[Federal Register Volume 60, Number 145 (Friday, July 28, 1995)]
[Rules and Regulations]
[Pages 38762-38765]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-18381]



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DEPARTMENT OF TRANSPORTATION
49 CFR Part 571

[Docket No. 85-07; Notice 10]
RIN 2127-AF23


Federal Motor Vehicle Safety Standards; Air Brake Systems Control 
Line Pressure Balance

AGENCY: National Highway Traffic Safety Administration (NHTSA), 
Department of Transportation.

ACTION: Final rule.

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SUMMARY: In response to a petition for rulemaking submitted by Sealco 
Air Controls, this document amends the control line pressure 
differential requirements in Standard No. 121, Air Brake Systems, for 
converter dollies and trailers designed to tow other air braked 
vehicles. The agency has concluded that the amendments will improve the 
braking compatibility of such vehicles by allowing the use of a relay 
valve known as a spool-type low opening valve.

DATES: Effective date. The amendments in this document become effective 
August 28, 1995.
    Petitions for reconsideration. Any petitions for reconsideration of 
this rule must be received by NHTSA no later than August 28, 1995.

ADDRESSES: Petitions for reconsideration of this rule should refer to 
Docket No. 85-07; Notice 10 and should be submitted to: Administrator, 
National Highway Traffic Safety Administration, 400 Seventh Street, 
S.W., Washington, D.C. 20590.

FOR FURTHER INFORMATION CONTACT: Mr. Richard Carter, Office of Vehicle 
Safety Standards, National Highway Traffic Safety Administration, 400 
Seventh Street, S.W., Washington, D.C. 20590 (202-366-5274).

SUPPLEMENTARY INFORMATION:

I. Background

    Standard No. 121, Air Brake Systems, establishes performance and 
equipment requirements for braking systems on vehicles equipped with 
air brakes, including requirements for pneumatic timing. NHTSA recently 
amended the control signal pressure differential requirements of 
Standard No. 121, with respect to converter dollies and towing 
trailers. (57 FR 37902; August 21, 1992) The amendment specifically 
requires that, for trailers and converter dollies manufactured after 
August 23, 1993, the pressure differential between the control line 
input coupling and a 50 cubic inch test reservoir connected to the rear 
control line output coupling shall not exceed 1 psi at all input 
pressures between 5 psi and 20 psi and 2 psi at all input pressures 
greater than 20 psi. Input pressures below 20 psi represent routine 
braking applications, while input pressures between 20 psi and 40 psi 
represent moderate to heavy braking applications, and input pressures 
above 40 psi represent severe braking applications.1

    \1\ In today's final rule, NHTSA has decided to modify the limit 
above 40 psi to allow a 5 percent differential (which at higher 
pressures exceeds the current limit of 2 psi) based on, among other 
things, the Society of Automotive Engineer's (SAE's) Recommended 
Practice SAE J1505, Brake Force Distribution Test Code Commercial 
Vehicles.
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    The August 1992 amendment was intended to ensure that the control 
signal ``passes'' through a towing trailer or dolly without being 
altered along the way. Since the control signal passes through 
unaltered, each vehicle in a combination unit receives the same brake 
control signal. This serves to increase the braking compatibility of 
combination vehicles, since each vehicle in a combination has 
comparable braking performance. By specifying the maximum permissible 
differential between the input and output control line pressures, this 
requirement addresses problems of heat buildup and brake fade during 
long, gradual downhill runs at relatively low 

[[Page 38763]]
pressure brake applications, caused by relatively large brake pressure 
differentials between the trailers and converter dollies in multiple 
trailer combinations.

