F PB97-916202

 NTSB/HAR-97/02/SUM

NATIONAL

TRANSPORTATION

SAFETY

BOARD

WASHINGTON, D.C. 20594

HIGHWAY ACCIDENT SUMMARY REPORT

TRUCK LOSS OF BRAKING CONTROL

ON STEEP DOWNGRADE AND COLLISION WITH A VEHICLE 

NEAR PLYMOUTH MEETING, PENNSYLVANIA

ON APRIL 25, 1996

6913
Abstract: On April 25, 1996, a truck with a concrete mixer body, unable to stop, proceeded through an

intersection and collided with and overrode a passenger car near Plymouth Meeting, Pennsylvania. The driver of

the car was fatally injured, and the truckdriver sustained minor injuries.

The major safety issues discussed in this report are the maintenance and truck inspection practices of JDM

Materials Company, Inc., and the adequacy of Federal and State guidelines for conducting truck air brake

system inspections.

As a result of its investigation, the Safety Board issued recommendations to the Federal Highway

Administration; the Commercial Vehicle Safety Alliance; the American Trucking Associations, Inc.; the National

Ready Mix Concrete Association; the JDM Materials Company, Inc.; the Pennsylvania Department of

Transportation; the Truck Manufacturers Association; the National Highway Traffic Safety Administration; and

the Society of Automotive Engineers.

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.

Information about available publications may be obtained by contacting:

National Transportation Safety Board

Public Inquiries Section, RE-51

490 L’Enfant Plaza, SW

Washington, DC 20594

(202) 314-6551

Safety Board publications may be purchased, by individual copy or by subscription, from:

National Technical Information Service

5285 Port Royal Road

Springfield, Virginia 22161

(703) 487-4600
TRUCK LOSS OF BRAKING CONTROL

ON STEEP DOWNGRADE

AND COLLISION WITH A VEHICLE

NEAR PLYMOUTH MEETING, PENNSYLVANIA

APRIL 25, 1996

HIGHWAY ACCIDENT SUMMARY REPORT

Adopted: October 17, 1997

Notation 6913

NATIONAL

TRANSPORTATION

SAFETY BOARD

Washington, DC 20594

National Transportation Safety Board

Washington, DC 20594

HIGHWAY ACCIDENT SUMMARY

Motor Carrier: JDM Materials Company, Inc.

Vehicle 1: 1988 Mack four-axle truck with a concrete mixer body

Vehicle 2: 1985 Subaru sedan

Accident Type: Loss of braking control leading to vehicle collision

Location: Plymouth Meeting, Pennsylvania

Date: April 25, 1996

Time: 3:25 p.m.

Injuries: One fatal and one nonfatal

On April 25, 1996, about 3:25 p.m., a

1988 Mack truck with a concrete mixer body

was unable to stop as it approached a “T”

intersection at the bottom of an exit ramp in

Plymouth Meeting, Pennsylvania. As the

truck proceeded through the intersection, it

collided with and overrode a 1985 Subaru

passenger car. The Subaru driver was killed;

the truckdriver sustained minor injuries. The

truckdriver was unrestrained; the Subaru

driver was found restrained in her vehicle.

The weather was clear and dry. No fire

ensued, and no other vehicle occupants were

involved in the accident.

In its investigation of the accident, the

Safety Board identified as safety issues the

maintenance and truck inspection practices

of JDM Materials Company, Inc., (the

owner of the truck) and the adequacy of

Federal and State guidelines for conducting

truck air brake system inspections. The

following discussion includes a narrative

description of the accident and the events

leading to it, a discussion of the safety

issues, and a list of conclusions and safety

recommendations developed to help prevent

future accidents of this type.
2

Preaccident Events

On April 25, 1996, about 6:30 a.m., the

truckdriver reported for work at JDM Materials

Company, Inc., in Plymouth Meeting,

Pennsylvania. The truckdriver’s duties consisted

of delivering concrete to customer locations in

the Philadelphia metropolitan area. At 7 a.m.,

the truckdriver departed the JDM yard in the

truck that had been assigned to him for the

previous 4 years, a 1988 four-axle Mack truck

with a concrete mixer body.

