INSTRUCTIONS:Access Case Study #1, the Mountainburg Arkansas Accident report from the NTSB,at the textbook companion web site by clicking here (Links to an external site.).Read the case study above; assuming your law office has been hired by the school district to bring a civil lawsuit against the trucking company, identify one legal issue related to the case that you would like to focus on for your research plan.In your research plan, be sure to include answers to the following: What is the issue or legal question to be researched for this case?Which jurisdiction, locality, county is involved?What types of resources will you use to find facts to support your client’s case?Where are the resources located?Which online resources are appropriate for this search?Paper #2 INSTRUCTIONS:Review your research plan from Week 2 Assignment 1.Use the online resources that you identified in your research plan, develop specific search queries appropriate for the search engine(s) or database(s) you are using.Use your search queries to gather online resources and list them for future reference, including title, publisher or organization, and URL.Write an internal memorandum to your supervisor, Attorney Owen Mason, summarizing the results of your research.In a brief 1-page memo to Attorney Mason, describe the results of your research and include at least five resources (title, publisher or organization, and URL) that directly relate to the issueNTSB/HAR-02/03
PB2002-916203
Highway Accident Report
UR I B US
UNUM
D
PL
ATION
SA
FE
E
RAN S PO
LT
RT
NAT I ONA
Collision Between Truck-Tractor
Semitrailer and School Bus
Near Mountainburg, Arkansas
on May 31, 2001
T Y B OA
R
National
Transportation
Safety Board
Washington, D.C.
this page intentionally left blank
Highway Accident Report
Collision Between Truck-Tractor
Semitrailer and School Bus
Near Mountainburg, Arkansas
on May 31, 2001
NTSB/HAR-02/03
PB2002-916203
Notation 7490
Adopted September 4, 2002
National Transportation Safety Board
490 L’Enfant Plaza, S.W.
Washington, D.C. 20594
National Transportation Safety Board. 2002. Collision Between Truck-Tractor Semitrailer and School
Bus Near Mountainburg, Arkansas, on May 31, 2001. Highway Accident Report. NTSB/HAR-02/03.
Washington, DC.
Abstract: On May 31, 2001, near Mountainburg, Arkansas, a Gayle Stuart Trucking, Inc., truck-tractor
semitrailer collided with a 65-passenger school bus operated by the Mountainburg, Arkansas, Public
Schools. Three school bus passengers were fatally injured; two other passengers received serious injuries.
Four passengers, the school bus driver, and the truckdriver sustained minor injuries.
The major safety issues discussed in this report are the poor condition of the tractor semitrailer brakes,
inadequate motor carrier inspections and oversight, the use of propane tanks on school buses, and occupant
protection within school buses.
As a result of its investigation, the Safety Board made recommendations to the Federal Motor Carrier
Safety Administration, the National Highway Traffic Safety Administration, the Commercial Vehicle
Safety Alliance, the National Fire Protection Association, and spring brake manufacturers. The Safety
Board reiterated a recommendation to the U.S. Department of Transportation.
The National Transportation Safety Board is an independent Federal agency dedicated to promoting aviation, railroad, highway, marine,
pipeline, and hazardous materials safety. Established in 1967, the agency is mandated by Congress through the Independent Safety Board
Act of 1974 to investigate transportation accidents, determine the probable causes of the accidents, issue safety recommendations, study
transportation safety issues, and evaluate the safety effectiveness of government agencies involved in transportation. The Safety Board
makes public its actions and decisions through accident reports, safety studies, special investigation reports, safety recommendations, and
statistical reviews.
Recent publications are available in their entirety on the Web at . Other information about available publications also
may be obtained from the Web site or by contacting:
National Transportation Safety Board
Public Inquiries Section, RE-51
490 L’Enfant Plaza, S.W.
Washington, D.C. 20594
(800) 877-6799 or (202) 314-6551
Safety Board publications may be purchased, by individual copy or by subscription, from the National Technical Information Service. To
purchase this publication, order report number PB2002-916203 from:
National Technical Information Service
5285 Port Royal Road
Springfield, Virginia 22161
(800) 553-6847 or (703) 605-6000
The Independent Safety Board Act, as codified at 49 U.S.C. Section 1154(b), precludes the admission into evidence or use of Board reports
related to an incident or accident in a civil action for damages resulting from a matter mentioned in the report.
iii
Highway Accident Report
Contents
Acronyms and Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi
Factual Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Accident Narrative . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Truck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
School Bus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Collision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Injuries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Medical and Pathological Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Toxicological Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Survival Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Emergency Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Survivability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Driver Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Truckdriver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
School Bus Driver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Vehicle and Wreckage Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Truck-Tractor Semitrailer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
School Bus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Highway Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Highway Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Tire Marks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Operational Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Gayle Stuart Trucking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Mountainburg Public Schools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Management Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Gayle Stuart Trucking Company . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Federal Oversight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
State Oversight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Meteorological Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Tests and Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Sight Distance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Brake Heat Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Other Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Brake Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Brake Adjustment Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Spring Brakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
The Accident . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Exclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Contents
iv
Highway Accident Report
Accident Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Truck Brakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Recommendation History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Accident Vehicle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Motor Carrier Inspection and Oversight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Recommendation History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Compliance Reviews . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Qualified Brake Inspector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
Fuel Tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Recommendation History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Mountainburg Accident School Bus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Occupant Kinematics and Survival Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Recommendation History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Mountainburg Accident School Bus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Probable Cause . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
Appendixes
A: Investigation and Public Hearing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
v
Highway Accident Report
Acronyms and Abbreviations
ASHTD
AASHTO
ArvinMeritor
Bendix
CDL
CFR
CVSA
DOT
EMTs
FHWA
Arkansas State Highway and Transportation Department
American Association of State Highway and Transportation
Officials
ArvinMeritor, Inc.
Bendix Commercial Vehicle Brake Systems
Commercial Driver’s License
Code of Federal Regulations
Commercial Vehicle Safety Alliance
U.S. Department of Transportation
emergency medical technicians
Federal Highway Administration
FMCSA
FMCSRs
FMCSR
FMVSSs
Haldex
Hammond
I-540
Kenworth
MCSAP
MUTCD
NFPA
NHTSA
OMC
psi
SH-282
Stuart Trucking
Federal Motor Carrier Safety Administration
Federal Motor Carrier Safety Regulations
Federal Motor Carrier Safety Regulation
Federal Motor Vehicle Safety Standards
Haldex Brake Systems
Hammond Yellow Coach Lines, Inc.
Interstate 540
Kenworth Truck Company
Motor Carrier Safety Assistance Program
Manual on Uniform Traffic Control Devices
National Fire Protection Association
National Highway Traffic Safety Administration
Office of Motor Carriers
pounds per square inch
State Highway 282
Gayle Stuart Trucking, Inc.
vi
Highway Accident Report
Executive Summary
On May 31, 2001, about 3:28 p.m. central daylight time, a southbound Gayle
Stuart Trucking, Inc., truck-tractor semitrailer exited Interstate 540 at State Highway 282
near Mountainburg, Arkansas. The driver was unable to stop at the stop sign at the bottom
of the ramp. The 79,040-pound combination unit was traveling approximately 48 mph
when it entered the intersection and collided with the right side of a westbound, 65passenger, 1990 Blue Bird Corporation school bus operated by the Mountainburg,
Arkansas, Public Schools. The school bus rotated approximately 300 degrees clockwise
and overturned; the body, which partially separated from the chassis, came to rest on its
right side on the eastbound shoulder of State Highway 282. The tractor semitrailer
continued across the roadway, rotated about 60 degrees clockwise, overturned, and came
to rest on its left side.
Three school bus passengers seated across from the impact area were fatally
injured; one was partially ejected. Two other passengers, one of whom was seated in the
impact area, received serious injuries, and four passengers had minor injuries. The school
bus driver and the truckdriver both sustained minor injuries.
The Safety Board determines that the probable cause of the accident was the
truckdriver’s inability to stop the tractor semitrailer at the stop sign at the bottom of the
ramp due to the reduced braking efficiency of the truck’s brakes, which had been poorly
maintained and inadequately inspected. Contributing to the school bus passengers’
injuries during the side impact were incomplete compartmentalization and the lack of
energy-absorbing material on interior surfaces.
The major safety issues discussed in this report are the poor condition of the tractor
semitrailer brakes, inadequate motor carrier inspections and oversight, the use of propane
tanks on school buses, and occupant protection within school buses.
As a result of its investigation, the Safety Board makes recommendations to the
Federal Motor Carrier Safety Administration, the National Highway Traffic Safety
Administration, the Commercial Vehicle Safety Alliance, the National Fire Protection
Association, and spring brake manufacturers. The Safety Board reiterates a
recommendation to the U.S. Department of Transportation.
1
Highway Accident Report
Factual Information
Accident Narrative
On May 31, 2001, about 3:28 p.m. central daylight time, a southbound Gayle
Stuart Trucking, Inc., (Stuart Trucking) truck-tractor semitrailer exited Interstate 540 (I540) at State Highway 282 (SH-282) near Mountainburg, Arkansas. The driver was unable
to stop the tractor semitrailer at the stop sign at the bottom of the ramp. The 79,040-pound
tractor semitrailer was traveling approximately 48 mph when it entered the intersection
and collided with the right side of a westbound, 65-passenger, 1990 Blue Bird Corporation
school bus, traveling about 50 mph, and operated by the Mountainburg, Arkansas, Public
Schools. The school bus rotated approximately 300 degrees clockwise, overturned, and
came to rest on its right side on the eastbound shoulder of SH-282. The tractor semitrailer
continued across SH-282, rotated about 60 degrees clockwise, overturned, and came to
rest on its left side.
Truck
The truckdriver departed his home in Vandalia, Missouri, on May 28, 2001, for a
4-day trip through Iowa, Missouri, and Arkansas. On May 31, the day of the accident, the
driver stated that he awoke about 8:00 a.m., conducted a 30-minute pretrip inspection, and
departed Kingdom City, Missouri, where he had slept in his sleeper berth the previous
night. He had picked up a load of bean meal in Mexico, Missouri, earlier that morning
(approximately 1:44 a.m., according to the bill of lading) and was en route to Atkins,
Arkansas (see figure 1). The driver stopped near Joplin, Missouri, about 1:30 p.m. for a
sandwich.
Factual Information
2
Highway Accident Report
Figure 1. Truck route.
