each one-third octave band as further discussed below. We expect sounds
produced by EVs and HVs will exceed the minimum one-third octave band
values in the final rule because manufacturers will design alert
systems in order to ensure a margin of compliance. For this reason, we
believe that vehicles complying with the final rule, the requirements
of which have been reduced by 4 dB in each one-third octave band from
the values provided by our revised detection model, will still emit
alert sounds that are loud enough for pedestrians to safely detect EVs
and HVs.
    During its research, NHTSA conducted a series of tests to determine
the actual level of variability in the one-third octave band
measurements.\153\ To do this, NHTSA analyzed data from a 2010 Ford
Focus, combining over 100 individual test runs recorded at the 10 km/h
test condition, including right and left side microphone recordings,
that were measured at three facilities (71 test runs at Transportation
Research Center in Marysville Ohio, 17 test runs at the Ford Motor
Company Proving Ground in Romeo, Michigan, and 16 test runs at the
Navistar test track in Fort Wayne, Indiana) over a period of 6 months.
Test data were considered valid if there were no anomalies apparent in
the sound recordings. The recorded files were analyzed using NHTSA's
sound analysis code.
---------------------------------------------------------------------------

    \153\ NHTSA Technical Report '' Repeatability, Reproducibility,
and Sameness of Quiet Vehicle Test Data'' (2016) Gerdus, E., Hoover,
R.L., and Garrott, W.R.
---------------------------------------------------------------------------

    The data from the test runs were further processed using a
bootstrap method \154\ into three datasets, consisting of 10,000 \155\
samples of eight randomly selected individual test runs, for each
facility. These samples were then processed into the one-third octave
bands utilizing the compliance procedure (the average of the first four
valid test runs within 2 dB), generating 10,000 sets of the 13 one-
third octave bands between 315 Hz and 5000 Hz. Analyzing the datasets
for the individual test sites, the maximum 95% confidence interval for
the individual one-third octave bands recorded on the TRC ISO sound pad
was 1.6 dB at 800 Hz and 1000 Hz. For the Ford MPG ISO test
pad, the maximum value for the 95% CI of the individual one-third
octave bands was 2.0 dB at 315 Hz, and at the Navistar ISO
pad it was 1.2 dB at 400 Hz. Looking at all three sites,
the overall effective maximum variation occurs in the 315 Hz one-third
octave band with a 95% CI of 2.5 dB. A summary of the
results is in Table 18.
---------------------------------------------------------------------------

    \154\ ``Bootstrap method'' is a statistical procedure wherein a
data set consisting of a relatively small set of measurements is
resampled many times over to obtain a much larger data set. This can
improve statistical estimates and confidence intervals. For example,
for the Ford Fusion tests on the TRC ISO sound pad at 10 km/h, NHTSA
ran twelve test series, each consisting of eight runs, for a total
of 96 runs. To improve our estimate of the variability in these 96
tests, we used a bootstrap method in which all of the 96 runs were
consolidated into one set. Single runs then were drawn randomly from
this set and the measurement values including one-third octave band
levels were recorded. The run drawn was then returned to the set.
This process was repeated thousands of times using the computational
capability of a computer. For the Fusion data, 80,000 runs
comprising 10,000 test series were drawn in this manner which made
it easy to directly determine the 95% confidence interval for these
vehicle tests. We used a similar procedure to evaluate vehicle
measurements from the Navistar and Ford MPG test facilities, to make
up three data sets (one from each of the three test facilities).
    \155\ The dataset size of 10,000 was selected to maximize the
overall accuracy of the analysis while maintaining a reasonable
total computation time.

                   Table 18--Comparison of Mean and 95% Confidence Limit for the One-Third Octave Frequencies for the Three Test Sites
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                        TRC                          Ford MPG                        Navistar
                                         ------------------------------------------------------------------------------------------------     Overall
                Frequency                                       95%                             95%                             95%        effective 95%
                                            Mean level      Confidence      Mean level      Confidence      Mean level      Confidence      confidence
                                          recorded dB(A)       limit      recorded dB(A)       limit      recorded dB(A)       limit           limit
--------------------------------------------------------------------------------------------------------------------------------------------------------
315.....................................            41.6             1.3            40.4             2.0            41.8             0.6             2.5
400.....................................            42.5             1.1            41.1             1.1            42.7             1.2             2.0
500.....................................            44.1             1.0            44.3             0.9            44.4             1.0             1.7

630.....................................            46.1             1.2            45.6             1.6            46.5             0.8             2.2
800.....................................            48.4             1.6            50.4             1.3            48.3             1.1             2.3
1000....................................            49.0             1.6            50.7             1.0            49.1             0.7             2.0
1250....................................            48.8             1.4            50.1             1.1            48.9             0.6             1.9
1600....................................            49.7             1.5            51.0             1.1            49.3             0.9             2.1
2000....................................            48.6             1.5            48.7             1.0            48.0             0.5             1.9
2500....................................            46.6             1.2            46.7             1.1            46.2             0.7             1.8
3150....................................            45.2             1.2            45.1             1.0            44.9             0.9             1.8
4000....................................            44.0             0.9            43.9             0.8            43.4             0.9             1.5
5000....................................            41.9             0.8            42.0             1.2            41.5             0.8             1.6
--------------------------------------------------------------------------------------------------------------------------------------------------------

    Furthermore, NHTSA conducted research into the effects of speaker
variability on one-third octave band repeatability using a limited
sample of vehicles. Testing was performed on a group of four model-year
2014 Toyota Prius V vehicles under stationary conditions, in a hemi-
anechoic chamber, with only the alert sound generator active to
minimize potential variability from other sources. This testing found
that when a single vehicle was tested in the chamber, run-to-run
variability had a 95 CI of 0.2 dB, operating with only the
speaker active. Overall speaker variability consists of more than just
the repeatability of any one individual speaker, as manufacturing
tolerances will add variability when multiple speakers are tested. To
estimate overall speaker variability, the agency analyzed the data
across all four Prius vehicles tested. When all four vehicles were
tested in the chamber, run-to-run variability increased to 0.8 dB.\156\
---------------------------------------------------------------------------

    \156\ See NHTSA Technical Report '' Repeatability,
Reproducibility, and Sameness of Quiet Vehicle Test Data'' (2016)
Gerdus, E., Hoover, R.L., and Garrott, W.R.
---------------------------------------------------------------------------

    Based upon the limited test data from this analysis, NHTSA
estimates an overall test variability of 3.3 dB, including
both the effective test procedure variability (2.5 dB) and
the measured speaker variability (0.8 dB). The commenters
indicated that the true variability is unknown and recommended that a 3
to 9 dB increase is appropriate. To account for other, unknown sources
of variability, the agency has decided to add an additional small
tolerance to the variability identified during its research.
Considering both the measured and the unknown variability, we have
concluded that a tolerance of 4 dB adequately accounts for actual test
variability.
    NHTSA agrees with Alliance/Global, as well as the other commenters
that manufacturers will take into account measurement variability when
designing alert systems to ensure compliance with the specified
performance requirements. It is possible that with this margin added,
the alert sound would significantly exceed the minimum sound
requirements. As such, NHTSA has decided in this final rule to reduce
the minimum levels that were indicated by our detectability modeling
effort. We are implementing a reduction of 4 dB in each one-third
octave band for all test conditions to offset the margin of compliance
that we acknowledge is needed to address test variability and that we
believe OEMs will build into their alert systems. As discussed above,
our repeatability analysis has shown that a 4 dB adjustment will be
adequate for this purpose.
    It must be made clear that the reduced minimum levels specified in
this final rule, which include the 4-dB adjustment described above, are
the absolute minimums allowed for safety purposes. Testing variability
is not a justification for failing to meet these minimums which have
been adjusted specifically to address concerns about test
repeatability. The agency intends to pursue potential enforcement
actions on measured levels below these minimum standards. The agency
believes that by virtue of this 4-dB reduction in the level specified
in each one-third octave band, manufacturers can build a reasonable
margin of compliance into their alert systems while maintaining
acceptable overall sound levels. We also believe this reduction, along
with other changes in the final rule compared to the NPRM such as the
reduction in the number of required one-third octave bands, further
addresses concerns about customer acceptance, noise intrusion, and
other concerns about the safety standard requiring alert sounds that
are excessively loud.
Ambient Noise Correction
    In the NPRM, NHTSA proposed that the ambient noise be measured for
at least 30 seconds before and after a series of vehicle tests. A 10-
second sample was then to be taken from these measurements and used to
determine both the overall ambient noise SPL and the ambient noise
level for each one-third octave band. The 10-second sample selected was
to include ambient levels that were representative of the ambient
levels that occurred during the actual vehicle measurement. As
explained in the NPRM, it is important to know the background noise
level during the test to get an accurate measurement of the sound made
by the vehicle alone. Because NHTSA's proposed requirements were
established using a one-third octave band basis, we stated that ambient
corrections should also be calculated on a one-third octave band basis.
    The NPRM explained that SAE J2889-1 contains a procedure for
correcting vehicle measurements at the overall sound pressure level to
account for ambient influence. In the NPRM, we also acknowledged that
the variance of a signal is greater on a one-third octave band basis
than at the overall level, and thus it may be difficult to apply the
ambient correction procedure in SAE J2889-1 to one-third octave bands.
The NPRM further stated that SAE J2889-1 requires a peak-to-peak
variation of less than 2 dB in order to do a valid correction. We also
pointed out that, even if the fluctuation of the overall sound pressure
level of the ambient is less than 2 dB, the fluctuation in some
individual one-third octave bands would likely be higher. To address
this concern, we proposed a procedure that

