Highway Accident Report

Collision Between Truck-Tractor

Semitrailer and School Bus

Near Mountainburg, Arkansas

on May 31, 2001

National 

Transportation 

Safety Board

Washington, D.C.

A

A

N TION

L TRA SPOR

ATIO

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B OARD

SAF E T Y

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E PLURIBUS UNUM 

NTSB/HAR-02/03

PB2002-916203

Highway Accident Report

Collision Between Truck-Tractor 

Semitrailer and School Bus

Near Mountainburg, Arkansas

on May 31, 2001

NTSB/HAR-02/03

PB2002-916203 National Transportation Safety Board

Notation 7490 490 LíEnfant Plaza, S.W.

Adopted September 4, 2002 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 <http://www.ntsb.gov>. 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 LíEnfant 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 Arkansas State Highway and Transportation Department

AASHTO American Association of State Highway and Transportation 

Officials 

ArvinMeritor ArvinMeritor, Inc.

Bendix Bendix Commercial Vehicle Brake Systems

CDL Commercial Driverís License

CFR Code of Federal Regulations

CVSA Commercial Vehicle Safety Alliance

DOT U.S. Department of Transportation

EMTs emergency medical technicians

FHWA Federal Highway Administration

FMCSA Federal Motor Carrier Safety Administration

FMCSRs Federal Motor Carrier Safety Regulations

FMCSR Federal Motor Carrier Safety Regulation

FMVSSs Federal Motor Vehicle Safety Standards

Haldex Haldex Brake Systems

Hammond Hammond Yellow Coach Lines, Inc.

I-540 Interstate 540

Kenworth Kenworth Truck Company

MCSAP Motor Carrier Safety Assistance Program

MUTCD Manual on Uniform Traffic Control Devices

NFPA National Fire Protection Association

NHTSA National Highway Traffic Safety Administration

OMC Office of Motor Carriers

psi pounds per square inch

SH-282 State Highway 282

Stuart Trucking 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, 65-

passenger, 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

truckdriverís inability to stop the tractor semitrailer at the stop sign at the bottom of the

ramp due to the reduced braking efficiency of the truckís brakes, which had been poorly

maintained and inadequately inspected. Contributing to the school bus passengersí

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

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. 

Figure 1. Truck route.
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 33

Serious 0 0 22

Minor 1 1 46

None 0 0 00

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 4 Highway Accident Report

Figure 2. Postcrash accident scene.
Factual Information 5 Highway Accident Report

Figure 3. Tractor semitrailer, postaccident.

Figure 4. School bus, postaccident.
Factual Information 6 Highway Accident Report

Medical and Pathological Information

The truckdriverís minor injuries included contusions on the right side of his head,

upper right arm, and left shoulder. The busdriverís 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 driverís 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 ìfloor,î 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 9 Highway Accident Report

Driver Information

Truckdriver

The 25-year-old truckdriver possessed a current Missouri class A Commercial

Driverís License (CDL), with no restrictions or endorsements, issued on March 15, 1999,

and scheduled to expire on March 15, 2002. A review of the driverís 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 driverís 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 driverís stated rest time, the times on

the receipts, and the driverís 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 driverís

blood. The driverís medical records did not indicate any other medical conditions.
Factual Information 10 Highway Accident Report

Table 2. Driverís off-duty/rest times.

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 busdriverís 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,

DATE

DRIVERíS STATED 

REST TIMES RECEIPTS

LIKELY TIMES

OF SLEEP 

TOTAL SLEEP 

(HOURS)

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

5 All school bus drivers are required to have an annual physical prior to the beginning of each school

year.
Factual Information 11 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 ìOK.î 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 ìOK.î 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 12 Highway Accident Report

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 ìbottoming outî a brake

chamber, the resulting pushrod stroke is the maximum stroke listed in the manufacturerís

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.

Figure 6. Brake diagram.
Factual Information 14 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.

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 ìtake grease.î 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 ìlooseî 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.

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
Factual Information 15 Highway Accident Report

Table 4. Brake adjustment.

* Manufacturersí 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

ìlooseî to prevent the trailer from slipping in wet and other conditions. He said that he had

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

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 semitrailerís 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 ArvinMeritor is a supplier of commercial vehicle components, including air brakes.

15 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 4Lís

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 11⁄2

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 manufacturersí

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 Boardís

request, inspectors from the Missouri Division of Motor Vehicle and Railroad Safety

conducted postaccident vehicle inspections on 12 Stuart Trucking vehicles (see

ìManagement Informationî 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 trailerís

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 vehicleís 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

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

Figure 7. S-cam diagram.

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

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

Figure 8. School bus propane tank.

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 vehicleís 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 driverís 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.

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.

Figure 9. School bus damage.
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 busdriverís 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 4-

foot 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

A 36-inch stop sign23 was in place on the traffic island north of the intersection. An

advance traffic control sign indicating ìstop aheadî24 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 ìstop aheadî 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 ìstop aheadî 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 ìstop aheadî 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

Figure 11. Exit ramp from I-540 south to SH-282.

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 Operating under USDOT number 376158 and ICC number 213891.

30 The lease agreement is a contract stipulating the contractorís 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 schoolsóa 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 districtís 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 driverís application and that the companyís 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 driverís 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 driversí 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, ìQualification of Brake Inspectors,î

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 Truckingís 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 Administrationís (FHWAís) 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:

ï Using a driver who was not medically examined and certified during the

preceding 12 months;

ï Failing to retain inquiries into the driverís driving record in the qualification

file;

ï Requiring or permitting a driver to drive more than 10 hours;

ï Requiring or permitting a driver to drive after having been on duty 15 hours;

Not adhering to the 70-hour rule;31 and

ï Entering a false report of records-of-duty status.

The review did not mention the missing ìQualified Brake Inspectorî certification.

31 The 70-hour rule limits drivers to 70 hours of working-driving time within 8 consecutive days.
Factual Information 28 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 carrierís 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 carrierís 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 carrierís vehicles at the

terminal and on the road. Of nine vehicles inspected at the motor carrierís 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 carrierís 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 carrierís size.

Table 5. Motor carrier safety rating factors.

Acute violations of the FMCSRs or Hazardous Material Regulation are those that

demand immediate corrective action regardless of the motor carrierís 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

carrierís 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 carrierís

safety rating (see table 6). Each of the six factors is given equal weight.

FACTOR APPLICABLE FMCSRs

 OR OTHER CRITERION

Factor 1 ñ General Parts 387 and 390

Factor 2 ñ Driver Parts 382, 383, and 391

Factor 3 ñ Operational Parts 392 and 395

Factor 4 ñ Vehicle Part 393 and 396

Factor 5 ñ Hazardous Materials Parts 171, 177, 180, and 397

Factor 6 ñ Accident Recordable Preventable Rate 
Factual Information 30 Highway Accident Report

Table 6. Motor carrier safety rating table.

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°. 

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

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 ìState parkî sign then in place north of the ìstop aheadî sign could impede a

motoristís view of the ìstop aheadî sign from a distance of 684 feet until the driver was

about 569 feet from the ìstop aheadî sign (see figure 13). Since the accident, Arkansas has

moved the ìState parkî sign to the other side of the ramp, where it does not impede a

driverís view of the ìstop aheadî sign, and has added ìstop aheadî 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 systemís ability to provide a

retarding force for the vehicle. 

35 AASHTO assumes a driverís 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 32 Highway Accident Report

Figure 13. Ramp sight distance.
Factual Information 33 Highway Accident Report

Table 7. Average brake temperature (° F).

