The California Highway Patrol first received the report of the crash at 3:40 p.m. about a half mile before Redtop Road.
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A white Mitsubishi Mirage crashed into a CHP vehicle that was pulled over on the right-hand shoulder, CHP Officer Dave Harvey said.
The Mitsubishi driver and both their right front and rear passengers were taken to the hospital with major injuries, according to Harvey. The CHP officer was taken to the hospital with moderate injuries.
Fairfield Fire Department and CHP officers are on the scene and the crash is currently under investigation.
Three lanes were closed due to the collision and a Sig-alert was issued at 4:32 p.m. Lanes have since been reopened.