II. Sealco Petition

    On June 18, 1993, Sealco Air Controls (Sealco), a valve 
manufacturer, submitted to NHTSA a rulemaking petition to amend 
Standard No. 121 with respect to the control line pressure differential 
requirements in S5.3.5. Specifically, Sealco requested that NHTSA amend 
these requirements to eliminate the need to modify the original design 
of its low opening valves (LOVs) that resulted from the August 1992 
amendment. Sealco stated that these modifications degraded the ability 
of its LOVs to maintain minimal air pressure differentials between the 
input and output of these valves. These valves are used as control line 
relay valves and service line relay valves in trailers and converter 
dollies. The petitioner stated that unlike other relay valves that use 
a common poppet, 2 the low opening valves have a balanced spool 
technology 3 that allows the valve to initially open at a 
relatively low pressure of 1.5 psi. The pressure at which a valve 
initially opens is referred to as the crack pressure. According to 
Sealco, the spool technology enables the output pressure delivered by 
the valve to closely follow (i.e., track) the input control air 
pressure. As a result, it claimed that hysteresis 4 is not so 
prevalent with low operating valves as with high crack pressures. This 
amendment will not significantly affect small businesses, small 
organizations, and small governmental units that purchase vehicles 
since this amendment will have no significant cost impact on vehicles.

    \2\ A poppet valve has a valve seat like a typical water faucet 
valve. The air flow is increased as the sealing lip is raised higher 
off the valve seat by varying the air pressure in the control line. 
The valve allows increased or decreased air flow from the supply 
line side of the system.
    \3\ A spool type valve has a cylinder which slides back and 
forth inside of a machined hole called a bore. As the spool slides 
past a port or opening on the side of the bore, the exposed side 
port then allows the air to flow past the valve spool.
    \4\ The phenomenon exhibited by a system in which the reaction 
of the system to changes is dependent upon its past reactions to 
change. With respect to braking, when the control line input 
pressure is increased, the relay valve's output (apply pressure) is 
usually a few psi lower than the control line output pressure, and 
is usually more than one or two psi above the descending control 
line pressure. Complications may arise when a subsequent brake 
application is made before the brakes have fully released after a 
prior application.
    Hysteresis in a valve may cause the output line pressure of the 
valve not to track properly the input control line pressure, which may 
cause the application pressure of the brakes in the trailer to be 
significantly different than the control line pressure signal. In such 
situations, the valve's hysteresis may not allow the same pressure to 
be applied to the trailer brakes as is signalled by the driver's 
application of the brake control. In the case of increasing brake line 
pressure, this will cause less braking in the trailer than in the 
tractor, causing the trailer to ``push'' the tractor. Similarly, when 
the driver decreases the brake application, the hysteresis in the valve 
may not allow the brake application in the trailer to decrease to the 
same degree, resulting in the trailer brakes still being applied to a 
greater degree than those in the tractor. This causes the kingpin to 
jerk on the inside of the fifth wheel. Under high speed congested 
traffic conditions in which the driver may go through several brake 
applications and releases in rapid succession, the jerking and pushing 
of the trailer or trailers could be difficult to control. In multiple 
trailer combinations, this same phenomenon can be a problem between 
successive trailers as well as between tractors and trailers.
    Sealco stated that the use of low operating valves would further 
NHTSA's goal of ensuring balanced braking in combination vehicles. 
However, the petitioner claimed that while its valve meets the 
amendment's application requirements, it does not meet the provision 
requiring release at high pressure ranges, given the valve's mechanics. 
To comply with the amendment, Sealco has drilled a hole in the valves' 
piston, thereby allowing pressure to bleed to the supply side. This 
action prevents the valves from cracking open when tested according to 
S5.3.5. Sealco believes that this modification to allow compliance with 
the amendment has reduced the valves' effectiveness.

