[Federal Register Volume 64, Number 175 (Friday, September 10, 1999)]
[Proposed Rules]
[Pages 49135-49139]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-23520]
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DEPARTMENT OF TRANSPORTATION
National Highway Traffic Safety Administration
49 CFR Part 571
[Docket NHTSA-99-5992, Notice 1]
Denial of Petition for Rulemaking; Federal Motor Vehicle Safety
Standards Rear Impact Guards
AGENCY: National Highway Traffic Safety Administration (NHTSA),
Department of Transportation (DOT).
ACTION: Denial of petition for rulemaking.
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SUMMARY: Federal Motor Vehicle Safety Standard (FMVSS) No. 223
specifies a test procedure for demonstrating that rear impact guards
comply with the strength and energy absorption requirements of the
standard. This procedure involves a quasi-static test in which the
horizontal member of the rear impact guard is slowly pushed for 125 mm,
while the amount of resistance it offers is measured. Next, the guard
is released and the amount of energy the guard absorbed is calculated.
The Truck Trailer Manufacturers Association (TTMA) submitted a
petition for rulemaking requesting three changes to the test procedure.
First, TTMA requested that we eliminate the lower bound of the range of
acceptable rates of force application, so that the force can be applied
in discrete start-stop steps. Second, TTMA requested that the
requirement to displace the guard by a full 125 mm be eliminated if it
appeared that the guard had met all requirements before that point.
Third, TTMA suggested that the elastic rebound from guards that rebound
very slowly following removal of the force not be subtracted from the
calculated energy absorption. Each of the proposed revisions purports
to ease the burden of testing on rear impact guard manufacturers,
especially small businesses.
We are denying the petition. TTMA has not demonstrated a need for
slower rates of force application. We have already lowered the
permissible rate of force application to a level that is not
[[Page 49136]]
burdensome, and even allow a manufacturer to specify, within a broad
range, the force application rate on which it based its certification.
Stopping the test before a displacement of 125 mm is not practical for
compliance testing. Since we would have no way of knowing how far a
guard would rebound, we could not know, in advance, how much energy the
guard would absorb. We have answered TTMA's third request by providing
an interpretation of the existing regulatory language. Making that
interpretation more explicit in the procedures is not necessary.
FOR FURTHER INFORMATION CONTACT: The following persons at the National
Highway Traffic Safety Administration, 400 Seventh Street, SW,
Washington, DC, 20590:
For non-legal issues: Mr. Mike Huntley, Office of Crashworthiness
Standards (202-366-0029), e-mail: mhuntley@nhtsa.dot.gov
For legal issues: Mr. Taylor Vinson, Office of the Chief Counsel
(202-366-5263), e-mail: tvinson@nhtsa.dot.gov
SUPPLEMENTARY INFORMATION:
I. Background
On January 24, 1996, we published a final rule establishing FMVSS
No. 223, Rear Impact Guards, which specifies performance requirements
that rear impact guards must meet before they can be installed on new
trailers and semitrailers. The standard (49 CFR 571.223) specifies
strength and energy absorption requirements, as well as the procedures
we will use to demonstrate compliance with the standard. Compliance
with the standard may be demonstrated on a non-vehicle rigid ``test
fixture'' or on a completed vehicle. We promulgated the energy
absorption requirements to address concerns that the rule would permit
overly rigid guards that would absorb little or no crash energy. We
regarded these guards as undesirable because they would result in a
greater likelihood of serious--and possibly fatal--driver and front
passenger head and chest injuries by causing a colliding vehicle to
stop too suddenly.
To demonstrate compliance with the strength requirements of the
standard, the final rule specified a quasi-static test. A guard is
tested for strength by slowly pushing it forward, as the guard is
oriented on the trailer, with a 203 mm by 203 mm (8 inch by 8 inch)
force plate at specified points along the rear side of the horizontal
member of the guard. As issued in January 1996, the final rule
specified that the guard be moved for a total distance of 125 mm (5
inches) at a constant rate of not less than 1 mm and not more than 1.5
mm per second (6.0 to 9.0 cm/minute). To pass, the guard must resist
the specified force within the first 125 mm of displacement. We
specified a quasi-static test, instead of a dynamic test (e.g., a crash
test), to reduce the cost of testing for the many smaller firms in the
trailer manufacturing industry. Such a firm which typically lacks the
engineering capabilities and the sophisticated and expensive test
equipment that would be required to properly conduct a dynamic test.
