Journal of Accident Investigation

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KRISTIN M. POLAND, LINDA McCRAY, AND AIDA BARSAN-ANELLI Figure 5. Two still images from the vehicle dynamics simulation show the impact between the bus and train and the separation of the bus body and chassis as the impact continued (Consauga, Tennessee). Figure 6. Kinematics of the rear-seated occupant in all three restraint conditions. (The front of the bus is toward the bottom of the image.) Figure 7. Kinematics of the three occupants in the front of the bus in all three restraint conditions (Consauga, Tennessee). (The actual restraint condition is shown on the left. The lap-belted condition is in the upper right and the lap/shoulder-belted condition is in the lower right.) 60 NTSB JOURNAL OF ACCIDENT INVESTIGATION, SPRING 2006; VOLUME 2, ISSUE 1
Testing and Simulation Full-Scale Crash Testing NHTSA reviewed data from its Fatality Analysis Reporting System (FARS), National Automotive Sampling System (NASS), General Estimates System (GES), and Special Crash Investigations (SCI), as well as State and local crash data and data from the Safety Board. NHTSA found that the most significant factors in two-vehicle, fatal school bus crashes were that they occurred on roadways with posted speed limits between -60 mph and that they involved heavy trucks. Based on these findings, NHTSA designed two full-scale crash tests to represent the real-world environment of large school bus crashes. Frontal Crash Test - The first crash test was conducted by frontally impacting a conventional school bus into a rigid barrier at 30 mph. The impact speed was chosen to ensure that sufficient energy would be imparted to the occupants to evaluate the protective capability of compartmentalization, and to provide a level at which other methods for occupant injury mitigation could be evaluated during sled testing. A 30-mph impact into the rigid barrier is also equivalent to two vehicles of similar size impacting at a closing speed of approximately 60 mph, which NHTSA found to be prevalent in their review of crash data sources. Figures 8 and 9 show the frontally impacted bus before and after the impact. As is typical of large school buses, the body of the bus was mounted to the frame rails of the chassis by a series of clips or clamps. This non-rigid mounting feature allowed the bus body to slide forward approximately 36 inches during impact (see figure 10). This dissipation of impact energy over a longer time reduced the acceleration levels experienced by the vehicle’s occupants. Accelerometers were positioned along the center aisle of the bus body to record accelerations during the crash. Ten dummies were used in the test: five Hybrid II and III 0th percentile adult male (representing adult and large, teenaged occupants), two Hybrid III th percentile adult females (representing average 12-year-old occupants), and three Hybrid II and III 6-year-olds. Four of the ten were ballast dummies, which were placed throughout the bus. See figure 11. Table 2 contains the dummy injury values for the frontal crash tests. The neck injury (Nij) value was calculated based on the criteria being used for the revised FMVSS No. 208,11 “Occupant Protection.” The pass/fail criterion for Nij was 1.0, 11 Code of Federal Regulations, Title 49, Chapter V–National Highway Traffic Safety Administration, Department of Transportation, Federal Motor Vehicle Safety Standard (FMVSS) No. 71.208; Occupant Crash Protection. OCCUPANT SAFETY IN LARGE SCHOOL BUSES Figure 8. The school bus in the frontal impact scenario before the impact. Figure 9. The school bus in the frontal impact scenario after the impact. Figure 10. Displacement of the bus body on the chassis during frontal impact. NTSB JOURNAL OF ACCIDENT INVESTIGATION, SPRING 2006; VOLUME 2, ISSUE 1 61
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