Journal of Accident Investigation

the final impact (the side slap), the upper torsos of simulated
occupants seated on the side opposite of the impact slid out
from their shoulder belts. Although previous research 9,10
indicated that the belt typically absorbs sufficient energy before
the torso is released, these simulations indicated a potential for
head injury after the torso slid from the upper restraint and the
head contacted the seat cushion.
Conasauga, Tennessee
On March 28, 2000, a southbound CSX Transportation, Inc.,
33-car freight train, en route to Atlanta, Georgia, collided with
the passenger side of a westbound Murray County, Georgia,
school bus at a railroad/highway grade crossing near Conasauga,
Tennessee. The school bus was on its morning route to pick
up children and had entered Liberty Church Road from U.S.
Route 411. On board were seven children and the driver. As
the school bus traversed the passive grade crossing, it was struck
by the train. Figure 4 shows the final resting position of the bus
body.
Figure 4. The bus body came to rest against
the side of the train (Consauga, Tennessee).
The school bus was equipped with video recording equipment
to monitor passenger behavior on the bus. These videotapes
showed that, on the day of the accident, the school bus did not
stop as required before attempting to cross the railroad tracks,
nor had it stopped at this crossing on eight previous occasions.
During the accident sequence, the driver and three children
were ejected. Two ejected passengers received serious injuries
and one was fatally injured. The driver, who had been wearing
a lap/shoulder belt that broke, received minor injuries. Of the
four passengers who were not ejected, two were fatally injured,
9 D. Cesari, R. Quincy, and Y. Derrien, “Effectiveness of Safety Belts under
Various Directions of Crashes,” Society of Automotive Engineers, Paper
No. 720973.
10 J. Horsch, “Occupant Dynamics as a Function of Impact Angle and Belt
Restraint,” Society of Automotive Engineers, Paper No. 801310.
OCCUPANT SAFETY IN LARGE SCHOOL BUSES
one sustained serious injuries, and one, who was restrained by
a lap belt, received minor injuries. The two train crewmembers
were not injured.
Using the human vehicle environment system and
MADYMO, the Safety Board conducted vehicle dynamics and
occupant kinematics simulations for this investigation.
The vehicle dynamics simulation (figure ) verified that
the train was traveling about 1 mph and the bus, about 1
mph at impact. The resultant peak accelerations experienced
by the bus during its initial lateral impact with the train were
30 g at the center of gravity, 39 g at the last row of seats, and
31 g at the first row of seats. The peak angular acceleration at
the center of gravity was approximately 2, 00 deg/sec2. The
angular accelerations were higher at the last row due to the
school bus’s clockwise rotation away from the impact point,
the pivoting of the bus about the front axle, and the distance
of the last row of seats from the impact location. During the
initial lateral impact, the velocity of the train changed by 1 to
2 mph due to emergency braking, while the lateral velocity
of the bus increased due to the velocity of the striking train.
Because the train was much larger and heavier than the school
bus, the severity of the collision was more extreme for the bus.
Occupant simulations showed that the occupant seated
at the rear of the bus was exposed to the highest forces and
thus was predicted to sustain the highest level of injury. This
occupant sustained high levels of injury in all simulated
restraint conditions (compartmentalized, lap-belted, and
lap/shoulder-belted). The combination of high-lateral
accelerations and high-rotational accelerations, which occurred
at the same time, contributed to the rapid lateral progress of this
occupant across the aisle (figure 6) and the high contact forces
experienced when impacting the side of adjacent seat back,
side wall, and window frame screw housing. In the front of the
bus, the opposite was true. Simulated occupants restrained by
either the lap belt or the lap/shoulder belt, as shown in figure 7,
were subjected to less-severe accelerations and were therefore
predicted to sustain less-severe injuries.
NTSB JOURNAL OF ACCIDENT INVESTIGATION, SPRING 2006; VOLUME 2, ISSUE 1 9