Journal of Accident Investigation

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