The Washington State Patrol says a 23-year-old man was injured when the car he was driving slammed into an attenuator - also known as a "crash cushion."
Witnesses said it appeared the man was ejected from the vehicle when it crashed, and Seattle Fire Department medics confirmed he was found outside the car.
The man was taken to Harborview Medical Center with major trauma but non-life-threatening injuries.
A state trooper at the scene said the crash is being investigated as a possible attempted suicide.
Three lanes were closed after the crash, causing a large backup. All lanes were expected to reopen by 2 p.m.