State police are investigating a single-vehicle fatal crash in Campbell County. The crash occurred July 4 at 12:45 p.m. on Leesville Road, less than a mile south of Charldon Drive.   A 2003 Honda Accord was traveling south on Leesville Road when it ran off the right side of the road, struck a culvert and overturned several times.    The driver, Tabitha F. White, 37, of Lynchburg, Va., was not wearing a seatbelt and was thrown from the vehicle. White died at the scene.    The crash remains under investigation. Speed was a factor in the crash.