[Federal Register Volume 73, Number 46 (Friday, March 7, 2008)]
[Proposed Rules]
[Pages 12354-12357]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E8-4460]
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DEPARTMENT OF TRANSPORTATION
National Highway Traffic Safety Administration
49 CFR Part 571
Federal Motor Vehicle Safety Standards No. 121; Air Brake Systems
AGENCY: National Highway Traffic Safety Administration (NHTSA), DOT.
ACTION: Denial of petition for rulemaking.
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SUMMARY: This Notice denies a petition by Mr. Wayne Walch of TP
Trucking in which the petitioner requested three changes to Federal
Motor Vehicle Safety Standard (FMVSS) No. 121, Air brake systems,
related to the air compressor operation and low air pressure warning
system. After reviewing the petition and the available real world data,
the agency has decided to deny it in its entirety because one of the
suggested changes is already in the standard, the second would not
result in any measurable safety benefit, and the third was, among other
things, not described in sufficient detail for the agency to evaluate
its function or purpose.
FOR FURTHER INFORMATION CONTACT: For non-legal issues, you may contact
Mr. Jeff Woods, Office of Crash Avoidance Standards, NHTSA, 1200 New
Jersey Avenue, SE., Washington, DC 20590 (Telephone: 202-366-6206)
(FAX: 202-366-7002). For legal issues, you may contact Mr. Ari Scott,
Office of the Chief Counsel, NHTSA, 1200 New Jersey Avenue, SE.,
Washington, DC 20590 (Telephone: 202-366-2992) (FAX: 202-366-3820).
SUPPLEMENTARY INFORMATION:
Table of Contents
I. Background
II. General Description of Air Brake Systems and FMVSS No. 121
Requirements
III. Function of Low Air Pressure Warning and Gauges in Normal and
Emergency Braking Conditions
IV. Real World Data
V. Agency Analysis and Decision
VI. Conclusion
[[Page 12355]]
I. Background
The agency received a petition for rulemaking dated October 20,
2006, from Mr. Wayne Walch of TP Trucking, located in Eagle Point,
Oregon. The petitioner suggested three improvements related to the air
compressor operation and low air pressure warning system, which he
believed would make air brake systems safer, and requested that Federal
Motor Vehicle Safety Standard (FMVSS) No. 121, Air brake systems, be
changed accordingly. These suggestions include:
A warning device that would activate when the air
compressor begins a new cycle.
A warning device that would activate if the air compressor
exceeds a predetermined amount of time to reach the cut-out pressure.
A warning device that would activate just before the
beginning of the air compressor cycle.
In his petition, Mr. Walch describes the typical operation of a low
pressure warning system in which an audible warning signal is activated
when the reservoir pressure is at 55 pounds per square inch (psi) or
below, or one half of the compressor governor cutout pressure,
whichever is less. The petitioner states that he believes this system
is not robust as it provides no indication of continual air loss or
when the compressor is constantly running and this can result in a
dangerous situation.
In arguing the merits of the petition, the petitioner describes
several scenarios in which the recommended systems would operate.
First, the petitioner describes a scenario in which a system has an air
leak and the compressor keeps running continuously. As the driver
applies the brakes, the compressor cannot maintain the needed pressure,
and the driver loses his brakes. If the truck is traveling down hill,
the driver could have a serious crash in this situation. The petitioner
states that even if the spring-operated parking brakes activate, they
do not have the stopping efficiency as the normal service brakes. The
petitioner further states that if the parking brakes activate due to
that condition, the vehicle could stop in an unsafe area, and that most
drivers will not know how to release the spring parking brakes. As
such, the petition asks for the above three changes to FMVSS No. 121 to
make air brakes safer. They are as follows:
1. Provide an indication to the driver upon air compressor cut-in.
Thus if the driver is aware that the air compressor is cycling but the
brakes aren't being used, the driver would be alerted to air system
leakage.
2. Set the time on new vehicles for the air compressor to increase
system pressure from cut-in to cut-out pressure. If the system is
taking too long to build pressure, then a warning needs to be displayed
to the driver.
3. Require a low air pressure warning device that activates just
before the start of the air compressor cycle. Items 1 and 2 above will
prevent this.
II. General Description of Air Brake Systems and FMVSS No. 121
Requirements
The operation of an air brake system relies on compressed air
stored in reservoirs (tanks) mounted on the vehicle (truck, bus, or
trailer). By storing compressed air in the reservoirs, the air is
readily available to make rapid application of the brakes possible.