III. Notice of Proposed Rulemaking

    On July 13, 1994, NHTSA published a notice of proposed rulemaking 
(NPRM) proposing to amend Standard No. 121 to permit the use of low 
opening valves. (59 FR 35672) Specifically, the agency proposed to 
amend S5.3.5 to address input pressures over 40 psi. Under the 
proposal, the pressure differential would not be permitted to exceed 2 
psi at any input pressure between 20 psi and 40 psi and would not be 
permitted to exceed 5 percent at any pressure over 40 psi. In other 
words, the pressure differential requirements would remain the same as 
the current requirements, except for applications resulting in 
pressures over 40 psi.
    In the NPRM, NHTSA explained that the current requirement may 
unnecessarily extend the 2 psi limit into the higher pressure ranges 
where it is not necessary for safety. The requirement is intended to 
prevent brake fade during relatively low brake applications below 20 
psi. The 2 psi limit is relatively more stringent for hard brake 
applications, i.e., those exceeding 40 psi. The agency requested 
comments about whether the modification to pressure levels over 40 psi 
might be detrimental to safety or otherwise inappropriate.

IV. Comments on the NPRM

    NHTSA received two comments on the July 1994 proposal to amend the 
control line pressure requirements. Mr. Robert Crail, a brake engineer, 
stated that ``The adoption of the proposed amendment will not have any 
adverse effect on safety.'' He agreed with the agency that the greater 
problem area with pressure differentials is at the lower end of the 
pressure range and not the upper range, which is being broadened 
slightly. Advocates for Highway and Auto Safety (Advocates) criticized 
the proposal for several reasons. Advocates was primarily concerned 
that there was no real world braking data to support the amendment, 
which it believed would degrade heavy vehicle braking.

V. Agency Decision

    After reviewing the comments and other available information, NHTSA 
has decided to amend Standard No. 121, with respect to the control line 
pressure requirements for converter dollies and trailers designed to 
tow other air braked vehicles. Specifically, the agency has decided to 
amend S5.3.4 to allow pressure differentials of up to 5 percent at 
pressures over 40 psi. The current 2 psi allowance is 5 percent of 40 
psi, and the agency believes that allowing the same percentage above 40 
psi is adequate. Based on its review of the available information, the 
agency has concluded that the amendment facilitates the use of an 
alternative technology, without being detrimental to safety. As it 
explained in the NPRM, NHTSA based the proposed requirement on the 
Society of Automotive Engineer's (SAE's) Recommended Practice J1505, 
Brake Force Distribution Test Code Commercial Vehicles. In addition, 
the agency also contacted all the major valve manufacturers about the 
pressure differential requirements. Based on its review, NHTSA believes 
that the 2 psi differential in the current requirement is 

[[Page 38764]]
unnecessarily stringent for towing trailers and dollies in hard brake 
applications over 40 psi. Therefore, the agency has decided to adopt 
the petitioner's request to permit pressure differentials of up to 5 
percent during hard brake applications.
    Advocates criticized several aspects of the proposal to amend the 
pressure differential requirements. Specifically, that organization 
expressed concern that the amendment (1) was not supported by real 
world testing data, (2) would adversely affect safety, (3) was 
inappropriate for certain braking techniques, and (4) would allow spool 
valves, which it viewed as inferior. As explained below, NHTSA has 
concluded that Advocates' concerns are without merit.
    Advocates contended that there is no real world safety data to 
support the proposed amendment. It stated that it is ``opposed to 
safety-related regulatory changes which rely only on a priori 
calculations for gauging probable safety consequences.'' It therefore 
requested the agency to specify real world braking demonstrations to 
establish that spool type valves will not degrade safety.
    NHTSA disagrees with Advocates' contention that there are no real 
world data to support the amendments to the control line pressure 
differential requirements. In fact, the agency has two reports 
containing a substantial amount of test data regarding real world 
braking.5 These reports cover a substantial amount of real world 
braking demonstrations, including actual control line pressures under a 
full range of conditions used in a wide range of braking applications. 
Supporting data also indicate that the cut off point of 40 psi exceeds 
the braking conditions addressed by this rulemaking. All the test data 
in the antilock report are real world fleet test data and the down-hill 
test data in the Braking Strategy study are also real world and based 
on dozens of test runs. These reports illustrate that the cut-off point 
of 40 psi is reasonable. They further illustrate that a higher pressure 
is not necessary since approximately 99 percent of heavy braking occurs 
below that pressure.

