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 />
the direct impact zone had a high probability <strong>of</strong> surviving the<br />
crash with only minor to moderate injuries.<br />
Sled Testing<br />
Sled tests were conducted to replicate the acceleration<br />
time history <strong>of</strong> the school bus full-scale frontal impact test.<br />
The derived sled pulse 13 agreed very well with the time<br />
duration (approximately 210 msec) and the peak acceleration<br />
(approximately 12-13 g). The leveling <strong>of</strong>f <strong>of</strong> the acceleration<br />
pulse <strong>of</strong> the crash test from about 40 to 90 msec was a result<br />
<strong>of</strong> the bus body sliding along the chassis. The sled test did not<br />
exactly replicate this plateau and allowed a somewhat higher<br />
acceleration level at this point in the curve. The result was<br />
a slightly more severe test pulse because the peak velocity<br />
<strong>of</strong> the sled was approximately 4 to mph higher than the<br />
barrier-equivalent velocity measured during the frontal crash<br />
test.<br />
Two different test bucks were used to evaluate bus safety<br />
restraint systems. For the first test buck, a section from the<br />
body <strong>of</strong> the school bus was mounted on the sled. This test buck<br />
was used to assess the degree <strong>of</strong> deformation/energy absorption<br />
by the bus floor and the floor’s interaction with the seats, and<br />
to assess any potential for occupant interaction with portions<br />
<strong>of</strong> the interior other than the seats themselves. The finished<br />
test buck is shown in figure 1 . The bus body contained three<br />
rows <strong>of</strong> seats on both the right and left side <strong>of</strong> the center aisle.<br />
This allowed for testing a maximum <strong>of</strong> two rows <strong>of</strong> dummies<br />
per test.<br />
Figure 15. This photograph shows the sled buck for<br />
the frontal crash testing.<br />
Testing with the first sled buck showed no significant<br />
interaction between the dummies and the walls or ceiling <strong>of</strong><br />
13 “Report to Congress on School Bus Safety: Crashworthiness Research,<br />
April 2002” page 19, Figure 6, at http://www-nrd.nhtsa.dot.gov/<br />
departments/nrd-11/SchoolBus/SBReportFINAL.pdf .<br />
the bus shell, although the floor <strong>of</strong> the bus shell sustained some<br />
incremental damage from loading by the mounted bus seats. 14<br />
For that reason, an open-frame, rigid-floor, test buck was used<br />
to provide a more consistent test platform. (See figure 16.)<br />
This test buck allowed for better high-speed imaging <strong>of</strong> the test<br />
event, which improved the analyses <strong>of</strong> the dummies and their<br />
interaction with the bus seats and restraint systems.<br />
Figure 16. A photograph <strong>of</strong> the modified sled buck used<br />
in the second test series.<br />
The sled tests were designed to evaluate occupant size,<br />
restraint strategies, loading conditions, seat spacing, and seat<br />
back height. The occupants were represented by Hybrid III<br />
0th-percentile male dummies, Hybrid III th percentile female<br />
dummies, and Hybrid III 6-year-old dummies. The restraint<br />
strategies that were evaluated included compartmentalization,<br />
use <strong>of</strong> lap belts (with compartmentalization), and use <strong>of</strong> lap/<br />
shoulder belts on bus seats with a modified, non-FMVSS<br />
222-compliant seat back. 1 Other conditions evaluated were<br />
seat spacing, seat-back height, and rear occupant loading.<br />
Results indicated that compartmentalization is an effective<br />
restraint strategy for frontal school bus crashes, in part due to<br />
the relatively low acceleration load in even a relatively severe<br />
crash condition. The padded seat backs appear to be effective<br />
in minimizing the potential for leg and head injury. During the<br />
frontal crash, occupant kinematics were such that chest loading<br />
was not a significant problem. However, these conditions<br />
created some degree <strong>of</strong> risk for neck injury as measured by the<br />
14 The deformation was very small for any single test and accounted for an<br />
insignificant amount <strong>of</strong> energy absorbed by the seats during the crash<br />
simulation.<br />
1 Code <strong>of</strong> Federal Regulations, Title 49, Chapter V–National Highway Traffic<br />
Safety Administration, Department <strong>of</strong> Transportation, Federal Motor<br />
Vehicle Safety Standard No. 71.222; School Bus Passenger Seating and<br />
Crash Protection.<br />
64 NTSB JOURNAL OF ACCIDENT INVESTIGATION, SPRING 2006; VOLUME 2, ISSUE 1