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

semitrailerís 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 semitrailerís 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.

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

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 truckís

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 semitrailerís 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 semitrailerís 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 semitrailerís postimpact speed was about 48 mph and that

the busís postimpact speed was about 39 mph. The simulation also showed that the berm

to the left of the ramp and the truckís left mirror may have interfered with the truckdriverís

view of the bus as the two vehicles approached the intersection.

To simulate the truckís 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 truckís 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 truckís 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, ìTruck Brake Statistics in the U.S.î Report of Proceedings of the North American

Brake Safety Conference, September 15-16, 2000 (Toronto, Canada: CVSA, 2001), p. 12.

50 John Meed, ìOperation Air Brake Report,î 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, ìone half inch [stroke] is

idealî when using the manual method; ìthe maximum allowable stroke, before

readjusting, is one inch.î52 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 Associationís 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 ìdull thudî becomes a ìringing sound,î 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 driverís braking habits. As explained in the Safety Boardís 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 Driverís Seat (Richmond, British Columbia, Canada: Presto

Print Limited, 1984), p. 17.

53 ìTMC Recommended Practice,î RP 609A, 2001.

54 <www.bendix.com/downloads/service_date_sheet/manualslacks.pdf>.

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 Nationís 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 driverís 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

truckís 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 driverís route and found no conflict with the

work-rest cycle he described. The driverís 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 truckís 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 truckís left mirror

obstructed the driverís 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 semitrailerís

speed at separation was about 48 mph and that the busís 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 neared the exit ramp. At the top

of the third ascent, the tractor semitrailerís speed was 22 to 27 mph, and as the vehicle

traversed the final descent, the driver probably pulsed the brakes with about 30 psi of

pressure to maintain speed. As the vehicle neared the ramp, the brakes heated beyond the

point at which they could slow the vehicle. The driver stated that he noticed this loss of

braking near the top of the ramp and tried to downshift, but to no avail. Even applying

more pressure, as the driver said he did, would not have provided sufficient braking force

to slow the vehicle on the rampís steep grade, since the brakes were almost useless due to

heating at this point. The tractor semitrailer continued to accelerate until impact.

The truckdriver was unable to stop his vehicle because the brakes did not provide

enough retarding force when he applied them. The vehicleís braking efficiency58 at

ambient temperature, excluding heat effects, was calculated to be 0.35, that is, the tractor

semitrailer brakes produced 35 percent of the stopping force that they could have

produced if the brakes had been fully adjusted and functioning. The braking efficiency

was reduced to this level because five brakes were out of adjustment and three others were

not functioning; four of these eight brakes provided no braking force whatsoever. 

Traveling down several grades before reaching the exit ramp would have increased

brake temperature, further decreasing braking efficiency. The truck was not equipped with

an engine retarder, so the driver had to rely solely on the brakes and downshifting to slow

the truck on the downgrades. The engine control module had been removed, allowing the

engine rpm to increase and further reducing the engineís ability to slow the vehicle when it

was in gear. The driver stated that he began slowing the truck on the interstate prior to the

exit ramp because he was unfamiliar with the ramp.59 Using the brakes, drag, and gravity

to slow the truck from an estimated 60 mph to a driver-reported speed of 25 mph

(simulated speed of 29 to 34 mph) would have caused the brake drums to expand, thereby

increasing the stroke required to apply braking force by approximately 0.1 inch per 100° F.

The brake drums would have expanded to the point that the brake shoes could no longer

apply pressure to the drums, even with the pushrod fully extended. The simulation showed

that the brake lining temperature exceeded 500° F, significantly reducing the friction

58 Braking efficiency calculations take into account air pressure, chamber size, stroke length, slack

length, drum radius, rolling radius of the wheels, and weight on each wheel.

59 However, simulations show that the driver began to slow before the last descent and maintained the

slower speed down the last descent prior to the ramp. The truck would not have been able to slow from 60

mph to 25 mph on the last downgrade due to the condition of the brakes.
Analysis 41 Highway Accident Report

between the lining and the drum. At this point, the truck had almost no braking capability.

Simulations confirm that brake temperatures under such conditions would have rendered

all of the truckís brakes out of adjustment. Even the brakes that were within adjustment

prior to heating (4L and 5R) left no skid marks on the ramp, indicating that these brakes

could not apply enough retarding force to lock the wheels. The Safety Board concludes

that poorly adjusted and nonfunctional brakes, together with the resulting high

temperatures in the functioning brakes, reduced the truckís braking efficiency to such an

extent that the truckdriver was unable to stop the vehicle at the end of the ramp. 

Truck Brakes

Recommendation History

The Safety Board has been concerned about proper brake adjustment for more than

25 years. Previous investigations have resulted in several safety recommendations relating

to brake adjustment that are relevant to the Mountainburg accident. 

Brake Adjustment Guidelines. In 1975, the Safety Board investigated an

accident involving a tractor semitrailer that lost braking capability while descending a

steep grade near Bishop, California.60 The vehicle began accelerating at a point 5 to 5 1⁄2

miles from a truck parking area, where the driver had stopped to adjust the brakes. While

attempting to negotiate a curve, the trailer separated from the tractor, overturned in front

of a pickup and attached camper-trailer traveling in the opposite direction, and struck the

other vehicle, causing it to burst into flames and killing all seven occupants. As a result,

the Safety Board recommended that the FHWA:

H-75-17

Develop and disseminate throughout the motor carrier industry, an ìOn Guardî

bulletin alerting drivers of commercial vehicles equipped with externally

adjustable braking systems of: a) the need to be familiar with company policies

and practices with respect to on-road adjustment of brakes; b) methods and

techniques for detecting potential or existing problems in adjustment; c) the scope

of the problem in insuring proper brake adjustment; d) methods or techniques for

the proper on-road adjustment of braking systems currently and generally in use.

In response, the FHWA developed a bulletin entitled ìDanger-Driver Adjusted

Brakes,î which was circulated to all carriers for display on bulletin boards and distribution

to drivers and safety supervisors. The Safety Board classified this recommendation

ìClosedóAcceptable Actionî on October 20, 1977.

60 National Transportation Safety Board, Francisco Flores Truck/Pickup Truck with Camper and

Trailer Collision, U.S. Route 395, Bishop, California, June 29, 1974, Highway Accident Report

NTSB/HAR-75/05 (Washington, DC: NTSB/1975).
Analysis 42 Highway Accident Report

A similar recommendation resulted from the Safety Boardís 1992 safety study on

heavy vehicle airbrake performance. The Safety Board recommended that the National

Private Truck Council, the Owner-Operator Independent Driver Association, and the

American Trucking Associations work with one another:

H-92-67, -72, and -74

To complete and distribute to member carriers appropriate brake maintenance

materials that clearly establish standard inspection techniques (including

adjustment indicators), inspection and adjustment interval guidelines, and an

adjustment method (covering both manual and automatic slack adjusters) for Scam brakes on heavy vehicles. Encourage members to provide a copy of the

information to each driver of a heavy vehicle and to each mechanic who services

heavy vehicles.

On July 29, 2002, the Safety Board classified this recommendation to the National

Private Truck Council ìClosedóUnacceptable Action/No Response Received.î

In 1993, the Owner-Operator Independent Driver Association produced and

distributed more than 15,000 copies of a brake videotape and accompanying booklet

entitled Whatís Stopping You? that stressed the importance of regular preventive brake

maintenance, provided an overview of roadside inspection procedures, and warned of the

potentially serious consequences of mismatching brake components. Also included was

information from the FHWA and the University of Michigan Transportation Research

Institute on downhill braking techniques. The Safety Board classified the recommendation

to the Owner-Operator Independent Driver Association ìClosedóAcceptable Actionî on

January 30, 2001.

