You know, I have this theory that there never was any truck driver. It was a vengeful ghost out for revenge because David Mann or his car or both bore a striking resemblance to the guy who murdered him. Think about it: we never see the truck driver besides a hand, his cowboy boots and his hat, he didn't get out at the last truck stop for miles and miles, the truck is clearly unkempt and beat-up, and he even helped out those kids in the stalled-out bus.