State troopers responded to the scene, the shoulder of southbound I-5 at South 200th Street, at about 1:15 a.m. after receiving reports of a serious crash.
A preliminary investigation found that two cars were pulled over on the shoulder as the occupants changed a flat tire on one of the cars.
They looked up, saw another car approaching at high speed and scrambled out of the way.
The speeding car then slammed into the two other cars and flipped over.
Medics treated the driver of the speeding car at the scene. The driver was then transported to Harborview Medical Center for treatment of non-life-threatening injuries.
It was not immediately known if alcohol or drugs were a factor in the crash.
None of the occupants of the other two cars were injured.