The Washington State Patrol and social workers at Harborview Medical Center in Seattle are working together to determine the man's identity, trooper Mark Francis said.
The man has been unable to speak since the March 26 accident.
He was not carrying identification. Police have not been able to find his family or friends.
The man was struck while apparently trying to cross the freeway about 5 a.m. near the 75th Street SE overpass.
He is believed to be Hispanic and in his 30s. He is about 5-foot-9, 190 pounds and has black hair and brown eyes.
At the time of the accident, he was wearing a blue-and-black backpack and using a walking stick.
Anyone with information should call 360-654-1204.
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