The truckdriver delivered several loads of

concrete during the morning hours. In the early

afternoon, he departed Philadelphia

International Airport en route back toward the

JDM terminal. The truck at that time was loaded

with about 7 yards of concrete. The truckdriver

traveled south on Interstate 95 and entered State

Route (SR) 476 north at the Plymouth Meeting

interchange. The truckdriver reported that, after

traveling about 6 miles on SR 476, he ran over a

truck tire carcass that was lying in the road. He

said he did not notice anything unusual about

the operation of his truck after he struck the tire

carcass.

The Accident

About 3:25 p.m. and about 12 miles past the

location where the truck had struck the object in

the roadway, the truckdriver entered the

deceleration lane for the off ramp leading to a

“T” intersection with Chemical Road. The

truckdriver stated that he downshifted into

fourth gear and was traveling about 35 mph near

the top of the exit ramp. A witness in the second

car behind the truck estimated the truck’s speed

to be between 30 and 35 mph at that point. The

truckdriver stated that he began applying brakes

about half way down the ramp, about 300 feet

from the intersection. The driver stated that, as

his truck descended the ramp, which was on a 6-

percent grade, the truck brakes felt “spongy”

and the truck did not slow down. He said he

applied the brakes several more times and pulled

on the hand control valve,1

 but the truck still did

not slow down. He said that the engine brake2

was in the “on” position.

According to the truckdriver, as the truck

came within about 150 feet of the intersection,

he realized that he would not be able to stop at

the bottom of the ramp. He said that he normally

turns to the right (southbound) onto Chemical

Road, but he had to move to the left lane to

avoid hitting several cars that were stopped in

the right traffic lane and directly in front of him.

He entered the intersection, where he planned to

negotiate a 90 degree left turn (northbound). A

witness3

 estimated that the truck’s speed was 25

mph as it approached the intersection. As the

truck crossed the intersection, it struck a 1985

Subaru sedan that had been proceeding

southbound on Chemical Road. The truck stuck

the automobile on the passenger side, overrode

it, and dragged it across the intersection before

the truck overturned and came to rest on its right

side. Both vehicles came to rest on the east side

of the intersection. (See figures 1 through 3 for

details at the accident scene.)

Postaccident Events

The truckdriver was transported to

Suburban General Hospital in Norristown,

Pennsylvania, where he was determined to have

sustained minor contusions to his chest and legs

and where a drug test was administered. The

toxicological tests results were negative for

alcohol and other specified drugs. Postaccident

toxicology testing on the automobile driver was

also negative for alcohol and other specified

drugs.

The chief mechanic for a local towing

company (who was a certified Pennsylvania

State vehicle safety inspector) conducted a

 

1

The hand control valve applies the rear axle brakes.

2

An engine retarder that acts to slow the vehicle

3

The same witness who had estimated the truck’s

speed at the top of the ramp.

INVESTIGATION
3

Figure 1 -- Accident scene, T-intersection, and off-ramp.

(Photograph courtesy of Plymouth Township police.)

Figure 2 -- Accident truck.
4

Figure 3 -- Accident vehicles at final rest position.

(Photograph courtesy of Plymouth Township police.)
5

postaccident examination of the truck during the

retrieval operation. The parking brake knob on

the truck instrument panel was found in the

depressed (off) position. The examination

revealed that the drain valve located on the

bottom of the air reservoir tank for the truck’s

secondary air system was broken off, and the air

in the tank was depleted. (See figure 4.) A

fractured piece of the valve was still threaded

into the drain port. Scrape marks were visible on

the underside of the tank in the area of the drain

valve port.

A search of the accident scene failed to

locate the missing broken drain valve.

Employees of JDM returned to the area where

the truckdriver said he struck a tire carcass a

short time before the accident. The employees

reported finding a tire carcass measuring 146

inches long, 12 inches wide, and 1 1/2 inches

thick, but they did not find the broken valve.

The day after the accident, the fractured

drain valve was replaced, and the truck’s

secondary air system was recharged. The truck’s

entire air brake system was then tested by the

chief mechanic of the towing company and

found to be in compliance with Pennsylvania

State safety inspection standards. Also, the

Pennsylvania State Police conducted a separate

inspection of the truck using the Federal Motor

Carrier Safety Assistance Program (MCSAP)

criteria. The MCSAP program, which is

administrated by the Federal Highway

Administration, has adopted the Commercial

Vehicle Safety Alliance out-of-service criteria

for air brake inspections of large trucks. The

inspection criteria have been adopted by most

States, including Pennsylvania. The accident

vehicle, including the air brake system, passed

the Pennsylvania State Police postaccident

MCSAP inspection.

