A Maryland State Police trooper died early Saturday on Interstate 95 in Howard County after his cruiser struck a tractor-trailer parked on the highway’s shoulder, police said.

Trooper 1st Class Shaft S. Hunter, 39, an 11-year police veteran and father of six children ages 4 to 19, died at the scene in the southbound lanes of I-95 near the Laurel rest area, police said. Southbound I-95 was closed for about six hours after the 2:40 a.m. crash.

Police said a witness saw the trooper following a speeding motorcycle moments before he crashed into the back of the tractor-trailer parked near the entrance ramp of the rest area.

The truck driver, Albert Sandino, 46, of California was not injured. He had been parked for about 15 minutes as he checked for directions, police said. Sandino was pulling a trailer of household bleach from Aberdeen, Md., to Virginia, police said.

No citations have been issued, but the investigation is continuing, said police spokeswoman Elena Russo. The motorcycle rider, described only as wearing a white helmet, has not been located, she said.

Hunter, who lived in Baltimore County, worked out of the state police barracks in Jessup and had been a captain in the Marine Corps, police said. His death, which came at the end of National Police Week honoring fallen officers, marked the 43rd Maryland State Police official killed in the line of duty.

Col. Terrence B. Sheridan, superintendent of the Maryland State Police, called Hunter “an outstanding trooper who was known for his dedication to duty.”