    \5\ See, (1) ``An In-Service Evaluation of the Performance, 
Reliability, Maintainability and Durability of Antilock Braking 
Systems (ABSs) for Semitrailers'', DOT HS 806059; October 1993, and 
(2) ``The Influence of Strategy on Brake Temperatures in Mountain 
Descents'' DTFH61-89-C-00106; March 1992.
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    Advocates claimed that the proposed amendments to the control line 
pressure requirements would have a deleterious effect on safety under 
severe braking conditions. That organization, however, did not state 
what it considers to be severe braking conditions.
    NHTSA believes that Advocates' concern that the amendment would 
adversely affect safety is without merit, since, as mentioned above, 
approximately 99 percent of braking occurs at 40 psi or less. At 75 
psi, which represents a panic stop on dry pavement that would most 
likely lock all the wheels unless the vehicle were fully loaded, the 
Sealco valves showed only a 1.5 psi tracking variation 6 in either 
the ascending or descending brake line pressures.

     6 Tracking variation is a measure of how well matched the 
air pressure is between the (control) line side of the air brake 
system and the actual (service) air pressure being sent to the brake 
chambers. For example, if the driver's foot is placed on the brake 
pedal such that a 20 psi signal is sent to the valve that releases 
the air from the air reservoir on the trailer and the control valve 
releases 20 psi to the brakes, there is ``zero'' tracking error. If 
the air pressure at the brake chambers is between 19 to 21 psi, the 
tracking error would be within the 1 psi requirement of the 
standard.
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    With regard to the safety of tracking error variation, the agency 
prefers a tracking error of zero as an ideal. However, that would be 
unrealistic for a valve manufacturer to achieve. Because of 
manufacturing variations in the valves along with hysteresis, 2 psi is 
a reasonable pressure limit at the low end.
    Advocates commented that the agency mischaracterized braking 
practices. It stated that while snubbing (i.e., intermittently exerting 
force on the brake pedal) brakes at relatively low pressures is the 
preferred braking technique, drivers often ``ride'' (i.e., exert a 
constant force on the brake pedal) the brakes at higher pressures in 
long downhill descents.
    NHTSA believes that Advocates' statement is not accurate, since all 
the agency's research data show that ``riding'' the brakes produces 
pressures that are approximately 50 percent lower than ``snubbing'' 
pressures. The agency further notes that Advocates' concern about 
snubbing or riding the brakes is not relevant since the air pressure 
requirements are being amended for pressures higher than those used in 
snubbing or riding the brakes. The air system pressure in either of the 
two braking methods is less than the 40 psi cut-off point established 
by this amendment. Worst-case conditions produced by snubbing in 
mountain grade descents average about 27 psi with peaks to 32 psi. 
Riding the brakes results in air pressure that seldom exceeds 10 psi, 
even on mountain descents.7

    \7\ A report titled ``The Influence of Strategy on Brake 
Temperatures in Mountain Descents'' DTFH61-89-C-00106; March 1992, 
contains extensive data by both VRTC and The University of Michigan 
which relate to the air brake pressure required in ``snubbing' and 
``riding'' of the brakes.
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    Advocates expressed concern that low pressure spool type valves 
could adversely affect safety compared to poppet valves. However, NHTSA 
notes that each type of valve is used in specific applications to its 
own best advantage. The agency is aware of no application in which 
either type should be restricted by performance requirements in 
Standard No. 121. There are no data available on the performance of air 
brake spool valves vs poppet type air brake valves, because the former 
type of values have not posed a problem.
    Effective date. Each order amending a safety standard is required 
to take effect no sooner than 180 days from the date the order is 
issued unless ``good cause'' is shown that an earlier effective date is 
in the public interest. NHTSA has determined that there is ``good 
cause'' not to provide the 180 day lead-in period given that this 
amendment will not impose any mandatory requirements on manufacturers. 
The public interest in being able to use an alternative technology will 
also be served by not delaying the introduction of the requirement. 
Based on the above, the agency has further determined that there is 
good cause to have an effective date 30 days after publication in the 
Federal Register.