Truckdriver Information

The 54-year-old truckdriver lived in

Norristown, Pennsylvania, and had been

employed by JDM as a truckdriver since March

1980. He possessed a valid medical certificate

and Pennsylvania commercial driver license that

certified him to operate the accident truck. The

truckdriver stated that he had rested comfortably

at home the night before the accident, and a

check of his work history for the previous 7

days indicated that he was in compliance with

Federal Motor Carrier Safety Regulations

regarding hours of service.

Motor Carrier Information

JDM is a Pennsylvania corporation that has

served eastern Pennsylvania and New Jersey

with ready mix concrete and quarry stone

products since 1956. At the time of the accident,

the company employed between 180 and 200

employees: 120 to 125 were full-time

truckdrivers, and 15 were full-time mechanics at

various company garages. The company

operated 165 trucks equipped with concrete

mixer bodies and 25 tractor semi-trailers of

various configurations. JDM is registered with

the U.S. Department of Transportation as an

interstate commerce motor carrier. However,

according to the JDM operations officer, about

90 percent of the company’s business is

conducted intrastate, and the truckdriver that

was involved in the accident was on an

intrastate trip. All the trucks are dispatched

daily and return nightly to their assigned garage.

Truck Inspections and Maintenance

JDM truckdrivers are required to conduct

daily pre and posttrip inspections of their

assigned vehicles. Any repairs or deficiencies

are recorded and forwarded to the garage

mechanics, who then schedule the truck for the

needed repair. Additionally, trucks are subject to

a Pennsylvania State inspection every 6 months.

Between March 23, 1994, and April 25, 1996,

(the day of the accident) the accident truck

successfully passed four Pennsylvania State

safety inspections.

According to the JDM shop supervisor,

about 90 percent of all repairs to the company’s

trucks are performed by JDM mechanics.

Preventative maintenance is scheduled for each

truck after every 300 to 400 hours of operation.

Service and repair records indicated that a

malfunctioning air brake treadle (foot pedal)

valve on the accident truck was replaced by

JDM mechanics on March 23, 1994. This was

the only documented maintenance performed on

the treadle valve of the accident vehicle. Except

for service brake adjustments, no other repairs

were recorded as having been performed on the

air brake lines of the accident truck between
6

1994 and the date of the accident. The service

brakes were last adjusted before the accident on

March 14, 1996. On the morning of the

accident, the driver performed part of his pretrip

inspection by pulling the truck forward and

applying the parking brakes to stop the truck. He

reported that he had no problems with the

brakes.

Air Brake System Operation

The truck was equipped with a dual air

brake system consisting of a primary and a

secondary air system. The primary and

secondary systems operate independently, and

each has its own air tanks and air brake lines. As

designed, the primary brake system delivers air

to the rear axle service brakes, and the

secondary system provides air to operate the

front axle service brakes. When the driver

presses the brake pedal, both air systems are

activated, applying both front and rear brakes

simultaneously. Additionally, the truck was

equipped with a spring brake system (parking

brake).

In heavy trucks, the majority of the braking

ability comes from the rear axle brakes. Thus,

most trucks are equipped with a safety device

designed to provide “backup” braking in the

event of a loss of air supply to the rear brakes.

In the accident truck, this safety device, a spring

brake inversion valve, monitored air pressure in

the primary air system. If the inversion valve

detected a loss of primary air pressure, it was

designed to direct air from the secondary air

system brake tank to the rear axle spring brake

control. The spring brake control would then

automatically apply the parking brakes

whenever the driver depressed the brake pedal,

thus providing some braking capability. The

secondary air system, because it was designed to

operate the less-safety-critical front brakes, was

not equipped with an inversion valve or any

other backup device.

An air pressure gauge mounted on the

instrument panel in front of the driver displayed

air pressure in both the primary and secondary

air systems. The single gauge had separate

needles for each system. The truck was also

equipped with a instrument-panel-mounted lowair-pressure warning light and buzzer that were

designed to alert the truckdriver in the event of a

loss of air pressure in either the secondary or

primary air tanks. The light and buzzer could be

activated by either of two (one for primary and

one for secondary) low-air-pressure warning

switches.

