The trooper was pulled off to the side of the road, with emergency lights on, about 10:30 p.m. on westbound I-90 near Cumberland Avenue, police said.
That's when an SUV veered off the roadway and hit the squad car, causing the SUV to roll over. The trooper was pinned in his car, police said.
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Firefighters from Chicago and Rosemont extricated both individuals, and they were transported to Lutheran General hospital in Park Ridge.
State police said the trooper has since been released from the hospital, but the driver of the SUV remains in serious condition.
It's not clear what caused the driver to lose control. The crash is under investigation.