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National Transportation Safety Board Safety Study

Crashworthiness of Large Poststandard School Buses

Report date: March 18, 1987
Report No. NTSB/SS-87/01

Abstract

This study reports on the crash performance of large poststandard schoolbuses (schoolbus manufactured after April 1, 1977, and weighing more than 10,000 pounds unloaded) in 43 accidents investigated by the Safety Board. The report discusses the Safety Board's findings as to how well the standards are working to protect passengers from injury and whether changes in the standards are needed. The study focuses solely on events during the crash: how well did the bus perform; how did occupants sustain their injuries, if any; and how serious were the injuries. Each schoolbus passenger's experience in the crash also was analyzed to determine the difference, if any, lap belt use would have made. The report concludes with recommendations to the National Highway Traffic Safety Administration, schoolbus body manufacturers, and the State Directors of Pupil Transportation.

Lap Belt Summary

     Based on the findings of this study, the Safety Board does not recommend that States or school districts allocated funds to retrofit or order large poststandard schoolbuses with lap belts for passengers. The Safety Board also does not recommend that Federal schoolbus safety standards be amended to require that all new large schoolbuses be equipped with lap belts for passengers. The safety benefits of such actions, both in terms of reduced injuries for schoolbus passengers and in seat belt use habit formation, have not been proven.
    For reasons outlined in the introduction to this chapter, arguments for and against lap belts on schoolbuses cannot rely on passenger card data for an answer. For this reason, the Safety Board analyzed the types of injuries sustained by unrestrained schoolbus passengers and tried to determine the difference lap belt use would have made on passenger injuries. The Safety Board concluded that, overall, the passengers in these cases would have received no net benefit from lap belt use. This finding of no overall benefit does not include the possibility of lap belt-induced injuries; if this possibility is counted, the introduction of lap belts would have had a negative effect on these passengers' safety. Without lap belt use, 90 percent of the unrestrained passengers in the study's cases (which were slanted toward the more serious accidents in an effort to uncover shortcomings in occupant protection) received minor or no injuries. What effect lap belt use would have had on these passengers is unknown, but it is unlikely lap belts would have reduced the minor injuries any further.
    The possible safety benefits and the installation feasibility of lap/shoulder belts for passengers on large poststandard schoolbuses are an even more unknown factor.
    If money is to be spent to increase the safety of schoolbus passengers, there are more effective ways of allocating funds to increase the chance of a greater safety payoff than introduction of restraint systems for passengers. Some of these ways are discussed later in this summary. Clearly, however, rapid retirement of any prestandard schoolbuses in the fleet and their replacement by poststandard buses should be a top priority.
    The Safety Board found that, overall, large poststandard schoolbuses perform very well, in a wide range of accidents in protecting schoolbus passengers from injury. This finding held true even when the rollover accidents investigated for this study were looked at separately. Eighty-six percent of the unrestrained schoolbus passengers involved in rollover accidents in this study received no injuries or only minor injuries (typically abrasions and contusions). Furthermore, of the small number of passengers who did sustain serious or greater injuries in the study's rollover cases, all of the passengers who died and slightly more than two-thirds of the passengers who survived with serious or greater injuries were injured during the impact which occurred before the rollover. These passengers usually had been seated in the direct impact zone, and it is unlikely that any restraint system would have made a difference.
    The Safety Board's cases also do not support an argument for the need for passenger lap belts to prevent ejection and to minimize the injuries associated with ejection. Very few schoolbus passengers were ejected in cases in the study (about 15 of the 1,119 unrestrained passengers were known to be fully or partially ejected). Unlike cars, schoolbus seats are not near a door which can open and allow the passengers to be ejected upon impact. Windows are partitioned, also making ejection more difficult.
    Lap belt use would not have necessarily reduced the level of injuries sustained by all of the schoolbus passengers who were ejected. Four passengers who were ejected received only minor injuries; if they had remained in their seats, they still could have received minor injuries. (In one case an ejected passenger who received only minor injuries could have been hurt more severely had he remained in his seat; his seat was pushed to within a few inches of the seatback in front of him.) Two ejected passengers received moderate injuries and nine received serious to critical injuries. Before the crash many of these ejected passengers were seated at positions which were penetrated by a striking vehicle. In fact, in some instances, lap belts probably would not have prevented ejected since the passengers' seats were ejected.
    Structural failure is sometimes involved in passenger ejections, but overall, the bodies of poststandard schoolbuses maintained their integrity very well during quite severe crashes; this was not the case in many prestandard schoolbus crashes investigated by the Safety Board.
    After retirement of prestandard buses, the real safety payoff for schoolbus occupants no doubt lies in accident prevention-better training for drivers, improved maintenance, improved equipment (such as better mirrors to overcome blind spots), and other preventive measures.
    Additional or improved equipment is one form of accident prevention. Replacement of the poorly designed driver lap belts now present in most schoolbuses is an obvious step in this direction since it would help ensure that drivers stay behind the wheel when involved in an accident. Investment in equipment to improve the safety of children in the schoolbus loading and unloading zone, where the majority of schoolbus- related pupil deaths occur each year, is another priority.
    Advocates of seatbelts on schoolbuses have proposed that installation of lap belts for passengers may help prevent accidents from occurring. They argue that lap belt use increases orderly behavior on the bus, thus decreasing distractions to the driver created by unruly passengers. Opponents, on the other hand, argue that a driver can be distracted trying to ensure that all passengers are belted.
    The NHTSA study on the possible carryover effects of belt use on schoolbuses cited earlier in this study found no evidence of carryover bud did find that both students and schoolbus drivers reported that discipline had improved on the buses with lap belts. This study, however, was conducted in school districts which had voluntarily installed lap belts on their schoolbuses, and thus were highly motivated populations. Whether the same use rates and increase in discipline would be evident in other school districts if they installed passenger lap belts on buses is not known. Even if it could be proved that discipline improved automatically on buses with lap belts, the effect this would have had on accident rates is unclear. Driver distraction due to discipline problems does not appear to be a common cause of schoolbus accidents.
    North Carolina is one State that has traditionally allowed high school students to serve as schoolbus drivers. It would not be unwarranted to expect that North Carolina might have a larger than usual number of accidents caused by driver distraction from failure to maintain discipline on the bus. After all, 16-year-old drivers might find it especially difficult to enforce order among their peers. Yet, when researchers at the University of North Carolina studied schoolbus accidents in a three-county area in the State to determine the cause of accidents, only 5 percent (3 out of 61 accidents) in a 2-year period were determined to have passenger distractions as a causal factor. The same researchers also analyzed statewide data to see to what extent driver distraction was listed as a problem. Since driver distraction was not listed as a separate item in the police report, it was necessary to examine the police officer's narrative description of each crash. In 1.5 percent (24 of 1,563) of the narratives, there was some indication that the schoolbus drivers had been distracted by their passengers. North Carolina researchers concluded that the true proportion of schoolbus crashes caused by schoolbus driver distraction in their State probably is between 1.5 and 5 percent.
    The North Carolina study did find that schoolbus driver error was responsible for 70 percent of the investigated crashes and that the most frequent bus driver errors involved turning too widely or sharply, driving left of center, improper backing, and failure to yield. Other studies of schoolbus accident causation also have found driver error to be the leading precipitating factor, with failure to yield right of way and excessive speed the most common error. Clearly, driver training is one area with potential for safety payoff.