Safety Board Tests and Calculations

Several days after the accident, a Safety

Board investigator, the chief mechanic for the

towing agency, and a representative of Mack

Truck, Inc., conducted another postaccident

inspection of the accident truck’s air brake

system. The inspection revealed several

anomalies, including the fact that two air lines

connected to the brake treadle valve had been

reversed. (See figure 5.) Because of the reversed

connections, on the day of the accident, the

accident truck’s rear brakes were being operated

by the secondary air system, and the front

brakes by the primary air system. The reversed

air lines were not detected during the

Pennsylvania State inspections before the

accident or during the postaccident inspections

conducted by the police or the local mechanic.

The Safety Board tested the two low-airpressure switches to determine if they were

operating properly. When air pressure was

completely exhausted from the secondary air

tank, the low-air-pressure warning light and

buzzer on the truck instrument panel did not

activate. The tests of the low-air-pressure switch

that normally monitored air pressure in the

primary air system found this switch to be

inoperative. However, because of the reversed

connections, this switch was monitoring air

pressure in the secondary system. The switch

that normally monitored pressure in the

secondary air tank (but that was actually

monitoring pressure in the primary air tank) was

tested and found to be operating properly.

JDM provided a similar (to the accident

truck) make and model truck from its fleet to be

used as an exemplar vehicle during the

investigation. A 1988 Mack truck with a

concrete mixer body was selected at random and

delivered to the inspection area. Safety Board

inspection of the air brake system on that truck

revealed that its air lines had been reversed in an

area where repairs had been made to the truck’s

frame. The JDM service records for this truck

revealed that the repairs to the frame and air
7

Figure 4 -- Location of missing drain valve indicated by arrow.
8

Low Air Low Air

Warning Warning

Buzzer Light

P-1l s-1

7

Inoperative I I f

|

_

Spring Brake

Control Valve

__

Improper- –– -

Connections

P-1

PP-1

PRIMARY

AIR TANK

\

‘,//’

-~ /“\ <_ Proper

Connections /’ ‘.

/ ‘d I

Low Air

Warning

Switch

~

1 S-1 J_S-1

SECONDARY

AIR TANK

‘P Missing Drain Valve

Figure 5- Air brake system diagram.

(Simplified for illustration only.)
9

brake lines had been performed on February 29,

1996. On March 16, 1996, this truck passed a

Pennsylvania State safety inspection.

At the Safety Board’s request, JDM

inspected its entire fleet to determine if any

more vehicles had reversed air brake lines

and/or inoperative low-air-pressure warning

switches. This inspection of the company’s 165-

truck fleet revealed that two additional trucks

had reversed air lines, and 12 additional trucks

had inoperative low-air-pressure warning

switches. The company reported that all

defective air systems were repaired and tested in

accordance with the brake manufacturer’s

guidelines.

The Safety Board performed brake

efficiency calculations4

 for the accident truck to

determine its braking capability with only front

brakes operational, with only rear brakes

operational, and with both front and rear brakes

operational. Brake efficiencies and vehicle

stopping distances were calculated and adjusted

for the estimated speed, heat generated by

overworking the front brakes, and minimum

engine retarder use.5

 

4

National Transportation Safety Board, Safety Study,

Heavy Vehicle Air brake Performance, NTSB/SS-92/01,

and Ronald Heusser, “Heavy Truck Deceleration Rates as a

Function of Brake Adjustment,” Society of Automotive

Engineers, 1991.

5

Engine retarders can provide some speed reduction

when the vehicle first starts to slow before making a stop;

however, engine rpm drops quickly as the vehicle comes to

a stop, and the retarder will provide very little engine

braking.

Calculations using the front axle brakes with

minimum engine retardation indicated that the

accident truck had a braking efficiency range

from 17 to 21 percent and required between 408

and 453 feet to stop. Calculations using rear

brakes with minimum engine retardation

indicated that the truck had an approximate

braking efficiency of 54 percent and would have

required between 123 and 157 feet to stop.

Calculations using full braking capability

indicated that the braking efficiency for that

truck ranged from 96 to 100 percent and that the

truck would have needed between 72 and 92 feet

to stop. Calculations using front axle brakes

with minimum engine retardation and the rear

spring brakes indicated that the truck needed

between 314 and 340 feet to stop.
10

In its investigation of this accident, the

Safety Board determined that neither weather

nor highway conditions were causal factors.

