The shooting happened just before 3 p.m. on I-93. Officers said two cars driving north on the highway got into a heated argument that escalated.
Someone in one of those vehicles fired a round at the other car but missed, and hit a vehicle in the southbound lane.
The man who was hit had an "extremely minor injury" and refused medical treatment, troopers said.
Police are investigating the shooting and processing evidence collected at the scene. State troopers briefly closed part of the road, but all lanes have reopened.
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