The driver said that in the vicinity of Fayetteville, Arkansas, he determined that he
would need fuel near Mountainburg, where he knew of a truck stop on SH-282. The driver
stated that he had stopped at the truck stop on several occasions while traveling
northbound on I-540, but had not exited there before while traveling southbound. About
3:28 p.m., as the driver was southbound on I-540, he exited the ramp to SH-282; he
estimated his speed to be approximately 20 to 25 mph, and he indicated that his truck was
in sixth gear. He said that he attempted to downshift and brake at the top of the ramp, but
the brakes did not operate. He stated that he continued to apply the brakes but was
unsuccessful in slowing the vehicle, and it continued to accelerate down the ramp. The
driver indicated that as he approached the intersection, he did not see any traffic ahead and
was unable to see any traffic on westbound SH-282 due to a berm to the left (east) of the
ramp. The driver said that he planned to try to stop the vehicle by proceeding directly
across SH-282 and onto the upgrade of the I-540 southbound entrance ramp. As he entered
the intersection, the driver stated that he saw the westbound school bus and was unable to
avoid the collision.
Factual Information
3
Highway Accident Report
School Bus
The school bus picked up students at Mountainburg Elementary School about 2:50
p.m., drove to Mountainburg High School to pick up more students, and departed the high
school between 3:00 and 3:05 p.m. for the afternoon route home. The bus had made three
stops on the route to unload students before dropping off a student at a truck stop on SH282 and proceeding westbound on SH-282 at a driver-estimated speed of 45 mph. The
driver stated that as he was nearing the ramp, he heard a passenger shout that a truck was
not going to stop at the stop sign on the ramp. The driver said he briefly looked to his
right, glimpsed the truck, and heard the loud sound of the collision.
Collision
The tractor semitrailer hit the bus on the right side in the area of the rear axle. The
truck continued south across SH-282, traveled 73 feet from the point of impact, rolled on
its left side, and traveled an additional 78 feet, rotating about 60 degrees clockwise (see
figures 2 and 3). The school bus traveled 96 feet southwest from the area of impact,
rotating about 300 degrees clockwise. The body, which partially separated from the
chassis, rolled onto its right side, while the chassis remained partially upright (see figure 4).
Injuries
Table 1. Injuries.1
INJURIES
SCHOOL BUS DRIVER
TRUCKDRIVER
BUS PASSENGERS
TOTAL
Fatal
0
0
3
3
Serious
0
0
2
2
Minor
1
1
4
6
None
0
0
0
0
Total
1
1
9
11
1
Title 49 Code of Federal Regulations (CFR) 830.2 defines a fatal injury as any injury that results in
death within 30 days of the accident. It defines a serious injury as an injury that requires hospitalization for
more than 48 hours, commencing within 7 days from the date the injury was received; results in a fracture of
any bone (except simple fractures of the fingers, toes, or nose); causes severe hemorrhages, nerve, muscle,
or tendon damage; involves any internal organ; or involves second or third degree burns or any burns
affecting more than 5 percent of the body surface.
Factual Information
Figure 2. Postcrash accident scene.
4
Highway Accident Report
Factual Information
5
Figure 3. Tractor semitrailer, postaccident.
Figure 4. School bus, postaccident.
Highway Accident Report
Factual Information
6
Highway Accident Report
Medical and Pathological Information
The truckdriver’s minor injuries included contusions on the right side of his head,
upper right arm, and left shoulder. The busdriver’s minor injuries included contusions on
the left side of his face, left shoulder, and left hip. Because of a coronary condition, he was
hospitalized after the accident as a precaution.
The passengers who sustained minor injuries were seated in seats 1A, 2A, 2C, and
2E (see figure 5). The passenger in seat 1A sustained a contusion on the left side of his
scalp. The passenger in seat 2A sustained a contusion on the left side of her scalp and a
possible contusion or laceration of the spleen. The passenger in 2C sustained lacerations
and contusions on the right elbow, and the passenger in seat 2E had lacerations and
contusions on her right elbow and on the back of both knees.
Figure 5. Mountainburg school bus seating chart.
Factual Information
7
Highway Accident Report
Two seriously injured passengers were seated in the rear of the bus. One was
seated in the area of impact (seat 10E) and sustained lacerations to his head and elbow and
a closed head injury. The other, seated across from the area of impact (seat 10A), sustained
multiple spinal fractures and a fractured right arm and leg.
The three fatally injured passengers were seated across from the area of impact.
The passenger in seat 9A sustained a fractured skull, fractured left clavicle, three fractured
ribs, and a compound fracture of the left leg; the passenger in 9C sustained multiple
lacerations and contusions, a right pelvic fracture, a liver laceration, a right renal
laceration, ruptured right hemidiaphragm, and vena cava injury; the passenger in 11A,
who was partially ejected, had a skull fracture, multiple spinal fractures, and a fractured
left tibia.
Toxicological Tests
Federal Motor Carrier Safety Regulations (FMCSRs)2 required that postaccident
alcohol and drug testing3 be performed on both the truckdriver and the busdriver. The
postaccident toxicological tests on the truckdriver, conducted by Arkansas State Police
and Crawford Memorial Hospital, were negative for alcohol and other drugs. A sample
was sent to the Civil Aerospace Medical Institute to test for Cetirizine, the main
component of Zyrtec, an allergy medication.4 Test results were negative. Results of
postaccident toxicological tests conducted by the Arkansas State Police for the school bus
driver were negative for alcohol and other drugs.
Survival Aspects
Emergency Response
The Crawford County Communications Center and the Mountainburg Police
Department received notification of the accident at 3:29 p.m. The Mountainburg police
chief arrived on scene at 3:31 p.m. and two rescue vehicles arrived at 3:35 p.m. The rescue
vehicles were manned by eight firefighters, five of whom were qualified first responders
and emergency medical technicians (EMTs). A triage area, where the injured were
evaluated and treated, was established on the left side of the school bus. After the triage
site was set up, a Lifeflight Air Ambulance (helicopter) was dispatched from Branson,
Missouri, about 45 minutes flying time from the accident site. Four additional fire
departments and one ambulance service, comprising 25 fire fighters and EMTs, three
rescue vehicles, a pumper truck, and seven ambulances, responded to the accident. By
2
Title 49 CFR Part 382.303.
3
Title 49 CFR Part 40.21 requires that drug testing be done for marijuana, cocaine, opiates,
amphetamines, and phencyclidine.
4
The driver stated that he occasionally took Zyrtec for allergies on an as-needed basis.
Factual Information
8
Highway Accident Report
3:45 p.m., the ambulances had transported eight of the injured passengers, the busdriver,
and the truckdriver from the scene (the helicopter was not needed). One partially ejected
passenger (seat 11A) was under the bus. He was extricated by 3:52 p.m. and pronounced
dead at the scene. At the postaccident critique attended by all participating agencies, the
consensus was that the response was timely and resources were adequate, according to the
on-scene police and firefighters.
Survivability
The truckdriver said he was wearing his lap belt only; the truck was equipped with
a separate shoulder belt. He said that during the accident sequence his leg became wedged
under the dashboard due to the deformation of the cab. After the truck came to rest, he was
able to slide the seat back to free his leg and climb out through the broken windshield.
The school bus driver stated that he was wearing his lap belt (the bus was only
equipped with a lap belt), which was found tied in a knot during postaccident examination
but still usable; no striations were found on the belt webbing. The driver reported that he
was unable to get out of the lap belt after the bus came to rest because the weight of his
body against the belt jammed the buckle and prevented him from unlatching it. One of the
passengers unlatched the driver’s belt. The driver reported that he struck his head, elbows,
and chest on the interior of the bus as it rolled over.
The busdriver and two passengers (seats 1A and 2B) were able to exit from the bus
on their own via the rear emergency door. The busdriver helped the seriously injured
passenger in seat 10E exit the bus. EMTs and passersby removed two fatally injured
passengers (seats 9A and 9C), one seriously injured passenger (seat 10A), and two
passengers with minor injuries (seats 2A and 2D) from the bus. EMTs extricated the third
fatally injured passenger (seat 11A) from underneath the bus; this passenger had been
partially ejected through the right side window at row 11.
The passenger in the front of the bus said that at the end of the impact sequence, he
was lying on the “floor,” which, postcollision, was the right side of the bus. The passenger
in seat 10E said he was lying on the right side of the bus when it came to rest and that the
passenger in seat 9A was laying across his legs. Evidence indicates the passengers in the
back of the bus struck the ceiling, right side windows, and sidewall during the impact
sequence.
Damage
Both the school bus and truck tractor were completely destroyed. The semitrailer
received minor damage and the load was unusable.
Factual Information
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Highway Accident Report
Driver Information
Truckdriver
The 25-year-old truckdriver possessed a current Missouri class A Commercial
Driver’s License (CDL), with no restrictions or endorsements, issued on March 15, 1999,
and scheduled to expire on March 15, 2002. A review of the driver’s record revealed a
speeding conviction while driving a personal vehicle on November 19, 2000, and a
failure-to-keep-right conviction while driving a commercial vehicle on July 30, 1999. The
driver had a valid medical certificate that was issued on May 7, 2001, and scheduled to
expire on May 7, 2003.
Interviews with the truckdriver and an examination of his employment records
showed that he started driving commercial vehicles professionally in March 1999. Stuart
Trucking was his first employer. He subsequently worked for McDowell Farms of Perry,
Missouri; Target Aluminum of Vandalia, Missouri; and Jennings Implement of Curryville,
Missouri, from June 2000 to April 2001. He returned to Stuart Trucking in April 2001.
The truckdriver acknowledged that the logs he kept between May 28 and 31, 2001,
were not accurate because he had reconstructed his activities and completed the logs at the
end of each day. Safety Board investigators reconstructed the driver’s off-duty rest times
based on an interview with the driver, fuel receipts, bills of lading, and travel times
between locations. Table 2, which follows, shows the driver’s stated rest time, the times on
the receipts, and the driver’s likely hours of sleep during the days prior to the accident.
The driver stated that he was in good general health, but occasionally suffered
from a chronic back problem stemming from a childhood injury. He said he was not
experiencing back pain on the day of the accident. He also suffered from a dust allergy and
occasionally took Zyrtec for relief of symptoms. He said he last used the medication 2
weeks before the accident, and toxicological tests did not reveal any Zyrtec in the driver’s
blood. The driver’s medical records did not indicate any other medical conditions.