Through its maintenance council, the American Trucking Associations developed

a training video on how to conduct truck brake inspection and maintenance. In 1992, the

American Trucking Associations informed the Safety Board that efforts were under way

with the FHWAís OMC to develop a method carriers could use to establish an appropriate

brake adjustment interval for their own operations. The FMCSA Web site now contains a

comprehensive list of brake maintenance materials and guidelines. The Safety Board

classified the recommendation to the American Trucking Associations ìClosedó

Acceptable Actionî on July 16, 2002. 

The intent of the safety recommendations issued in 1975 and 1992 was to inform

carriers and drivers of the need to maintain brake adjustment and to perform the

adjustment properly, but the materials may not have reached or been used by all carriers.

Safety Board investigators were unable to determine whether Stuart Trucking received

any of these materials. Informing drivers about standard inspection techniques and

adjustment methods is an important first step in proper brake maintenance. Although the

Mountainburg driver described to investigators the correct procedure for adjusting brakes,

he apparently did not apply that knowledge in the case of the accident vehicle.
Analysis 43 Highway Accident Report

Automatic Slack Adjusters and Out-of-Adjustment Indicators. Beginning in

1978, the Safety Board made several safety recommendations to require that vehicles be

equipped with automatic slack adjusters and out-of-adjustment indicators.61 In 1977 and

1978, the Safety Board investigated five accidents in which commercial vehicle drivers

were unable to maintain speed control on downgrades. The major causal factor in four of

these accidents was improper adjustment of the vehiclesí service brakes, and in the fifth,

the trailer brakes were totally inoperative. In two instances, the owners and operators had

failed to ensure that the vehicles were safe for operation before they were dispatched.

In its 1992 study of Heavy Vehicle Airbrake Performance, the Safety Board issued

safety recommendations that superseded those resulting from the investigations conducted

in the 1970s and 1980s. The Board cited numerous brake deficiencies, including serious

instances of out-of-adjustment brakes, as causal or contributing factors in the accidents

investigated to support the 1992 safety study. The Safety Board urged NHTSA to:

H-92-50

Require that air-braked vehicles be equipped with visible adjustment indicators

that will allow one person to check the level of adjustment.

H-92-51

Expedite the proposed rulemaking to require automatic adjusters on vehicles

equipped with airbrake systems.

NHTSA issued a final rule on October 20, 1992, amending FMVSS 121, ìAir

Brake Systems,î and FMVSS 105, ìHydraulic Brake Systems,î to require automatic brake

adjusters on all air-braked and hydraulic-braked vehicles manufactured after October 20,

1994. Consequently, the Safety Board classified both recommendations ìClosedó

Acceptable Actionî on December 21, 1992.

The Safety Board also recommended that the FHWA:

H-92-57

Encourage the installation of vehicle brake adjustment indicators on all vehicles

equipped with airbrake systems for easy detection of adjustment levels.

In 1995, the FHWA published a report entitled Evaluation of Brake Adjustment

Criteria for Heavy Trucks, which presented analyses, findings, and recommendations

concerning the brake adjustment criteria of the ìNorth American Uniform Driver-Vehicle

Inspection Criteria for Heavy Trucks.î The FHWA also issued a final rule requiring motor

carriers that have vehicles manufactured on or after October 20, 1994, to retain automatic

brake adjustment indicators. Therefore, the Safety Board classified this recommendation

ìClosedóAcceptable Actionî on February 5, 1996.

61 Safety Recommendations H-78-48 and H-88-30 were superseded by Safety Recommendation H-92-

50. Safety Recommendations H-81-1 and H-88-32 were superseded by Safety Recommendation H-92-51. 
Analysis 44 Highway Accident Report

The safety recommendations issued in 1992 resulted in the Federal requirement

that all commercial vehicles manufactured after 1994 have automatic slack adjusters and

brake adjustment indicators, which were in place on the trailer involved in the

Mountainburg accident. The tractor was built prior to the rulemaking requiring the use of

these systems. While the automatic slack adjusters did maintain the adjustment on two of

the trailerís brakes, they could not maintain proper adjustment on two other brakes

because of broken springs and an improperly installed spring brake. Automatic slack

adjusters can only function as designed if the other brake components are properly

installed and maintained. 

Accident Vehicle

Brake Adjustment. The tractor semitrailer in the Mountainburg accident was

equipped with manual slack adjusters on the tractor brakes and automatic slack adjusters

on the trailer. Eight of the 10 brakes were either out of adjustment or nonfunctional at the

time of the accident, and 4 brakes were unable to provide any braking force, even without

taking into account heat buildup and drum expansion.

The driver said that the tractor brakes were last adjusted on May 27, 2001, when he

and the owner had installed manual slack adjusters on the second and third axles of the

tractor. The owner admitted that he did not keep the front axle brakes fully adjusted and

backed them off æ turn. According to accepted maintenance practices, brakes should only

be backed off either until the drum turns freely or a maximum of 3/8 to 1⁄2 turn. NHTSA

has conducted extensive research to evaluate the need for front steering axle brakes.

Following a series of tests, the agency concluded:

Drivers were clearly able to achieve better performance with full front brakes than

without under all circumstances. They stopped in shorter distances under full

control with full front brakes. Without front brakes, best stopping distances were 5

to 130 percent longer and drivers were more likely to lose control.62

Because the front brakes on the accident vehicle had not been adjusted properly,

they were either out of adjustment or close to being out of adjustment at the start of the

trip, decreasing the braking ability of the front axle brakes. The drum on axle 1R was

rusty, indicating that the brake shoe was not contacting the drum when the brakes were

applied, so this brake provided no braking force at all.

The owner of the truck had installed manual slack adjusters on the second and

third axles of the tractor 4 days before the accident. He said he adjusted the brakes at that

time using prescribed procedures, that is, turning the adjusting nut until the shoes touched

the drums and then backing off the adjusting nut 1⁄2 turn. The driver said he watched Stuart

Truckingís mechanic adjust the brakes on the trailer 2 or 3 weeks before the accident. 

62 U.S. Department of Transportation, National Highway Traffic Safety Administration, A

Demonstration of the Safety Benefits of Front Brakes on Heavy Trucks, DOT HS 807 061 (Washington, DC:

NHTSA, 1986).
Analysis 45 Highway Accident Report

When some brakes are out of adjustment, the remaining brakes must provide

greater braking force whenever they are applied in order to stop the vehicle, increasing the

rate at which they wear and thus become out of adjustment. The brakes on the first axle

(1R and 1L) provided limited braking force because they were improperly adjusted (1R

provided no braking force for a period of time before the day of the accident, as evidenced

by the rusted brake drum reported by the driver). Brakes on axles 3L, 4R, and 5L could not

provide much, if any, braking force since they were nonfunctional owing to poor

maintenance and other broken components. Therefore, the remaining 5 brakes (3 on the

tractor and 2 on the trailer) had to provide the braking force for 10 brakes.

Heat can also speed the rate at which brakes become out of adjustment. When

some brakes on a vehicle are out of adjustment, those brakes that are within adjustment

heat more rapidly because of the additional workload placed on them. Following the

accident, the only brakes found to be within adjustment were those without broken

components and equipped with automatic slack adjusters, which compensated for pushrod

slack, adjusting accordingly.

