Duel Part 1 Richard Matheson

He was heading west, en route to San Francisco. It was Thursday and unseasonably hot for April. He had his suitcoat off, his tie removed and shirt collar opened, his sleeve cuffs folded back. There was sunlight on his left arm and on part of his lap. He could feel the heat of it through his dark trousers as he drove along the two-lane highway. For the past twenty minutes, he had not seen another vehicle going in either direction.

Then he saw the truck...