re: So the wiff asked a question I never thought of.....why do cars have exhausts

In an off-road situation, it is possible to drag the rear bumper of a truck mashing a rear exhaust closed. This is why they are often dumped out behind a rear tire

I scanned your answers and didn’t see it. If you’ve ever put a camper on a pickup with exhaust out the back, you wouldn’t be asking. The air at the back of any vehicle going down the road is a vacuum. With exhaust out the back you are putting exhaust in that vacuum. With a camper, unless the back window is sealed perfectly (they never are) you are drawing exhaust into the bed. If you have one of those seals between a sliding back glass and the camper, you are drawing exhaust into the cab. You can kill yourself.