The truck had only been driven about 1,600 miles, primarily on level roadways,

since the new manual slack adjusters had been installed on May 27, or 4 days before the

accident. Even so, during postaccident inspection, investigators found that the brakes were

out of adjustment. According to industry representatives from Kenworth and Bendix,

brakes should require adjustment every 6,000 to 8,000 miles. The Safety Board concludes

that the six brakes on the tractor were out of adjustment either because the owner had not

properly adjusted them, or because the brakes became out of adjustment due to a

disproportional workload, or both. 

The driver said that he did a visual inspection of the brakes on the day of the

accident and did not find them to be out of adjustment. The Commercial Driverís License

Manual recommends that during a pretrip inspection, the driver, at a minimum, pull on the

pushrod and measure the stroke. If the stroke exceeds 1⁄2 to 1 inch, the brakes should be

adjusted. Postaccident inspection showed that the stroke on five of the six tractor brakes

exceeded 2 inches and that one other (3L), on which the stroke was restricted to 1 7/8 inch

by a broken spring, also needed adjustment. Accident damage would not have affected the

brakesí stroke.

The driver did not follow recommended practice for measuring stroke during the

pretrip inspection, and a visual inspection did not allow him to determine that the brakes

were out of adjustment. While the CDL practice is only recommended, not mandatory, it is

an important part of the pretrip inspection because of the safety-related nature of the brake

system and the possible consequences, as in the case of this accident, when brakes are not

adjusted properly. The Safety Board concludes that the driver did not conduct a

sufficiently thorough pretrip inspection on either the tractor or the trailer to discover the

brake deficiencies. 

As 49 CFR 383.111(e)(4) and (g)(5) state, all commercial vehicle operators must

have knowledge of procedures for conducting safe and accurate pretrip inspections and

knowledge of airbrakes. Title 49 CFR 383.113 requires that all CDL applicants
Analysis 46 Highway Accident Report

demonstrate pretrip inspection skills pertaining to airbrakes, including the ability to

determine brake conditions and proper adjustment. Interviews with the accident driver

indicated that he knew how to adjust brakes. While the accident driver did have a CDL, he

did not demonstrate that he was knowledgeable about procedures for conducting a safe

and accurate pretrip inspection on the day of the accident or about the consequences of not

conducting a thorough pretrip inspection. However, 49 CFR 396.13(a) only stipulates that

a driver be satisfied that the motor vehicle is in safe operating condition before driving it;

the regulations specify neither what must be done during a pretrip inspection, nor which

procedures must be performed daily on a vehicle.

The Safety Board has investigated other accidents in which pretrip inspection

procedures were lax as well. On March 2, 1999, near Santa Fe, New Mexico, a

motorcoach began descending a 14-mile mountainous roadway, and halfway down, the

driver found that the brakes were providing no retarding force.63 The driver lost control of

the bus, and it departed the right side of the roadway, crashed into a rock embankment, and

overturned. Investigators found that four of the busís six brakes were out of adjustment at

the time of the accident and two brakes were nonoperational. Company mechanics did not

routinely examine driver pretrip inspection forms and did not know whether company

drivers completed pretrip inspections. The busdriver reported that in the 10 months he had

worked for the company, he had never completed a pretrip vehicle inspection. A review of

company maintenance records revealed that some drivers were occasionally completing

vehicle inspection reports.

Had the Mountainburg and Santa Fe drivers been required to measure the stroke on

each brake and to determine its adjustment before they began driving on the day of the

accident and had they fulfilled such a requirement, they may have discovered that some

brakes were out of adjustment and taken appropriate corrective action. The Safety Board

believes that the FMCSA should revise CFR 396.13, Driver Inspection, to require

minimum pretrip inspection procedures for determining brake adjustment. 

Spring Brakes. Of six brakes on the tractor semitrailer equipped with spring

brakes for emergency-parking brake application (axles 3, 4, and 5), three had broken

springs. The 3L brake spring was broken in three pieces, restricting total stroke by 3/8

inch. Thus, even though the 3L brake appeared to be within adjustment at 1 7/8 inches, it

was not. 

The 4L brake spring was broken in two pieces, and dynamic testing of the vehicle

showed that the broken spring did not prevent service brake application; the service brakes

even locked during one test. When the emergency-parking brake was applied during

another test, the 4L brake provided some braking force (the service brake locked on gravel

but not on concrete), indicating the emergency-parking brake force was reduced due to the

broken spring, but was not completely eliminated. 

63 National Transportation Safety Board, Motorcoach Loss of Control and Overturn, New Mexico State

Route 475, March 2, 1999, Highway Accident Brief NTSB/HAB-01/01 (Washington, DC: NTSB, 2001).
Analysis 47 Highway Accident Report

The 5L brake spring was also broken and blocking the pushrod, thereby limiting

pushrod stroke and preventing it from reaching the minimum 11⁄2 inches necessary for the

automatic adjuster to begin readjustment. During testing, 5L did not provide any braking

force when either the emergency-parking brake or the service brake was applied. In other

words, both the emergency-parking brake and the service brake were nonfunctional.

Thus, a broken spring, in addition to reducing the braking ability of the

emergency-parking brake or rendering it inoperable, can have a detrimental effect on the

service brakes, as was the case in this accident. Broken springs on two of the vehicleís

three brakes prevented proper brake adjustment, thereby contributing to a reduction of the

tractor semitrailerís braking efficiency.

The caging that houses brake springs makes detection of broken springs difficult

because access to the closed chamber is restricted. One method of detection involves

inserting an optical device called a borescope into the caging port. Another entails

inserting a finger inside the caging port, but doing so can be extremely dangerous during

roadside inspections; if the truck moves, the spring breaks, or the driver applies or releases

the parking brake, the inspector can be injured. If the spring brake is equipped with an

integrated caging bolt, then it has no port for accessing the spring. Brake springs are

neither a CVSA out-of-service item nor an inspection item. However, as this accident

demonstrates, broken springs can have safety consequences when they prevent proper

adjustment of the service brake or decrease the braking capability of the emergencyparking brake. The Safety Board concludes that because of the spring brake design,

examining the springs to determine whether they were broken was difficult on three of the

truckís brakes. Therefore, the Safety Board believes that the manufacturers should

develop a spring brake that allows inspectors or mechanics to view components safely to

determine whether the spring is broken. Safety Board staff participates in CVSA

committees, and once the spring brakes are redesigned, staff will work with the CVSA to

incorporate inspection of spring brake components into the vehicle inspection criteria.

Springs break for various reasons, including exposure to the elements, number of

brake applications, age, or material properties. Contaminants can enter spring brake

chambers through the caging ports unless dust covers (small caps) are in place to prevent

contaminants from entering. These contaminants, such as salt and water, can weaken the

material properties of the spring, making it more susceptible to breakage. On the accident

vehicle, dust covers were missing on all four spring brakes that had standard nonintegrated

caging ports. Evidence of a white substance, probably salt deposits, was present inside the

4L spring chamber, and salt can corrode a spring, leading to its failure. The Safety Board

concludes that dust covers on the caging ports of the accident vehicleís spring brakes

would have reduced the chance of corrosion to the spring, possibly prolonging the life of

the spring and, in turn, the life of the emergency-service brakes. The Safety Board

believes that the CVSA should include spring brake caging port dust covers as an

inspection item during Motor Carrier Safety Assistance Program roadside inspections.
Analysis 48 Highway Accident Report

Motor Carrier Inspection and Oversight

Recommendation History

The Mountainburg accident is one of many in which the Safety Board has

identified the inadequacy of motor carrier inspections, including compliance reviews, as

cause for concern. In 1995, for example, the Safety Board investigated a motorcoach

accident in which the bus overturned when it entered an exit ramp in Indianapolis,

Indiana;64 2 passengers sustained fatal injuries and 13 sustained serious injuries.