Additionally, the truckdriver was not fatigued,

impaired, or suffering from any medical

conditions that may have influenced his

performance in this accident. Postaccident

examination and testing of the accident truck

operating systems revealed that the only

deficiencies were in the truck’s braking system,

specifically, a broken drain valve on the

secondary air brake air reservoir tank, an

inoperative low-air-pressure warning switch,

and reverse-connected air brake lines at the

truck’s treadle valve. Assuming that all three of

these conditions existed at the time the truck

entered the exit ramp for Chemical Road, the

truck would have been without rear brakes as

the truckdriver attempted to slow and stop at the

Chemical Road intersection. The Safety Board

attempted to determine if these conditions

existed before the accident.

Because the broken drain valve was never

located, it could not be immediately determined

when the damage had occurred; however, if the

drain valve had been fractured during the impact

sequence, the driver would have had full braking

(front and rear brakes) as he descended the exit

ramp leading to Chemical Road. Instead, the

truckdriver applied the available service brakes

as he approached the intersection, but he stated

that the brakes felt spongy and that he was

unable to stop the truck in time to avoid the

collision. Thus, it is unlikely that he had full

braking on the downgrade.

If the drain valve had been fractured while

the truck was en route to the accident site, the

truckdriver, because of the reversed air line

connections, would not have been able to apply

his rear brakes after the air pressure was

depleted from the secondary air tank. A Mack

Truck engineer confirmed that the truckdriver’s

account of the spongy brakes was consistent

with what would have occurred if the truck had

had limited braking (front brakes and minimum

engine retardation). The Safety Board therefore

concludes that the drain valve on the secondary

air supply tank was probably fractured when the

truck struck a tire carcass while en route to the

accident site.

Safety Board calculations indicated that the

accident truck with front brakes operational and

minimum engine retardation had a braking

efficiency range from 17 to 21 percent. With

this level of braking efficiency, the cargo load,

and the 6-percent downgrade, the accident truck

would have needed between 408 and 453 feet to

stop. With full front and rear brakes operating,

the truck’s braking efficiency ranged from 96 to

100 percent, and it would have been able to stop

within 92 feet. The driver indicated that he

began applying his brakes about 300 feet from

the intersection. Based on all available

information, the Safety Board concludes that the

accident truck probably had only its front brakes

operational with minimum engine retardation

when it reached the intersection and that it was

therefore unable to stop in time to avoid the

accident.

On the accident truck, the low-air-pressure

warning switch for the primary air system was

monitoring pressure in the secondary air supply,

but because this switch was inoperative, it did

not warn the truckdriver when the secondary air

supply tank became depleted. The Safety Board

concludes that had both low-air-pressure

warning switches on the accident truck been

operable, the truckdriver would have had earlier

warning of the depleted air supply and may have

been able to stop the truck and avoid the

accident.

The spring brake system (parking brake) on

a heavy truck can be manually applied at any

time. The truckdriver could have applied the

parking brakes as he descended the grade, and

this may have slowed the truck. However, the

truckdriver stated that he had already applied

the foot brake and pulled the hand control valve

to apply the rear axle brakes and that the truck

was not slowing. About 150 feet from the

intersection, the truckdriver chose to steer

SAFETY ISSUES
11

around the stopped traffic. The brake

calculations performed by the Safety Board

revealed that at this point the truckdriver would

not have been able to stop the truck with the

parking brake in combination with the front axle

brakes and minimum engine retardation.

In its investigation, the Safety Board

identified as safety issues the maintenance and

truck inspection practices of JDM Materials

Company, Inc., and the adequacy of Federal and

State guidelines for conducting truck air brake

system inspections.

Motor Carrier’s Truck Maintenance and

Inspection Practices

The air brake lines on the accident vehicle

were most likely reversed during March 1994

when JDM mechanics performed the only

documented maintenance on the treadle valve of

the accident truck. At no time before the

accident did the motor carrier’s mechanics

detect the reversed air lines, even though the

accident truck was in service in this condition

for almost 2 years before the accident.

So long as both of the truck’s air systems

remained intact, the operation of the truck’s

brakes appeared normal; however, the reversed

air lines bypassed a vital backup in the air brake

system. The rear axle spring brakes, which

automatically activate when a loss of air occurs

in the primary air system, did not activate in this

accident, because the primary air system

remained intact. The secondary air system,

which on the accident truck was providing air to

operate the rear brakes, was not equipped with a

backup system. The Safety Board concludes that

the motor carrier’s improper installation of the

treadle valve air lines on the accident truck

effectively bypassed an important safety feature

and resulted in reducing the truck’s braking

capability under certain emergency conditions.

