National
Transportation Safety Board
Highway Accident Report
Crashworthiness
of Small Poststandard School Buses
NTSB Safety Study SS-89/02
Report Date: October 11, 1989
This 228-page study examines the crashworthiness of small, poststandards
school buses
Summary
This study reports on the crash performance of small
poststandard (manufactured after April 1, 1977) school buses and vans
used for school transportation. Occupants of these small school buses
generally fared well in the accidents investigated. As a result of this
safety study, recommendations were issued to the National Highway Traffic
Safety Administration, manufacturers of small school buses, and various
associations of school transportation officials and contractors. The
recommendations focus on the following safety issues: design of restraining
barriers; feasibility of providing lap/shoulder belts or other restraints
with upper torso support for passengers; deficiencies in roof and joint
strength; lack of Federal performance standards for school bus windshield
retention; design of the boarding door controls in certain small school
buses; and the need to correct improper installation and use of lapbelts
and other restraints.
Table
of Contents
INTRODUCITON 1
Definition of Small Versus Large School Bus 2
Why This Study Was Conducted 6
Previous Studies of Large School Buses 7
Studies of Passenger Car Crashes 7
Accident Selection Criteria 10
How the Investigations Were Conducted 12
DIFFERENCES IN FEDERAL MOTOR VEHICLE SAFETY STANDARDS
FOR SMALL AND LARGE SCHOOL BUSES 14
Lapbelts 14
Vehicle Structure 14
Seating 14
OVERVIEW OF RESTRAINT USE AND INJURY ANALYSIS 18
RESTRAINT USE 20
Deficiencies in Official Reports of Restraint Use 21
Restraints Incorrectly Coded as Lapbelts 21
Improper Use of Lapbelts 22
Usual Configuration and Installation of Restraints 22
INJURY OUTCOME 28
Overall Passenger Outcome 28
Minor Injuries 28
Moderate and Above Injuries 28
Importance of Seating Position 30
Differences Between Safety Board and Police
Accident Report Data on Injury Severity 30
Uniform School Bus Accident Reporting Form 31
RESTRAINING BARRIERS 33
Crash Performance of Barriers 34
Consequences of Barrier Design 34
Risk of Head Injury 38
Canadian Crash Tests on Risk of Head Injury 39
Anchorage Strength for Restraining Barriers 40
Criteria for Head Protection 40
Lack of Criteria for thorax or Abdominal Injury 43
Possible Solutions to the Problem of Restraining Barrier Design 44
Removal of Restraining Barrier 44
Redesign of Barrier 44
Installation of Lap/Shoulder Belts 46
Rear-Facing Seats 48
Summary 49
STRUCTURAL INTEGRITY 51
Windshields 51
Inadvertent Door Opening 52
Joint Separations 55
EVACUATION 61
Fire and Fuel Tank Leaks 63
Emergency Exits 63
Special Students 64
Lapbelt Release 64
CONCLUSIONS 66
RECOMMENDATIONS 69
REFERENCES 72
APPENDIXES 75
A Index to Safety Board Study Cases Involving School Vehicles
Built to Federal School Bus Standards 75
B Case Summaries of School Buses Built to
Federal School Bus Standards 79
C Summary of Safety Issues by Case Number 160
D Index to and Case Summaries of Small
School Vehicles Not Built to Federal School Bus Standards 164
E Examples of Conflicting Classifications of School Buses 181
F Data on Public School Transportation, 1986-87 185
G School Bus Sales by Body Type, 1974-88 186
H School Bus Type Designations 187
I Abbreviated Injury Scale (AIS) 189
J Comparison of KABCO and AIS Injury Scales 191
K Limitations of the KABCO Injury Codes 194
L Data on Fatal School Bus Accidents 196
M Federal Motor Vehicle Safety Standards (FMVSS)
Mentioned in Safety Recommendations 197
CONCLUSIONS
1. Because of the differences (size, mass, exterior and interior features)
between a small school bus and large school bus, findings based on investigations
of accidents involving large school buses cannot be extrapolated to
smaller school vehicles.
2. The small school buses involved in the 24 accidents investigated
for the Safety Board's study generally provided good crash protection
to both restrained and unrestrained passengers.