Postaccident inspection of the vehicle revealed out-of-adjustment brakes; as a result, the

bus had only 50 percent braking efficiency, which probably contributed to the accident.

The OMC conducted an after-accident compliance review of the operator, Hammond

Yellow Coach Lines, Inc., (Hammond) that resulted in an unsatisfactory rating (10 of 10

vehicles reviewed were placed out of service) and a subsequent out-of-service order

because of noncompliance within 45 days of the proposed unsatisfactory rating.

However, Hammond already had significant safety problems before the accident

and yet was still permitted to operate. The OMC had inspected Hammond nine times

between 1987 and 1995. In 1993, the OMC gave Hammond an unsatisfactory rating,

citing the carrierís accident rate and hours-of-service violations; 3 months later, the

agency upgraded that rating to satisfactory. In 1994, the OMC used Indiana State Police

terminal inspection results to determine the rating for its compliance review. Because of

the high number of vehicles (63 percent) meeting out-of-service criteria, Hammond

received a conditional rating for the vehicle factor component of the compliance review.

But the OMC rated all other factors satisfactory, resulting in an overall rating of

satisfactory and Hammond continued to operate with unsafe vehicles. Following the

Indianapolis accident, the Safety Board asked the DOT to:

H-99-6

Change the safety fitness rating methodology so that adverse vehicle and driver

performance-based data alone are sufficient to result in an overall unsatisfactory

rating.

On December 14, 1999, the OMC (now FMCSA) responded that it expected to

issue a notice of proposed rulemaking calling for a more performance-based means of

determining carrier fitness to conduct commercial motor vehicle operations. The OMC

stated that it would take into account the Safety Boardís recommendation, along with any

comments received, in developing a new rating system. The Safety Board classified the

recommendation ìOpenóAcceptable Responseî on March 17, 2000, based on the

expected notice of proposed rulemaking. Safety Recommendation H-99-6 was also added

to the Safety Boardís Most Wanted Transportation Safety Improvements list to increase

the publicís awareness of and support for action to adopt safety steps that can help prevent

accidents and save lives. Since then, the FMCSA has developed a rating system that

64 National Transportation Safety Board, Selective Motorcoach Issues, Highway Special Investigation

Report NTSB/SIR-99/01 (Washington, DC: NTSB, 1999).
Analysis 49 Highway Accident Report

allows it to focus compliance reviews on the carriers who have had safety problems in the

past. On July 12, 2002, the FMCSA advised the Safety Board that it would address Safety

Recommendation H-99-6 in an upcoming notice of proposed rulemaking on ìSafety

Fitness Procedures.î Like Hammond, the carrier in the Indianapolis accident, Stuart

Trucking had significant safety defects on the accident vehicle and other vehicles,

numerous driver violations, and unqualified brake inspectors, yet was still permitted to

operate.

Compliance Reviews

Stuart Truckingís most recent compliance review prior to the Mountainburg

accident took place on December 5, 1989, and resulted in a satisfactory rating. Following

the accident, the FMCSA conducted a compliance review that resulted in a conditional

rating for factor 2 (driver factor), an unsatisfactory rating for factor 5 (accident factor),

and a conditional rating overall. FMCSA staff did not inspect any vehicles during this

review, even though the accident was vehicle-related. They relied instead on the motor

carrier profile report, which listed 29 roadside inspections in the previous 12 months,

resulting in four out-of-service vehicles (14 percent), all with out-of-adjustment brakes.

The regulations at 49 CFR Part 385, Appendix B, state that if fewer than 34 percent of

vehicles (the national average) inspected in the previous 12 months (when more than three

vehicles receive roadside inspections) are placed out of service, then the carrier is rated

satisfactory for the vehicle factor, as was the case in the postaccident compliance review

of Stuart Trucking.

Safety Board investigators were concerned that the FMCSA did not inspect any of

Stuart Truckingís vehicles. This accident involved a vehicle in which 8 of 10 brakes were

out of adjustment and the carrierís mechanic was not a qualified brake inspector,

suggesting that more vehicles may have had brake problems than were detected in the 12

months of roadside inspections, yet the FMCSA did not inspect any vehicles during the

compliance review immediately following this accident. Consequently, the Safety Board

asked the Missouri Division of Motor Vehicles and Railroad Safety to conduct an

additional review of the carrier and inspect all its vehicles. Of 12 vehicles examined, 5

vehicles (42 percent) had out-of-service violations. Not only did this review reveal an outof-service rate higher than the FMCSA recorded in its compliance review, but

investigators also determined that the brakes had not been maintained properly. Improper

maintenance, which cannot be detected without conducting vehicle inspections, can be

telling as to the condition of a carrierís vehicles. The Safety Board concludes that based on

the inspection conducted by the Missouri Division of Motor Vehicles and Railroad Safety

that followed the accident, had FMCSA staff inspected Stuart Truckingís vehicles during

the 2001 compliance review, the carrier would probably have received a conditional rating

in factor 4 (vehicle factor) instead of a satisfactory rating. 

The FMCSAís overreliance on roadside inspections when conducting compliance

reviews may lead to underestimating the number of out-of-service vehicles. As noted

above, the percentage of out-of-service vehicles found during the terminal inspection of

Stuart Trucking was triple that found during the previous 12 months of roadside

inspections. The Safety Board is concerned that carriers may be operating unsafe vehicles
Analysis 50 Highway Accident Report

that are not detected during a roadside inspection or compliance review and that, as a

result, the carrierís rating may be inaccurate because it misrepresents the proportion of

out-of-service vehicles. The FMCSA will not conduct a terminal inspection if three or

more of a companyís vehicles received roadside inspections in the previous 12 months.

But the vehicles that receive roadside inspections may not be representative of the entire

fleet. The Safety Board believes that the FMCSA should require that vehicle inspections

of a motor carrierís fleet be conducted during compliance reviews. 

Furthermore, even if its vehicle factor rating had been changed as a result of the

2001 compliance review, Stuart Truckingís overall rating would have remained

conditional. Under current compliance review procedures, one unsatisfactory factor rating

and two or fewer conditional factor ratings result in an overall conditional rating. The

2001 rating for Stuart Trucking underscores the failure of compliance reviews to identify

unsafe carriers. This carrier had not been rated in more than 11 years at the time of the

accident. Despite having unsafe vehicles on the road, no qualified brake inspectors, and

numerous driver violations, Stuart Trucking still received a conditional rating. 

The tragic consequences of this accident add urgency to the Safety Boardís Safety

Recommendation H-99-6 to change the safety fitness rating methodology. The FMCSA

continues to respond that it plans to issue a notice of proposed rulemaking that would lead

to a more performance-based safety fitness rating system. To date it has not done so.

Therefore, the Safety Board reiterates Safety Recommendation H-99-6 to the DOT urging

it to change the safety fitness rating methodology so that adverse vehicle and driver

performance-based data alone are sufficient to result in an overall unsatisfactory rating.

Qualified Brake Inspector

Title 49 CFR Part 396.24, ìQualification of Brake Inspectors,î requires that each

brake inspector successfully complete an apprenticeship program or a training program or

have a certificate or experience totaling 1 year; in addition, the motor carrier must

maintain evidence of qualifications. Stuart Truckingís mechanic, who was responsible for

maintaining most of the companyís tractors and trailers, had not received any formal

training in brake inspection, although he did have more than 1 year of experience and,

under current rules, was eligible for certification. The owner said that he was not aware of

the regulations requiring anyone who inspects or maintains brakes to be certified.