Factual Information
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Highway Accident Report
Table 2. Driver’s off-duty/rest times.
LIKELY TIMES
OF SLEEP
DATE
DRIVER’S STATED
REST TIMES
MAY 26
0100-0900 (Home)
8.0
MAY 27
0100-1000 (Home)
9.0
MAY 28
0001-1030 (Home)
2330-2400 (Truck,
Mt. Pleasant, Iowa)
2053 (Bowling Green,
Missouri)
2330 (Mt. Pleasant, Iowa)
0001-1030
2330-2400
10.5
0.5
MAY 29
0001-0500 (Truck,
Mt. Pleasant, Iowa)
0900-1100 (Truck,
Davenport, Iowa)
1250 (Davenport, Iowa)
1756-1821 (Eddyville, Iowa)
0001-0500
5.0
MAY 30
0001-0630 (Truck,
Mexico, Missouri)
1300-1400 (Truck,
Siloam Springs,
Arkansas)
0714 (Kingdom City, Missouri)
1247-1508 (Siloam Springs,
Arkansas)
1629-1736 (Noel, Missouri)
2310 (Meta, Missouri)
0001-0630
6.5
MAY 31
0230-0830 (Truck,
Kingdom City,
Missouri)
0144 (Mexico, Missouri)
0230-0800
5.5
RECEIPTS
TOTAL SLEEP
(HOURS)
School Bus Driver
The 76-year-old school bus driver possessed a current Arkansas class B CDL, with
a passenger endorsement and a school bus restriction, that was issued on April 7, 1999,
and scheduled to expire on March 18, 2003. A review of the busdriver’s record revealed
no traffic convictions. He had been involved in a traffic accident on February 15, 2001;
while exiting school property, the bus struck the right side of a passenger car as he entered
the roadway. No one was injured and the busdriver was not cited for the accident. The
busdriver had passed his most recent annual physical examination on August 1, 2000, as
required by the Mountainburg Public Schools.5 He had been driving school buses for 14
years and had been driving this route for 3 years.
Vehicle and Wreckage Information
Truck-Tractor Semitrailer
The accident vehicle, a 1989 Kenworth Truck Company (Kenworth) model T600A
conventional-cab, three-axle tractor, was equipped with a nine-speed transmission and had
a sleeper berth; it was towing a two-axle, 43-foot hopper6 semitrailer, model DWH-400,
5
year.
All school bus drivers are required to have an annual physical prior to the beginning of each school
Factual Information
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Highway Accident Report
built by Wilson Trailer Company in 1996. The tractor, leased to Stuart Trucking, was
powered by a six-cylinder Caterpillar diesel engine without an engine brake; it was
originally equipped with an electronic control module that had been removed in 1999.
Both the odometer, which read 2,967.2 miles at the time of the accident, and speedometer
had been replaced.7 The tractor had a wheelbase of 222 inches and a curb weight of 16,805
pounds. According to Stuart Trucking records, the tractor had received its mandatory
annual inspection, performed by an employee of Stuart Trucking, on April 17, 2001; the
inspection form listed all brake components as “OK.” Prior to that inspection, the tractor
had been idle for about 2 years.
The hopper, owned by Stuart Trucking and used to haul grain and animal feed,
weighed about 10,100 pounds empty. It had received its annual inspection, performed by
an employee of Stuart Trucking, on July 3, 2000; the inspection form listed all brake
components as “OK.” The hopper had been used as a spare at least once a month for about
18 months prior to the accident.
Brakes. A Safety Board postaccident examination revealed that all three tractor
axles had air brakes (see figure 6) with standard S-cam/drum foundation (service) brakes
(see figure 7) fitted with manual slack adjusters.8 The semitrailer (hopper) had air brakes
with standard S-cam/drum foundation brakes; its two axles had automatic slack adjusters.
The third axle of the tractor and both trailer axles had emergency-parking spring brakes.
Background. About 95 percent of large (26,000 pounds or greater) commercial
vehicles are equipped with air brakes with S-cam/drum foundation brakes. The purpose of
the service brake components is to convert air pressure into mechanical forces used to
decelerate the vehicle. Once air has been directed through lines and valves, it reaches a
brake chamber (see figure 6). Brake chambers vary in size and provide a wide range of
output forces. Compressed air flows into the brake chamber, where it acts on a pressure
plate attached to a pushrod. The air forces the pressure plate to move, extending the
pushrod with a force proportional to the air pressure applied to the brake chamber. (This
movement is referred to as the pushrod stroke or travel.) Under ideal circumstances, a
pressure of 40 pounds per square inch (psi) supplied to a brake chamber with a pressure
plate of 30 square inches (a Type 30 brake chamber) results in 1,200 pounds of force on
the pushrod. This ideal situation excludes any losses due to friction, loose bearing
surfaces, or component stretch and expansion. Such losses reduce actual pushrod forces.
6
A hopper is a box-shaped container with a funnel at the bottom used for delivering grain and other
agricultural products.
7
Because the original electronic speedometer did not work when the engine control module was
removed, the speedometer was replaced.
8
A slack adjuster multiplies and converts the force from the pushrod into torque on the shaft running
perpendicular to the brake drum, rotating the S-cam and spreading the brake shoes inside the brake drum. A
manual slack adjuster is adjusted by the operator, who turns the adjusting nut to compensate for lining wear
so the pushrod is not required to extend farther out than it is able. An automatic slack adjuster performs this
function automatically.
Factual Information
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Highway Accident Report
Figure 6. Brake diagram.
In an S-cam air brake system, the pushrod is attached to one end of a lever called a
slack adjuster (see figure 7). The slack adjuster multiplies and converts the force from the
pushrod into torque on the shaft running perpendicular to the brake drum. As the pushrod
is extended from the brake chamber, the slack adjuster rotates, in turn rotating the shaft
connected to it. The S-cam also rotates, spreading the brake shoes inside the brake drum.
When the brake shoes are spread apart, the brake linings (riveted to the shoes) come into
contact with the inside of the brake drum. The friction created slows the rotation of the
brake drum and, thus, the wheel and the vehicle.
To compensate for lining wear, slack adjusters are equipped with an adjusting
mechanism. If they were not, the pushrod would be required to extend continually farther
out as the lining wore down until the pressure plate in the brake chamber came into
contact with the bottom of the brake chamber. Known as “bottoming out” a brake
chamber, the resulting pushrod stroke is the maximum stroke listed in the manufacturer’s
brake literature. Bottoming out results in no braking because the pushrod cannot travel far
enough to rotate the S-cam sufficiently to expand the brake shoes so that they make
contact with the drum. Manual slack adjusters must be adjusted by hand with a wrench,
while automatic slack adjusters compensate for lining wear without being adjusted
manually.
Factual Information
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Highway Accident Report
During postaccident inspection, investigators measured the brake stroke for each
of the brakes with 90 psi of air supplied.10 Of the 10 brakes on the tractor semitrailer, 8
were found to be out of adjustment or nonfunctional.
Table 3. Brake types and manufacturers.
AXLE
CHAMBER
SIZE
SLACK
ADJUSTER
EMERGENCY
PARKING/SPRING BRAKE
CAGING PORT
1 Left (tractor)
T-20
Midland
Manual
None
None
1 Right (tractor)
T-20
Midland
Manual
None
None
2 Left (tractor)
T-30
Midland
Manual
None
None
2 Right (tractor)
T-30
Midland
Manual
None
None
3 Left (tractor)
T-30/30
Midland
Manual
Remanufactured
Standard
3 Right (tractor)
T-30/30
Midland
Manual
Anchorlok
Standard
4 Left (trailer)
T-30/30
Rockwell
Automatic
Midland
Standard
4 Right (trailer)
T-30/30
Rockwell
Automatic
Anchorlok
Fixed Integrated
5 Left (trailer)
T-30/30
Rockwell
Automatic
Midland
Standard
5 Right (trailer)
T-30/30
Rockwell
Automatic
Anchorlok
Fixed Integrated
Table 4 shows the adjustment for each brake. The driver stated that he and the
owner of the tractor (his father) had installed manual slack adjusters on the second and
third axles of the tractor on May 27, 2001, as preventive maintenance, because the old
slack adjusters would not “take grease.” The owner said he adjusted the brakes on the
second and third axles at that time by tightening the shoe against the drum and then
backing off the adjusting nut about 1/2 turn. The owner also stated that he liked the
steering axle brakes (first axle) to be adjusted “loose” and backed off the adjusting nut 3/4
turn.
10
Because of accident damage, the tractor brakes were operated using the brake pedal and shop air; the
trailer brakes were operated from the brake pedal of an auxiliary tractor compressing its own air.
Factual Information
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Highway Accident Report
Table 4. Brake adjustment.
AXLE
MAXIMUM STROKE
ALLOWED*
MEASURED
STROKE
NOTES
1 Left (tractor)
1 3/4 inches
2 1/8 inches**
1 Right (tractor)
1 3/4 inches
2 3/8 inches**
2 Left (tractor)
2 inches
2 3/8 inches**
2 Right (tractor)
2 inches
2 1/4 inches**
3 Left (tractor)
2 inches
1 7/8 inches**
Parking/emergency brake
spring broken, restricting
pushrod travel; no dust cover
3 Right (tractor)
2 inches
2 1/2 inches**
No dust cover
4 Left (trailer)
2 inches
1 1/2 inches
Parking/emergency brake
spring broken; no dust cover
4 Right (trailer)
2 inches
1 3/4 inches**
Incorrectly installed brake
chamber
5 Left (trailer)
2 inches
1 inch**
Parking/emergency brake
spring broken, restricting
pushrod travel; no dust cover
5 Right (trailer)
2 inches
1 1/2 inches
* Manufacturers’ recommended maximum adjustment length.
** Out of adjustment or not functioning properly.
The driver reported that he checked his brakes about 8:00 a.m. on the day of the
accident by doing a walk-around inspection and looking at the brakes while the parking
brake was on. He said that the brakes did not appear to need adjustment, although he
noticed that the right-front axle brake chamber was rusted. He stated that he did not climb
beneath the vehicle to observe the brakes. To check manual slack adjusters on S-cam
brakes, according to the Model Driver’s Manual for Commercial Vehicle Driver Licensing:
A driver should park on level ground and chock the wheels to prevent the vehicle
from moving. He must then turn the parking brake off in order to move the slack
adjuster by hand. If the slack adjuster moves more than one inch where the push
rod attaches then it probably needs adjustment.11
The driver said that the brakes on the tractor were adjusted weekly, even though
doing so might not be necessary, and he described to investigators the correct procedure
for adjusting brakes. He also stated a preference for adjusting the trailer axle brakes
“loose” to prevent the trailer from slipping in wet and other conditions. He said that he had
11
American Association of Motor Vehicle Administrators, Commercial Driver License Manual Version
2.0 (Arlington, VA: AAMVA, 1996).