allowed one-third octave band correction within certain limits on both
the peak-to-peak ambient fluctuation and the level difference between
the vehicle measurement and the ambient. These criteria were provided
in Table 6 in the regulatory text contained in the NPRM. They were
chosen in order to provide a high degree of confidence that
contamination due to an unobserved, random fluctuation would not impact
the final reported level by more than about one half of one decibel. In
the NPRM, we explained that increasing the acceptable peak-to-peak
variability in the ambient correction procedure will allow for testing
to be conducted in ambient sound environments in which the agency would
expect to be able to make accurate measurements. NHTSA conveyed its
position that this approach would increase flexibility in the locations
and times when outdoor testing can be conducted without significantly
compromising the accuracy of measurements. We sought comment on this
topic.
    NHTSA received comments on ambient noise correction from Alliance/
Global, Honda, OICA and SAE. The comments from these organizations on
this topic have been divided into three issues: Validity of applying
ambient correction to one-third octave bands; a conflict in the
correction procedure; and ambient measurement time interval.
    All commenters stated that measured one-third octave band sound
levels generated by the vehicle could not be corrected for ambient
noise while maintaining adequate repeatability. As stated by Honda
``[t]he time-to-time variance of the one-third octave level of ambient
noise is large and the ambient noise measurement and vehicle noise
measurement are not simultaneous so that compensating by one-third
octave level is not realistic for achieving repeatability.'' All four
organizations therefore recommended only performing ambient noise
correction for the measured overall SPL generated by the vehicle using
the procedures contained in SAE J2889-1.
    OICA questioned the proposed procedure to correct the measured one-
third octave band sound levels generated by the vehicle for ambient
noise. They pointed out that the proposed procedure contains a
contradiction. It requires measurement of both the sounds generated by
the test vehicle during a test and of the ambient noise at the same
time and using the same equipment. The problem is that sound
measurement during testing records both sounds generated by the vehicle
(signal) and ambient noise. There is no objective method to disentangle
the signal from the ambient noise in the recorded signal.
    Finally, OICA questioned which 10 seconds should be analyzed out of
each 30-second-long ambient noise measurement since NHTSA did not
specify which 10 seconds.
Agency Response to Comments
    NHTSA believes, based upon data collected and testing experience
gained over the past several years, that measured one-third octave band
sound levels generated by a vehicle can be corrected for ambient noise
while maintaining adequate repeatability.
    NHTSA conducted a substantial amount of vehicle sound measurement
repeatability testing using a 2010 Ford Fusion (with an internal
combustion engine) to develop this rule.\157\ That testing included a
large number of ambient noise measurements. Testing was performed on
the ISO sound pad of the Transportation Research Center, Inc. in East
Liberty, Ohio, and was analyzed to examine ambient noise variability.
All of this testing was performed at night to minimize the ambient
noise.
---------------------------------------------------------------------------

    \157\ Garrott, W.R., Hoover, R.L., Evans, L.R., Gerdus, E., and
Harris, J.R., ``2012 Quieter Vehicle Testing Report: Measured Sound
Levels for Electric, Hybrid Electric, and Low Speed Vehicles''
Washington DC, DOT/NHTSA, November 2016.
---------------------------------------------------------------------------

    Analyses of NHTSA's measured ambient sound data found substantial
variability. The overall ambient SPL varied over a 15.9 dB range from a
low of 29.5 dB to a high of 45.4 dB. The ambient one-third octave band
levels varied over a 24.4 dB range with a low of 13.6 dB and a high of
38.0 dB.\158\ This ambient sound data was measured over a six month
period from April to September of 2012.
---------------------------------------------------------------------------

    \158\ Ibid.
---------------------------------------------------------------------------

    NHTSA's calculations indicate that these large variations in
ambient noise levels had only a minimal effect on the measured one-
third octave band sound levels generated by the vehicle following
ambient noise correction.
    As per the procedure proposed in the NPRM, any sound generated by
the vehicle at the one-third octave band level (and per SAE J2889-1 for
the overall SPL) will not be corrected at all if it is more than 10 dB
above the ambient noise level. NHTSA examined its vehicle sound
measurement repeatability testing to see how frequently this situation
occurred.
    NHTSA analyzed MY2010 Ford Fusion sound data measurement
repeatability for five scenarios: Stationary, reverse, 10 km/h pass-by
test, 20 km/h pass-by test, and 30 km/h pass-by test. The vehicle was
quietest during the stationary and reverse scenarios.
    None of the Ford Fusion sound data collected during the 10 km/h
pass-by test, 20 km/h pass-by test, or 30 km/h pass-by test were within
10 dB of ambient levels. Therefore, no ambient noise correction was
performed for any of these tests at the overall SPL and one-third
octave band level.
    For the stationary scenario, 82.3 percent of tests were more than
10 dB above ambient noise levels and did not require correction. The
remaining 17.7 percent of tests needed to have either the overall SPL
or one or more measured one-third octave band levels corrected.
However, none of these tests had measured signal levels that were less
than 3 dB above ambient noise levels (the differential below which
tests are considered invalid).
    Electric or hybrid vehicles with an alert meeting the requirements
of this rule may be quieter than is the 2010 Ford Fusion. This may
result in more electric and hybrid vehicle sound tests not giving
results that are 10 dB or more above ambient. Nevertheless, NHTSA
believes that the effects of ambient level variability on vehicle sound
measurement repeatability will be limited.
    The purpose of ambient noise correction is to reduce variability in
vehicle sound measurements due to variations in the ambient noise
level. NHTSA uses the minimum ambient noise levels, collected before
and after a test series, for ambient correction. By doing so, the
ambient noise levels are expected to vary little with time during a
test session. Distinct, transient loud sounds such as chirping birds,
overhead planes, car doors being slammed, etc., will affect the maximum
ambient noise levels but not the minimum ambient noise levels. The
minimum ambient noise levels are expected to be primarily the result of
more slowly varying environmental factors such as steady state wind
speed, the test site geometry, and the foliage on nearby vegetation.
Therefore, NHTSA believes that the minimum ambient noise levels used
for correction will typically be similar before, during, and after a
test series. The ambient noise correction is expected to eliminate the
effects of this slowly varying ambient noise from the measured sound
levels for a vehicle.
    NHTSA also recognizes that distinct, louder events such as passing
vehicles or wind gusts could, if they were to occur at certain times
during a vehicle's operational sound measurement, increase both the
measured vehicle sound and sound measurement variability. Therefore,
NHTSA has

added regulatory text in the final rule stating that measurements
containing any distinct, transient, loud sounds (e.g., chirping birds,
overhead planes, passing trains, car doors being slammed, etc.) are
considered invalid. Further discussion about determining the validity
of vehicle measurements can be found in Section III.K.
    In September 2014, the agency received a copy of the latest draft
of ISO 16254, Acoustics--Measurement of sound emitted by road
vehicles,\159\ and in December 2014 SAE issued a revised version of SAE
J2889-1.\160\ Both standards are of interest to the agency because,
unlike the May 2012 version of SAE J2889-1, they both attempt to
address measurements at the one-third octave band level as well as
overall SPL level. These standards appear to agree with the various
comments, including the comments received from SAE, advising against
ambient corrections at the one-third octave band level. Both standards
specifically state, ``Background compensation is not permitted for one-
third octave band measurements.'' Both standards also specify that when
analyzing the one-third octave band measurements the level of
background noise in each one-third octave band of interest shall be at
least 6dB below the measurement of the vehicle under test in each
respective one-third octave band. In effect, both standards state that
the one-third octave bands cannot be corrected for ambient noise and
that the only one-third octave bands useful for evaluation are those
bands found to have at least a 6 dB difference between the vehicle
measured value and the ambient measured value.
---------------------------------------------------------------------------