Although the person responsible for maintaining the brakes on the trailer of the

accident vehicle had experience in brake maintenance, the condition of the trailerís brakes

belied this experience, since three of the trailerís four brakes had broken parts or were

nonfunctional at the time of the accident. Two brakes (4L and 5L) had broken springs, and

during installation of one spring brake (4R), the pushrod was cut too short, rendering the

automatic slack adjuster inoperable. Stuart Truckingís mechanic did not detect the latter

problem in the 4 years between installation of the 4R spring brake in 1997 and the

accident. In fact, brakes 4R and 5L had quite likely been inoperative for some time, since

the brake drums were rusted, indicating the shoes had not been in contact with the drums.

A qualified mechanic should have noticed this problem during routine maintenance and

inspections.
Analysis 51 Highway Accident Report

In addition, the absence of grease at the fittings and brake camshaft bushings

suggested a lack of periodic lubrication, and the Arkansas Highway Police and

ArvinMeritor staff both commented on the poor overall condition of the trailerís brake

system. During their follow-up vehicle inspection, Missouri Division of Motor Vehicle

and Railroad Safety inspectors stated that Stuart Trucking staffís knowledge of truck

maintenance seemed to be lacking; these inspectors also noted that some defects they

found were obvious and did not appear to be recent. A brake inspector with sufficient

training and knowledge would probably have identified the problems with the brakes on

this semitrailer and fixed the brakes so that they were operative. The Safety Board

concludes that the Stuart Trucking mechanic lacked proper training in brake maintenance

and inspections, did not detect the poorly adjusted or inoperative brakes on the trailer, and

did not perform recommended maintenance. 

The Safety Board has investigated other accidents in which a motor carrier did not

use a certified brake inspector to perform maintenance on its vehicles. In the

aforementioned accident near Santa Fe in 1999, investigators found that the steering and

drive axle brakes were out of adjustment, that the auxiliary weight-bearing axle brakes

were not operational because they were ìcammed over,î65 and that both drums were worn

beyond the manufacturerís acceptable limits. During postaccident inspection of the carrier

by the New Mexico Motor Transport Division, all but two of the inspected motorcoaches

were placed out of service due to mechanical defects, most of which were related to the

brake systems. The carrier did not keep brake mechanic qualification records, as required,

and none of the three company mechanics interviewed could adequately describe the

maximum brake adjustment levels for the brakes on the motorcoaches, how to conduct a

vehicle brake inspection, or how to adjust brakes.

Under the current compliance review process, the FMCSA does not consider

violation of 40 CFR 396.25 ìcritical.î Thus, if a motor carrier does not have a qualified

brake inspector, it does not affect the carrierís rating. In fact, in its compliance review of

Stuart Trucking, the FMCSA did not even note that a qualified brake inspector certificate

was not on file. The Safety Board believes that during compliance reviews, the FMCSA

should rate companies as unsatisfactory in the vehicle factor category if the mechanics and

drivers responsible for maintaining brake systems are not qualified brake inspectors. 

As the Mountainburg and Santa Fe accidents demonstrate, experience working in a

maintenance shop is not always sufficient to ensure that a mechanic has the knowledge

necessary to maintain a truck brake system. The FMCSA is remiss in permitting

mechanics to work on brakes without knowing whether they have the requisite skills in

brake maintenance. The Safety Board believes that the FMCSA should revise 49 CFR

396.25, Qualifications of Brake Inspectors, to require certification after testing as a

prerequisite for qualification and specify, at a minimum, formal training in brake

maintenance and inspection. 

65 A condition in which the S-cam rotates beyond the service brake cam rollers and remains lodged in

this position. The cause is generally a combination of out-of-adjustment brakes, worn brake shoes, and an

excessively worn drum.
Analysis 52 Highway Accident Report

Fuel Tanks

Recommendation History

While it has not made specific recommendations addressing retrofitted propane

tanks on school buses, the Safety Board has recommended protecting fuel tanks on school

buses to minimize the risk of fire. On February 29, 1972, a 1961 sedan ran a stop sign near

Reston, Virginia,66 and collided with a school bus carrying four children. The impact

ruptured the school bus fuel tank, knocked it from the bus, and disabled the school bus

service door. A fire ensued in the sedan due to gasoline spilled from the ruptured and

detached school bus fuel tank, which was in a vulnerable location and lacked crash

protection design features. The Safety Board urged that NHTSA and the Vehicle

Equipment Safety Commission:

H-72-2

In consideration of the unnecessary hazards posed by locating school bus fuel

tanks adjacent to service doors, act promptly to determine the ìbestî and ìsafestî

location for school bus fuel tanks and to specify such location, as well as any

protective shield or structural changes, to minimize the likelihood that a collision

which might disable the service door or the emergency exit will also initiate a

school bus fuel tank fire, and vice versa.

NHTSA replied that the rigorous side- and rear-impact barrier collision test

requirements of FMVSS 301 afforded a high level of protection for fuel systems on all

vehicles up to 10,000 pounds gross vehicle weight rating. In addition, on September 19,

1974, the agency stated that a program to develop fuel system integrity tests for large

school buses was planned. Such tests were later incorporated into FMVSS 301, and the

Safety Board classified the recommendation ìClosedóAcceptable Actionî on September

6, 1985.

On May 14, 1988, a pickup truck traveling north in the southbound lanes of

Interstate 71 struck a southbound church activity bus head-on near Carrollton, Kentucky.67

The church bus fuel tank was punctured during the collision sequence and a fire ensued,

engulfing the bus. The busdriver and 26 bus passengers were fatally injured, 34

passengers received minor to serious injuries, and 6 passengers were not injured. As a

result of its investigation of this accident, the Safety Board asked that NHTSA:

66 National Transportation Safety Board, School Bus/Automobile Collision and Fire Near Reston,

Virginia, on February 29, 1972, Highway Accident Report NTSB/HAR-72/02 (Washington, DC: NTSB,

1972).

67 National Transportation Safety Board, Pickup Truck/Church Activity Bus Head-on Collision and Fire

Near Carrollton, Kentucky, on May 14, 1988, Highway Accident Report NTSB/HAR-89/01 (Washington,

DC: NTSB, 1989).
Analysis 53 Highway Accident Report

H-89-6

Revise Federal Motor Vehicle Safety Standard 301 to provide additional

protection for school buses in severe crash situations based on an evaluation of the merits of relocating fuel tanks, providing additional structure to

protect fuel system components, and frangible valves in critical locations.

NHTSA replied on August 16, 1989, enclosing copies of an advance notice of

proposed rulemaking to make the crash standards more stringent. In an April 11, 1991,

letter, NHTSA stated that responses to the advance notice of proposed rulemaking did not

provide clear direction for proposing changes to FMVSS 301. Thus, for the next step,

NHTSA said it was considering several options, including a research program to develop

the technical information necessary to evaluate ways to improve the fuel system integrity

of buses. On October 20, 1995, NHTSA reported that those commenting on the advance

notice of proposed rulemaking agreed that FMVSS 301 was adequate and that

manufacturers generally comply with the requirements by adding a cage around the fuel

tank. The Safety Board classified the recommendation ìClosedóAcceptable Actionî on

May 15, 1996, citing its understanding that school bus manufacturers generally comply

with stringent regulatory crash test requirements for large school bus fuel systems by

adding a cage around the fuel tank.

