A policeman stops a car that is going very slowly on the I40 highway, and says to the driver "Why are you going so slow? You're holding up traffic!"
"Well," says the man, "the signs say I40."
"That's the road number," says the policeman, "not the speed limit."
Then he notices a woman in the back seat, trembling all over. "Is your passenger all right, sir?" he asks.
"Don't worry officer," says the man, "my wife is always like that when we come off Hwy I170."