Factual Information
16
Highway Accident Report
not personally adjusted the brakes on the trailer but was present when the mechanic at
Stuart Trucking did so 2 to 3 weeks before the accident.
Safety Board investigators conducted tests on June 2, 2001, to determine whether
the trailer brakes were operational. The trailer was connected to a truck tractor and driven
at 20 mph and 40 mph. When the service brakes were applied at both speeds, only the 4L
(fourth axle, left side) and 5R (fifth axle, right side) trailer brakes locked, and the tires slid
on the roadway; wheels 4R (fourth axle, right side) and 5L (fifth axle, left side) were free
rolling with the brakes fully applied.
Investigators tested the semitrailer’s emergency-parking brakes,12 using an
auxiliary tractor to pull the trailer on the cement pavement, on June 6, 2001. When the
emergency-parking brake was applied, only the 5R wheel locked. When pulled on gravel
on a slight downhill slope, both the 4L and 5R wheels locked. In all tests, the 4R and 5L
wheels rolled freely.
On September 27, 2001, Safety Board staff and Arkansas Highway Police met
with Haldex Brake Systems (Haldex)13 personnel to test the four Midland Brake, Inc.,
(Midland) manual slack adjusters from the tractor (axles 2 and 3) and to examine and
disassemble the spring brakes. The manual slack adjusters for axles 2 and 3 were fitted
onto a test spline and rotated manually. All four adjusters functioned properly. When
disassembled, the emergency-parking brake spring on brake 3L was found broken into
three pieces. The broken spring disabled the emergency-parking brake and restricted the
service brake pushrod return by 3/8 inch.
During the postaccident inspection, investigators discovered that the angle
between the pushrod and the slack arm on brake 4R was greater than the 90 degrees that
specifications allowed. When measured against a slack adjuster template, the pushrod was
about 1 inch shorter than the pushrod on the left side of the trailer, causing the greater
angle. According to the manufacturer, the automatic slack adjuster was bottoming out,
thus preventing full release of the pushrod and preventing the brakes from automatically
adjusting. The 4R brake drum was rusty and the brake did not appear to be functioning.
On July 12, 2001, Safety Board staff met with ArvinMeritor, Inc.,
(ArvinMeritor)14 personnel to examine and disassemble the automatic slack adjuster on
brake 4R and found it to be nonfunctional. Disassembly of the component revealed that
the piston retaining ring15 was broken, probably, according to ArvinMeritor personnel, as a
result of the angle between the pushrod and slack arm, which, in turn, disabled the
12
All tractors and semitrailers are required to be equipped with emergency-parking brakes. In this and
most cases, the brake operates by means of a spring that expands to apply the brakes when the air pressure
drops.
13
Midland, now owned by Haldex, manufactured two of the three broken spring brakes and examined
the third as a courtesy. Midland manufactured all of the manual slack adjusters.
14
15
ArvinMeritor is a supplier of commercial vehicle components, including air brakes.
The piston retaining ring creates the clearance gap for the actuator piston, which is part of the
adjusting mechanism. If the ring is broken, the clearance gap cannot be created, preventing adjustment.
Factual Information
17
Highway Accident Report
automatic slack adjuster. When reassembled with a new piston retaining ring, the
automatic slack adjuster functioned as designed. An outside mechanic had replaced the
spring brake chamber on the right fourth axle (semitrailer) on June 5, 1997. Often, to
replace a spring brake chamber, the pushrod must be cut and realigned.
When disassembled during the inspection at Haldex, the spring in brake 4L’s
emergency-parking brake chamber was found to be in two pieces and a white coloration,
consistent with the presence of salt, was present inside the brake chamber. The interior
brake drum surface was shiny. The service brake appeared to function normally during
dynamic testing on the roadway.
The parking/emergency brake spring was found to be in three pieces when brake
5L was disassembled. After a manual caging bolt was installed, the chamber retracted an
additional 5/8 inch, indicating that the broken spring was preventing full pushrod release,
according to Haldex personnel. The spring was fractured in such a way that it prevented
full return of the pushrod; thus, the automatic slack adjuster did not have the minimum 1½
inches of stroke necessary to activate the adjusting mechanism. When disconnected from
the air chamber, the automatic slack adjuster operated properly on a test device.
Four of the six spring brakes on axles 3, 4, and 5 were equipped with standard
caging ports, none of which had dust covers to keep out contaminants. The other two
spring brakes were equipped with fixed integrated caging bolts,16 which do not require
dust covers.
Investigators also measured brake shoe lining thickness. On brake 5R, the lining
was 3/16 inch, or 1/16 inch less than the required minimum of 4/16 inch; all other brake
shoes were in compliance with minimum requirements. The brake drums were examined
and the inside diameters measured. While none of the drums exceeded the manufacturers’
maximum service diameter, they did approach it, making them more susceptible to brake
heat than new drums because less drum mass was available to absorb the heat. The drums
on brakes 1R, 4R, and 5L exhibited rust.
The tread depths on all tires met FMCSRs and Commercial Vehicle Safety
Alliance (CVSA) requirements of 4/32 inch on the front tires and 2/32 inch on the
remaining tires. TRW, Inc., personnel disassembled and examined the steering gear on
August 7, 2001, and found no defects.
According to an Arkansas Highway Police mechanic and ArvinMeritor staff, the
general condition of the brake system on the trailer was poor. At the Safety Board’s
request, inspectors from the Missouri Division of Motor Vehicle and Railroad Safety
conducted postaccident vehicle inspections on 12 Stuart Trucking vehicles (see
“Management Information” section); they found that grease was absent at the fittings and
brake camshaft bushings, suggesting a lack of periodic lubrication. The inspectors stated
that Stuart Trucking staff did not seem to be knowledgeable and that some of the defects
noted were obvious and did not appear to be recent.
16
An integrated caging bolt is a bolt in the spring brake case that is turned to release the spring brakes.
Factual Information
18
Highway Accident Report
Damage. The tractor sustained damage to the front part of the frame, which was
bent to the right about 10 degrees; the entire cab was shifted rearward, the windshield and
right door window were broken, and both doors were damaged. The engine was dislodged
from its mount, and parts within the engine compartment, as well as the front engine
support, were broken;17 the left fuel tank was dislodged and the right fuel tank was
punctured; and the muffler stack was broken off. Due to accident damage, the tractor
lights could not be tested to determine whether they were operational. The hopper trailer’s
front left upper clearance lights were damaged, the left side of the trailer was scraped, both
outside left trailer wheels were bent, and the tires were flat.
School Bus
The 65-passenger, 1990 Blue Bird Corporation school bus had a Chevrolet model
60 chassis with a V-8, 366-cubic inch engine reconfigured to operate with propane. The
school bus was equipped with a four-speed General Motors Corporation manual
transmission with a two-speed differential, power-assisted steering, hydraulic brakes with
a dual master cylinder, and a motorized booster pump.
The tire tread depths exceeded FMCSRs and CVSA requirements. After the
accident, the front brakes were tested and operated properly. The rear brakes could not be
tested because of a severed hydraulic line caused by collision damage. The lights that were
not damaged in the accident operated during postaccident testing.
The bus had 10 rows of three-passenger bench seats on both sides of the bus. The
eleventh row had a three-passenger bench seat on the right side and a two-passenger bench
seat on the left side to accommodate the vehicle’s one emergency exit door at the rear.
Buses manufactured before September 1, 1994, were only required to have one emergency
exit door.18
The school bus had been retrofitted with a 66.5-gallon propane tank located 34
inches forward of the rear axle on the right side, about 4 inches behind the caged gasoline
tank, which had been drained (see figure 8). The propane tank was mounted outside the
frame and was secured by two steel straps. The cylindrical propane tank, manufactured by
Brunner Engineering and Manufacturing, was 64 inches long and 18 inches in diameter.
The tank shell was 0.187 inch thick and the heads (ends of the tank) were 0.173 inch thick.
The tank was equipped with an overfill protection device valve, designed to vent in case of
overfill or fire. Part of the valve was inside the propane tank and part outside; if the outer
part of the valve was damaged or destroyed, gas flow to the engine was supposed to shut
off automatically.
17
The pressurized power steering line was broken at the steering gear box, the input shaft to the
steering box was separated at the universal joint, the flywheel housing and bell housing were broken,
damage indentations were present on the firewall, the gearshift lever was broken off at the isolated pin, the
air filter assembly was damaged, and the batteries were dislodged.
18
Title 49 CFR 571.217.S5.2.3.4.
Factual Information
13
Highway Accident Report
Figure 7. S-cam diagram.
Air brakes, when heated due to repeated applications, can also cause bottoming
out, resulting in loss of braking capability. When heavy vehicle air brakes heat up, several
components can be adversely affected. Heated brake drums expand, thereby increasing the
distance that the brake shoes must move so that the lining contacts the drum; as a result,
the S-cam must be rotated farther, requiring an extra, or reserve, pushrod stroke. (The
reserve stroke refers to the distance remaining before the pressure plate in the brake
chamber contacts the bottom of the chamber at the time of brake application.) If little
reserve stroke remains on a cool brake (when brakes are out of adjustment), a hot brake
can easily use up the small amount of extra stroke. If the brakes become too hot and do not
have enough reserve stroke left, the pressure plate can bottom out in the chamber and the
shoes will not contact the brake drum. Bottoming out causes an air-braked vehicle to lose
its braking capability when descending a grade. It usually takes place when brakes near
the limit of adjustment are repeatedly applied during a long descent.
Accident Vehicle Brakes. Table 3 lists the accident vehicle brake types, slack
adjuster types and manufacturers, spring brake manufacturer, and type of spring brake
caging port.9
9
A caging port is a hole in the spring brake assembly into which a tool can be inserted to release the
spring brake in the event that the vehicle needs to be towed.
Factual Information
19
Highway Accident Report
Figure 8. School bus propane tank.
Mountainburg Public Schools began converting school buses to propane fuel in the
mid-1980s because propane was about 75 cents cheaper per gallon than regular gasoline.