JDM officials told the Safety Board that its

mechanics use service manuals provided by

component manufacturers and by Mack Truck in

performing vehicle repairs and periodic

maintenance. Mack Truck publishes an air brake

service manual that also contains individual

component maintenance information. The brake

maintenance section of the Mack maintenance

and lubrication manual includes brake

adjustment procedures and specifications;

however, the manuals in use before this accident

did not contain procedures for comprehensively

testing the operation of dual-circuit brake

systems. Also, the Mack Truck air brake service

manual did not provide any system function test

procedures that would have detected reversed

lines or malfunctioning low-air-pressure

warning switches.

The treadle valve manufacturer publishes an

air brake troubleshooting guide (see appendix

A) that outlines a test procedure that would have

detected reversed treadle valve air line

connections and inoperative low-air-pressure

warning switches. The Safety Board concludes

that if JDM employees had followed the treadle

valve manufacturer’s installation tests and

inspection procedures when performing

maintenance on the treadle valve of the accident

truck, they would probably have recognized the

improper installation problems and/or

inoperative brake components, and the accident

may have been prevented.

The Safety Board discussed with

representatives of Mack Truck the fact that the

company’s maintenance manuals did not contain

information on installing and testing a

dual-circuit brake system. As a result of these

discussions, the 1997 model year Mack Truck

maintenance and lubrication manual includes a

dual-circuit brake system function test for

detecting reversed air lines and inoperative lowair-pressure warning switches. (See appendix

B.)

The Safety Board notes JDM’s prompt

postaccident inspection of its entire truck fleet

as a result of the preliminary findings of this

accident investigation. However, to further

improve the effectiveness of the company’s

maintenance procedures, the Safety Board

believes that JDM should implement procedures

that will ensure that air brake manufacturers’

suggested installation, inspection, and functional

test procedures are adhered to by company

mechanics performing maintenance on the

company’s truck brake systems.

The repair and installation problems

highlighted in this accident are not unique to

Mack Truck vehicles. The air brake system

configuration used on the accident truck is
12

similar to that used on other trucks with

concrete mixer bodies. According to the Bureau

of the Census, about 61,000 such trucks are in

operation nationwide. The JDM fleet inspection

found that about 1 percent of its trucks had air

lines reversed and about 7 percent had

inoperative low-air-warning switches. Based on

these findings, the Safety Board concludes that a

significant number of dual-air-brake-systemequipped trucks nationwide may have

undetected air brake deficiencies similar to

those found on the accident truck. The Safety

Board believes that the American Trucking

Associations, Inc., and the National Ready Mix

Concrete Association should notify their

members of the circumstances of this accident

and urge them to implement procedures that will

ensure that air brake manufacturers’ suggested

installation, inspection, and functional test

procedures are adhered to during and after

routine maintenance on truck air brake systems.

Adequacy of State and Federal

Inspection Procedures

After the treadle valve on the accident truck

was replaced in 1994, the truck successfully

passed four semiannual Pennsylvania State

safety inspections. The reversed air brake lines

were not detected during any of the inspections.

The postaccident inspection of the truck was

conducted by MCSAP-trained police using the

Federal Highway Administration Office of

Motor Carrier Safety’s guidelines.

The inspections also failed to detect the

inoperative low-air-pressure warning switch.

The air brake testing procedures used by the

State and MCSAP inspectors involves depleting

the air pressure from both air brake systems

simultaneously until the low-air-pressure

warning buzzer sounds. Using this procedure,

either both low-air-pressure warning switches or

the warning buzzer or light itself would have to

be inoperable for the vehicle to fail the test. The

Safety Board therefore concludes that had the

Pennsylvania State and MCSAP inspection

procedures been adequate to detect the reversed

air brake lines or the inoperative low-airpressure warning switch or both, the air brake

system deficiencies in the accident truck may

have been discovered, and the accident may not

have occurred. The Safety Board believes that

the Pennsylvania Department of Transportation

should develop an easily administered

inspection protocol for detecting reversed air

lines and inoperative low-air-pressure warning

switches on dual air brake system vehicles.