When the driver applies the service brakes, the compressed air flows
from the reservoirs into the service brake chambers that actuate the
brake mechanism at each wheel. The air in the reservoirs is replenished
by an air compressor on the engine of the truck or bus, which is
controlled by a governor that activates the air compressor (cut-in
pressure) and then turns off the air compressor once the reservoirs are
fully charged (cut-out pressure). Trailers are also equipped with
reservoirs, which receive their air supply from a towing vehicle that
is typically a truck or truck tractor. In the case of multiple trailer
combination vehicles, the tractor supplies air to all of the trailers
in the combination.
As the driver applies the brakes, the air flows from the reservoirs
into the service brake chambers at a pressure corresponding to the
position of the brake pedal (treadle valve). Therefore, a light brake
application would typically result in 10 to 20 psi of compressed air in
the brake chambers, and a hard brake application would typically result
in 40 psi or higher pressures in the brake chambers. Since the brake
chambers are filled with compressed air taken from the reservoirs and
upon releasing the service brakes the air is vented to the atmosphere,
the air pressure in the reservoirs becomes slightly depleted whenever
the brakes are applied. When the reservoir pressure drops to cut-in
pressure, the governor activates the air compressor to build the system
pressure back up to the cut-out pressure.
The process of the air compressor activating at reservoir cut-in
pressure, then building to reservoir cut-out pressure, is known as
compressor cycling, and the time between cycles can vary greatly among
vehicle types and the type of driving that is experienced. The most
frequent compressor cycling occurs in stop-and-go operations, such as
experienced by transit buses and refuse trucks, whereas the least
frequent compressor cycling would typically be on a tractor trailer
combination vehicle being operated at highway speeds with infrequent
brake applications.
The service brake system on air braked vehicles is typically split
into a primary and a secondary air system. The primary system usually
controls the brakes on the drive axle(s) and the secondary system
controls the brakes on the steer axle. Both systems have their own
reservoirs that are typically fed by a supply reservoir that receives
air directly from the air compressor. The primary and secondary air
reservoirs are equipped with check valves for isolation so that a loss
of pressure in one system does not cause a loss of pressure in the
other system. In case one system loses pressure, the remaining system
still provides an emergency braking capability on the vehicle, as well
as continuing to operate any trailer service brakes, and keeps the
parking brakes in the released position. Most parking brakes on heavy
vehicles are of the spring brake design that require adequate brake
system air pressure in order to release them so the vehicle can be
moved.
FMVSS No. 121 has several requirements relating to the reservoirs
and air compressor systems on trucks, buses, and trailers. The minimum
size of the reservoirs is specified in FMVSS No. 121 so that an
adequate reserve of air is available to repeatedly apply the brakes
without an excessive loss of system air pressure. For trucks and buses,
S5.1.2.1 requires that the total reservoir volume (combined volume of
primary, secondary, and supply reservoirs) is at least 12 times the
combined volume of all of the service brake chambers on the vehicle.
Slight exceptions are provided in Table V--Brake Chamber Rated Volumes,
so that vehicle manufacturers can install long-stroke brake chambers in
place of standard-stroke brake chambers without having to increase the
size of the reservoirs. For trailers, S5.2.1.1 requires that trailers
have a reservoir capacity that is at least eight times the combined
volume of the brake chambers, and again an exception is provided via
Table V for the use of long-stroke brake chambers.
S5.1.1 Air compressor requires that an air compressor has
sufficient capacity to increase the pressure in the reservoirs from 85
psi to 100 psi within the time, in seconds, expressed by the equation:
[Actual reservoir capacity x
[[Page 12356]]
25] / [required reservoir capacity], with the engine at maximum
recommended r.p.m. Thus if a truck had minimum-sized air reservoirs,
the compressor must be able to reach 100 psi from 85 psi within 25
seconds with the engine at maximum recommended rated speed. S5.1.1.1
Air compressor cut-in pressure requires that the governor cut-in
pressure is at least 85 psi for a bus and at least 100 psi for a truck.
S5.1.4 Pressure gauge requires a pressure gauge that is visible to
the driver for each service brake system. In a typical split air brake
system there are two independent air subsystems (primary and secondary)
that each have a reservoir or series of reservoirs. The air pressure
gauge has two pressure indicators (pointers)--one for the primary
system, and one for the secondary system, or, two separate gauges can
be used with one gauge provided for each system.
S5.1.5 Warning signal requires a low air pressure warning signal
that is either visible to the driver, or if it is not directly in front
of the driver, is both visible and audible. The warning signal must
activate when the pressure in any reservoir system is below 60 psi and
the vehicle's ignition is in the ``on'' position.
