Wheeland was headed north about 5:10 p.m. when she drove into oncoming traffic and collided with a southbound van.
A tractor-trailer also struck Wheeland's car.
Two people in the 1995 Chevrolet Lumina van, Simone F. McAdoo, 38, of Olympia and Caroline A. McAdoo, 63, of Rochester, were in good condition Tuesday at Providence St. Peter Hospital in Olympia, a spokeswoman said.
A third passenger, Jennifer Cartwright, 39, of Crestwell, Ore., also was taken to St. Peter, where she was treated for minor injuries and released, the State Patrol reported.
After colliding with the van, Wheeland's car was run over by the tractor-trailer and split in two. The passenger portion of the vehicle was dragged about 150 feet, the State Patrol reported.
The tractor-trailer driver, Richard E. Howe, 61, of Clackamas, Ore., was not injured, the State Patrol reported.
State Patrol investigators do not think alcohol was a factor in the collision. Investigators aren't aware of any health problems that could have caused Wheeland to lose control of her car, Trooper Johnny Alexander said.
"It's way too soon," he said.
Despite heavy rain that dampened the road, troopers don't think bad weather was responsible.
One driver said she saw two cars speeding and weaving through traffic just before the accident, as if they were racing. She thinks the two cars might have caused the collision.
"We knew it was going to happen," said Andrea McDevitt, 24, who was driving north on I-5 with her mother and daughter. The two cars cut her and others off, and topped 80 mph, she said.
McDevitt said one car was white with a big spoiler and a bumper sticker that read: "Don't even try to race me."
"They were speeding out of control," she said. McDevitt said she had not yet talked to the State Patrol.
Alexander said troopers had not received any reports of racing in the area.