FMVSS No. 223's test for energy absorption is conducted by applying
a force in the same manner as in the test for strength, but only at
either of two specified test points. The force is recorded at least 10
times per 25 mm (1 inch) of displacement until the 125 mm (5 inch)
displacement is reached and the force plate is completely withdrawn
from the guard. The guard energy absorption is calculated from a force
vs. deflection diagram plotted using the data recorded from the tested
location. To discourage the manufacture of overly rigid guards, only
plastic deformation (permanent deformation) is counted toward meeting
the required amount of energy absorption--elastic rebound of the guard
does not count. The minimum guard energy absorption of 5,650 joules
(4,170 foot-pounds) is sufficient to absorb about 12 percent of the
total kinetic energy of a 48 kph (30 mph) centric collision with a
1,135 kg (2,500 lb) vehicle.
In petitions for reconsideration, Great Dane Trailers, Inc. and
STRICK Corporation asked us to reconsider the final rule and to
increase the permissible range of force application during the strength
and energy absorption tests. Both Great Dane and STRICK said they
believed that the requirement to maintain a constant rate of between 1
mm and 1.5 mm per second would require them to invest in new and
expensive test equipment to meet this requirement, and that the rate of
displacement is not a significant indicator of the performance of the
guard. In addition, STRICK petitioned the agency to change the
requirement from maintaining a constant rate of displacement to one
that is ``approximately constant over a time of 1 to 5 minutes.''
We published a response to petitions for reconsideration on January
26, 1998, which incorporated slight modifications to the test procedure
(63 FR 3654). We accepted the assertions of the petitioners that new
and expensive equipment might be required to achieve the original force
application rate, especially when testing stronger guards. Noting that
the rate of force application should not make a significant difference
in test results when testing guards made of steel (the most common
guard material), we significantly broadened the acceptable range of
force application to 2.0 to 9.0 cm/minute. We also eliminated the word
``constant'' from the test procedure, as having to maintain a
``constant'' designated displacement rate would make it practically
impossible for us to conduct compliance testing. Instead, we allowed
the guard manufacturer to designate the displacement rate, within the
range of 2.0 to 9.0 cm/minute, on which it based its certification. If
we conduct compliance tests, we will use the manufacturer's designated
rate, plus or minus 10 percent.
II. Summary of the TTMA Petition for Rulemaking
The TTMA petition requests three changes, each of which is intended
to ease the burden of testing on guard manufacturers:
A. TTMA recommends eliminating the 2.0 cm/min lower bound for the
force application rate. TTMA contends that this would facilitate
testing using simple measuring equipment in a ``stepped'' manner by
which a manufacturer could apply a force, measure the force and the
corresponding displacement, apply more force, measure the new force and
displacement, and continue in this start-and-stop manner until the
specified energy absorbed or displacement is achieved. TTMA believes
that the 2.0 cm/min lower bound on the force application rate, as a
practical matter, prevents manufacturers from using this stepped
application of force. Such an application of force could be
accomplished using inexpensive test equipment such as manually-
controlled pumps and simple measuring devices. A May 27, 1998 memo from
TTMA stated that ``the step application of the force for the energy
absorption test per our petition of March 26, 1998, could be
accomplished in under 30 minutes.'' We assume from this that TTMA would
endorse, as an alternative to eliminating the lower bound of the force
application rate, a further reduction of the lower bound so that the
test could take as long as 30 minutes.
B. TTMA suggests that the test procedures be altered so that it is
not necessary to displace the guard the full 125 mm as currently
specified in S6.6(c). TTMA believes that if the minimum amount of
energy absorption specified in that section has been exceeded during a
displacement of less
[[Page 49137]]
than 125 mm, and little elastic rebound is anticipated, completion of
the test represents an unnecessary expenditure of test resources and
money. For example, with a very rigid guard, application of a force
sufficient to deflect the guard to 125 mm may destroy the test
equipment.
C. TTMA requests the addition of an explicit description to the
standard of the point at which the energy absorption test is considered
complete. TTMA states that a guard may be designed to displace a
material or fluid which, over a period of time, may return the guard to
near its original position. TTMA contends that the potential energy
stored in this type of guard should not be subtracted from the measured
energy absorption in the test per S6.6(c) and Figure 2 of the standard.
TTMA suggests that the following phrase be add to the energy absorption
test procedures: ``any reduction in displacement (rebound) of the guard
one second or more after the force has been removed shall not be
subtracted from the measured energy absorbed.''
