A 51-year-old Dumas man was killed Monday morning in a one-vehicle accident on I-530 at the 16-mile marker.

According to a preliminary report, Gregory Bess was northbound on the Interstate when for unexplained reasons the tractor-trailer he was driving ran off the road on the eastside and struck a tree. Bess was pronounced dead at the scene.

The accident was reported at 7:42 a.m. and the death was the 531st reported so far this year on the state’s highways.