Brain Teaser?

You are a police officer on a highway patrol. You come across an accident in which two cars have collided in an off-highway rest area. Each driver claims that he has been at the rest area for over two hours eating lunch and sleeping and that the other driver drove in from the highway and ran into his car a few minutes ago. You cannot tell from the position of the vehicles which one is telling the truth. There are no witnesses. Can you think of how you might sort out the claims on the spot? What form of reasoning have you used?