If it was a state highway, he had to be going to/from someplace fairly close, otherwise he would have been on an interstate..I agree with Mr. Mountain William, when you get time, start stopping in on some local truck stops for a cup of Jo..Not too many questions, but a lot of listening and watching..BS about some crappy curves in the area..Bet someone knows that 135 pretty well..
Good luck..Maybe we should start the BBI (Bolter Bureau of Investigation)

Steve