These safety recommendations, issued over the past 3 decades, encouraged

NHTSA and the school bus manufacturers to make fuel tanks on school buses safer.

However, none of NHTSAís fuel tank safety requirements for school buses apply to

propane tanks.

Mountainburg Accident School Bus

The propane tank, which had been retrofitted on the accident school bus, was

installed in accordance with NFPA Standard 58, ìStandard for the Storage and Handling

of Liquefied Petroleum Gases.î The Safety Board is concerned that this standard does not

adequately protect propane fuel systems during a crash. Unlike gasoline and compressed

natural gas systems, which are fitted onto school buses by the manufacturer, propane and

other retrofitted fuel systems are not required to meet NHTSA crash test standards

specified in FMVSSs 301 and 303. These standards require that gasoline and compressed

natural gas systems mounted on a vehicle withstand a barrier crash test. Propane systems

must pass no such test, and NHTSA cannot even regulate propane system testing because

propane systems are aftermarket installations and therefore not subject to NHTSA safety

standards. Most States (Idaho is the only exception) require that propane systems meet

NFPA standards. While propane systems must have a discharge valve, this valve will not

prevent a fire from occurring during a severe crash if the fuel system is compromised. 

To further protect gasoline and diesel fuel tanks on school buses from being

compromised, school bus manufacturers place them within a cage, even though not

required to do so. In fact, a rigid safety cage enclosed the manufacturer-installed fuel tank

on the accident school bus. The propane tank did not have such protection. As discussed

above, the Safety Board has investigated school bus crashes in which cages did not

enclose fuel tanks, and severe fires and loss of life ensued. The Safety Board concludes
Analysis 54 Highway Accident Report

that catastrophic fires involving vehicles equipped with propane tanks could happen

because these tanks are not protected from collision and, thus, could rupture if struck. The

Safety Board believes that the NFPA should amend Standard 58, Storage and Handling of

Liquefied Petroleum Gas, to require that (1) propane fuel systems installed in school buses

be protected and (2) propane fuel systems meet the equivalent to FMVSS 301 crash

protection standards. 

Current legislation generally prohibits NHTSA from regulating aftermarket

equipment installed on vehicles. However, in this case, the children riding on the school

bus did not receive the same level of protection as those children riding on buses equipped

with gasoline, diesel, or compressed natural gas tanks, which NHTSA does regulate. The

Safety Board believes that NHTSA should obtain the authority, as necessary, and include

propane fuel system integrity standards for aftermarket installations in the FMVSSs. 

Occupant Kinematics and Survival Factors

Recommendation History

In its special investigation report on bus crashworthiness issues,68 adopted on

September 21, 1999, the Safety Board found that some passengers not seated in the direct

intrusion area were seriously or fatally injured in school buses involved in lateral impacts

with large vehicles and rollovers. The Safety Board concluded:

Current compartmentalization is incomplete in that it does not protect school bus

passengers during lateral impacts with vehicles of large mass and in rollovers,

because in such accidents, passengers do not always remain completely within the

seating compartment.

The Safety Board recommended that NHTSA:

H-99-45

In 2 years, develop performance standards for school bus occupant protection

systems that account for frontal impact collisions, side impact collisions, rear

impact collisions, and rollovers. 

In response to this recommendation, NHTSA is conducting a study to develop

ways to enhance the safety of the interior environment for school bus passengers. The

agency completed front and side impact full-scale crash testing on large school buses and

published the results of the frontal impact restraint testing in May 2002. One of its

conclusions was that requiring lap belts on large school buses would have little, if any,

benefit in reducing serious or fatal injuries in severe frontal crashes. NHTSA also found

that use of lap/shoulder belts could provide some benefit on large school buses, potentially

68 National Transportation Safety Board, Bus Crashworthiness Issues. Highway Special Investigation

Report NTSB/SIR-99/04 (Washington, DC: NTSB, 1999).
Analysis 55 Highway Accident Report

saving one life per year, if used properly 100 percent of the time. NHTSA recommended

that seat heights be increased from 20 inches to 24 inches to prevent passenger override in

a collision and that standardized test procedures be developed for voluntarily installed

lap/shoulder belts. 

The side impact testing and research report will not be completed until spring

2003. Preliminary test results show that crash test dummies away from the impact area do

not travel across the width of the bus and strike the sidewall,69 contrary to what the Safety

Board has observed in accident investigations. The Safety Board is concerned about

NHTSA relying on the one side impact test as indicative of all severe side impact crashes.

The impact point was soft (not an axle) and the collision energy was absorbed by the

deformation. Furthermore, the crash test lacked an angular velocity or acceleration

measurement, thereby invalidating any comparisons between the test and real world

crashes. Injury values were low for dummies away from the impact area. The Safety

Board classified Safety Recommendation H-99-45 ìOpenóAcceptable Responseî on

April 18, 2001.

During a train-school bus collision at a highway-rail grade crossing in Conasauga,

Tennessee, on March 28, 2000,70 six passengers were seriously injured or killed because

they struck surfaces within the bus, such as nonenergy-absorbing seat frames and sidewall

components, which are exempt from FMVSS passenger protection standards. On

December 11, 2001, following its investigation of this accident, the Safety Board asked

that NHTSA:

H-01-40

Develop and incorporate into the Federal Motor Vehicle Safety Standards

performance standards for school buses that address passenger protection for

sidewalls, sidewall components, and seat frames.

On April 23, 2002, NHTSA responded that it is addressing this issue as part of a

research program scheduled to be completed in spring 2003. If protection is deemed

feasible, NHTSA said it will upgrade FMVSS 222, ìSchool Bus Passenger Seating and

Crash Protection,î to include requirements for passenger protection at sidewalls, sidewall

components, and seat frames. The Safety Board classified this recommendation ìOpenó

Acceptable Responseî on July 16, 2002. 

In the Mountainburg accident, Safety Board investigators also found that occupant

motion, similar to that seen in previous accidents, resulted in injuries to passengers who

69 The side impact crash test was conducted on a bus equipped with a rear engine; thus the center of

gravity was further rearward than in a front-engine bus because the weight was concentrated at the rear

rather than the front. This difference could affect the angular velocity and acceleration (which were not

measured) experienced by the occupants in the rear of the bus.

70 National Transportation Safety Board, Grade Crossing Accident Involving a CSX Corporation

Freight Train and a Murray County, Georgia, School District School Bus, Conasauga, Tennessee, on March

28, 2000. Highway Accident Report NTSB/HAR-01/03 (Washington, DC: NTSB, 2001).
Analysis 56 Highway Accident Report

did not remain within their seating compartment and traveled across the width of the bus

during impact.

Mountainburg Accident School Bus

During the Mountainburg collision sequence, the bus rotated about 300 degrees

clockwise about the front axle. At the end of the accident sequence, the bus body became

partially separated from the chassis and rolled onto its right side.

The occupants in the front of the bus at first probably experienced limited lateral

acceleration and motion forward and toward the right because of their proximity to the

front of the bus and the rotation of the bus about the front axle. Occupants at the rear of the

bus quite likely moved forward and toward the right more rapidly than those in the front

due to the busís rotation about the front axle and the greater lateral acceleration they

experienced. Because the passengers in the front were seated close to the busís point of

rotation (the front axle), they did not experience the high lateral and rotational

accelerations experienced by those seated further from the front axle. All passengers in the

front of the bus received less serious injuries than those seated in the back. 

