Journal of Accident Investigation

Linear Acceleration (g)
accelerations on the bus, which occurred immediately after
impact with a resultant 18. g. The side slap of the semitrailer
into the side of the rotating bus during the third impact (time =
0.8 seconds) was extremely severe, resulting in a 2821 deg/sec2
maximum yaw angular acceleration of the bus.
Simulation results revealed significant differences in the crash
pulse and the change in velocity between the center of gravity
of the bus and points at the rear of the bus, possibly contributing
to the severity of the injuries for passengers seated there. Table
1 illustrates these differences.
The greatest variance occurred during the last collision when
the bus side-slapped the semitrailer. The simulation showed
that, as a result of this collision, the change in velocity at the
rear of the bus was 44 mph versus 12 mph at the center of gravity
of the bus. The simulation also showed that during this same
collision, portions of the bus located forward of the center of
gravity underwent a smaller change in velocity than the center
of gravity.
In the compartmentalized condition, the simulated occupants
in the rear of the bus first went forward in their seats and then
contacted the seat in front of them with their legs, chests, and
heads. As the bus rotated clockwise, the simulated occupants
slid toward the right side of the bus. Those seated on the right
side of the bus quickly contacted the side of the bus and the
windows and stayed in that position until the third impact (side
slap) of bus and semitrailer. Those originally seated on the left
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Time (sec)
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Figure 2. The two-dimensional linear and angular accelerations of the school bus during
the collision with the tractor semitrailer in the Monticello, Minnesota, crash.
OCCUPANT SAFETY IN LARGE SCHOOL BUSES
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side of the bus contacted the edges of the adjacent seats and
also hit other simulated occupants during the motion. The bus
continued to rotate clockwise until the third impact of the bus
with the semitrailer. This impact started a counterclockwise
rotation of the bus, which caused the simulated occupants to
slide back toward the left side of the bus. Those closest to the
left side of the bus originally impacted the left-side windows
and the left side of the bus, typically with their heads or upper
torsos. Injuries were predicted for these occupants. Those
seated farther from the left side of the bus impacted other
simulated occupants while sliding toward the left and toward
the impacting semitrailer.
Figure 3 illustrates the occupant kinematics simulated for
lap-belted and lap/shoulder-belted occupants. (The figure does
not show the actual or compartmentalized condition.)
In the lap belt restraint simulation, the simulated occupant’s
pelvis was essentially fixed to the seat, causing a whip-like action
for the upper torso. This whip-like action caused the simulated
occupants seated opposite the impact to pivot about the pelvis
and impact their heads and torsos on the seat cushions. Head
injuries were predicted from these impacts. In addition, because
of the configuration of the seats and the dynamics of the bus,
hyperextension of the neck was documented as simulated
occupants on both sides of the bus rotated about the seat back.
For the lap/shoulder restraint, the simulated occupants
displayed similar kinematics as with the lap restraints. During
NTSB JOURNAL OF ACCIDENT INVESTIGATION, SPRING 2006; VOLUME 2, ISSUE 1 7
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Angular Acceleration (deg/sec^2)