III. Function of Low Air Pressure Warning and Gauges in Normal and
Emergency Braking Conditions
During normal driving, the reservoir systems are automatically
recharged by the air compressor, and the driver can monitor the air
pressure gauges to see that the air pressure in the reservoirs is
staying between the cut-in and cut-out pressure limits. Most drivers of
air-braked vehicles are aware of the function of the low air pressure
warning signal and air pressure gauges on heavy vehicles. The vast
majority of drivers of air-braked vehicles have commercial drivers
licenses (CDL's). In order to obtain a CDL with an endorsement to drive
vehicles with air brakes, drivers are required to demonstrate that they
possess the knowledge and skills to operate a vehicle equipped with air
brakes. After starting the engine, the air brake system builds pressure
in the primary and secondary systems as indicated by the gauges, and
the low pressure warning turns off indicating normal system operation.
However, the minimum pressure for the low air pressure warning system
activation as required in FMVSS No. 121 is ``below 60 psi'' which is
slightly higher than stated by the petitioner (55 psi, or one-half the
compressor governor cut-out pressure, whichever is less). The
petitioner cited the North American Standard Out-of-Service Criteria
for the low pressure warning device published by the Commercial Vehicle
Safety Alliance and these air pressure values are slightly lower than
required by FMVSS No. 121 that applies to the manufacturers of new
vehicles. To ensure compliance with the ``below 60 psi'' requirement in
FMVSS No. 121, the actual low pressure warning typically activates
slightly above 60 psi when measured on vehicles.
There are several common types of brake system failures that can
cause the low pressure warning signal to activate. To begin, minor
leaks in the system can often be overcome by the capacity of the air
compressor to re-supply air to the brake system. However, this
discussion focuses on substantial leaks and failures that the air
compressor cannot overcome, as well as failures of the air compressor
itself.
A substantial leak in a brake hose supplying a service brake
chamber, or in a service brake chamber (e.g., due to a failed
diaphragm), will result in leakage whenever the brake pedal is applied.
If the leak is sufficiently large and the brake pedal is applied for a
long duration, the pressure in either the primary or secondary
reservoir may become sufficiently low to activate the warning signal,
which is required to activate when the air pressure in the service
reservoir system is below 60 psi. However, the remaining service brake
system (secondary or primary) will remain intact and provide for an
emergency braking capability, and will continue to keep the parking
brakes released. The driver would be able to determine by viewing the
air pressure gauges the rate of pressure loss and whether the loss was
in the primary or secondary system.
Failures or leaks can also occur in the air supply portion of the
system, including the governor, air compressor, compressor discharge
hose, and the air dryer located between the air compressor and the
service reservoirs. Whether the compressor does not cut-in, or its
discharge air is vented to atmosphere because of a hose failure
downstream of the compressor, the result is that as the driver depletes
air in both reservoir systems during the application of the service
brakes, the pressure in both the primary and secondary systems
continues to drop until the low-pressure warning system activates.
Typically, the primary system will activate the low pressure warning
signal first while the secondary system will have a higher pressure. At
this point the vehicle is in emergency braking mode and the driver has
the ability to pull off the roadway. If for some reason the brakes were
repeatedly applied, the pressure in both the primary and secondary
systems would become further depleted and the spring brakes would
eventually apply automatically which would also bring the vehicle to a
stop. Truck drivers with CDLs are generally knowledgeable about these
aspects of air brake system failures and the importance and meaning of
low pressure warning signals.
IV. Real World Data
The petitioner cites two scenarios for truck crashes that it states
are related to the inadequacy of the currently required low air
pressure warning system. The first is runaway trucks on downgrades that
the petitioner claims is caused by air leaks. The petitioner provided
no data to support this conclusion. Similarly, the agency is not aware
that this is a prevalent crash mode. Our experience indicates that
runaway truck crashes are most often due to brake fade from overheated
and/or out-of-adjustment S-cam drum brakes that result in a loss of
brake effectiveness, often exacerbated by excessive speed on a
downgrade. We have no indications that runaway truck crashes are being
caused by air leaks or contributed to by inadequate low pressure
warning systems.
The other crash scenario presented by the petitioner was a truck
stopping in an unsafe area because of an air leak that caused the
parking brakes to apply and most drivers would not know how to move the
vehicle. While it is true that this can happen, the agency has no
indications of widespread problems with trucks being stranded on
roadways or in unsafe areas due to loss of air pressure in the brake
system and being involved in crashes. The petitioner also did not
provide such data. Additionally, as we have previously stated, the
current low-pressure warning system already alerts the driver of a
substantial loss of air pressure and the truck's braking system can be
operating in the emergency braking mode. As such, the driver can still
make several brake applications to safely bring the truck to a stop off
of a travel lane.
