Four people were treated for minor injuries after a driver rear-ended a police squad car during an overnight traffic stop in Minneapolis.

Around 2 a.m., an officer had stopped a driver on Interstate 35W near 36th Street, according to Minneapolis police spokesman Corey Schmidt. A male driver rear-ended the squad car, which then hit the stopped vehicle. The citizen’s vehicle then swerved into traffic and was struck by another vehicle, Schmidt said.

The officer and three other drivers were taken to Hennepin County Medical Center. The driver of the vehicle who initiated the crash was tested for drug or alcohol; results are not yet available, Schmidt said.

“When it happened, a number of squads responded to shut down the freeway and tend to the injured,” he said.

Minneapolis police and the Minnesota State Patrol are investigating.