This incidentally is why used school buses from Colorado are highly desirable in the skoolie community (a skoolie is a used school bus converted to a motorhome). In addition to the generally high-quality transmissions and retarders (essentially for handling mountainous terrain), the "sand" you use doesn't promote rusting-out of the bus bodies like road salt does. In a sense, though, this is still bad for the environment: the extended lifespan of these vehicles keeps them on the road spitting out carbon dioxide longer then they otherwise would.