The Southampton man, whose name was not released, slammed into the back of a Northampton patrol car around 9:30 p.m. along Mount Tom Road near Island Road, police said.
The officer had been called to the area after a tree fell and knocked down power lines. They were sitting in the "fully illuminated" cruiser awaiting backup to direct traffic when the car slammed into the rear of the vehicle, Northampton police said in a Facebook post.
The officer was treated and released from Cooley Dickinson Hospital in Northampton for a minor head wound.
Police closed the road for four hours as they cleaned, cleared, and investigated the scene.
The Southampton man remained at the crash site. Authorities arrested him on charges of operating under the influence and negligent operation of a motor vehicle, police said.
He was not injured.
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