When the price of propane rose in the mid-1990s, the school district stopped converting
the school buses because the savings were minimal; at the time of the accident, the school
district had two propane-fueled buses on regular routes and two spares.
With the assistance of the Mountainburg Public Schools transportation supervisor,
Butane Gas Company of Mountainburg installed the tank on the accident bus some time in
the early 1990s. The supervisor said that he was not aware that installation of the tank had
to comply with any special regulations. The owner of Butane Gas Company stated that his
firm followed all National Fire Protection Association (NFPA) and National Highway
Traffic Safety Administration (NHTSA) regulations, as well as instructions from the
manufacturer, in installing the tank.
The National School Transportation Specifications and Procedures19 recommends
that all propane tanks, including those installed on vehicles, comply with NFPA standard
58,20 which specifies requirements for the propane tanks themselves and for their
placement and installation. The NFPA requires that propane tanks be located where the
possibility of damage is minimized. It states that containers in the rear of vehicles should
be protected by substantial bumpers; those near the engine or exhaust system should be
shielded from direct heating. Containers should not be mounted on the roof, ahead of the
19
The National School Transportation Specifications and Procedures is a compilation of guidelines,
not requirements, for school transportation. Representatives from industry and most of the States develop
and modify the guidelines every 5 years.
20
National School Transportation Specifications and Procedures, 2000 Revised Edition (Warrensburg,
Missouri: Missouri Safety Center, 2000), p. 16.
Factual Information
20
Highway Accident Report
front axle, or behind the rear axle and should not protrude beyond the vehicle’s sides or
top. Containers mounted between the axles should have ample road clearance and should
not be lower than the lowest point of the body, frame, engine, or transmission. The NFPA
further requires that the container be securely mounted to prevent jarring loose, slipping,
or rotating.
Neither the National School Transportation Specifications and Procedures nor the
NFPA standards require cages surrounding propane tanks on school buses or crash tests
for propane tanks installed on school buses. The Federal Motor Vehicle Safety Standards
(FMVSSs) issued by NHTSA require that all fuel tanks installed by the original
equipment manufacturer meet crash test standards; manufacturers comply with this
requirement by placing cages around fuel tanks. NHTSA generally can only regulate
equipment placed on vehicles when originally manufactured; the FMVSSs do not apply to
aftermarket equipment, such as the retrofitted propane tank on the accident bus.21
Exterior damage to the school bus was limited to the right side and right roof area,
extending 7 feet 2 inches from a point 2 feet forward of the right rear corner (see figure 9).
The primary point of impact was in the area of the rear axle on the right side. After impact,
the body partially separated from the chassis, which remained attached to the body below
the driver’s section. The propane tank, located underneath the floor on the right side of the
bus about 4 feet forward of the impact area, was not damaged. The emergency exit door,
located at the rear of the bus, was operable after the accident. The boarding door, which
was underneath the bus when it came to rest, could not be opened.
Figure 9. School bus damage.
21
NHTSA regulates new vehicles and items of equipment. If equipment is installed after the first
consumer purchase, 49 United States Code 30122 is relevant to the product. It states that a manufacturer,
distributor, dealer, or motor vehicle repair business may not knowingly make inoperative any part of a
device or element of design installed on or in a motor vehicle or equipment in compliance with an applicable
motor vehicle safety standard.
Factual Information
21
Highway Accident Report
Inside the bus, intrusion occurred between rows 5 through 11; the area of greatest
intrusion, approximately 25 inches, was between rows 7 and 8. The seats on the right in
rows 6, 7, 8, and 9 shifted to the left, blocking the center aisle. The inboard seat legs and
horizontal seat supports were fractured in rows 7 through 11 on the right side. The floor
joints separated behind the busdriver’s seat and at rows 5, 7, and 9; the linoleum flooring
remained intact, so no openings were created. On the left side windows, glazing remained
intact, except for the window adjacent to row 9; the glazing was broken on all right side
windows, except for the top window adjacent to row 7.
Highway Information
Highway Design
The accident occurred at the intersection of SH-282 and the exit ramp from
southbound I-540 (see figure 10). Construction on this part of I-540 began in January
1987, and it opened to traffic in January 1999. The exit ramp from southbound I-540 to
SH-282 was completed summer 1999. Arkansas State Highway and Transportation
Department (ASHTD) records show that no accidents were reported in the intersection for
the 2 years that it had been open.
The exit ramp (see figure 11) from I-540 is a 15-foot-wide paved concrete lane,
with tined surface texture, bordered by 6-foot paved asphalt shoulders to the west and 4foot paved asphalt shoulders to the east, each delineated with thermoplastic edge lines.
The exit ramp, as measured from the gore area22 to the intersection curb line of SH-282, is
approximately 1,342 feet long, with a difference in elevation of about 85 feet. The only
ramp curvature is a horizontal curve as the ramp transitions from the interstate. The
average grade of the ramp is about 6 percent; the steepest grade is 9.42 percent,
encompassing a distance of about 293 feet and ending about 413 feet from the end of the
ramp, after which the ramp transitions to a 0.03 percent grade 69 feet before the
intersection, as measured on scene.
22
The gore area is the triangular piece of land between the interstate and the ramp as the ramp
transitions away from the interstate.
Factual Information
22
Highway Accident Report
Figure 10. Intersection of ramp from I-540 south and SH-282.
Factual Information
23
Highway Accident Report
Figure 11. Exit ramp from I-540 south to SH-282.
A 36-inch stop sign23 was in place on the traffic island north of the intersection. An
advance traffic control sign indicating “stop ahead”24 was about 581 feet north of the stop
sign in the grassy right-of-way on the right side of the exit ramp. A recreational area guide
sign25 was approximately 191 feet north of the “stop ahead” sign. Following the accident,
the ASHTD installed additional signing. The ASHTD replaced the 36-inch stop sign with
a 48-inch stop sign and erected another 48-inch stop sign on the left side of the ramp. It
placed an additional 48-inch “stop ahead” sign on the left side of the ramp across from the
original one, which is approximately 581 feet north of the stop sign. The ASHTD added a
third 48-inch “stop ahead” sign on the right side of the ramp, approximately 881 feet north
of the stop sign, and moved the recreation guide sign to the left side of the ramp.
The speed limit on I-540 is 70 mph for cars and 65 mph for trucks. No advisory
speed signs are present on the exit ramp. In placing signage at the ramp, the ASHTD
followed the Manual on Uniform Traffic Control Devices (MUTCD) guidelines, which
state that a warning sign should be used to call attention to unexpected conditions and
should be based on an engineering study or judgment.26 The ASHTD did not believe these
conditions applied at this ramp.
A review of the I-540 construction plans indicates that the truck descended four
hills (and ascended three) between the Bunyard tunnel and the accident location (see
23
U.S. Department of Transportation, Federal Highway Administration, MUTCD 2000: Manual on
Uniform Traffic Control Devices, Millennium Edition (Washington, DC: FHWA, 2000), section 2B.04 (sign
R1-1).
24
MUTCD, section 2C.26 (sign W3-1a).
25
MUTCD, section 2H.01.
26
MUTCD, sections 2C.01 and 2C.02.
Factual Information
24
Highway Accident Report
figure 12). While traveling southbound from the tunnel, the truck descended an average
grade of 2.7 percent (steepest grade was 4.9 percent) over 3.84 miles; an average grade of
2.3 percent (steepest grade, 4.1 percent) over 3.40 miles; and an average grade of 1.8
percent (steepest grade, 2.5 percent) over 0.47 mile. On its approach to the ramp, the truck
was descending an average grade of 3.3 percent (steepest grade, 4.4 percent) over 0.66
mile.
The annual average daily traffic for I-540 in 2000, as tabulated by the ASHTD, was
14,600 vehicles, of which about 21 percent were trucks. A 24-hour traffic count on June 13,
2001, showed that 36.7 percent of the 312 vehicles exiting onto the southbound ramp from
I-540 were trucks. The June 13 ASHTD traffic count showed that trucks accounted for 32.3
percent of the 460 eastbound and 13.2 percent of the 988 westbound vehicles on SH-282.
Figure 12. Grade map.
Factual Information
25
Highway Accident Report
In the vicinity of the accident, SH-282 is a two-way, two-lane paved asphalt
roadway running east-west. At the time of the accident, a combination of painted
markings and raised, mountable concrete islands (2 inches high at the edges and 6 inches
high overall) channelized the traffic lanes on both sides of the intersection. A left turn
lane, about 12 feet wide, was available for westbound traffic turning onto the entrance
ramp to southbound I-540. The east and westbound traffic lanes were about 11 feet wide
and bordered by paved shoulders about 8 feet wide and delineated by painted edge lines.
Standard pavement markings (a yellow painted double centerline) divided opposing lanes
of traffic. The speed limit for SH-282, as posted on a sign approximately 1 mile east of the
accident site, was 55 mph.
Tire Marks
The truck-tractor semitrailer produced multiple tire marks beginning on the east
shoulder of the exit ramp, about 30 feet north of the area of impact, and continuing
southwest across the intersection. The left front tire created a scuff mark,27 and a series of
chips in the asphalt surface were in line with the scuff mark. From the area of impact, the
longest tire mark, about 89 feet, traversed the south traffic island and continued toward the
area where the truck tractor came to rest. The truck-tractor semitrailer produced multiple
north-south scrape marks28 after the unit had rolled onto its left side.
Investigators observed no tire marks on SH-282 leading to the area of impact. The
school bus produced multiple tire marks beginning at the area of impact and continuing
southeast intermittently over a distance of about 110 feet. The longest tire marks
terminated in the area where the school bus came to rest. The school bus produced a single
deep scrape mark that ran west to east at the area of impact; investigators found no other
scrape marks related to the collision.
Operational Information
Gayle Stuart Trucking
Stuart Trucking began operating as a for-hire interstate carrier29 of agricultural
commodities, grain, feed, hay, and dry bulk in Vandalia, Missouri, in 1988; the company
also conducted farming operations. At the time of the accident, the motor carrier owned 16
tractors and 23 trailers; leased30 3 tractors and 2 trailers; and traveled about 1.777 million
miles annually. The motor carrier reported 17 full-time drivers, including 3 who drove
leased vehicles, on its payroll.
27
Scuff marks result when a tire slides while the wheel is still rotating.
28
Scrape marks are produced when any part of a vehicle, other than the tires, contacts the ground while
the vehicle is still in motion.