Before the 1970s, heavy trucks were

equipped with a single air brake system, and

manufacturers of air brake systems developed

inspection protocols for those systems. In the

1970s, as a result of Federal regulations, the

single air brake system was upgraded to the dual

air brake system, and the brake industry

responded with the appropriate inspection

procedures that would identify reversed air

brake lines. However, the Federal and

Pennsylvania State governments have not

developed inspection protocols to accommodate

dual air brake systems. The Safety Board

believes that the Federal Highway

Administration, in cooperation with the

Commercial Vehicle Safety Alliance, should

develop an inspection protocol that could be

easily administered by inspection personnel for

detecting either reversed air brake lines or

inoperative low-air-pressure warning switches

on commercial vehicles equipped with dual air

brake systems.

The Safety Board further believes that the

National Highway Traffic Safety Administration

and the Society of Automotive Engineers should

work together to develop specifications and

requirements for the installation, in heavy trucks

with a dual air brake system, of separate lowair-pressure warning devices that will

independently alert drivers to a loss of air

pressure in either system. In the meantime, the

Safety Board believes that the Truck

Manufacturers Association should notify its

membership of the circumstances of this

accident and urge them to install, on all the

commercial trucks they manufacture with dual

air brake systems, separate low-air-pressure

warning devices that will independently alert

operators to a loss of air pressure in either

system.
13

Findings

1. Neither the weather or highway conditions

contributed to the accident. Also, the

truckdriver was not fatigued, impaired, or

suffering from any medical conditions that

may have influenced his performance in this

accident.

2. The drain valve on the secondary air supply

tank was probably fractured when the truck

struck a tire carcass while en route to the

accident site.

3. The accident truck probably had only its

front brakes operational with minimum

engine retardation when it reached the

intersection, and it was therefore unable to

stop in time to avoid the accident.

4. Had both low-air-pressure warning switches

on the accident truck been operable, the

truckdriver would have had earlier warning

of the depleted air supply and may have

been able to stop the truck and avoid the

accident.

5. The motor carrier’s improper installation of

the treadle valve air lines on the accident

truck effectively bypassed an important

safety feature and resulted in reducing the

truck’s braking capability under certain

emergency conditions.

6. If JDM employees had followed the treadle

valve manufacturer’s installation tests and

inspection procedures when performing

maintenance on the treadle valve of the

accident truck, they would probably have

recognized the improper installation

problems and/or inoperative brake

components, and this accident may have

been prevented.

7. A significant number of dual-air-brakesystem-equipped trucks nationwide may

have undetected air brake deficiencies

similar to those found on the accident truck.

8. Had the Pennsylvania State and MCSAP

inspection procedures been adequate to

detect the reversed air brake lines or the

inoperative low-air-pressure warning switch

or both, the air brake system deficiencies in

the accident truck may have been

discovered, and the accident may not have

occurred.

Probable Cause

The National Transportation Safety Board

determines that the probable cause of this

accident was the improper maintenance of the

accident truck by the JDM Materials Company,

Inc., the fracture of the drain valve, and the

inoperative low-air-pressure warning switch,

which resulted in the driver’s loss of braking

control. Contributing to the accident was the

lack of Federal and State inspection procedures

for commercial vehicles with dual air brake

systems that can detect either reversed air brake

lines or inoperative low-air-pressure warning

switches.

CONCLUSIONS
14

As a result of its investigation of this

accident the National Transportation Safety

Board makes the following safety

recommendations:

--to the Federal Highway Administration :

In cooperation with the Commercial

Vehicle Safety Alliance, develop an

inspection protocol that could be easily

administered by inspection personnel

for detecting either reversed air brake

lines or inoperative low-air-pressure

warning switches on commercial

vehicles equipped with dual air brake

systems. (H-97-31)

--to the Commercial Vehicle Safety

Alliance:

In cooperation with the Federal

Highway Administration, develop an

inspection protocol that could be easily

administered by inspection personnel

for detecting either reversed air brake

lines or inoperative low-air-pressure

warning switches on commercial

vehicles equipped with dual air brake

systems. (H-97-32)

--to the American Trucking Associations,

Inc.:

Notify your members through sources,

such as the Transport Topics magazine,

of the facts and circumstances of this

accident and, in cooperation with the

American Trucking Associations’

Maintenance Council, urge your

membership to implement procedures

that will ensure that air brake

manufacturers’ suggested installation,

inspection, and functional test

procedures are adhered to during and

after maintenance on truck air brake

systems. (H-97-33)

--to the National Ready Mix Concrete

Association:

Notify your membership through

sources, such as your Dispatcher

newsletter, of the circumstances of this

accident and urge them to implement

procedures that will ensure that air

brake manufacturers’ suggested

installation, inspection, and functional

test procedures are adhered to during

and after routine maintenance on truck

air brake systems. (H-97-34)

