Ah... I misunderstood... thought you were addressing C3H8's comment that most busses run around essentially unloaded even with the kids in them... I'd have to agree with that observation... around here I'd guess about 30 (of the ~72 seats) are filled with about 120lb (estimated avg) worth of kid. I thought you were saying that the ones you rode on had 72 seats filled with kids that had an avg weight of 200lbs. That's why I said
!
But you're right... the busses ought to be designed as if each seat holds a large young adult (or regular adult) plus stuff. So 200lbs or more makes sense for a design goal.