I haven’t seen the inside of a school bus lately, but I can tell you that regular buses don’t have seat belts. Heck, when they’re crowded enough, people stand and hold onto bars.
It occurs to me that large vehicles may have less need of seat belts. They don’t get jostled as much in crashes, and they’re not likely to drive very fast.
Perhaps I should have said “with no sci-fi or fantasy elements.”