29
30
Operating under USDOT number 376158 and ICC number 213891.
The lease agreement is a contract stipulating the contractor’s responsibilities regarding insurance,
maintenance, driver control, and payment. The contractor is responsible for maintaining the vehicle.
Factual Information
26
Highway Accident Report
The motor carrier used State United Laboratories of Omaha, Nebraska, for preemployment, random, and postaccident drug testing. State United Laboratories conducted
random tests every 3 months, testing 1 to 6 drivers each period.
Mountainburg Public Schools
Mountainburg Public School District includes three schools—a high school, a
middle school, and an elementary school. It covers 197 square miles and the school buses
transport 790 students more than 111,250 miles annually; in addition, activity trips
account for about 25,000 miles. At the time of the accident, the school district had 12
school bus routes, 11 full-time busdrivers, 2 part-time drivers, and 10 substitute drivers.
The school district uses a local medical clinic to conduct alcohol and drug testing
of its busdrivers. Safety inspections are conducted on the school buses before the school
year begins and at midyear. All district school buses are equipped with cellular telephones
for communication with the school district and maintenance shop and for emergencies.
The Arkansas State Department of Education trains the district’s school bus
drivers. In August, the department conducts annual recertification of school bus drivers,
covering topics such as driving techniques, loading and unloading procedures, bus stop
location, and changes in operating procedures. In 2000, the school district superintendent
conducted an additional meeting with the bus drivers before the school year began; it
covered areas such as reporting times, policies and procedures, problems that developed
since the previous school year, and route changes.
Management Information
Gayle Stuart Trucking Company
The Stuart Trucking corporate structure comprised a president, vice president, and
safety manager. Company officials said they conducted telephone interviews with
previous employers listed on a driver’s application and that the company’s insurance
carrier provided motor vehicle driving records on all drivers.
Before starting work at Stuart Trucking, according to company officials, drivers
received 3 hours training in hopper-bottom trailer operation, brake adjustment procedures,
and logbook entry. The motor carrier reported that it held safety meetings every 6 months
attended by all drivers; the meetings covered issues such as driving procedures, loading
and unloading trucks, and load securement. The motor carrier said that it conducted
periodic recurrent training in logbook entry, trailer cleaning, and other operational
problems. The accident driver had attended the safety meetings but had not attended any
recurrent training. Stuart Trucking did not conduct mountain-driving training.
Company practice was for all drivers to be home on weekends, according to the
carrier, and drivers turned in their logbooks each week for auditing by company safety
personnel, who reported no problems with the accident driver’s logbook prior to the
Factual Information
27
Highway Accident Report
accident. Nonetheless, Safety Board investigators found errors when they reviewed the
logbook, and the driver admitted to falsifying his logbook. In its June 1, 2001, compliance
review, the Federal Motor Carrier Safety Administration (FMCSA) found at least one
instance of falsified logbooks during its compliance review of Stuart Trucking. In
comparing several other drivers’ logbooks with data from a Global Positioning System on
the trucks that tracked and recorded truck locations over the previous 10 days, inspectors
found that the logbook entries correlated with the truck locations.
Stuart Trucking employed one mechanic, who also drove for the company and
worked on farm equipment. Title 49 Part 396.25, “Qualification of Brake Inspectors,”
states that the brake inspector is any employee of the motor carrier or any other person
who is responsible for ensuring that all brake inspections, maintenance, service, or repair
meet Federal standards. The CFR goes on to say that the brake inspector is required to be
certified 1) by participating in a training program sponsored by a brake or vehicle
manufacturer or a Federal or State agency or 2) by having experience performing brake
maintenance or inspection for a period of at least 1 year. Additionally, any employee who
is responsible for the inspection, maintenance, service, or repair of any brakes on
commercial vehicles must meet the minimum qualifications. Stuart Trucking’s mechanic
had more than 1 year of experience performing brake maintenance and service. Stuart
Trucking reported that neither its drivers nor its mechanic had the required certification,
and the owner said he was not aware of the regulation.
On December 5, 1989, the Federal Highway Administration’s (FHWA’s) Office of
Motor Carriers (OMC), now the FMCSA, conducted a safety review of Stuart Trucking
that resulted in a satisfactory rating. Following this accident, the FMCSA conducted a
compliance review on June 1, 2001, that resulted in a conditional rating for the driver
factor because of the following violations:
•
Using a driver who was not medically examined and certified during the
preceding 12 months;
•
Failing to retain inquiries into the driver’s driving record in the qualification
file;
•
Requiring or permitting a driver to drive more than 10 hours;
•
Requiring or permitting a driver to drive after having been on duty 15 hours;
Not adhering to the 70-hour rule;31 and
•
Entering a false report of records-of-duty status.
The review did not mention the missing “Qualified Brake Inspector” certification.
31
The 70-hour rule limits drivers to 70 hours of working-driving time within 8 consecutive days.
Factual Information
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Highway Accident Report
The motor carrier received an unsatisfactory rating for the accident factor because
its accident rate was 1.688 recordable crashes per million miles traveled.32 The
combination of a conditional rating in one factor and an unsatisfactory rating in another
resulted in an overall conditional rating, which Stuart Trucking still maintained in August
2002. The review noted that the motor carrier’s maintenance records were in compliance
with the FMCSRs requirements.
The FMCSA did not inspect any vehicles during the 2001 compliance review; it
included only information from roadside inspections in the compliance review report.
Title 49 CFR Part 385 requires vehicle inspections during a compliance review if fewer
than 3 trucks were inspected during roadside inspections in the previous year or if more
than 34 percent of roadside inspections in the previous year resulted in trucks being placed
out of service. In the 12 months before the accident, the FMCSA had conducted 29
roadside inspections on Stuart Trucking vehicles, four of which (14 percent) were placed
out of service for brake adjustment violations. Therefore, FMCSA inspectors were not
required to inspect the carrier’s vehicles during the compliance review. Other out-ofservice violations noted in the roadside inspections related to logbooks, equipment, and
alcohol.
Following the accident, Safety Board investigators asked the Missouri Division of
Motor Vehicles and Railroad Safety to inspect all of the motor carrier’s vehicles at the
terminal and on the road. Of nine vehicles inspected at the motor carrier’s facility, four had
out-of-service defects (a 44 percent out-of-service rate).33 Of three units inspected on the
road, one was placed out of service for inoperative stop lamps; one driver was placed out
of service for logbook violations. According to company officials, Stuart Trucking
conducted general maintenance, including brake adjustment, every 15,000 miles and
extensive maintenance every 30,000 to 40,000 miles. The Missouri inspectors stated that
Stuart Trucking staff seemed to be lacking in knowledge of maintenance and that some
defects found were obvious and did not appear to be recent.
Federal Oversight
The Motor Carrier Safety Act of 1984 directed the U.S. Secretary of
Transportation to establish procedures to determine the safety fitness of commercial motor
vehicle owners and operators engaging in interstate and foreign commerce. Subsequently,
the FHWA promulgated a set of safety fitness standards and established a methodology for
determining whether a carrier has adequate safety management controls to ensure
acceptable compliance with the safety requirements. As a result of the Motor Carrier
Safety Act of 1990 and a 1997 rulemaking, the FHWA modified the original methodology.
32
Carriers that operate in an area more than 100 miles in radius and that have an accident rate greater
than 1.5 recordable crashes per million miles traveled receive an unsatisfactory rating (see 49 CFR Part 385,
appendix B).
33
These defects included brakes out of adjustment, defective or inoperative brakes, defective leaf
spring assemblies, defective axle positioning parts, suspension cracks, and inoperative rear turn signals.
Factual Information
29
Highway Accident Report
Six factors (see table 5) provide the basis for determining a carrier’s safety rating,
that is, the degree to which the carrier is in compliance with the FMCSR and therefore
meets the safety fitness standard. Each factor is rated satisfactory, conditional, or
unsatisfactory. A satisfactory rating means the carrier has not violated any acute
regulations (see definition below) or shown a pattern of noncompliance with critical
regulations for that factor. A conditional factor means the carrier has violated one acute
regulation or has a pattern of noncompliance with critical regulations. An unsatisfactory
rating means the carrier has violated two or more acute regulations or has patterns of
noncompliance with two or more critical regulations. Factor 6, the accident factor, is based
on the number of accidents in relation to the carrier’s size.
Table 5. Motor carrier safety rating factors.
FACTOR
APPLICABLE FMCSRs
OR OTHER CRITERION
Factor 1 – General
Parts 387 and 390
Factor 2 – Driver
Parts 382, 383, and 391
Factor 3 – Operational
Parts 392 and 395
Factor 4 – Vehicle
Part 393 and 396
Factor 5 – Hazardous Materials
Parts 171, 177, 180, and 397
Factor 6 – Accident
Recordable Preventable Rate
Acute violations of the FMCSRs or Hazardous Material Regulation are those that
demand immediate corrective action regardless of the motor carrier’s overall safety
posture. For example, requiring or permitting the operation of a vehicle declared out of
service before repairs are made (49 CFR 396.9[c][2]) is an acute violation.
Critical violations are regulatory violations that indicate breakdowns in a motor
carrier’s management controls. For instance, requiring or permitting a driver to drive after
having been on duty for 15 hours (49 CFR 395.3[a][2]) is a critical violation.
The rating for the first five factors and the accident rate for the 12 months before
the review are entered into a rating table, which is used to establish the motor carrier’s
safety rating (see table 6). Each of the six factors is given equal weight.
Factual Information
30
Highway Accident Report
Table 6. Motor carrier safety rating table.
FACTOR RATING
SAFETY RATING
Number of
Unsatisfactory Ratings
Number of
Conditional Ratings
Resultant
Safety Rating
0
2 or less
Satisfactory
0
more than 2
Conditional
1
2 or less
Conditional
1
more than 2
Unsatisfactory
2 or more
0
Unsatisfactory
State Oversight
Missouri. The Missouri State Police administer the Motor Carrier Safety
Assistance Program (MCSAP)34 in Missouri, and the State Police handle motor carrier
enforcement and roadside inspections. The Division of Motor Carrier and Railroad Safety
conducts terminal audits similar to those conducted by the FMCSA, and the division
conducted the follow-up inspection of Stuart Trucking requested by Safety Board
investigators.