3. If student passengers were injured, injuries usually were minor,
regardless of their restraint status. The head and face were the body
parts most commonly injured among both lapbelted and unrestrained passengers.
4. Seating position was a more important factor than restraint status
in determining injury severity.
5. Accidents in this study offered examples of both the advantages and
disadvantages of lapbelt use.
6. Restraint status, injury severity, and seating location of occupants
often were not accurate in official police reports of the school bus
accident. Evaluation of lapbelt performance based on these sources may
be misleading.
7. Restraint use was high among school bus occupants in the study, probably
reflecting that States or local school districts have policies requiring
that occupants of small school vehicles wear the available seatbelts,
the limited number of youth of the passengers, and presence of adult
aides on limited number and youth of the passengers, and presence of
adults aides on some buses. Nearly three-fourths of the school bus drivers
and two-thirds of the passengers were restrained.
8. Restraint use was low among adult aides on board the school bus.
Only one of seven adult aides; who were charged with ensuring passenger
belt use, was wearing a seatbelt at the time of the crash.
9. The school bus drivers and passengers sometimes did not wear their
seatbelts properly. The most common mistake was failure to adjust the
manual lapbelt to fit snugly. Almost one-third of the lapbelted passengers
were wearing their belts improperly.
10. In some cases, passenger lapbelts and other restraints had been
installed or modified after initial purchase of the vehicle by employees
of the school district or bus contractor in a manner inconsistent with
Federal standards for seatbelts, diminishing crash protection and increasing
the potential to induce injury.
11. Passengers seated in the front rows of Type A school buses are at
special risk of injury in a frontal crash. Type A school buses are not
required to have a restraining barrier forward of the front seats, and
if they do, these barriers do not have to meet the same standards as
those found in other types of school buses. The Safety Board has documented
the danger of being unrestrained in a school bus without a frontal barrier
as well as the danger of being lapbelted and interacting with a barrier
in a frontal crash.
12. Restraining barrier supports and anchors in Type A school buses
sometimes came loose during the crash. Sharp metal edges were sometimes
exposed, and the separations allowed the barrier to move rearward into
passenger seating space.
13. Data from Canadian crash tests suggest that merely requiring that
Type A school buses have frontal restraining barriers identical to those
mandated in larger schoolbuses (Type B, C, and D) will not provide a
solution for head protection. Lapbelted anthropomorphic dummies seated
in the front seats of type A school buses equipped with large school
bus barriers registered unacceptable head injury scores, more than twice
the allowable limit.
14. The Federal Government currently has no injury criteria for abdominal,
spinal or thorax injuries. Researchers do not know how much force and
at what duration will result in fatal or serious injuries to these regions
of the body of lapbelted and unrestrained occupants. Hence, performance
standards for restraining barriers and seatbelts regarding abdominal,
spinal, or thorax injuries do not exist.
15. In multivehicle crashes and other crash scenarios, small school
buses lack the built-in crash advantage of superior size and weight
provided by large school buses. Current Federal standards allow Type
A school buses to be built with roofs less able to withstand rollover
forces than larger school buses. Body joints in Type A school buses
are exempt from Federal joint strength standards.
16. Joint separations were documented in 6, possibly 7, of the 19 cases
involving Type A school vehicles; 5 of the 6 were van conversions. Joint
separations were documented in 1 of the 5 cases investigated involving
Type B school buses.
17. In some accidents, the right side boarding doors opened inadvertently
during the crash, and front windshields were displayed. Retention within
the vehicle is advantageous to survival, so any opening in the school
bus body poses danger to an unrestrained or improperly restrained occupant.
18. School bus windshields are exempt from FMVSS 217, "Bus Window Retention
and Release."
19. The boarding door controls of some small school buses have no positive
latch locking mechanism.
20. In 7 out of 24 cases, the passenger boarding door was unavailable
for use as an emergency exit because of damage sustained during the
accident due to poor design of door control, structural weakness near
the door area, or deformation of the roof above the door.
21. For a variety of reasons, student passengers rarely released themselves
from their lapbelts after the crash. Adults at the scene usually released
the student passengers.
22. Lapbelt use usually did not hinder evacuation efforts, even in rollover
crashes when the school bus came to rest on its side.
23. In the Safety Board's cases, the fuel tanks of the small school
buses (both Type A and B) did not leak after the crash, and there were
no postcrash fires.
