From Virginia State Police: SALEM, Va. – Virginia State Trooper C.V. Cintron is investigating a fatal motor vehicle crash on Interstate 81 in Roanoke County.  The crash occurred at 3:11 p.m. at the 140.5 mile marker, one half mile south of Route 419 in Roanoke County.A 1998 International tractor trailer was traveling north on Interstate 81 when the truck ran off the right side of the roadway, struck the guardrail and continued down an embankment.The driver was identified as Joseph Daniel McDowell, 53, of Richmond, Va.  Mr. McDowell was wearing his seatbelt and died at the scene.The tractor trailer was carrying wood products and a fuel spill was involved.  Crews worked into the evening cleaning up the spill and removing the truck.The crash remains under investigation.