Conclusions

1. Postandard large schoolbuses are an extremely safe form of transportation compared to other modes of transportation.

2. The Federal schoolbus safety standards, providing for "compartmentalization," worked well in the Safety Board-investigated crashes to protect schoolbus passengers from injury in all types of accidents. Ninety percent of the unrestrained passengers in the accidents in the Safety Board's schoolbus study received only minor or no injuries.

3. If schoolbus passengers were injured, they were most likely to receive minor injuries. Moderate injuries were rare, and serious to critical injuries extremely rare. Intrusion was responsible for the most of the moderate or greater injuries.

4. Intrusion was responsible for all but 2 of the 13 schoolbus passenger fatalities in this study and for all of the schoolbus driver fatalities.

5. Schoolbus occupant deaths and the serious or worse injuries sustained by survivors in the study were, for the most part, attributable to the occupants' seating position being in direct line with the crash forces. It is unlikely that the availability of any type of restraint would have improved their injury outcome.

6. Schoolbus accidents involving collisions with a heavy truck were the most serious injury-producing crashes in the study in terms of schoolbus passenger outcome. Accidents involving passenger cars were the least harmful to schoolbus passengers.

7. Ejection was extremely rare among the unrestrained schoolbus passengers in the study. Approximately 15 of the 1,119 unrestrained passengers were either partially or totally ejected. Since the accidents in the study represent the more severe end of the schoolbus accident scale, and include a disproportionate number of rollovers, it is reasonable to believe that ejection is extremely rare in the overall population of all schoolbus crashes.

8. The post-1977 Federal schoolbus standards requiring increased side panel and roof strength appear to have been successful in eliminating the structural failures responsible for many of the ejections which occurred in prestandard schoolbuses.

9. Schoolbus maintenance access panels failed to withstand crash forces in five cases, which included moderate as well as severe accidents, and came free, becoming a source of injury for passengers.

10. Schoolbus seat cushions were unsecured following 16 crashes; in some cases, schoolbus passengers were injured by contact with the loose cushions or the exposed seat frame.

11. Rollover accidents in the Safety Board's study were associated with higher levels of schoolbus passenger injuries than nonrollovers but to a much smaller degree than anticipated; nearly 86 percent of all the schoolbus passengers involved in rollover crashes were either uninjured or received only minor injuries.

12. The slight increase in the schoolbus passenger injury severity associated with rollover accidents in the study was due primarily to one type of rollover accident: rollover preceded by collision. The initial impact, not the rollover, was responsible for the higher injury levels.

13. Analysis which aggregates rollover accidents, regardless of severity or prior collision, may inflate the importance of the rollover itself as the injury-producing event and mask the importance of other events during the accident, i.e., crush from the initial impact crash forces, and lateral rotation.

14. Lap belt use probably would have made no change in the total number of schoolbus passengers who died in the crashes investigated for this study (possibly one more death would have resulted).

15. Lap belt use probably would have made no change in the number of surviving schoolbus passengers with severe or worse injuries.

16. At best, lap belt use probably would have reduced somewhat the injuries of less than a third (8) of the 24 surviving schoolbus passengers with injuries in the study and made no change for the majority (12). At worst, it might have increased the injury to almost as many passengers with serious injuries as it improved.

17. Lap belt use probably would have worsened the outcome for one-fifth of the 58 schoolbus passengers with moderate injuries. The Safety Board cannot determine the effect belt use would have made on the remainder of the passengers with moderate injuries.

18. The Safety Board cannot estimate the probable net effect of lap belt use on the unrestrained schoolbus passengers in the study who were uninjured or received only minor injuries; it is unlikely that it would have reduced the minor injuries.

19. Almost half of the schoolbus drivers in the study, although required to be restrained when the bus is in motion, were not wearing their lap belts.

20. The lap belted schoolbus driver did not fare better, overall, than the unrestrained drivers, an outcome probably attributable to the nature and severity of the crashes involving lap belted drivers.