Troopers responded to the scene, the southbound lanes of I-5 near 220th Street SE, just after midnight after receiving a report of a serious injury rollover crash.
Arriving at the scene, they found a Subaru Outback rolled over on its roof and a Ford Fusion in the ditch. An injured driver was in each vehicle.
A preliminary investigation found that the driver of the Subaru, a 25-year-old Seattle man, was heading south at high speed when he slammed into the rear of the Ford, troopers said.
The force of the impact caused the Ford to swerve right into the ditch, where it came to rest. The driver of the Ford, a 30-year-old Edmonds woman, sustained minor injuries in the crash.
The Subaru veered to the left after the crash, went up an embankment and rolled onto its top. The driver of the Subaru sustained serious injuries and was taken to Harborview Medical Center. He is being investigated for possible DUI.
Both cars were totaled in the crash.