V. Agency Analysis and Decision
The first requested change made by the petitioner is:
There needs to be a way to make the driver aware of when the air
compressor is starting a new cycle. This lets the driver know there
is a loss of air in the system. If he is not using the brakes and
the air compressor is cycling he should stop the vehicle and do an
inspection for an air leak or call for repairs to the air system
before continuing on or before a possible accident on a downhill
grade.
[[Page 12357]]
The agency believes that this change would mean that a lamp on the
instrument panel would illuminate (or some other type of indicator
would signal) every time that the air compressor cycled on at cut-in
pressure. Since cycling of the compressor occurs during normal
operation of a vehicle equipped with an air brake system, the agency
believes that most truck drivers would find this to be a nuisance,
particularly when driving at night. The agency's fleet evaluation
experience in the early 1990's with antilock brake systems (ABS)
warning lamps was that drivers would sometimes remove the bulb or cover
it with opaque tape because of a perceived nuisance (when in fact it
was indicating a malfunction in the ABS that, under hard braking, could
result in a loss-of-control crash). A warning system that activates
during normal operation may have a limited safety benefit, and
activations are more effective when they only occur when there is a
condition that warrants some type of intervention by the driver.
Therefore, we do not believe it would be appropriate to adopt the
petitioner's first request. However, we note that neither FMVSS No.
101, Controls and Displays, nor FMVSS No. 121 prohibits the addition of
a compressor cycling lamp, if a truck operator chooses to have such a
system installed.
The second requested change is:
They need to set the time on new vehicles at the factory on how
long it takes the air compressor at the start of its cycle to meet
the cut off pressure. If it is taking to[o] long or continuous
running occurs there needs to be something to warn the driver there
is a major problem. This is a very unsafe situation and should have
a priority warning to the driver.
Regarding the requested change by the petitioner to set the
required time for air pressure build time, we note that this facet of
air brake systems is addressed in the previously discussed section
S5.1.1 in FMVSS No. 121, which requires the air compressor to have
sufficient capacity to increase the air system pressure from 85 to 100
psi in the specified amount of time. However, this requirement allows
for some variation in the amount of time needed to charge the air
system. Under FMVSS No. 121, the time for charging the air system is
measured with the engine at maximum rated speed, so the actual charging
time during normal driving can vary based upon actual engine speed and
gear selection. Compared to charging time with the engine at maximum
rated speed, the charging time would be longer when the truck is
sitting at idle. Other factors, such as the frequency of brake
application, number of towed units, air being supplied to increase air
suspension pressure, etc., would cause air to be depleted at the same
time the air compressor is charging the system. Therefore, these would
also affect the charging time, and we believe that requiring a warning
to activate when a constant time period has elapsed is an impracticable
requirement, given the variable nature of the charging period under the
current regulatory scheme. We note that our safety standard already
regulates performance in the area of air pressure charging time, but we
believe that it does so more appropriately than the proposed change.
For this reason, we are not adopting the petitioner's second request.
The final requested change is:
It would be some help to have a low air pressure warning device
that comes on just before the start of the air compressor cycle.
When this low air warning comes on the vehicle is in a dangerous
situation. Number 1 and 2 will prevent this.
The third requested change in the petition is not clearly defined
for the agency to fully evaluate. The statement ``just before the start
of the air compressor cycle'' has two meanings. The first meaning is a
pressure slightly above the cut-in pressure, e.g., approximately 105 to
110 psi. The second meaning is a pressure slightly below the cut-in
pressure, e.g., approximately 90 to 95 psi. Based upon the information
in the petition, the agency does not understand the concept of this
warning lamp, and how its operation differs from the currently-required
low pressure warning signal required in FMVSS No. 121, other than being
set to activate at a higher air pressure. It also seems nearly
identical to/redundant with the petitioner's first requested change, as
this warning would activate just before the start of a new air
compressor cycle, and then the warning from the first request would
activate when the compressor began that new cycle. Furthermore, we note
that activation of a warning signal at either of these pressures would
result in the warning being activated extremely frequently, including
during normal driving operations. Given these reasons, we are denying
the petitioner's third requested change.
VI. Conclusion
Based upon this review of the petition, the agency is denying it.
In summary, it appears that one or two warning lamps would be required
to activate upon each cut-in of the compressor cycle, and this would
not provide additional information to the driver beyond the information
that is already available from the existing air pressure gauges. In
addition, we believe that warning systems that activate frequently
during normal driving conditions can be perceived as a nuisance, and
may have limited safety effect. Finally, we are not aware of any known
safety problems not addressed by the existing low pressure warning
signal requirements in FMVSS No. 121.
Issued: March 3, 2008.
Stephen R. Kratzke,
Associate Administrator for Rulemaking.
[FR Doc. E8-4460 Filed 3-6-08; 8:45 am]
BILLING CODE 4910-59-P