    \159\ NHTSA-2011-0148-0334.
    \160\ In December 2014, SAE issued a revised SAE J2889-1. That
version of J2889-1 contains the same proscription on background
correction at the one-third octave band level as does ISO 16254.
---------------------------------------------------------------------------

    The NPRM proposed that no corrections are needed at the one-third
octave band level when there is at least a 10 dB difference between the
vehicle measured value and the ambient measured value. The ISO and SAE
standards reduce this cut-off point for one-third octave band levels to
a 6 dB difference. Based upon the earlier discussion of test data, our
experience has been that very few ambient corrections are required at
the 10 dB difference level. Even fewer would be required at the 6dB
difference level, which has the potential to reduce the number of test
runs needed for a vehicle compliance evaluation. We agree with the
commenters that one-third octave bands are not viable if they are
within 3 dB of the ambient, and thus it is not necessary to consider
whether bands at that difference level should be corrected or not.
    Accordingly, we have decided to revise the required difference
between the vehicle and ambient at the one-third octave band level from
10dB as proposed in the NPRM to 6 dB, the same as in the draft ISO and
revised SAE standards, as the threshold difference between when one-
third octave bands should or should not be corrected for ambient
conditions. Additionally, for the one-third octave bands having 3 dB to
6 dB separation between the vehicle and ambient measurements, the
agency has decided to continue to correct as proposed in the NPRM. The
draft ISO and SAE standards reject all the one-third octave bands with
separation less than 6dB whereas now the agency's procedure considers
them usable in an attempt to reduce possible test burden by rejecting
fewer sound measurements. Finally, as proposed in the NPRM, any bands
found to have a separation of less than 3 dB would be considered
unusable. These revisions have been incorporated into the respective
tables in the final rule.
    Finally, based upon further consideration of the comments received,
evaluation of the ambient data collected, and review of the latest ISO
and SAE documents received, we have decided to make a few additional
revisions to the ambient correction paragraph S6.7 in the final rule.
These additional revisions to S6.7 are as follows:
     Ambient corrections may be required at the overall sound
pressure level when considering which four valid test runs can be used
for performance evaulation during each operating scenario. Ambient
corrections at the one-third octave band level may also be required
during the one-third octave band evaluations for each operating
scenario. For clarification purposes Table 6 as proposed in the NPRM
will be replaced with two new tables, Tables 6 and 7, one for overall
SPL corrections and one for one-third octave band corrections when
required. As in the NPRM, both of these tables are derived from Table 2
in SAE J2889-1.
     The first column in Table 2 of SAE J2889-1 and Table 6 in
the NPRM differentiate between ambient noise levels greater than or
less than 25 dB. We do not believe this differentiation is required.
Table 2 in SAE J2889-1 applies to overall SPL correction. NHTSA
understands that SAE J2889-1 included the 25 dB breakpoint to separate
overall SPL correction because an ambient noise of less than 25 dB in
an outdoor setting is extremely quiet and unlikely to occur. If such a
low ambient did occur, then the overall vehicle SPL would require
correction only if it was within 10 dB of the ambient noise, i.e., if
the overall SPL of the vehicle test was quieter than 35 dB. However,
any vehicle that produces an overall SPL of less than 35 dB is very
quiet and most likely would not comply with the requirements of this
final rule or be heard by pedestrians. SAE J2889-1 states that in this
situation, no overall SPL correction should be made. Instead, the
technician conducting the test should report that the corrected overall
SPL will be less than the measured signal overall SPL. NHTSA desires to
correct both overall SPL and one-third octave band levels when
necessary. Since overall SPL is the antilog of the logarithmic sum of
all one-third octave band levels, the one-third octave band levels
will, for any wide-band sound, be substantially lower than overall SPL.
During NHTSA's outdoor testing, we have never seen an ambient overall
SPL that is below 25 dB. However, we routinely have seen ambient one-
third octave band levels below 25 dB, with some being as low as 14 dB.
Furthermore, for some scenarios and one-third octave bands, NHTSA's
minimum safety standard criteria are set at a level below 35 dB. NHTSA
needs a robust correction procedure that is applicable when one-third
octave band ambient levels are below 35 dB. If ambient is less than 25
dB in one or more one-third octave bands and the difference between
ambient and vehicle measurements in those bands is less than 6 dB, we
still need a way to make corrections. Therefore, NHTSA has decided to
use the ambient noise correction procedure regardless of the level of
ambient noise present. To accomplish this, we have removed the 25 dB
limitation by deleting the first column and the last two rows from both
tables.
     The second column in Table 6 of the NPRM and Table 2 of
SAE J2889-1 sets peak-to-peak limits on the variability of measured
ambient conditions relative to the corresponding differences measured
between the vehicle alert sound profile and the measured ambient sound
levels. According to the tables, the larger that difference, the larger
the acceptable ambient peak-to-peak variation. OICA mentioned that the
proposed procedure for ambient noise correction was confusing and
contained a contradiction. According to OICA, the notes to NPRM Table 6
indicated that in some test scenarios the ambient noise levels must be
measured at the same

time as the actual vehicle, i.e., during the vehicle pass-by run, and
using the same microphones. The NPRM did not state how this should be
done. We have considered OICA's comment and agree that the notes in
conjunction with the proposed Table 6 are confusing and contradictory.
Ambient measurements during actual vehicle tests are not possible
without subjective determination as to what sounds are ambient noise
versus what are generated by the test vehicle. NHTSA does not intend to
measure ambient and vehicle sounds at the same time through the same
microphones. The purpose of column 2 is to ensure the validity and
minimum variability of ambient sound files collected just prior to and
after vehicle tests. The objective is to avoid ambient sound
measurements that contain any distinct, transient, sounds (e.g.,
chirping birds, overhead planes, car doors being slammed, etc.) for
correcting vehicle sound files. We understand that column 2 is intended
to provide a quantitative method for determining when distinct,
transient, sounds are too loud and risk causing excessive variability
in ambient sound measurements. Clearly, a high variability in ambient
sound can have a compounding effect on vehicle sound pressure
variability. Such variability could have a major impact on measurement
repeatability. Due to ambient differences, test results from one day to
another for the same vehicle might not be the same. To minimize the
likelihood of ambient variability, the agency has decided, as
originally proposed in the NPRM, to use the minimum ambient level
instead of the maximum ambient level. Use of the minimum ambient was
discussed in more detail previously in this section. Furthermore,
variability of the ambient sounds measured during any vehicle test may
also cause difficulties in capturing the true vehicle alert profile. To
address OICA's issue we have deleted the entire second column and the
associated notes from NPRM Table 6. We have also added regulatory text
stating that measurements containing any distinct, transient, loud
sounds (e.g., chirping birds, overhead planes, car doors being slammed,
etc.) are considered invalid.
     The entries in some cells in Column 4 of NPRM Table 6 and
Table 2 of SAE J2889-1 are confusing. It is not clear what an entry of
``Do not correct, but report OBLtestcorr,j <
OBLtest,j'' means in the context of a NHTSA compliance test.
Since, as previously discussed, the last two rows of NPRM Table 6 have
been deleted, the entry of ``Do not correct, but report
OBLtestcorr,j < OBLtest,j'' appears in
only one cell of the table. The row containing this cell will only be
used when the separation between the measured vehicle sound (signal)
and the ambient (either overall SPL or one-third octave band level as
appropriate) is less than or equal to 3 dB. NHTSA believes that a
signal- to-ambient difference of 3 dB or less is too small to ensure
the ambient is not influencing the measurement. Therefore, test runs
performed for which the overall measured SPL does not exceed the
ambient measured SPL by more than 3.0 dB should be considered not valid
and should not be used. For test runs for which the overall measured
SPL exceeds the ambient measured SPL by more than 3.0 dB, it is
possible that the measured sound level may not exceed the ambient sound
level in one or more one-third octaves. When this happens, it is
acceptable to use the data from the one-third octave bands for which
the measured sound levels exceeded the ambient sound levels by more
than 3.0 dB. However, the data for those particular one-third octave
bands for which the measured sound level was too close to the ambient
sound are considered not valid and cannot be used.
    Appropriate modifications also have been made to paragraph S6.7 of
the regulatory text, describing how to perform ambient noise
corrections.
    These decisions are clarifications and refinements that are needed
for consistent compliance testing. Because they address practical
issues that arise from application of the ambient correction procedures
of the NPRM, which in turn are based as closely as possible on SAE
J2889-1, we believe these changes are within the scope of the NPRM. In
one case, we deleted a specification that doesn't apply to NHTSA
testing and thus is not relevant for this final rule. Another change
clears up confusion arising from a contradiction in the ambient
correction table as it appeared in the NPRM. Another arises from the
agency's decision to do ambient corrections at the one-third octave
band level which the agency explicitly proposed in the NPRM (some
commenters disagreed with that approach, and we have addressed those
comments in this preamble.)
    Overall, these technical changes are consistent with the SEA/ISO
standard which the agency has referenced in the NPRM and which
commenters urged NHTSA to adhere to. Furthermore, as we've noted, these
refinements in the ambient correction procedure will have a very
minimal impact on the outcomes of a small minority of tests, and they
do not constitute any greater test stringency or an increase in the
required sound levels over those proposed in the NPRM.
    In response to OICA's question as to which 10 seconds should be
analyzed out of each 30 seconds (or more), NHTSA has decided that the
entire ambient noise measurement (including an interval of 30 seconds
or more taken before a test series and another interval of 30 seconds
or more taken after a test series) should be analyzed. Since ambient
noise correction is based upon the minimum ambient noise collected
before and after a test series, analyzing the entire period collected
instead of two 10-second periods may result in a lower minimum ambient
noise. Having a lower minimum ambient noise makes it less likely that
ambient noise correction of the measured vehicle sound will be
necessary. In the event that ambient noise correction is necessary,
having a lower minimum ambient noise reduces the magnitude of the
resulting correction resulting in a slightly easier compliance pass/
fail criterion.
    It is NHTSA's belief that making this change to the ambient noise
correction procedures will have no effect on safety because NHTSA
intends to perform compliance testing on ISO sound pads during times
with as low an ambient noise as is reasonably achievable. This will
minimize the need for ambient noise corrections during NHTSA compliance
testing.
Conditions for Discarding Results
    The NPRM discussed the agency's approach for measuring the sound
produced by hybrid vehicles (HVs) without their associated internal
combustion engines (ICEs) operating because of the need to measure the
sound of those vehicles' in their quietest state. As explained, the
proposal was designed to ensure that HVs and EVs emit a minimum level
of sound in situations in which the vehicle is operating in electric
mode because in that mode these vehicles do not provide sufficient
sound cues for pedestrians. Therefore, we proposed to control the
situation in which an ICE engine does start operating during a test by
invalidating test measurements that are taken when a vehicle's ICE is
operating. The proposed test procedure stated that when testing an HV
with an ICE that runs intermittently, measurements that contain sounds
emitted by the ICE are not considered valid.
    The NPRM also discussed that tests occurring within the temperature
range specified in SAE J2889-1 can produce

