Journal of Accident Investigation

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