Arkansas. In Arkansas, the MCSAP is administered by the Arkansas Highway
Police, which is the primary enforcement agency for all laws pertaining to axle and gross
weights, the movement of oversize loads or vehicles, vehicle licensing, motor fuel tax, and
special distillate motor vehicle fuel tax. The Arkansas Highway Police conduct all motor
carrier enforcement.
Meteorological Information
At the Fort Smith, Arkansas, Regional Airport, approximately 23 miles from the
accident site, the weather was partly cloudy with winds from the west at about 13 mph at
3:53 p.m. on May 31, 2000. The temperature was 69° F and the dew point was 60°.
34
The MCSAP is a Federal program administered by the FMCSA that provides funds to the States and
U.S. Territories in support of commercial motor vehicle safety.
Factual Information
31
Highway Accident Report
Tests and Research
Sight Distance
Safety Board investigators conducted sight distance tests after the accident. At a
driver eye height of 74 inches35 above the pavement, a motorist could see the stop sign
from the transition area36 to the end of the ramp, a distance greater than that prescribed by
the American Association of State Highway and Transportation Officials (AASHTO).
The “State park” sign then in place north of the “stop ahead” sign could impede a
motorist’s view of the “stop ahead” sign from a distance of 684 feet until the driver was
about 569 feet from the “stop ahead” sign (see figure 13). Since the accident, Arkansas has
moved the “State park” sign to the other side of the ramp, where it does not impede a
driver’s view of the “stop ahead” sign, and has added “stop ahead” signs. When the ramp
was constructed, it was cut into existing terrain, and a grass berm runs parallel to and east
of the ramp. A stop sign for traffic exiting I-540 onto SH-282 is in place at the
intersection. Safety Board visibility test results showed that, when stopped at the
intersection, a driver has a clear line of sight to the east exceeding 582 feet. A driver on
westbound SH-282 is not able to see traffic on the exit ramp until the driver is 51 feet east
of the intersection.
Brake Heat Tests
From September 5 to 7, 2001, Safety Board investigators measured the brake
temperatures37 of 65 tractor semitrailers traversing the same ramp used by the accident
truck. Table 7 lists the daily average brake temperatures for each axle.
As brakes heat up, for example, through repeated application, the drum expands,
requiring a greater stroke for the same brake force, and the lining friction decreases.
Stroke can increase by about 0.1 inch per 100° F.38 At temperatures above 700° F, even a
well-adjusted brake can reach out-of-adjustment limits, requiring more than 0.5 inch of
additional stroke, and the brake may run out of stroke before the shoe contacts the drum.
Brake linings are composed of glue and strengthening material, and when they
become hot, the glue softens and begins to melt. As a result, the linings become slick and
provide less friction, no longer offering the same level of resistance to the rotation of the
drums. When brake lining temperatures exceed 500 to 600° F, the friction between the
lining and the drum drops abruptly, further reducing the brake system’s ability to provide a
retarding force for the vehicle.
35
AASHTO assumes a driver’s eye height is 70 to 94 inches for large trucks and uses 94 inches for
design purposes. The Safety Board investigator who conducted the tests has an eye height of 74 inches.
36
The transition area, which is adjacent to the gore area, is the curved portion of the ramp as it departs
from the interstate.
37
Investigators used an infrared thermometer (Omega OS533) and took measurements directly from
the exterior of each brake drum.
38
U.S. Department of Transportation, Federal Highway Administration, Evaluation of Brake
Adjustment Criteria for Heavy Trucks, FHWA-MC-94-016 (Washington, DC: FHWA, 1995), p. 8.
Factual Information
Figure 13. Ramp sight distance.
32
Highway Accident Report
Factual Information
33
Highway Accident Report
Table 7. Average brake temperature (° F).
AXLE 1
LEFT
AXLE 2
LEFT
AXLE 3
LEFT
AXLE 4
LEFT
AXLE 5
LEFT
September 5
127
225
232
247
265
September 6
121
244
258
258
251
September 7
133
201
209
221
234
If some brakes are out of adjustment, the brakes that are within adjustment provide
a disproportionate share of the braking, thus heating more rapidly, further reducing overall
braking efficiency more quickly.39 Rockwell International tested the effects of poorly
adjusted brakes in the late 1980s.40 Researchers used various initial brake temperatures to
compare brakes fully adjusted with brakes backed off beyond the recommended stroke. At
150° F, the average stopping distance from 60 mph for a 55,000-pound truck-tractor
semitrailer increased 34 percent when brakes were backed off beyond the recommended
stroke, and at 400° F, the stopping distance increased 76 percent.
The accident truck, which was not equipped with an engine retarder, descended
four grades over the 11.3 miles from Bunyard tunnel to the exit ramp onto SH-282. A
grade severity computer analysis41 showed that, had the driver used his brakes to slow on
the first three downgrades, he may have noticed some degradation in the accident tractor
semitrailer’s braking capability, since the temperature exceeded 900° F at the bottom of
the second downgrade. The brakes would have cooled somewhat on the upgrades and on
the third descent,42 resulting in the tractor semitrailer’s brake temperature at the top of the
final hill reaching approximately 800° F.
The grade severity computer analysis also showed that if all the brakes had been
properly adjusted, they would have heated to 119° F at the top of the ramp and to 234° F
when the vehicle reached the final stop at the end of the ramp.
39
National Transportation Safety Board, Heavy Vehicle Airbrake Performance, Safety Study
NTSB/SS-92/01 (Washington, DC: NTSB), p. 31.
40
Leonard C. Buckman, Commercial Vehicle Braking Systems: Air Brakes, ABS and Beyond
(Warrendale, PA: Society of Automotive Engineers, 1988), p. 79.
41
The Grade Severity Rating System (GSRS) is a computer program developed under an FHWAfunded project. The purpose of the GSRS is to assist highway engineers in signing grades in order to reduce
the number of runaway heavy trucks. The GSRS also predicts the brake temperature as a vehicle travels
down the grade.
42
The average grade on the third descent was 1.7 percent, so not much braking was needed; the truck’s
aerodynamic drag was 1.4 percent.
Factual Information
34
Highway Accident Report
Simulation
Using the HVE system43 and the SIMON44 and EDSMAC445 software programs,
Safety Board investigators simulated the tractor semitrailer’s final ascent and descent to
the accident site and the collision with the school bus. Based on the physical evidence, the
EDSMAC4 simulation showed that the tractor semitrailer’s speed immediately prior to
impact was about 48 mph and the school bus was traveling about 50 mph. The simulation
results indicated that the tractor semitrailer’s postimpact speed was about 48 mph and that
the bus’s postimpact speed was about 39 mph. The simulation also showed that the berm
to the left of the ramp and the truck’s left mirror may have interfered with the truckdriver’s
view of the bus as the two vehicles approached the intersection.
To simulate the truck’s braking capability as the brakes heated due to repeated
application during the descent, investigators obtained truck brake performance data
related to temperature from ArvinMeritor. The data terminated at 603° F. Safety Board
staff extrapolated that data to take into account the higher temperatures for this tractor
semitrailer during the descent with the brakes out of adjustment. Staff incorporated into
the SIMON simulation a braking strategy that entailed pumping the brakes using 30 pounds
per square inch of pressure for 3 seconds.46 This strategy, according to the FHWA, is the
most efficient method of braking. The simulation showed that the tractor semitrailer was
traveling 55 to 60 mph at the bottom of the third descent, reduced its speed as it traveled
up the last ascent to between 22 and 27 mph at the crest, and was traveling 29 to 34 mph in
sixth gear at the top of the ramp. On the final descent prior to the ramp, the simulation
showed that the driver was able to apply the brakes about seven times to prevent the
tractor semitrailer from accelerating, but the brakes continued to heat to the point that with
each subsequent brake application, the truck’s braking force decreased and the truck
gained more speed, even while the brakes were applied, accelerating to 48 mph at impact.
43
The Engineering Dynamics Corporation developed HVE, a Human, Vehicle, Environment system,
for engineers and scientists to use as a simulation tool to study vehicle and occupant kinematics.
44
Simulation Model Non-linear, or SIMON, allows users to simulate the response of one or more
vehicles to driver inputs and environmentally related factors. It is designed to fully utilize the HVE Brake
Designer.
45
EDSMAC4, or the Engineering Dynamics Corporation Simulation Model of Automobile Collisions,
fourth revision, permits simulation of single- or multiple-vehicle crashes and is based on SMAC, which
Calspan developed for NHTSA.
46
Paul S. Fancher, Christopher B. Winkler, et al., Influence of Braking Strategy on Brake Temperature
in Mountain Descent, UMTRI-92-11/FHWA/MC-93/002 (Washington, DC: FHWA). This publication
recommends applying 20 psi on a truck with adjusted brakes, but because of this truck’s poor brake
condition, 30 psi was used.
Factual Information
35
Highway Accident Report
Other Information
Brake Data
Currently, data are not available that provide information on the extent to which
brakes cause or contribute to truck-related accidents. The U.S. Department of
Transportation (DOT) is conducting a study on large truck crash causation that is
scheduled to be completed in 2004. According to the FMCSA, the report will contain such
data.
In 1990, the Safety Board inspected 1,520 vehicles and found that 56 percent of
the trucks inspected had been placed out of service for brake violations; that figure
included 46 percent placed out of service for out-of-adjustment brakes.47,48 Results of a
1996 National Fleet Safety Survey found that 29 percent of trucks randomly inspected at
roadside were placed out of service; about 49 percent of the out-of-service violations were
brake-related.49
The CVSA sponsors Operation Air Brake annually to promote and reinforce the
need for drivers to check and adjust air brake systems and to educate drivers on the serious
risks associated with operating a heavy vehicle that has inadequate brakes.50 The results of
inspections conducted on six occasions during Operation Air Brake in 2000 and 200151
showed that, on average, 13 percent of commercial vehicles inspected were placed out of
service for having brakes out of adjustment. An average of 9.6 percent of brakes equipped
with manual slack adjusters were out of adjustment and 4.3 percent of brakes equipped
with automatic slack adjusters were out of adjustment. Approximately 65 percent of the
brakes checked had automatic slack adjusters.
Brake Adjustment Methodology
Automatic slack adjusters have been offered as optional equipment since the late
1960s and have been required on all new commercial vehicles since October 20, 1994.
Brake adjustment indicators have also been required on all new commercial vehicles since
October 20, 1994. Any vehicle manufactured before that date does not have to be
retrofitted and can continue to operate using manual slack adjusters.
