A Maryland state trooper was injured on the Capital Beltway Sunday morning when a passenger car ran into the back of his patrol car, while it was on the shoulder of the highway. The driver of the passenger car was also injured.

The incident occurred shortly before 8 a.m. on the Inner Loop near Route 1 as the trooper was parked to monitor traffic, police said. The other car left the travel portion of the road for “unknown reasons,” and struck the trooper’s patrol car, trapping him inside, police said.

Trooper First Class Robert Cearfoss, who is assigned to road patrol duties at the College Park barracks was flownby state police helicopter to the Maryland Shock Trauma Center where he was undergoing treatment Sunday, the police said.

They said the other driver, whom they identified as Elwin J. Cedilloz, 23, of Washington, was taken by ambulance to Prince George’s Hospital Trauma Center.

Portions of the Beltway were closed for three hours.