Officials say a Washington Metro system subway train crashed into the back of another at a rail yard, injuring three workers.

D.C. Metro said in a Sunday news release that the injuries were minor and not life-threatening. No passengers were on board.

Metro says a six-car train was returning to the West Falls Church Rail Yard Sunday morning when it rear-ended a parked six-car train. Two workers were cleaning the parked train to get it ready for service.

Metro officials are investigating.

The crash was the latest accident involving Washington's subway system. A June crash killed eight passengers and the train operator. A track repairman was killed in August when he was hit by a gravel spreader. Another worker was killed when he was hit by a train in September.