The passengers in the rear of the bus were subjected to the impact force, tractor

intrusion, and lateral and rotational accelerations imparted to the bus during the collision

sequence. The passenger in seat 10E on the right was directly in the area of impact but

survived. Because of his proximity to the side of the bus where the impact occurred and

the subsequent intrusion, the difference in relative velocity between his body and the side

of the bus was minimal. His serious injuries resulted from being in direct line with the

impact forces; his injuries were predominantly on the right side of his body and included

lacerations to his head, face, and shoulder from glass fragments and a closed head injury.

The passengers seated on the left side of the bus in the rear were probably thrown

forward and across the width of the bus toward the striking truck. They did not remain

within their seating compartment during impact because compartmentalization, the

current occupant protection strategy inside large school buses, only provides protection

during frontal impacts. Three of these passengers (in seats 9A, 9C, and 11A) received fatal

injuries, primarily to the head and upper torso, most likely as a result of being thrown from

their seating compartment and striking nonenergy-absorbing surfaces, including the

ceiling, sidewalls, and window frames, after traveling the width of the bus. The passenger

in seat 11A may also have sustained injuries as a result of being partially ejected through

the right side window of the bus, which rolled on top of him. The passenger in seat 10A

sustained serious injuries. In previous accidents, investigators found that passengers

possibly struck other passengers during lateral collisions. In this case, the passengers

seated across from (seat 10E) or in front of (seat 9C) the passenger in seat 10A may have

protected him from more severe or even fatal injuries as they moved out of their

compartmentalized seating area. The Safety Board concludes that the impact and

subsequent rotation of the bus caused passengers seated in the rear to be thrown from their

seating compartment and into the area of intrusion; incomplete compartmentalization and

impact with nonenergy-absorbing surfaces within the bus contributed to the serious and

fatal injuries sustained by these passengers. 
Analysis 57 Highway Accident Report

The Safety Board addressed the issue of incomplete compartmentalization and the

lack of energy-absorbing material on interior surfaces in its special investigation report on

bus crashworthiness issues and in its investigation report on the Conasauga accident. This

accident demonstrates again the need for NHTSA to continue its work on occupant

protection for lateral impacts and its work to reduce the nonenergy-absorbing surfaces

within school buses. Both efforts have the potential to reduce injuries to those occupants

seated outside the area of impact.
58 Highway Accident Report

Conclusions

Findings

1. There was no evidence of drug or alcohol use by the drivers; 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.

2. Poorly adjusted and nonfunctional brakes, together with the resulting high

temperatures in the functioning brakes, reduced the truckís braking efficiency to such

an extent that the truckdriver was unable to stop the vehicle at the end of the ramp.

3. The six brakes on the tractor were out of adjustment either because the owner had not

properly adjusted them, or because the brakes became out of adjustment due to a

disproportional workload, or both; the driver did not conduct a sufficiently thorough

pretrip inspection on either the tractor or the trailer to discover the brake deficiencies. 

4. Because of the spring brake design, examining the springs to determine whether they

were broken was difficult on three of the truckís brakes. 

5. Dust covers on the caging ports of the accident vehicleís spring brakes would have

reduced the chance of corrosion to the spring, possibly prolonging the life of the

spring and, in turn, the life of the emergency-service brakes. 

6. Based on the inspection conducted by the Missouri Division of Motor Vehicles and

Railroad Safety that followed the accident, had the Federal Motor Carrier Safety

Administration inspected Stuart Truckingís vehicles during the 2001 compliance

review, the carrier would probably have received a conditional rating in factor 4

(vehicle factor) instead of a satisfactory rating. 

7. The Stuart Trucking mechanic lacked proper training in brake maintenance and

inspections, did not detect the poorly adjusted or inoperative brakes on the trailer, and

did not perform recommended maintenance. 

8. Catastrophic fires involving vehicles equipped with propane tanks could happen

because these tanks are not protected from collision and, thus, could rupture if struck.

9. The impact and subsequent rotation of the bus caused passengers seated in the rear to

be thrown from their seating compartment and into the area of intrusion; incomplete

compartmentalization and impact with nonenergy-absorbing surfaces within the bus

contributed to the serious and fatal injuries sustained by these passengers.
Conclusions 59 Highway Accident Report

Probable Cause

The National Transportation Safety Board determines that the probable cause of

the accident was the truckdriverís inability to stop the tractor semitrailer at the stop sign at

the bottom of the ramp due to the reduced braking efficiency of the truckís brakes, which

had been poorly maintained and inadequately inspected. Contributing to the school bus

passengersí injuries during the side impact were incomplete compartmentalization and the

lack of energy-absorbing material on interior surfaces.
60 Highway Accident Report

Recommendations

As a result of this accident, the National Transportation Safety Board makes the

following safety recommendations:

To the Federal Motor Carrier Safety Administration:

Revise 49 Code of Federal Regulations 396.13, Driver Inspection, to

require minimum pretrip inspection procedures for determining brake

adjustment. (H-02-15)

Require that vehicle inspections of a motor carrierís fleet be conducted

during compliance reviews. (H-02-16)

Revise 49 Code of Federal Regulations 396.25, Qualifications of Brake

Inspectors, to require certification after testing as a prerequisite for

qualification and specify, at a minimum, formal training in brake

maintenance and inspection. (H-02-17)

During compliance reviews, rate companies as unsatisfactory in the vehicle

factor category if the mechanics and drivers responsible for maintaining

brake systems are not qualified brake inspectors. (H-02-18)

To the National Highway Traffic Safety Administration:

Obtain the authority, as necessary, and include fuel system integrity

standards for aftermarket installations in the Federal Motor Vehicle Safety

Standards. (H-02-19)

To the Commercial Vehicle Safety Alliance:

Include spring brake caging port dust covers as an inspection item during

Motor Carrier Safety Assistance Program roadside inspections. (H-02-20)

To the National Fire Protection Association:

Amend National Fire Protection Association Standard 58, Storage and

Handling of Liquefied Petroleum Gas, to require that (1) propane fuel

systems installed in school buses be protected and (2) propane fuel systems

meet the equivalent to Federal Motor Vehicle Safety Standard 301 crash

protection standards. (H-02-21)
Recommendations 61 Highway Accident Report

To Spring Brake Manufacturers:

Develop a spring brake that allows inspectors or mechanics to view

components safely to determine whether the spring is broken. (H-02-22)

The National Transportation Safety Board also reiterates the following

recommendation:

To the U.S. Department of Transportation:

Change the safety fitness rating methodology so that adverse vehicle or

driver performance-based data alone are sufficient to result in an overall

unsatisfactory rating for the carrier. (H-99-6)

BY THE NATIONAL TRANSPORTATION SAFETY BOARD

MARION C. BLAKEY

Chairman

CAROL J. CARMODY

Vice Chairman

JOHN A. HAMMERSCHMIDT

Member 

JOHN J. GOGLIA

Member

GEORGE W. BLACK, JR.

Member

Adopted: September 4, 2002

63 Highway Accident Report

Appendix A

Investigation and Public Hearing

The National Transportation Safety Board was notified of the Mountainburg,

Arkansas, accident on May 31, 2001. An investigative team was dispatched with members

from the Washington, D.C.; Fort Worth, Texas; Denver, Colorado; and Atlanta, Georgia,

offices. Groups were established to investigate human performance; motor carrier

operations; and highway, vehicle, and survival factors.

Participating in the investigation were representatives of the Federal Motor Carrier

Safety Administration, the Arkansas State Police, and the Arkansas State Highway and

Transportation Department.

No public hearing was held; no depositions were taken.