24. The definitions of "small" versus "large" school buses used in the
Federal Motor Vehicle Safety Standards, in Federal program guidelines,
by Congress, by State and local school transportation officials, and
by the school bus industry, are not uniform.
RECOMMENDATIONS
As a result of this study, the National Transportation Safety Board
recommends:
--to the National Highway Traffic Safety Administration:
Determine the feasibility of requiring lap/shoulder belts or other restraint
systems that provide upper torso restraint at front seat passenger seating
positions on Type A school buses (gross vehicle weight rating of 10,000
pounds or less). Amend Federal Motor Vehicle Safety Standard (FMVSS)
222, "School Bus Passenger Seating and Crash Protection," and FMVSS
210, "Seat Belt Assembly Anchorages," or any other standards, as needed,
should standards prove incompatible. (Class II, Priority Action) (H-89-46)
Conduct research, including computer simulation and sled crash tests
using Hybrid III dummies if needed, to determine the relationship between
restraining barrier design and injuries to restrained and lapbelted
pass- engers of different sizes on small school buses (gross vehicle
weight rating of 10,000 pounds or less). Research should focus on the
height, width, padding, location, and anchorage strength of the barrier,
and the spacing between the barrier and front seats. Amend Federal Motor
Vehicle Safety Standard 222, "School Bus Passenger Action) (H-89-47)
Amend Federal Motor Vehicle Safety Standard 217, "Bus Window Retention
and Release," to include a performance standard for the minimum retention
of windshields in all sizes of school buses. (Class II, Priority Action)
(H-89-48)
Collect and evaluate accident data on the crash performance of the roof
and emergency exits on small school buses (gross vehicle weight rating
of 10,000 pounds or less) in rollovers. Data should not be limited to
van-based buses. Based on analysis, ascertain whether it is appropriate
to amend Federal Motor Vehicle Safety Standard 220. "School Bus Rollover
Protection," to make roof performance tests for small school buses (gross
vehicle weight of 10,000 pounds or less) to be identical in all aspects
to those now required of large school buses (gross vehicle weight rating
of more than 10,000 pounds). If such tests are not appropriate, modify
the test for small school buses to stress the roof more than the present
force application plate test does. (Class II, Priority Action) (H-89-48)
Collect and evaluate accident data involving small school buses to ascertain
whether school buses with a gross vehicle weight rating of 10,000 pounds
or less should be required to meet joint strength requirements of Federal
Motor Vehicle Safety Standard 221, "School Bus Body Joint Strength."
(Class II, Priority Action) (H-89-50)
Specify in new rulemaking or in an amendment of Federal Motor Vehicle
Safety Standard 206, "Door Locks and Door Retention Components," a requirement
for a positive latch locking mechanism on the passenger loading doors
of small school buses (gross vehicle weight rating of 10,000 pounds
or less) to eliminate the possibility of inadvertent door opening during
a frontal crash or rollover. Work with school bus and school van manufacturers
to develop the performance standards. (Class II, Priority Action) (H-89-51)
Urge manufacturers to provide means to retrofit positive latch locking
mechanisms on existing door controls of small school buses (gross vehicle
weight rating of 10,000 pounds or less). (Class II, Priority Action)
(H-89-52)
--to
members of the School Bus Manufacturers Institute and manufacturers
of van conversion school buses:
Work with National Highway Traffic Safety Administration to develop
performance standards for a locking mechanism for the boarding doors
of school buses with a gross vehicle weight rating of 10,000 pounds
or less to eliminate the possibility of inadvertent door opening during
frontal or rollover crash. (Class II, Priority Action) (H-89-53)
Provide retrofit kits for small school buses (gross vehicle weight rating
of 10,000 pounds or less) currently without positive latch door control
locking mechanisms. (Class II, Priority Action) (H-89-54)
--to
the National Association of State Directors of Pupil Transportation,
the National Association of Pupil Transportation, and the National School
Transportation Association:
Alert your members to the dangers inherent in improper installation
of seatbelts and/or installation of restraint systems not meeting Federal
standards or guidelines in school buses and urge them to correct such
installations. Also alert your members of the need to instruct students
to wear lapbelts properly. (Class II, Priority Action) (H-89-55)
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