A portion of U.S. Route 250 had to be shut down for a short time yesterday morning, following a one-vehicle accident in New Pittsburg.  According to the Highway Patrol, the accident happened when a semi went off the roadway, hit a utility pole and overturned, spilling its load of coal.  The semi driver, a 44-year Canton man, said he swerved to avoid hitting another vehicle that had entered his lane.  The man was treated at the scene for minor injuries.