All lanes of the freeway opened just before 3 p.m.
Four people sustained minor injuries in the crash, including a 1-year-old baby.
State troopers and medics responded to the scene, I-5 just south of South Michigan Street, at about 9:40 a.m. after receiving a report that a northbound semi truck had crashed.
They found a semi on its side in the median between the northbound and southbound lanes. Three northbound lanes were closed and two southbound lanes as a safety precaution and to leave room for emergency crews and vehicles.
The driver of the semi sustained minor injuries in the crash and was taken away in an ambulance. Three people in a passenger car clipped by the semi - a 35-year-old man, a 34-year-old woman and a 1-year-old child - also sustained minor injuries
State troopers were still investigating the cause of the crash.
The semi truck driver told KOMO News that he was traveling from Fife to Blaine carrying machine parts in the middle lane when a car with California plates cut him off. To avoid hitting several cars he swung the truck to the left, crashing through the guard rail.
The truck clipped another car with the three occupants inside before smashing through the guard rail, then landed on its side halfway down the embankment. The car with California plates sped away from the scene, the semi driver said.
As of 1:30 p.m., traffic backups extended for about six miles from the scene on southbound I-5 and about three miles on northbound I-5.
Crews used cables and a winch to slide the semi down to the bottom of the embankment on its side, then reopened all lanes to traffic by mid-afternoon.
When traffic thins out later Wednesday night around 10:30, two lanes will be closed again so the semi can be righted with a crane.