Two police officers were injured when a driver fell asleep and crashed into a squad car Sunday evening in west suburban Carol Stream.

At 6:46 p.m., the officers had a driver stopped along the shoulder of westbound North Avenue near Schmale Road, according to Carol Stream police.

During the traffic stop, another vehicle drove onto the shoulder and struck the rear of the squad car, ramming it into the vehicle the officers had stopped, police said.

Both officers were taken by ambulance to Central DuPage Hospital in Winfield, where they were treated for non-life-threatening injuries and released, police said.

The driver and passenger in the stopped vehicle were also taken to Central DuPage with non-life-threatening injuries, police said.

The driver of the vehicle that struck the squad car was taken with minor injuries to GlenOaks Medical Center in Glendale Heights, where he was treated and released, police said.

He told police he fell asleep behind the wheel. He was issued five citations, including failure to yield to an emergency vehicle, failure to reduce speed to avoid an accident, improper lane usage, driving on the shoulder and operation of an uninsured motor vehicle.

The crash remains under investigation by the DuPage County Accident Reconstruction Task Force.