III. Analysis of the Petition
A. Stepped Application of Force
The final rule was designed in large part to accommodate the needs
of small businesses. In specifying a quasi-static test as opposed to a
dynamic (full speed crash) test, we sought to reduce the costs for the
many small manufacturers that are common in the trailer manufacturing
industry. We did this because we believe that a smaller manufacturer
may lack the engineering capabilities and the sophisticated and
expensive test equipment that would be required to properly conduct a
dynamic test. Moreover, in adopting a standard that applies to
equipment, we intended to allow small trailer manufacturers to purchase
certified guards on the open market without having to conduct any tests
before installing them on their trailers.
Our concern for small businesses was also reflected in our January
1998 response to petitions for reconsideration. Great Dane Trailers and
STRICK Corporation expressed concern about the need to purchase
expensive and sophisticated precision testing equipment to replace
their current devices in order to meet the requirement stated in the
final rule to maintain a constant rate of force application of between
1 mm and 1.5 mm per second (6.0 cm and 9.0 cm per minute) during
strength and energy absorption tests. In response, we acknowledged that
the specified rate of displacement during force application may have
been too narrow to accommodate slow-pumping force application
equipment. We accepted Great Dane's and STRICK's assertions that new
and expensive equipment would be required for those companies to
achieve the specified rate, noting that more powerful hydraulic pumps
are required to achieve higher rates of displacement during the test--
especially with stronger guards. Accordingly, we revised the lower
bound for displacement rate to 0.33 mm/sec (2.0 cm/minute). We stated:
Regarding the lower bound for displacement rate, the agency
believes that 6.3 minutes is adequate time to achieve the required
displacement without the need for sophisticated control equipment
and powerful pumps. No petitioner has requested a longer period and,
unless the agency is presented with evidence of a problem with this
rate, it will consider longer periods as unnecessarily prolonging
certification and compliance testing. As explained earlier,
reasonably slower displacement rates will probably not make a
significant difference in test results anyway. Therefore, NHTSA is
granting part of STRICK's request and widening the specified
displacement rate range to allow displacement rates as low as 0.33
mm/sec. Testing at this rate will allow a 125 mm (5 inch) test
displacement to be achieved in a period of about 6 minutes.
(63 FR 3659, emphasis added)
Thus, we have already significantly broadened the acceptable range
of force application rate from a minimum of 6.0 cm/minute to a minimum
of 2.0 cm/minute, to accommodate small manufacturers.
Our establishment of the revised lower bound of 2.0 cm/minute was
based, at least in part, on an evaluation of the capabilities of the
relatively unsophisticated test equipment used by the Vehicle Research
and Test Center (VRTC) test program to evaluate the effectiveness of
rear impact guard designs during the development of the final rule.
Most modern test equipment is controlled by a computer with a feedback
system capable of quickly and automatically adjusting the displacement
rate. However, we recognized that precise adjustment of the rate
without computer control may be impracticable. In an effort to be
sensitive to smaller manufacturers, who may not have computer-
controlled equipment, we revised the standard to specify the distance
on a per-minute time scale (as opposed to a per-second time scale as
initially required) to allow for practical adjustments of the rate of
displacement within each minute.
When we conduct compliance testing, we use a continuous application
of force, such that the displacement rate of the force application
device is the rate, plus or minus 10 percent, of that designated by the
guard manufacturer within the range of 2.0 cm per minute to 9.0 cm per
minute. The petitioner does not address whether or how this test
protocol would be compared with certification testing using a stepped
application of force, versus a continuous application, as currently
required. Eliminating the lower bound of force application rate
altogether could theoretically allow guard manufacturers to perform a
stepped application of force in a certification test over a period of
many hours or even days if they believed that the physical properties
of the guard material being used would somehow allow it to perform
better with the force applied in small increments over extended time
periods.
We did not contemplate such a slow application of force when we
concluded from the testing leading up to the final rule that a quasi-
static test would be an adequate alternative to a dynamic test. It is
possible that some brittle materials with low ductility could pass the
test under these conditions but fail at a force application rate higher
than 2.0 cm/min. Obviously, such materials would not perform adequately
as underride guards. Moreover, as we noted in our response to petitions
for reconsideration, at some point, the slowing of force application
rate creates administrative difficulties because it unnecessarily
prolongs compliance testing.
