But the main reason is that school buses incorporate a passive restraint system called compartmentalization, which is designed to protect children without seat belts. What does compartmentalization have to do with why seat belts are not required in school buses? Seat belts are not required in school buses over 10,000 lbs. gross vehicle weight rating (G.V.W.R.) because the federal government concluded from available research that compartmentalization is a better safety measure. Some of the key arguments favoring compartmentalization rather than seat belts are as follows:
Compartmentalization is more manageable. The protection exists and is in force without depending on any action by the children or any extra special supervision by drivers or monitors. Seat belts require discipline and supervision to keep them clean, unraveled, in use, and properly adjusted.
Compartmentalization works equally well for one, two or three students per seat. Today’s 39-inch wide standard seats may contain three small children or two large ones or any combination in between. Arranging seat belts to properly handle any combination is difficult, if not impossible; the best known solution with seat belts is to restrict each seat to two students and two belts, which has the disadvantage of sharply reducing the carrying capacity of bus fleets. Compartmentalization works whether students have fully developed abdominal areas or not. Conventional seat belts, which are lap restraints only, are not suitable for small children (under 8 years of age) whose abdominal area and bone structure are not adequately developed to take the force of a lap belt alone. They need the help of chest harnesses also, which adds to the complexity of a proper safety belt solution.
Compartmentalization, once it has done its energy absorbing job, leaves the student free to escape the bus. Seat belts could leave students strapped in, upside down, perhaps unconscious, in burning or flooding buses.
Compartmentalization is most affordable. Although not a part of the DOT reasoning, this is a factor to be considered. In evaluating the cost of seat belts, one should include the cost of retractors and chest restraints, also, since those appear to be needed. Even more important to cost projections is the probability that a seat belt solution will lead to two students per seat and greater spacing between seats, thereby requiring more buses for the same student load.
After extensive research during the 1970’s, the Department of Transportation and its agency, the National Highway Traffic Safety Administration (NHTSA), determined that the safest and most practical arrangement for school bus seating would be a “compartmentalization” concept. Accordingly, the new safety regulations that were effective for school buses manufactured on or after April 1, 1977, included this requirement among other improvements made that year.
Under the compartmentalization concept, seat backs in school buses are higher, wider and thicker than before. All metal surfaces are covered with foam padding. This structure must then meet rigid test requirements for bending and absorbing energy, such as would be required if a student’s body were thrown against the padded back. In addition, the equivalent of a seat back, called a “barrier,” is placed in front of the first row of seats at the front of the bus.
In addition to padding, today’s seats also must have a steel inner structure that springs and bends forward to help absorb energy when a child is thrown against it. The steel frame must “give” just enough to absorb the child in the seat ahead. Also, of course, the seat is required to be anchored to the floor so strongly that it will not pull loose during this bending action. And the floor itself must be so strong that it will not be torn by the pulling action of the seat anchors during a crash.
Seats are spaced close together as another safety protection to ensure containment of children after a crash. If the seats are spaced too far apart, the student could be thrown too far before being cushioned and/or could be thrown outside the compartment altogether. Current regulations require that seats are no more than 24-inches apart.