divergent results when a vehicle is tested at different temperatures.
In high ambient temperatures, the battery cooling fan, part of the
thermal management system on electric vehicles, can activate
intermittently while the vehicle is operating. As discussed, the agency
decided to address the issue of intermittent vehicle sound caused by
the vehicle's battery cooling fan by requiring that any vehicle sound
measurements taken while the cooling fan is operating be discarded.
While the agency believed that this would address repeatability issues
caused by battery cooling fans, we noted that there may be other
vehicle functions that produce inconsistent sound levels as a result of
the ambient temperature. The agency tentatively concluded that we had
sufficiently controlled this situation in the test procedure by
invalidating measurements in which any component of the vehicle's
thermal management system (i.e. a cooling pump or fan) is engaged. We
solicited comments on other vehicle functions that produce varying
noise levels at different ambient temperatures.
    Furthermore, to ensure the goal of testing the vehicle in its
quietest state, the NPRM specified the vehicle test condition that all
accessory equipment on the vehicle should be turned off. This step was
included because the vehicle's air conditioning system, heating system,
and windshield wipers, for example, can all produce sound when
activated which can introduce inconsistency into the acoustic
measurements.
    The NPRM went on to explain that for all operating conditions, the
proposed test procedure (and that of SAE J2889-1) specified that four
consecutive valid measurements be within 2 dB(A). This repetition and
decibel level restriction are to ensure repeatability of vehicle sounds
without the presence of unwanted ambient spikes, other non-vehicle
sounds, or intermittent sounds the vehicle may happen to make that are
not associated with its quiet operating state.
    As explained in the NPRM, the agency has no preference in how
manufacturers choose to comply with the minimum sound level
requirements in this standard. If the agency could rely on battery
cooling fans on electric vehicles or the ICEs on hybrid vehicles to be
activated whenever the vehicle is turned on or is moving, this may be a
satisfactory manner for a manufacturer to comply with the minimum sound
level requirements. However, if the battery cooling fans and the ICEs
on hybrid-electrics are only running intermittently, then sounds
produced by these vehicle systems cannot be relied upon to provide
sound to pedestrians for safety purposes under all conditions. While
the proposed specifications requiring four valid measurements within 2
dB(A) would to some extent address repeatability issues caused by
intermittent vehicle noise, the agency explained that it wanted to
guard against a situation in which measurements are accepted with the
battery cooling fans active on an EV or the ICE engaged on a hybrid-
electric if those noise sources are intermittently engaged.
    The agency also acknowledged, as discussed in the NPRM, that it may
be possible that not all the HVs to which this proposal would apply are
designed to be operated in EV-only mode for every operating condition
for which the safety standard would specify requirements. Because the
agency would be testing HVs in their quietest state, the test procedure
and requirements as proposed were not designed to test a vehicle that
produces added sound while its ICE is operating. Therefore, the agency
stated it would not require that HVs meet the requirements of the
proposal for a given operating condition if they are not capable of
operating in electric-only mode in that operating condition. For
example, if a vehicle is not designed to operate in electric-only mode
above 25 km/h, it would not be required to meet the requirements in the
proposal at any speed above that (e.g. at 30 km/h). The NPRM also
included a provision to exclude an HV from meeting the minimum sound
requirement for a given operating condition after ten consecutive tests
during which the vehicle's ICE is operating during the entire test.
    In response to the NPRM and the issue of invalid test results,
OICA, Alliance/Global, Nissan, SAE and Advocates provided comments.
    OICA recommended discarding any measurements that are influenced by
the presence of vehicle functions that produce intermittent sounds.
According to OICA, intermittent sound sources include cooling fans and
pumps, and air conditioning components. OICA said that turning off the
A/C and minimizing powertrain operation before executing a test will
reduce the incursion of these sounds. OICA explained that ``experienced
engineers must know what is truly an intermittent sound for a specific
vehicle, and what is part of the normal vehicle emitted sound.'' OICA
also asked the question about how the regulation will handle a vehicle
whose thermal management system is always operational.
    The comments received from Alliance/Global were similar to those
provided by OICA. These commenters recommended that the agency clarify
for testing purposes that all auxiliary equipment capable of being shut
off actually is shut off as part of the test procedure. Alliance/Global
along with OICA provided several suggested regulatory text edits to
address their related concerns.
    Nissan stated that given the complexity of EV and HEV technology
and the expectation for future system innovation, it believes that OEMs
would need to identify potential vehicle systems and components which
could contribute to the overall noise measurement on a model-by-model
basis.
    SAE explained that the 2dB criteria was included in the SAE and ISO
standards as a data quality check and was designed to provide some
objective criteria to assist the user of the standard to know when
unrelated transient sounds are likely to have occurred. SAE said that
engineering judgment by an experienced test engineer is still required
to determine when other unrelated sounds have occurred, and a decision
to invalidate a measurement must be made. SAE noted that there may be
certain accessories that cannot be turned off. When tested, those
accessories should be in the lowest noise emission mode. SAE referred
to paragraphs <IP_ADDRESS> and <IP_ADDRESS> in SAE J2889-1 May 2012 which further
defines accessory loads and multi-mode operation.
    Advocates for Highway Safety commented that the requirements should
prohibit use of any test results which include sounds from any vehicle
systems other than those which would be constantly engaged under the
specified test conditions (backing, active but stationary, forward
motion).
Agency Response to Comments
    The agency has considered the comments received and the suggested
changes to the regulatory text. Based on review of the comments, NHTSA
finds general agreement with the agency's overall approach for
identification of valid and invalid test runs. The goal is to identify
and utilize those test runs that exhibit a vehicle's quietest operating
mode. In consideration of Nissan's comments about the complexity of EV/
HV technology, the agency anticipates that there will be a need to
inquire about specific noise-generating technologies and systems
utilized on test vehicles prior to