Before we will eliminate or again lower the permissible force
application rate specified in FMVSS No. 223, a petitioner must clearly
demonstrate that a hardship exists. A petition for rulemaking must
``set forth facts which it is claimed establish that an order is
necessary'' (see 49 CFR 552.4). TTMA's petition does not provide
sufficient evidence that a significant number of smaller trailer
manufacturers are currently unable to conduct testing because of the
expense and sophistication of the test equipment required. It does not
provide specific information regarding the number (or percentage) of
trailer manufacturers that are being negatively affected, the cost
differential between the equipment that is required to meet the current
standard versus that which could be used if the proposed amendment were
to be adopted, or any other supporting information that would persuade
us that a hardship exists. Without such information, we are unable to
conclude that there is a need for eliminating or further reducing the
minimum force application rate specified in S6.6(a) of FMVSS No. 223.
[[Page 49138]]
B. Ending the Energy Absorption Test Prior to Full Guard Displacement
TTMA wants the test procedures revised to specify that the energy
absorption test ends before 125 mm of displacement ``if 5,650 J of
energy absorption has been exceeded.'' TTMA contends that if the
minimum amount of energy absorption required by S6.6(c) has been
exceeded during a displacement of less than 125 mm, ``and little
elastic rebound is anticipated,'' it is not necessary to fully displace
the guard to 125 mm as currently specified in S6.6(c). TTMA presumably
believes that if little elastic rebound is anticipated, completion of
the test to a full 125 mm after the guard has apparently exceeded the
amount of energy absorption required would not change the test results,
and therefore represents an unnecessary expenditure of test resources
and money.
Our compliance test procedure is very explicit regarding how far
the guard must be displaced, and is consistent with the final rule. The
guard energy absorption portion of our compliance test procedure, TP-
223-01, dated October 20, 1997, states:
Apply force to the guard in a forward direction * * * until
displacement of the force application device has reached 130 mm, +
0,-5 mm. Then reduce the load until the guard no longer offers
resistance to the force application device. Determine the energy
absorbed in the guard by calculating the area bounded by the curve
in the force vs. displacement plot. See Figure 2. Record the energy
absorbed, and the maximum load and displacement on Data Sheet 3.
Include the force vs. displacement plot with the data sheet.
BILLING CODE 4910-59-P
[GRAPHIC] [TIFF OMITTED] TP10SE99.001
BILLING CODE 490-59-C
(Not actual test date--for illustrative purposes only.)
TTMA's suggested revision is not practicable. As noted earlier, the
amount of energy is determined by calculating the area enclosed within
the force deflection curve, and the elastic rebound (the small triangle
in the lower right of the figure above) is not counted. When we conduct
compliance testing, it is impracticable for us to predict the amount of
elastic rebound that a given guard design will exhibit. While in some
cases a premature end to the test might produce a force-deflection
curve with enough area enclosed within it to pass the test, in other
cases, it might not. If we ended the test prematurely and the guard
unexpectedly exhibited excessive elastic rebound, it might not pass the
test. In this case, we would need to conduct another test, pushing the
guard to the full 125 mm in order to eliminate the possibility that the
guard would experience more plastic deformation during the final
centimeters, causing it to rebound less after the force was removed,
and passing the test because of the increased area in the curve.
Moreover, basing a test procedure on assumptions that we make
during a particular test would not meet the statutory requirement that
our standards be objective. The required performance level must be
based on a specific test procedure in order to be objective.
Finally, we note that manufacturers are free to conduct their
certification tests in any way they wish. They may follow the test
procedures in the FMVSS. Those are the procedures that the agency will
follow in conducting its compliance tests. Alternatively, the
manufacturers may follow other procedures or they use methods of
analysis that do not involve testing, so long as they are reasonably
likely to give the same results as the procedures in the FMVSS.
For example, in the specific case of FMVSS No. 223, it is
reasonable to believe that a guard that absorbs the required amount of
energy when displaced some amount less than 125 mm will absorb more
energy when deflected by the full 125 mm. Therefore, a manufacturer
could reasonably certify compliance based on a test that was ended
prior to its completion. However, we will follow the test procedures in
the FMVSS when conducting compliance tests. Further, the 125 mm
requirement was specified based on the energy absorption of a NHTSA
designed and built complying guard when subjected to a dynamic crash of
a vehicle colliding with the guard at 48 kph (30 mph). Changing the
test conditions would result in compromising the level of protection of
the occupants of the colliding vehicle.
