State troopers responded to the scene, on I-5 near the Puyallup River, at about 10:45 p.m. after receiving a report of a pedestrian being struck.
The man was taken to a local hospital with serious injuries. Troopers could smell intoxicants on his breath and believe he had been drinking before he was hit.
A preliminary investigation found that the man was wearing dark clothes while walking in the northbound lanes of travel. He was struck by a 2005 Hyundai Elantra being driven by a 69-year-old Yelm man.
The driver of the Hyundai sustained minor facial injuries in the crash. He was interviewed by troopers and showed no signs of impairment.
"Our investigating currently indicates the pedestrian is at fault for causing the collision," the Washington State Patrol said in a tweet.
Two lanes of I-5 were closed during the investigation and have now reopened.