conducting FMVSS No. 141compliance testing. We note that NHTSA uses
this approach to enforce other safety standards. For example, in FMVSS
No. 126; Electronic Stability Control Systems, there is a requirement
for the vehicle manufacturer to make available technical documentation
about the ESC understeer countermeasures. Similarly, in FMVSS No. 226,
Ejection Mitigation, there is a requirement for the vehicle
manufacturer to make technical information about rollover sensing
systems available to NHTSA. With this information, the agency can
identify which systems produce noise continuously rather than
intermittently. Once this is established, test runs that include sounds
from intermittent ICE operations and/or intermittent thermal management
system activations can and will be deemed invalid.
    Advocates recommended modifying the language to ``prohibit use of
any test results which include sounds from any vehicle systems other
than those which would be constantly engaged under the specified
performance conditions (backing, active but stationary, forward motion
up to 18 mph).'' During testing, all accessory equipment that can be
physically turned off will be turned off. OICA asked about a thermal
management system that is operational at all times. To address that,
systems and accessories that cannot be turned off will be operated in
their quietest mode. As mentioned by SAE, the agency agrees that
engineering judgment by an experienced test engineer will be required
to determine when other unrelated sounds have occurred, and a decision
to invalidate a measurement must be made.
    In consideration of the comments received and associated changes to
the regulatory text that were suggested, the agency has decided to
revise the regulatory text in the final rule accordingly.
    The NPRM regulatory text addressed situations where the ICE
``remains active for the entire duration of the test,'' but we also
need to be concerned with an ICE or thermal management system that
operates intermittently. If any of these three conditions occur during
ten consecutive tests the vehicle is not required to meet the
applicable requirements. The agency has considered the total number of
tests that may have to be executed to acquire the necessary four valid
tests and has decided to include an absolute number of tests that must
be attempted before the test sequence can be terminated.
    The NPRM regulatory text did not specifically state that all
accessories that can be physically shut off should be shut off during
testing. That text has been added to the final rule.
Calculation of Results
    The NPRM explained that the proposed compliance test procedure was
consistent with the Society of Automotive Engineers Surface Vehicle
Standard J2889-1, ``Measurement of Minimum Noise Emitted by Road
Vehicles,'' September 2011,\161\ and that several sections of the SAE
standard were incorporated by reference into the proposed FMVSS
regulatory text. The agency further discussed that for all pass-by
operating conditions, the proposed test procedure (and that of SAE
J2889-1) specified that at least four valid test trials must be
completed while recording corresponding acoustic sound measurements for
each operating condition, and upon completion of testing the first four
valid trials with an overall SPL within 2 dB(A) of each other would be
chosen for analysis. We explained that this repetition and decibel
level restriction were to ensure repeatability of vehicle sound
measurements without unwanted ambient disturbances, other non-vehicle
sounds, or intermittent sounds the vehicle may happen to make that are
not associated with its operating mode.
---------------------------------------------------------------------------

    \161\ The agency recognized that SAE had published an updated
version of J2889-1 in May 2012. At that time we had not yet
evaluated the new version, but said we intended to do so before
publishing a final rule.
---------------------------------------------------------------------------

    The proposed rule required that for each pass-by test, the sound
emitted by the vehicle at the specified speed be recorded throughout
the measurement zone specified in S6.4. The regulatory text
specifically stated in S7.3(a), ``The test result shall be the lowest
value (average of the two microphones) of the four valid pass-bys. The
test result shall be reported to the first significant digit after the
decimal place.'' The proposed regulatory text also stated in S7.3(b),
``The test result shall be corrected for the ambient sound level in
each one-third octave band according to the procedure in S6.7 and the
correction criteria given in Table 6 and reported to the first
significant digit after the decimal place.''
    The NPRM also explained that to ensure measurements can be
duplicated repeatably on the same vehicle at one facility or at
different facilities, the instruments used to make the acoustical
measurements should meet the requirements of paragraph 5.1 of SAE
J2889-1. Since the filter roll-off rates used affect the results of the
acoustic measurements at the one-third octave band level, the NPRM
explained that SAE J2889-1 requires conformance with ANSI S1.11. ANSI
S1.11 specifies a wide range for filter roll-off rates, and these
rates, if selected at the upper and lower extremes of the range, could
produce different results. The agency sought comment on whether the
test procedure should specify a maximum roll-off rate that is finite.
    The agency also considered in the NPRM whether the procedures for
analyzing the frequency spectrum in SAE J2889-1 were sufficient to
ensure that the results of the acoustic measurements were recorded in a
consistent manner. The agency asked additional questions about which
filter roll-off rates have been used, if the one-third octave band
analysis should be done in the frequency domain or in the time domain,
and if an exponential window should be used when conducting the
frequency analysis.
    Several organizations including Alliance/Global (combined comment),
SAE, OICA, NFB, Honda, and Toyota submitted comments regarding the need
to clarify the procedures for processing the acoustic measurements used
to determine vehicle compliance.
    Alliance/Global stated that the NPRM was ambiguous as to what SPLs
should be reported when four sets of measurements are made with two
microphones. They suggested that the agency proposal was not clear if
side-to-side measurements are to be averaged with the lower of the four
measurements reported or if each side's four measurements are to be
averaged and the lower measurement reported. Alliance/Global also
stated that they do not agree with the use of the SAE J2889-1 ambient
background correction procedures when applied to one-third octave band
measurements as proposed because it differs from the ISO/SAE procedures
which recommends correcting for ambient background only at the overall
SPL level, not at the one-third octave band level. According to the
Alliance/Global, its members said that they support the test procedures
as specified in SAE J2889-1.
    SAE commented that, ``Section S7.3(a) proposed text is unclear.''
SAE explained that the four measurement runs are to be averaged
independently per side, and then the lower of the two sides is chosen
to be the intermediate or final result, as applicable, in accordance
with SAE J2889-1. The NFB supported the SAE comments on the proper
measurement procedure. OICA said that the overall SPL values should be
averaged per side and that the reported final result is from the
vehicle side with the lower average overall SPL level.
    Toyota stated, as mentioned in the Alliance/Global joint comment,
that the

measurement procedure in the NPRM introduces significant variability
within the results and that a more appropriate measurement procedure
would be that which is specified by SAE J2889-1. Honda stated that it
supports the principle of taking four measurements, averaging the lower
values from each side, and reporting the calculated value, per SAE
J2889-1.
    In regards to roll-off filter selection for post processing
acoustic files, Alliance/Global supported the use of ANSI S1.11-2004
Class 1 one-third octave filters as specified in SAE J2889-1. While
they acknowledged the agency's concern regarding filter roll-off rates,
they stated that the roll-off rate has a very small impact on the one-
third octave results (approximately 0.15 dB). Honda also voiced
concerns regarding filter roll-off rates, in that specifying a maximum
and sub-infinite roll-off rate in this test procedure would represent a
change to the general standard of one-third octave analysis already
commonly used by automakers. Honda stated that this change would create
an extra testing burden and would require additional time for
development of the appropriate test instruments and test procedures.
Agency Response to Comments
    It has been the agency's intention to follow the SAE J2889-1 \162\
test procedures, when feasible and consistent with the agency's focus
on safety. As discussed in the NPRM and in this final rule, the agency
has decided to evaluate HVs and EVs for detectability and recognition
at the one-third octave band level rather than at the overall sound
pressure level. To do this, the agency will follow the procedures
specified in SAE J2889-1 for: (1) Obtaining the ambient sound files
both before and after execution of a series of test trials; (2)
measuring the sound profiles for each of the first four valid test
trials as appropriate for each test condition; and (3) determining
which recorded sound files to use for the one-third octave band
evaluation. It should be noted that the agency's final rule test
procedure augments SAE J2889-1 by specifying how exactly the selected
acoustic measurements will be corrected for ambient conditions and
evaluated at the one-third octave band level, which is a critical step
in the compliance test procedure and one that is not fully detailed in
SAE J2889-1.
---------------------------------------------------------------------------

