Riverside police had just wrapped up a call involving a suicidal person on the 91 Freeway east of Van Buren Boulevard. The two cars collided as vehicles were clearing the scene shortly after 4 p.m.
The officer suffered serious injuries and was in the hospital, where he was reported to be in stable condition.
"Caltrans hopes for a full recovery for the Riverside officer injured in today's collision. We are fully cooperating with the California Highway Patrol in their investigation and will provide comment after the investigation is complete," read a statement by Caltrans.
The Caltrans worker was not hurt. The crash is under investigation.