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Status Report, Vol. 37, No. 8 | September 14, 2002 Subscribe

Lap belts on school buses won't improve safety in frontal crashes

A government report concludes that putting lap belts on school buses would have "little, if any, benefit" in reducing serious to fatal injuries in severe frontal crashes and could cause more neck injuries. Lap/shoulder belts on school buses could be beneficial. But if they're misused — with the shoulder part of the belt put behind the back or under the arm — lap/shoulder belts would offer no more benefit than lap belts.

The report from the National Highway Traffic Safety Administration (NHTSA) comes in response to a request from Congress, which asked the agency to study the benefits of equipping school buses with safety belts (see Status Report special issue: child safety, Oct. 2, 1999).

When it comes to improving occupant protection on school buses, it's important to understand that the people riding on these vehicles already are at low risk of crash injury. School buses get into relatively few crashes. For the most part they're driven at slower speeds than other vehicles, and the other vehicles are required to stop for them when they're loading or unloading passengers. When school buses do crash, their larger size and weight mean the people inside are less likely to be injured than they'd be in a smaller vehicle.

There's a longstanding debate about whether belts would further improve the safety of occupants on school buses. The federal government never has mandated belts in full-size school buses, but some states already require belts and other states are considering it. California requires new school buses to have lap/shoulder belts. New Jersey and New York require lap belts. Lap or lap/shoulder belts are required on all new school buses in Florida and will be required in Louisiana starting in 2004.

To assess the potential benefits of requiring belts, NHTSA conducted a series of sled tests comparing lap belts and lap/shoulder belts with compartmentalization, which refers to the protective envelope formed by strong, closely spaced seats with padded, energy-absorbing seatbacks.

Compartmentalization currently is required on all school buses. The sled tests simulated a 30 mph frontal crash into a rigid barrier using dummies representing a 6-year-old child, a 12-year-old child (5th percentile female dummy), and a large high school student (50th percentile adult male dummy). Compartmentalization proved to be effective in minimizing the risk of head, chest, and leg injuries in the simulated frontal impacts. Neck injury measures, however, were above tolerance limits in half of the tests. All dummies except the adult male were kept within the compartment by the height of the seatbacks.

Lap belts kept the dummies in their seats but produced even higher neck injury measures than compartmentalization alone. Lap/shoulder belts performed best overall, NHTSA reports. The belt systems prevented or limited impact with the seatback and produced lower head and neck injury measures compared with compartmentalization. But lap/shoulder belts weren't as effective when positioned either with the shoulder portion of the belt behind the back or under the arm. Neck injury measures were high, suggesting that "when worn improperly, the lap/shoulder belt restraint system can be potentially as dangerous to the passenger as the lap belt restraint system."

The agency stops short of saying whether lap/shoulder belts should or shouldn't be installed on school buses. The agency simply warns that "potential negative consequences ... have not been adequately researched at this time to allow a full determination of the overall cost/benefits."

Based on the findings of this study, NHTSA might upgrade the federal safety standards applying to smaller buses (those weighing less than 10,000 pounds). Instead of the current requirement for lap belts on these smaller buses, the federal standards might be changed to require lap/shoulder belt systems. The agency also is considering a measure to raise the minimum height of the seatbacks on school buses to reduce the potential for larger passengers to ride over the seats.

As part of its ongoing research, NHTSA will evaluate two other potential restraint systems. One is a bus seat with an integrated lap/shoulder belt, and the other is a seat with an airbag/lap belt system. These systems weren't available for the first round of tests. The agency also will look at side impact protection.

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