    \162\ In the NPRM the agency officially referenced SAE Standard
J2889-1, dated September 2011, and noted that SAE had published an
updated version of J2889-1 in May 2012 but that we had not evaluated
that later version and intended to do so before publishing the final
rule. In the May 2012 version, SAE added testing protocols for
vehicle commencing motion sound and for frequency shift
measurements, neither of which the agency has decided to utilize as
discussed in this final rule. The May 2012 version also included
paragraph updates and re-numbering. In December 2014, SAE issued
another revision to J2889-1. In the final rule we have decided to
update the official reference for the SAE J2889-1 standard from the
September 2011 version to the December 2014 version and have updated
references throughout the FMVSS No. 141 standard accordingly. A
number of OEMs, including some of those that commented on the FMVSS
No. 141 NPRM, are parties to the SAE committee that created J2889-1,
and they presumably had a hand in subsequent updates. The agency has
decided to use the Dec. 2014 version since that is the most up-to-
date and since the older versions seemed to leave open some
important technical details that are addressed to some extent in the
latest version. Safety groups and other non-industry commenters did
not address SAE recommended practices, so we assume they are
indifferent about which version of the SAE standard is referenced in
this final rule.
---------------------------------------------------------------------------

    All of the commenters indicated that the agency's proposed ambient
correction and test procedure, S6.7 and S7, do not exactly follow the
procedures in SAE J2889-1. SAE specifically said that our proposed
regulatory text was unclear, and the Alliance/Global stated our
proposed text was ambiguous. More specifically, the commenters noted
that the proposed regulatory text specified that, for each of the four
consecutive valid test runs collected during the pass-by tests, the
left and right microphone files are averaged together and then the one
run with the lowest overall SPL value was used to evaluate the one-
third octaves to determine compliance. On the other hand, the
commenters noted that SAE J2889-1 clearly requires that the four data
files recorded on the left side of the test vehicle are averaged, and
the four data files recorded on the right side of the vehicle are
averaged, and then the side of the vehicle with the lowest average
overall SPL value should be selected to evaluate the one-third octave
bands for compliance.
    The agency has evaluated these comments and has further scrutinized
the proposed text and the procedure specified in SAE J2889-1. We have
decided that the regulatory text as proposed did not match that in SAE
J2889-1 and agree that the text should be unambiguous. We note that the
agency's intent has been to follow SAE J2889-1 as closely as possible
but to expand and add the necessary details not currently specified in
SAE J2889-1 for the final evaluation of the one-third octave bands.
    We further considered how the recorded acoustic data files should
be evaluated, and we have concluded that averaging the data files on
each side of the test vehicle separately as required in J2889-1
provides the most realistic results. During a pass-by scenario, a
pedestrian listening to a vehicle driving by will be positioned on
either the left or right side of the vehicle. Since the pedestrian will
be on one side of the vehicle or the other as it passes, the SAE J2889-
1 procedures appropriately select the side of the vehicle that is found
to be the quietest during the test runs. Taking an average that
includes sound from both the left and right microphones as specified in
the NPRM would not provide an accurate representation of what any
pedestrian would hear. Therefore, the regulatory text has been revised
to agree with the SAE standard.
    As mentioned previously, Alliance/Global suggested that the
proposed regulatory text was ambiguous in regards to the steps involved
in analyzing vehicle acoustic measurements. Upon closer examination of
our proposed text, we believe the text should be revised to add some
clarification and additional detail. To that end, we are providing here
a detailed, step-by-step explanation in conjunction with several
figures to further illustrate the process. The corresponding regulatory
text in this final rule has been revised accordingly to make the
procedures as unambiguous as possible.
    The process of executing vehicle measurements in each test
condition (stationary, reverse, pass-bys), collecting necessary sound
files, determining test run validity, and processing sound files to
verify vehicle compliance can be broken down into five main steps,
which are discussed in detail later in this section, and which can be
briefly summarized as follows:
    1. For a given test condition, execute test runs and collect
acoustic sound files;
    2. Eliminate invalid test runs and discard the corresponding sound
files;
    3. Identify the first four valid vehicle test runs that have
overall SPLs within 2dBA of each other;
    4. Take an average of the four overall SPLs from the left side of
the test vehicle; separately, take an average of the four overall SPLs
from the right side of the test vehicle; the lesser of these two
averages will determine whether the left side or right side sound data
are to be used for one-third octave band analysis.
    5. Evaluate either the left side or right side sound data
(whichever had the lower average in Step 4) at the one-third octave
band level to determine compliance.
    Each of these five steps is discussed in more detail below.
    For a given test condition, execute test runs and collect acoustic
sound files: To begin the process, multiple test runs (at

least four, but generally five to seven based on NHTSA's experience)
must be completed for each test condition (stationary, reverse, pass-
by) as specified in the regulatory test procedures. Immediately before
and after each test condition, at least 30 seconds of ambient noise
must be recorded. During each test run, a left (driver's side) and
right (passenger side) acoustic sound data file must be recorded. For
the stationary tests, data from a third microphone located directly
ahead of the test vehicle is also recorded.
    Eliminate invalid test run acoustic sound files: The sound files
collected from each microphone during each test run are evaluated for
validity. The specifics for determining validity of each test run sound
file are discussed in Section III.K, Conditions for discarding
measurements. Each test run deemed valid must be numbered sequentially
based upon the chronological order in which it was executed on the test
track, and each must include a left (driver's side), right (passenger
side), and for the stationary test condition a front center acoustic
sound file. Sound files shall be identified with, and shall retain,
their test run sequence number and their association with left side and
right side microphone locations.
    Identify first four valid test run sound files within 2dBA: After a
group of test run sound files have been determined as valid, further
evaluation is required to identify the ``first four valid test run
sound files with overall SPLs within 2dBA.'' Figure 10 identifies a
flow diagram that depicts this process which is derived directly from
SAE J2889-1.
[GRAPHIC] [TIFF OMITTED] TR14DE16.013

    For each test run, a valid left (driver's side) and a valid right
(passenger side) sound file must exist. For each sound file the maximum
overall SPL must be determined. Ultimately, the four test runs to be
used for the compliance evaluation must be sequentially the first four
valid test runs that have four left side files within 2.0dB(A) overall
SPL and four right side files within 2.0 dB(A) overall SPL. The left
and right side files must come from the same set of four test runs.
This test run selection process as depicted in Figure 10 is as follows:
    Step 1: Number each valid sound measurement test run sequentially
in the chronological order it was completed on the test track- e.g.,
Run 1, Run 2, Run 3, . . . Run N. Each test run must have a
corresponding left (driver's side) and right (passenger side) acoustic
sound file.
    Step 2: Determine the maximum overall SPL value for the left and
right side sound files from each of the first 4 test runs.
    Step 3: Compare the four left side (driver's side) maximum overall
SPL values. Calculate the difference between the largest and smallest
of the four values. Use the same process to determine the difference
between the largest and smallest of the four right side (passenger
side) maximum overall

