Why don't school buses have seat belts? Are school buses safe without seat belts?

The National Transportation Safety Board (in the US) says

Large school buses are heavier and distribute crash forces differently than do passenger cars and light trucks. Because of these differences, the crash forces experienced by occupants of buses are much less than that experienced by occupants of passenger cars, light trucks or vans. NHTSA decided that the best way to provide crash protection to passengers of large school buses is through a concept called “compartmentalization.” This requires that the interior of large buses provide occupant protection such that children are protected without the need to buckle-up. Through compartmentalization, occupant crash protection is provided by a protective envelope consisting of strong, closely-spaced seats that have energy-absorbing seat backs.

In another article on their site, the NHTSA says that in some cases, seat belts in buses can worsen injuries. However, my interpretation of the way they stated that is that generic seat belts in school buses may not be safer but restraint devices designed with school bus seating in mind still may be beneficial. In the first article I linked to, they do say "Over the past 30 years, some States have required new large school buses to come equipped with seat belts. There have been no documented injuries or fatalities resulting from use of the seat belts on school buses."

From the Ontario Ministry of Transportation:

Why no seat belts?

Information from all types of school bus collisions demonstrates that the current school bus design provides a high level of protection to occupants and that seat belts may actually adversely affect the safety of children on school buses (Transport Canada).

Instead of requiring seat belts, school buses are designed and constructed differently from passenger cars. School buses protect passengers through "compartmentalization", a design that includes:

• Seats with high backs;
• Seats filled with energy-absorbing material;
• Seats placed close together to form compartments;
• Strong seat anchorages.

Studies have shown that adding seat belts to the current seating configuration of a school bus can increase the chance of head and neck injuries. For a seat belt to be effective, it must be worn correctly, snug and on the upper thighs. Because school vehicles carry passengers from the very young to high school students, if seat belts were used, they would need to be readjusted and their use monitored. A seat belt not worn correctly may cause serious injuries.

The Transport Canada article mentioned on that excerpt from the MTO site has further details, including full references.

Also, think about how hard it is to keep a seat belt on a small child in a car, now have one adult trying to keep seat belts on 30 kids. If the belts are not connected and an accident does occur, the belt ends could become projectiles and cause a pretty bad injury in itself.