VI. Rulemaking Analyses and Notices

1. Executive Order 12866 (Federal Regulatory Planning and Review) and 
DOT Regulatory Policies and Procedures

    This rulemaking was not reviewed under E.O. 12866. NHTSA has 
analyzed this rulemaking and determined that it is not ``significant'' 
within the meaning of the Department of Transportation's regulatory 
policies and procedures. A full regulatory evaluation is not required 
because the rule has no mandatory effects and therefore imposes no 
costs. Further, it does not make possible cost savings. Instead, the 
rulemaking simply permits the use of spool valve technology.

2. Regulatory Flexibility Act

    In accordance with the Regulatory Flexibility Act, NHTSA has 
evaluated the effects of this action on small entities. Based upon this 
evaluation, I certify that the amendment will not have a significant 
economic impact on a substantial number of small entities. Vehicle and 
brake manufacturers typically do not qualify as small 

[[Page 38765]]
entities. For these reasons, no regulatory flexibility analysis has 
been prepared.
3. Executive Order 12612 (Federalism)

    This action has been analyzed in accordance with the principles and 
criteria contained in Executive Order 12612, and it has been determined 
that the rule will not have sufficient Federalism implications to 
warrant preparation of a Federalism Assessment. No State laws will be 
affected.

4. National Environmental Policy Act

    The agency has considered the environmental implications of this 
rule in accordance with the National Environmental Policy Act of 1969 
and determined that the rule will not significantly affect the human 
environment.

5. Civil Justice Reform

    This rule will not have any retroactive effect. Under section 
103(d) of the National Traffic and Motor Vehicle Safety Act (49 U.S.C. 
30111), whenever a Federal motor vehicle safety standard is in effect, 
a state may not adopt or maintain a safety standard applicable to the 
same aspect of performance which is not identical to the Federal 
standard. Section 105 of the Act (49 U.S.C. 30161) sets forth a 
procedure for judicial review of final rules establishing, amending or 
revoking Federal motor vehicle safety standards. That section does not 
require submission of a petition for reconsideration or other 
administrative proceedings before parties may file suit in court.

List of Subjects in 49 CFR Part 571

    Imports, Motor vehicle safety, Motor vehicles, Rubber and rubber 
products, Tires.

    In consideration of the foregoing, the agency is amending Standard 
No. 121, Air Brake Systems, part 571 of Title 49 of the Code of Federal 
Regulations as follows:

PART 571--[AMENDED]

    1. The authority citation for Part 571 continues to read as 
follows:

    Authority: 49 U.S.C. 322, 30111, 30115, 30117, and 30166; 
delegation of authority at 49 CFR 1.50.

    2. In Sec. 571.121, S5.3.5 introductory text and S5.3.5(a) are 
revised to read as follows:


Sec. 571.121  Standard No. 121; Air brake systems.

* * * * *
    S5.3.5  Control signal pressure differential--converter dollies and 
trailers designed to tow another vehicle equipped with air brakes.
    (a) For a trailer designed to tow another vehicle equipped with air 
brakes, the pressure differential between the control line input 
coupling and a 50-cubic-inch test reservoir attached to the control 
line output coupling shall not exceed the values specified in 
S5.3.5(a)(1), (2), and (3) under the conditions specified in 
S5.3.5(b)(1) through (4):
    (1) 1 psi at all input pressures equal to or greater than 5 psi, 
but not greater than 20 psi; and
    (2) 2 psi at all input pressures equal to or greater than 20 psi 
but not greater than 40 psi; and
    (3) not more than a 5-percent differential at any input pressure 
equal to or greater than 40 psi.
* * * * *
    Issued on: July 20, 1995.
Ricardo Martinez,
Administrator.
[FR Doc. 95-18381 Filed 7-27-95; 8:45 am]
BILLING CODE 4910-59-P