SPL values. If the difference is less than or equal to 2.0 dB(A) on
both the left and right sides, then these four test runs will be used
for the compliance evaluation, and the test run selection process for
the given operating condition is complete. The selected runs will be
considered the ``first four valid test runs within 2dBA.'' Otherwise,
continue to Step 4.
    Step 4: Add data from a fifth test run to the analysis.
    Step 5: For the driver`s side microphone, list all possible
combinations of four runs for which the largest overall SPL from any of
the four runs minus the smallest overall SPL from any of the four runs
is less than or equal to 2.0 dB(A).
    Step 6: For the passenger side microphone, list all possible
combinations of four runs for which the largest overall SPL from any of
the four runs minus the smallest overall SPL from any of the four runs
is less than or equal to 2.0 dB(A).
    Step 7: Examine the list of run combinations developed in both Step
5 and Step 6. If a set of four runs (e.g., Run 1, Run 2, Run 4, and Run
5) appears in both the Step 5 and Step 6 lists, enter it into a new
list (the Step 7 list).
    Step 8: The Step 7 list can possibly contain zero, one, or more
entries. If the Step 7 list has zero entries, skip to Step 10. If the
Step 7 list contains exactly one entry, then that entry is the set of
runs for which final data will be analyzed. For this case, terminate
the run selection procedure. This set of runs will be considered the
``first four valid test run sound files within 2.0dBA.'' If the Step 7
list contains more than one entry, go to Step 9.
    Step 9: Case for which the Step 7 list contains more than one
entry. Sum the run numbers for each set of runs in the Step 7 list. For
example, if an entry contains Run 1, Run 2, Run 4, and Run 5, then the
sum of its run numbers would be 12 (1+2+4+5). Select the entry which
has the lowest sum of run numbers. This set of runs is the set for
which final data will be analyzed for compliance. At this point,
terminate the run selection procedure. This set of runs will be
considered the ``first four valid test run sound files within 2.0dBA.''
[Note: When there are five runs being considered, it is mathematically
impossible for the sums of the run numbers for the two entries in the
Step 7 list to be exactly the same. One entry will always have a lower
value. However, in NHTSA's experience there have been cases in which
six or seven test runs are needed to find a set of four shared by the
driver's and passenger's sides that have Overall SPLs within 2.0 dB(A).
It might be possible (although the agency has not yet had it happen) in
these situations for the sums of the run numbers for the two entries in
the Step 7 list to be exactly the same. If this occurs, our procedure
will be to eliminate the combination of four runs containing the
highest run number. If the highest run number is the same in both four-
run combinations, we then will eliminate the combination of four runs
containing the second highest run number, and so on.]
    Step 10: Case for which the Step 7 list contains zero entries. In
this situation, add data from another test run to the analysis and
return to Step 5. [Note: In NHTSA's experience, there have been
instances in which it was necessary to examine data from as many as
seven runs to find a set of four that are shared by the driver's and
passenger's sides that have Overall SPLs within 2.0 dB(A).]
    Note that, although data recorded by the front microphone are not
considered when determining the ``first four valid test runs within
2dB(A),'' those data are used when evaluating compliance with the
directivity requirement. The front microphone data to be used for
directivity are the data recorded during the ``first four valid test
runs within 2dB(A)'' determined according to the procedure above.
    Average sound files on test vehicle left and right sides to
determine final files for one-third octave band processing: After the
``first four valid test runs within 2.0dBA'' have been identified, the
four acoustic sound files from each side of the vehicle recorded during
those four runs are analyzed to determine which side of the vehicle was
the quietest during test execution. Figure 11 is a flow diagram that
depicts the process used to further identify the acoustic data files on
a particular side of the test vehicle that will be used to evaluate
vehicle compliance at the one-third octave band level. For each of the
eight acoustic sound data files (four left side files and four right
side files) the maximum overall SPL value must be identified. Each of
the eight acoustic data file maximum overall SPL values are then
corrected for the recorded ambient conditions as specified in the final
rule. Finally, the four ambient-corrected maximum overall SPL values on
each side of the vehicle are averaged together for one comprehensive
ambient-corrected value for each side of the vehicle. The side of the
vehicle with the lowest average ambient-corrected maximum overall SPL
value is the side of the vehicle that is further evaluated for
compliance at the one-third octave band level. Each of the four
acoustic data files on the side of the vehicle with the lowest average
ambient-corrected maximum overall SPL value are then used for the one-
third octave band evaluation as depicted in the flow diagram in Figure
12.

[GRAPHIC] [TIFF OMITTED] TR14DE16.014

    In the event that the average corrected maximum overall SPL values
for the driver's and passenger's sides are exactly equal, then the
sound from the passenger's side will be analyzed.
    Evaluate final sound files at one-third octave band level for
compliance verification: Figure 12 indicates the flow process for
analyzing the selected four acoustic data files for the one-third
octave band analysis. As shown in Figure 11, the side of the vehicle
found to have the lowest overall average and corrected SPL value is the
side of the vehicle that is further evaluated for compliance
verification. The side selected has four individual acoustic data
files. Each file is broken down into its one-third octave band levels.
The identified one-third octave band levels in each of the four files
are then corrected for the measured ambient levels as specified in the
final rule. The four corrected values in each one-third octave band are
then averaged together to get the average corrected sound pressure
level in each one-third octave band. The averaged corrected values in
each one-third octave band are then compared directly to the minimum
standards specified in this final rule to determine compliance.
    The stationary test condition, ``first four valid test runs within
2dB(A)'' also has front microphone acoustic data. Each sound file for
the front microphone is broken down into its one-third octave band
levels. The identified one-third octave band levels in each of the four
files are then corrected for the measured ambient levels as specified
in the final rule. The four values calculated in each one-third octave
band are then averaged together to get the average ambient-corrected
sound pressure level in each one-third octave band. The averaged,
corrected values in each one-third octave band are then compared
directly to the minimum standards specified in this final rule to
determine compliance.
    As explained previously, the process established in this final rule
augments the process specified in the SAE standard by clarifying the
steps depicted in Figure 12 for processing the selected sound files for
the one-third octave band analysis. The current version of SAE J2889-1
does not correct one-third octave band data, as required in this final
rule.

[GRAPHIC] [TIFF OMITTED] TR14DE16.015

    To address commenter issues discussed above and to add
clarification, the final rule test procedure (paragraph S7) replaces in
its entirety the proposed regulatory text of the corresponding section
of the NPRM.
Data Post-Processing
    In the NPRM, the agency sought comment on data post-processing
topics including filter roll-off rates, measurement domains and type
windows used for frequency analyses. Few comments were received, but
the one topic that was commented on was filter roll-off rates. The
commenters strongly supported using the ANSI S1.11-2004 Class 1 one-
third octave filters as specified in SAE J2889-1.
    We agree that the ANSI S1.11 filters should be used for processing
the acoustic sound files. However, as mentioned in the NPRM, the
selected filter roll-off rates could affect the results of the acoustic
measurements at the one-third octave band level. Furthermore, there are
other attributes (i.e., sound analysis code window size, time used for
exponential averaging, and the precise details of the implementation of
the sound analysis code) that should also be considered for use in the
data post-processing routines that can impact the final results. All of
these critical attributes must be evaluated and defined to ensure an
objective test procedure is specified that provides reproducible and
repeatable test results.
    Over the past few years, the agency has used two different sound
analysis codes for processing acoustic sound files. The first code,
which NHTSA licensed from Bruel and Kjaer, is the B&K Pulse Reflex\TM\
Code (the B&K Code), and is an integral part of a commercial off-the-
shelf acoustic sound measurement system. NHTSA has utilized this system
and software code for much of its early research testing. The B&K Code
is a data analysis software that uses preprogrammed building blocks,
known as elements, to form processing chains. For the purpose of
processing sound recordings two processing chains were used, one for
determining the overall sound pressure levels and one for determining
the 13 one-third octave sound levels.
    The second analysis code that has been used by the agency is one
developed by the Volpe National Transportation Systems Center (the
Volpe Code). This sound analysis code was written using
MatlabTM. While Matlab is a proprietary engineering based
technical programming language, the source code developed for acoustic
data processing is the property of the United States Department of
Transportation and can be made publically available. This code uses a
more traditional, language based, programing structure.
    The agency is aware of other acoustic measurement instrumentation
and associated codes that can also be used to collect and process
acoustic sound files but none of these other systems/codes have been
evaluated. It is our understanding that among these codes, the two used
by NHTSA and some of the other available codes function similarly.
Figure 13 depicts the general process used by these various codes to
derive the overall and one-third octave band sound values.
    The general process involves loading the sound data file, applying
the defined acoustic sound weighting, and then performing the necessary
respective processing to arrive at both the overall sound pressure
level and one-third octave band values. The respective processing
routines will be further outlined in the following sections.

[GRAPHIC] [TIFF OMITTED] TR14DE16.016

    For evaluation purposes, the sound data recorded during some test
runs were analyzed using both the B&K Pulse code and the Volpe code.
Some test runs were also analyzed using two different sets of user-
specified parameters. Analysts looking at the results from these runs
noted that there were slightly different overall sound pressure levels
and one-third octave band levels for the exact same sound data
depending upon the sound analysis code and the user-selectable
parameters used. While the differences that were seen were not large
(less than 2.0 dBA), NHTSA believed that it needed to understand the
source of the differences before either code could be used in a
compliance test. Therefore, NHTSA undertook further research work after
publication of the NPRM to evaluate and resolve this issue.
    The objective of this research was to select one sound analysis
code and one set of user-selectable parameters for use in compliance
testing of measured vehicle sound data. Our criteria for choosing an
appropriate sound analysis code were:
     The code must generate correct results for mathematically-
generated test cases for which the correct result is known.
     The code must meet all of the filter requirements for one-
third octave band filters that are contained in the ANSI S1.11-2004
Class 1 standard.
     The code can be made publically available so all
individuals and organizations know the exact methods, specified
parameters, and filtering being used by NHTSA.
    Table 19 shows the standard settings for the user definable
parameters that can be set in each of the code packages that were
evaluated.

