Journal of Accident Investigation
Journal of Accident Investigation
Journal of Accident Investigation
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KRISTIN M. POLAND, LINDA McCRAY, AND AIDA BARSAN-ANELLI<br />
researchers have studied the crashworthiness <strong>of</strong> large school<br />
buses and the associated occupant safety systems inside the<br />
bus.<br />
The main focus <strong>of</strong> this paper is to review large school bus<br />
crashworthiness and the role <strong>of</strong> compartmentalization in<br />
protecting occupants. Included are reviews <strong>of</strong> recent crash<br />
investigations, full scale crash tests, sled tests, and simulation<br />
modeling conducted by the NTSB and the National Highway<br />
Traffic Safety Administration (NHTSA).<br />
Crash investigations, testing, and modeling are reviewed in<br />
an effort to assess the level <strong>of</strong> current protection provided to<br />
school bus occupants and also to assess potential future design<br />
considerations.<br />
INVESTIGATIONS AND TESTING<br />
<strong>Accident</strong> <strong>Investigation</strong>s<br />
The Safety Board investigates many <strong>of</strong> the severe, though<br />
rare, school bus accidents that occur in the United States. In<br />
each <strong>of</strong> these cases, investigators thoroughly reconstruct the<br />
accident by collecting detailed physical evidence, documenting<br />
vehicle damage, impact points, and witness marks, and studying<br />
the crash sequence through the use <strong>of</strong> simulation. The Board<br />
investigated more than six large school bus crashes as part <strong>of</strong> its<br />
1999 Bus Crashworthiness Issues report. 3 Since that time, four<br />
additional large school bus crashes have been investigated. 4<br />
Two <strong>of</strong> the crashes investigated by the Board are discussed here<br />
to illustrate the process and to reinforce the recommendations<br />
from the 1999 Board report.<br />
Monticello, Minnesota<br />
On April 10, 1997, a 77-passenger-capacity school bus was<br />
traveling west on Wright County Road 39, near Monticello,<br />
Minnesota, toward the intersection with Wright County Road<br />
11. On board were 13 children, ages to 11, and the driver.<br />
Meanwhile, a Mack truck tractor, pulling an empty semitrailer,<br />
was traveling north on Wright County Road 11, at a witnessestimated<br />
speed <strong>of</strong> 0 to mph.<br />
As both vehicles approached the intersection, the truck<br />
combination failed to stop for a posted stop sign and, leaving<br />
skid marks extending into the intersection, collided with the<br />
3 National Transportation Safety Board, Bus Crashworthiness Issues,<br />
Highway Special <strong>Investigation</strong> Report, NTSB/SIR-99/04 (Washington,<br />
DC: NTSB, 1999).<br />
4 Conasauga, Tennessee (HWY00MH036); Central Bridge, New<br />
York (HWY00FH001); Omaha, Nebraska (HWY02MH004); and<br />
Mountainburg, Arkansas (HWY01MH02 )<br />
See .<br />
school bus. At impact, the front <strong>of</strong> the school bus hit the right<br />
front side <strong>of</strong> the truck tractor at the tractor’s right front wheel<br />
with about 43 inches <strong>of</strong> overlap. A second impact occurred<br />
when the right truck tandems and the right front corner <strong>of</strong><br />
the semitrailer struck the left side <strong>of</strong> the bus body, about 9<br />
feet behind the forward edge <strong>of</strong> the bus body. A third impact<br />
occurred when the rear <strong>of</strong> the school bus rotated clockwise into<br />
the right side <strong>of</strong> the semitrailer. See figure 1.<br />
Figure 1. Damage to the bus in the Monticello, Minnesota, crash.<br />
The lap/shoulder belt-restrained truck driver and three bus<br />
passengers were killed. The lap belt-restrained school bus<br />
driver received moderate injuries, five students received minor<br />
to moderate injuries, and five students received serious to severe<br />
injuries. The bus was not equipped with any form <strong>of</strong> passenger<br />
restraints.<br />
Using a human vehicle environment system, 6 m-smac<br />
s<strong>of</strong>tware, 7 and Mathematical Dynamical Models (MADYMO), 8<br />
the Safety Board conducted vehicle dynamics and occupant<br />
kinematics simulations for this investigation. Six simulated<br />
occupants, located in the rear <strong>of</strong> the bus, were modeled. These<br />
occupants were chosen because the passengers who sustained<br />
fatal injuries in the Monticello accident were reportedly riding<br />
in three rear seats on the driver’s side and because <strong>of</strong> the<br />
potential interaction with the surrounding occupants.<br />
The vehicle simulation results indicated that, at impact, the<br />
tractor semitrailer was traveling approximately 49.4 mph and<br />
the bus, approximately 0 mph. Figure 2 details the linear and<br />
angular acceleration time history <strong>of</strong> the bus as predicted by the<br />
simulation. The three impacts, described earlier, can be seen in<br />
the plot. The severity <strong>of</strong> this crash is indicated by the peak linear<br />
6 HVE Human Vehicle Environment, Version 3, Engineering Dynamics<br />
Corporation, Beaverton, Oregon 97008.<br />
7 R.R. McHenry, B.G. McHenry, McHenry <strong>Accident</strong> Reconstruction, 1998<br />
McHenry Seminar, McHenry Engineering.<br />
8 MADYMO, User’s Manual 3D Version 5.4, May 1999, Copyright 1999,<br />
TNO Automotive. MADYMO is a general-purpose s<strong>of</strong>tware package<br />
that allows users to design and optimize occupant safety systems using<br />
both a rigid and flexible body.<br />
6 NTSB JOURNAL OF ACCIDENT INVESTIGATION, SPRING 2006; VOLUME 2, ISSUE 1