"You do realize, I hope, why seat belts aren't necessary? Think about it -- what is the purpose of seat belts in cars? Is it not to keep you from going through the windshield in a head-on collision? (yes, it is, because the belts lock up when they are advanced out too quickly, as would happen when a body moves forward.) Having gained that knowledge, ask yourself what difference a seat belt would make in a school bus when the seatbacks are already tall enough to prevent that kind of forward motion. It's a little trick called compartmentalization." - Garrett W.