C. Definition of Termination of Energy Absorption Test
TTMA wants us to include in the energy absorbed any rebound that
occurs more than one second after the force has been removed.
After the final rule was issued, we received a request for
interpretation on this subject from Mr. Robert S. Toms. He asked
whether the requirement that the energy absorption be accomplished by
[[Page 49139]]
plastic deformation would preclude the use of a material produced by
his company that returns to its original shape (i.e., elastic) very
slowly, on the order of approximately 24 hours. In summary, our
response to Mr. Toms stated that such slow-rebounding elastomeric
materials could be used if the guards equipped with them passed the
compliance test procedures.
Our August 4, 1998 response to Mr. Toms explained that the purposes
of the standard could be fulfilled using a guard with a slow-rebounding
elastomeric material. The requirement that guards absorb energy was
intended to ensure that guards were not too rigid during the onset of
force in a crash. The requirement that they absorb the energy by
plastic deformation was to ensure that the guard did not subsequently
return the absorbed energy to the colliding vehicle, because that
energy return could increase the risk of death or injury to the
occupants. Therefore, any rebound occurring after the crash event,
especially slow rebound such as is produced by guards using some slow-
acting elastomeric materials, would not, in the real world pose any
threat to passenger vehicle occupants. Therefore, for real world safety
purposes, the time frame within which a material must retain its
deformed shape to be considered ``plastic'' is the duration of a crash
event.
The relevant time period for compliance purposes, however, is
longer. Standard No. 223 employs a quasi-static test, not a dynamic
test, in testing for compliance with its requirements. We have no way
of determining whether a material would rebound within the time frame
of the crash. Therefore, if an elastomer reacts in such a way that it
passes the test procedure, it will have passed the requirements.
Identification of the end of the test is therefore critical in
determining whether a material will pass the test. The interpretation
defined the end of the test as follows:
A specific event determines when the test ends. The force
application/withdrawal portion of the test procedure is over as soon
as the guard no longer offers resistance to the force application
device. Since S6.6(c) is a list of steps to be performed, it is
reasonable to assume that once a certain step is completed, the next
step will be commenced. The step of reducing the force proceeds only
``until the guard no longer offers resistance.'' In practical terms,
the guard will generally cease to offer resistance when it loses
contact with the force application device. NHTSA has no way of
determining any small amount of residual force generated by your
elastomer after that point. A properly calibrated load cell (a
typical load measuring device) should register zero load, and the
force deflection trace should meet the abscissa of the graph upon
separation. After that happens, the test itself is completed and all
that remains is the computation of the amount of energy absorbed
using the area within the force deflection curve.
Therefore, while we generally agree with TTMA that the test should
end when the force has been reduced to zero, there is no need to wait
for one second to see if the guard re-connects with the test plate.
Ending the test immediately when the test plate separates from the
guard satisfies TTMA's concern. As explained in the interpretation
letter, there is adequate support for that procedure in the existing
regulatory text. The current language ``[r]educe the force until the
guard no longer offers resistance to the force application device''
sufficiently describes the completion of the test for purposes of
calculating the amount of energy that has been absorbed. We do not
believe any change to the text of the standard is necessary to define
the end of the test.
IV. Conclusion
For the reasons given above, we conclude that TTMA has not
justified the need for further rulemaking on this standard. TTMA has
not provided information demonstrating a need for a lower force
application rate. It is not practicable or objective for compliance
tests to end prematurely based on assumptions that we make about
particular guard designs or materials. And, while we agree that the
industry needs to understand precisely at what point the energy
absorption test ends, the existing regulatory language on this issue
has already been clarified through interpretation. We believe it is
sufficiently explicit.
In accordance with 49 CFR part 552, this completes the agency's
review of the petition. We have concluded that the TTMA has not
adequately documented problems with the current procedures. Based on
the available information, we believe that there is no reasonable
possibility that the actions requested by TTMA would be taken at the
conclusion of a rulemaking proceeding and that the problem alleged by
TTMA does not warrant the expenditure of agency resources to conduct a
rulemaking proceeding. Accordingly, we deny TTMA's petition.
Authority: 49 U.S.C. 30103, 30162; delegation of authority at 49
CFR 1.50 and 501.8.
Issued on: September 7, 1999.
L. Robert Shelton,
Associate Administrator for Safety Performance Standards.
[FR Doc. 99-23520 Filed 9-9-99; 8:45 am]
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