Two common methods are used to measure brake adjustment on S-cam brakes,
which are the most frequently used type of service brake. Using the manual method, one
person, who pulls on the pushrod by hand or uses a pry bar, can measure the stroke.
47
NTSB/SS-92/01, p. 39.
48
A vehicle is out of service if 20 percent or more of its brakes are out of adjustment.
49
Terry Shelton, “Truck Brake Statistics in the U.S.” Report of Proceedings of the North American
Brake Safety Conference, September 15-16, 2000 (Toronto, Canada: CVSA, 2001), p. 12.
50
John Meed, “Operation Air Brake Report,” Report of Proceedings of the North American Brake
Safety Conference, September 15-16, 2000 (Toronto, Canada: CVSA, 2001), p. 15.
51
The CVSA conducted the inspections on the same days in a number of States. In May 2000, the
inspections took place in 27 States; in September 2000, in 22 States; in October 2000, in 25 States; in May
2001, in 28 States; in September 2001, in 29 States; and in October 2001, in 17 States.
Factual Information
36
Highway Accident Report
According to Allan C. Wright, author of a book on air brakes, “one half inch [stroke] is
ideal” when using the manual method; “the maximum allowable stroke, before
readjusting, is one inch.”52 This method can result in inconsistent measurement due to
variables such as the strength of the person pulling the pushrod, the length of the pry bar,
or the force exerted on the pry bar. The second, more accurate method requires two
people, one to apply the brake to an air pressure of 80 to 90 psi and another to measure the
stroke.
Ideally, a brake shoe should be adjusted as close as possible to the drum without
dragging (the shoe touching the drum). The American Trucking Association’s Technology
and Maintenance Council recommends backing off the adjusting nut until the wheel turns
freely, making the stroke as short as possible without the brakes dragging.53 This
adjustment can also be accomplished without jacking up the vehicle by backing off the
adjustment nut while simultaneously hitting the drum with a small hammer or wrench.
When the “dull thud” becomes a “ringing sound,” the adjustment nut should no longer be
turned, since the ideal shoe-drum clearance has been reached. Bendix Commercial Vehicle
Brake Systems (Bendix) recommends adjusting the slack adjuster so that the pushrod
travels 3/8 inch when manually extended to contact the brake shoes with the brake
drums.54
Determining when to adjust the brakes depends on many variables, including
terrain traveled, weight of load, use of engine retarders, size of brakes, miles traveled, age
of brakes, and driver’s braking habits. As explained in the Safety Board’s 1992 study of
Heavy Vehicle Airbrake Performance, industry recommendations for the adjustment
interval varied: Kenworth suggested the pushrod travel be checked and adjusted every
6,000 miles; Bendix suggested every month, 300 operating hours, or 8,000 miles; and
Rockwell International and Eaton Corporation suggested adjustment be made whenever
the pushrod stroke exceeded adjustment limits.
Spring Brakes
Federal regulations require that a vehicle be held by mechanical means (without
use of electrical power) when parked after all air has been bled out of the system.55 When
the vehicle is operating, a continual supply of air to the emergency-parking chamber
compresses the power spring so that the spring applies no force to the pushrod. When air is
released from the chamber, the spring force moves the chamber pushrod, applying the
service brakes. The operational life of the power spring depends on factors such as the
quality of the spring material, spring size, application cycle, and exposure to natural
elements (water and salt, for example). According to Haldex, springs under adverse
conditions, such as salt-treated roadways and frequent use, may last only 1 or 2 years
before they need to be replaced; Holland Anchorlok56 springs are guaranteed for 6 years.
52
Allan C. Wright, Airbrakes From the Driver’s Seat (Richmond, British Columbia, Canada: Presto
Print Limited, 1984), p. 17.
53
“TMC Recommended Practice,” RP 609A, 2001.
54
.
55
Title 49 CFR Part 571.121.S5.6.3.2.
56
Haldex purchased Anchorlok in January 2002.
Factual Information
37
Highway Accident Report
A broken spring, which is difficult to detect, can reduce emergency-parking brake
forces or render the emergency-parking brake inoperable, and the broken spring pieces
can be displaced, thus shortening the pushrod stroke or preventing the automatic slack
adjuster from functioning. The extent of the broken spring problem is undetermined.
Radlinski and Associates, a brake consulting firm, reported to investigators that in an
inspection of 11 five-axle combination trucks at a large firm with an excellent
maintenance program, an inspector found an average of two broken spring brakes on each
tractor semitrailer.
Broken spring brakes are not an out-of-service item if detected during CVSA
inspections, nor is visual examination of spring brakes an inspection item. Regulations do
not require use of dust covers over the caging port to prevent contaminants from getting
into the spring brake assembly.
38
Highway Accident Report
Analysis
Truck-tractor semitrailers represented 4 percent of all vehicles on the road in 2000
and accounted for 8 percent of vehicle miles driven; 12 percent of fatalities occurred in
accidents involving these vehicles.57 The Safety Board has investigated numerous
accidents involving tractor semitrailers in the past 30 years and made many safety
recommendations related to truck brakes, which are the most common reason trucks are
placed out of service. The Mountainburg accident again clearly demonstrates that when
brakes do not function properly, they compromise vehicle safety, sometimes with tragic
consequences.
Statistically, school buses are one of the Nation’s safest modes of transportation;
on average, fewer than 10 passengers die each year as a result of school bus accidents. The
fatalities that do occur, as in the case of the Mountainburg accident, generally happen
when a train or large truck strikes a bus laterally. In this accident, the brakes on the truck
were out of adjustment, thereby degrading its braking capability, and the truck was unable
to stop before colliding with the school bus.
In the following analysis, the Safety Board will first exclude those factors that did
not cause or contribute to the accident and then examine those factors that were causal or
otherwise had a role. The discussion will focus on the poor condition of the brakes,
inadequate motor carrier inspections and oversight, the use of fuel tanks on school buses,
and occupant protection within school buses. The Safety Board has addressed these issues
in previous accident investigations and will consider them below in the context of relevant
safety recommendations from the earlier investigations.
The Accident
Exclusions
The accident occurred in midday when the weather was clear and dry. Postaccident
inspection of the school bus revealed no mechanical problems. Results of postaccident
drug and alcohol tests for both the truckdriver and the busdriver were negative. Both
drivers held valid commercial driver’s licenses and medical certificates. The roadways
were in good condition and complied with AASHTO guidelines; the interstate and ramp
signing was in compliance with the MUTCD. Emergency response was timely and
adequate. The school bus was traveling about 50 mph at the time of the collision; the
speed limit on SH-282 was 55 mph. The truckdriver admitted that he had falsified his
logbooks to appear to be in compliance with Federal hours-of-service rules, and he later
57
U.S. Department of Transportation, National Highway Traffic Safety Administration, Traffic Safety
Facts 2000: Large Trucks, DOT HS 809 325 (Washington, DC: NHTSA, 2001).
Analysis
39
Highway Accident Report
described his actual work and rest times to Safety Board investigators. Until May 28 (3
days before the accident), he was off duty at home for 3 days, where he said he maintained
a normal work-rest cycle, that is, awake and active during daylight hours and resting
during nighttime hours. During the 3 days before the accident, he said he slept in the
truck’s sleeper berth each night, maintaining a normal work-rest cycle. Investigators
compared data available from fuel receipts and bills of lading for the accident vehicle
against travel times between locations on the driver’s route and found no conflict with the
work-rest cycle he described. The driver’s schedule did not include the required 8 hours
off-duty time, and the truckdriver obtained 5.5 to 6.5 hours of sleep per night.
However, the accident scenario does not indicate that the driver was fatigued. He
successfully steered the truck onto the exit ramp and applied the brakes in an attempt to
slow the truck before the accident. Had the driver not applied the brakes, the truck would
have been traveling much faster due to the downgrades on the interstate and ramp. While
investigators could not determine whether the driver was fatigued, his actions just prior to
the collision do not suggest that fatigue was a factor in this accident.
The Safety Board concludes that there was no evidence of drug or alcohol use by
the drivers and that the weather, mechanical condition of the school bus, design and
signing of the highways, emergency response, and truckdriver fatigue did not contribute to
the accident.
Accident Discussion
The tractor semitrailer did not stop for the stop sign at the bottom of the ramp
because the brakes, all of which were either out of adjustment, poorly maintained, or
overheated, could not provide enough retarding force. The driver said he slowed his
vehicle prior to the exit and, as he was departing I-540, applied the brakes to slow further,
but the vehicle did not respond. He stated that he saw the stop sign at the end of the ramp
and realized that he would be unable to stop the vehicle or, given the truck’s speed, make
the turn onto SH-282 without overturning the vehicle. Therefore, he decided to continue
across the highway and up the opposite ramp in an attempt to slow the truck. The driver
hoped that traveling up the entrance ramp to I-540 would reduce vehicle speed sufficiently
to allow him to bring it under control. As the simulation indicated, he could not see the
school bus on SH-282 because the berm to the left of the ramp and the truck’s left mirror
obstructed the driver’s view of the bus as the two vehicles approached the intersection.
Before impact, the tractor semitrailer was traveling an estimated 48 mph and the school
bus was traveling about 50 mph. The simulation showed that the tractor semitrailer’s
speed at separation was about 48 mph and that the bus’s postimpact speed was about 39
mph.
As the grade severity computer analysis and the simulation showed, the driver
probably used his brakes to maintain speed as he descended the first three downgrades
from the Bunyard tunnel. Each time he applied the brakes, the brake temperatures
increased. At the bottom of the second descent, the brake temperatures exceeded 900° F,
according to results of the grade severity computer analysis, and the brakes quite likely
could provide little braking force. At this point, the driver may have perceived that the
Analysis
40
Highway Accident Report
brakes were not functioning properly. He probably did not suspect a serious problem with
the brakes because his father had installed slack adjusters on the tractor 4 days earlier.
The driver was familiar with the location of the Mountainburg exit and the hills
near it because he had driven this route often, but he stated that he had never exited onto
SH-282 from I-540 southbound. He would not have had to apply the brakes too forcefully
to maintain speed going down the third descent because of its moderate grade. At the
bottom of the third descent near the sign for the exit, the simulation showed that the tractor
semitrailer was traveling 55 to 60 mph. The simulation also indicated that the driver did
not accelerate while going up the third ascent, probably in an effort to limit his speed so
that he would not have to use his brakes extensively as he …
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