RECOMMENDATIONS
15

--to JDM Materials Company, Inc.:

Implement procedures that will ensure

that air brake manufacturers’ suggested

installation, inspection, and functional

test procedures are adhered to by

company mechanics performing

maintenance on the company’s truck

brake systems. (H-97-35)

--to Pennsylvania Department of

Transportation:

Develop an easily administered

inspection protocol for detecting

reversed air lines and inoperative lowair-pressure warning switches on dual

air brake system vehicles. (H-97-36)

--to the Truck Manufacturers Association:

Notify your membership of the

circumstances of this accident and urge

them to install, on all the commercial

trucks they manufacture with dual air

brake systems, separate low-air-pressure

warning devices that will independently

alert operators to a loss of air pressure

in either system. (H-97-37)

--to the National Highway Traffic Safety

Administration:

In cooperation with the Society of

Automotive Engineers, develop

specifications and requirements for the

installation, in heavy trucks with a dual

air brake system, of separate low-airpressure warning devices that will

independently alert drivers to a loss of

air pressure in either system. (H-97-38)

--to the Society of Automotive Engineers:

In cooperation with the National

Highway Traffic Safety Administration,

develop specifications and requirements

for the installation, in heavy trucks with

a dual air brake system, of separate lowair-pressure warning devices that will

independently alert drivers to a loss of

air pressure in either system. (H-97-39)

BY THE NATIONAL TRANSPORTATION SAFETY BOARD

JAMES E. HALL

Chairman

ROBERT T. FRANCIS II

Vice Chairman

JOHN A. HAMMERSCHMIDT

Member

JOHN J. GOGLIA

Member

GEORGE W. BLACK, JR.

Member

October 17, 1997

17

APPENDIX A

Bendix Dual Circuit Brake System Troubleshooting Test #5

“RETEST TO CHECK ALL ITEMS REPAIRED OR REPLACED”

1. Drain front axle reservoir to 0 PSI.

a. Rear axle reservoir should not lose pressure.

b. On combination vehicles, the trailer air system shoulder remain charged.

c. Tractor and trailer brakes should not apply automatically.

2. With no air pressure in the front axle reservoir, make a brake application.

a. Rear axle brakes should apply and release.

b. On combination vehicles the trailer bakes should also apply and release.

c. The stop lamps should light.

3. Slowly drain rear axle reservoir.

a. Spring brake push pull valve should pop out between 35 and 45 PSI.

b. Tractor protection valve should close between 45 and 20 PSI, and trailer supply hose should be

exhausted.

c. Trailer brakes should apply after tractor protection closes.

4. Close drain cocks, recharge system, and drain rear axle reservoir to 0 PSI.

a. Front axle reservoir should not loose pressure.

b. On combination vehicles, the trailer air system should remain charged.

5. With no air in the rear axle reservoir, make a brake application.

a. Front axle brakes should apply and release.

b. On combination vehicles, the trailer brakes should apply and release.

c. If the vehicle is equipped with an inverting relay spring brake control valve, the rear axle brakes

should apply and release.

19

APPENDIX B

fdi!i!b 8: AIR BRAKE SYSTEM ●

DUAL CIRCUIT BRAKE SYSTEM FUNCTION TEST

The following Dual Circuit Brake System Function Test should be performed at each C and D inspection interval, or after any air system service procedures that involve disconnecting and reconnecting air lines

where incorrect reconnection, such as the treadle valve, is a possibility.

1.

2.

3.

4.

5.

6.

7.

8.

Block the wheels to prevent the vehicle from moving.

Start the engine and build air system pressure to governor cut-out.

Stop the engine.

Completely drain one air reservoir.

Release the parking brakes.

Apply and hold the treadle valve.

Have an assistant check for proper results by observing the movement of the slack adjusters as indicated below

TRUCK:

● The brakes on the rear drive axle(s) should always apply as

indicated by movement of the slack adjuster.

● The low-air warning buzzer and warning lamp should activate

for at least two of the tests.

TRACTOR:

● The brakes on either the steering axle or the rear drive

alxe(s) should always apply as indicated by movement of the

slack adjuster.

● The low-air warning buzzer and warning lamp should activate

for at least two of the tests.

Repeat the above procedures for the remaining air reservoirs (do

not include air reservoirs for air starter if so equipped).