Seat belts for all school buses, or just some?

MSNBC:

The Bush administration on Monday proposed a new rule to improve the safety of school bus seats and expand the use of shoulder belts, but stopped short of ordering that all new buses include seat belts.
Secretary of Transportation Mary Peters rode a packed school bus to Morrisville Elementary School — among the first schools in the country to equip some of its new buses with shoulder straps — then announced a proposed rule that would:

  • Increase the height of seat backs on all school buses from 20 inches to 24 inches to help protect older children and adults from being thrown over the seats during accidents.
  • Require all new short school buses — the style more prone to rollover accidents than longer buses — to begin using shoulder straps.