The trooper was doing a routine traffic stop at around 10 p.m. in the northbound lane of the interstate near milepost 106 when he was hit, according to Trooper Guy Gill.
"The trooper went up and got the driver's information, walked back and sat down in his car and was struck," Gill said.
No one was hurt.
The man who drove into the trooper told Gill he saw the trooper's lights, but didn't realize he was driving on the shoulder of the road.
"He said the windshield was a little bit foggy and all of a sudden he struck the patrol car," Gill said.
Gill said the driver showed no obvious signs of impairment.
The crash temporarily blocked the right northbound lane of the interstate, Gill said.
It's the second crash involving a State Patrol trooper in Thurston County this week.
Another trooper was struck by a car while checking on an abandoned car in a ditch off state Route 8 Tuesday night.
The trooper was inside his patrol car at 9:24 p.m. near Old Olympic Highway when the driver of a red 2004 Ford Explorer driving too fast for the conditions lost control and pushed the patrol car into a tree.
The trooper suffered head, neck and shoulder pain. He was taken to the hospital and has since been released and is recovering at home, Gill said.
"These are 100 percent avoidable collisions," Gill said. "It took error by the driver for these to occur and they are totally avoidable."
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