The accident occurred just after 3:30 a.m. in the southbound lanes of I-5 just north of Highway 531.
Traffic was blocked for several hours.
The accident involved a 2001 Honda Accord that was driven by an 87-year-old Camano Island man and a tractor-trailer, Washington State Patrol Sgt. Kirk Rudeen said.
The woman who died was identified as Barbara E. Humberson, 75, of Blaine. The truck's driver, a Stanwood man, 44, was not injured.
The truck hit the Honda from behind. The car apparently was stopped in the far right lane of southbound I-5.
The truck driver tried to slow down to avoid hitting the car, but couldn't stop in time, Rudeen said.
The Honda was pushed across the southbound lanes and came to rest in the median.
Robert L. Gwaltney, the driver of the Honda, was taken by helicopter to Harborview Medical Center in Seattle. He was in critical condition.
Troopers were trying to determine why the car was barely moving or stationary at the time of the collision, Rudeen said.
Southbound traffic on I-5 was detoured off at Highway 530, then to Smokey Point Boulevard, then to 172nd Street NE and back onto I-5.
Eric Stevick: 425-339-3446; firstname.lastname@example.org.
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