                               Table 19--Analysis Code User-Selectable Parameters
----------------------------------------------------------------------------------------------------------------
                                      Acoustic test data analysis settings
-----------------------------------------------------------------------------------------------------------------
            Parameter                             B&K Pulse                             Volpe Matlab
----------------------------------------------------------------------------------------------------------------
General Settings:
    Sampling Frequency...........  65536 Hz..............................  65536 Hz.
    Processing Window............  Test Scenario Dependent...............  Test Scenario Dependent.
    Acoustic Weighting...........  A or Linear Weighting.................  A or Z Weighting.
Overall Sound Pressure Level
 Settings:

    Frequency span...............  25600 Hz..............................  24000 Hz.
    Overall Averaging............  Linear................................  None.
    Averaging time...............  0.05..................................  None.
One-Third Octave Band Analysis
 Settings:
    Bandwidth (Fractional Octave)  \1/3\--Base 10 Exact..................  \1/3\--Base 10 Exact.
    Upper Nominal Center           5000 Hz...............................  5000 Hz.
     Frequency.
    Lower Nominal Center           315 Hz................................  315 Hz.
     Frequency.
    Type of Octave Band Averaging  Exponential...........................  Exponential.
    Type of Time Weighting.......  Fast..................................  Fast.
    Averaging Time...............  \1/4\ seconds.........................  \1/4\ seconds.
    Tau (Time Constant)..........  \1/8\ seconds (Fast)..................  \1/8\ seconds (Fast).
----------------------------------------------------------------------------------------------------------------

    NHTSA began evaluating both codes by running the same vehicle sound
data file through both code packages, looking to see how consistent the
codes were relative to each other. The outcome was that each code gave
slightly different results, even while using consistent parameter
settings.
    To systematically determine the differences between the two
packages, both the B&K and the Volpe sound analysis codes were checked
to ensure that they provided known output results for known input
values. This was done through the development of test cases that were
processed using each of the sound analysis codes. The test cases
consist of simple pure tones which are computer-generated rather than
taken from actual sound recordings, and thus they have none of the
complexity of actual acoustic measurements. The test cases provide
elemental inputs for which the correct outputs are known in advance.
The test cases were used to evaluate the accuracy of a given code's
analysis routine and to compare the outputs of the two different
analysis methods.
    Test Case 1 was a series of pure tones. The sound pressure of each
tone as a function of time is given by a constant-amplitude, constant-
frequency, single sine wave. Multiple pure tones were generated, each
at a different constant-frequency. For this research, two constant-
amplitudes corresponding to 40 and 60 dB sounds were used. To be
certain of capturing all important effects for each of the 13 one-third
octave bands of interest to NHTSA (which have nominal center
frequencies ranging from 315 Hz to 5,000 Hz), the pure tones for Test
Case 1, developed using Matlab\TM\, were generated at 201 individual
frequencies each corresponding to \1/8\th of a one-third octave band
(\1/24\th of a full octave). The frequency range over which they span
is, nominally, 70Hz-22,300Hz. This range encompasses six full one-third
octave bands both above, and six full one-third octave bands below, the
13 one-third octave bands of interest to NHTSA. This range was chosen
to ensure a full profile of how each code responds to known inputs was
generated and understood.
    The following aspects of sound analysis code were checked using
Test Case 1 data files:
     The correctness of the calculated amplitude, when no
frequency weighting (Z-weighting) was applied, for a pure tone at a
frequency corresponding to the center of each of the one-third octave
bands of interest.
     The correctness of the calculated amplitude, when A-
weighting was applied, for a pure tone at a frequency corresponding to
the center of each of the one-third octave bands of interest.
     The correctness of the band-pass filters that split
frequency-weighted sound pressure level data into 13 one-third octave
bands. NHTSA and commenters want these band-pass filters to meet all of
the Type 1 filter requirements for one-third octave band filters that
are contained in the standard ``ANSI S1.11-2004''. The Test Case 1
frequencies include all of the frequencies listed in Table B1,'' of
ANSI S1.11-2004 for the 13 one-third octave bands of interest to NHTSA.
    For the second test case, Test Case 2, thirteen pure tones were
superimposed to form one sound-pressure signal. These thirteen pure
tones were at the frequencies corresponding to the center of each of
the one-third octave bands of interest. No frequency weighting (i.e.,
Z-weighting) was applied.
    Two test runs were made using Test Case 2. The first had a 40 dB
pure tone centered at each of the one-third octave bands of interest
(giving an Overall SPL for this test run of 51.1394 dB). The second
used thirteen pure tones at 60 dB (giving an Overall SPL for this test
run of 71.1394 dB). This test case was used to check the correctness of
the calculated amplitudes when no frequency weighting (Z-weighting) was
applied to a complex sound data waveform.
    In general, in comparing the two analysis codes using Test Case 2,
NHTSA found very little or no difference between the calculated
amplitudes regardless of weighting type (A- or Z-weighting) for the
individual pure tones located at the center frequencies of each of the
13 one-third octave bands. Each code set gave either 40 or 60 dB at
each center frequency, as expected. The results from the two analysis
codes were also consistent when the overall SPL for the 13 center
frequencies were combined, and both the Volpe Matlab code and the B&K
Pulse code produced the correct results of 51.1 dB and 71.1 dB for the
40 dB and 60 dB inputs, respectively.
    However, in looking at the test results from Test Case 1, the two
analysis codes were not consistent regarding their band-pass filter
function that splits frequency-weighted sound pressure data into the 13
one-third octave bands. When comparing the output of each of the 201
frequencies described in Test Case 1 to the requirements specified in
ANSI S1.11-2004, NHTSA found that the B&K software tended to
insufficiently attenuate the frequency bands away from the nominal one-
third octave band. An example of this is shown below in Figure 14 which
plots the minimum and maximum ANSI filter requirements, the output of
the B&K Pulse code, and the output of the Volpe Matlab code, for the
one-third octave band centered at 1000 Hz.

[GRAPHIC] [TIFF OMITTED] TR14DE16.017

    While some bands displayed better adherence to the ANSI S1.11
specifications, all of the 13 one-third octave bands displayed similar
results as the 1000 Hz band shown above for the B&K software. On the
other hand, the Volpe Matlab code processed data fell well within the
filter attenuation limits specified in ANSI S1.11-2004 Class 1 across
all bands. Complete results for all the individual one-third octave
bands can be found in the corresponding NHTSA research report.\163\
---------------------------------------------------------------------------

    \163\ Dr. W. Riley Garrott, Richard, L. Hoover, Eric Gerdus, and
Sughosh J. Rao, ``Selecting a Sound Analysis Code for Use With NHTSA
Test Procedure to Characterize Vehicle Sound'' NHTSA Technical
Report.DOT HS 812 284.
---------------------------------------------------------------------------

    The results of our research indicate that the two codes analyzed
have different filter algorithms. This results in the two codes
calculating slightly different one-third octave band levels. The exact
filtering algorithm used in the B&K code is unknown because the code is
proprietary. The filtering algorithm used in the Volpe code is known
and can be made public. Given the results of our examination of the two
post-processing methods, NHTSA has decided to use the Volpe Matlab code
for the agency's future compliance testing programs. As explained
above, one reason for this is that the Matlab code appears to be in
full agreement with ANSI S1.11-2004 specifications and requirements.
Also, the source code is not proprietary, and it can be made publically
available. To resolve any potential problems with post-processing code
conflicts, the agency will make the Matlab code to be used publically
available, either as part of the agency's compliance test procedure, or
posted on the agency's Web site. This approach will help the agency
with its recent efforts to increase public communications and
transparency. In reference to the other parameters that the agency
inquired about in the NPRM, measurement domains and type windows used
for frequency analyses, no direct comments were received so the agency
has made decisions according to what it believes are technically
correct. All the parameters that will be used for post processing the
acoustic files will be specified in the publically available Matlab
code.

L. Phase-In of Requirements

    The PSEA directed NHTSA to establish a phase-in period to set forth
the dates by which production vehicles must comply with the new FMVSS
No. 141. The PSEA also stated that NHTSA must require full compliance
``on or after September 1st of the calendar year that begins three
years after the date on which the final rule is issued.''
    To address these requirements in the PSEA, the NPRM proposed a
phase-in over three model years for new hybrid and electric vehicles
produced for sale in the U.S., and full compliance of all new hybrid
and electric vehicles by September 1, 2018. The three-year phase-in was
based on a `30/60/90' phase-in schedule. Given that the NPRM assumed
publication of a final rule in calendar year 2014, the phase-in
requirements proposed in the NPRM were: 30 percent of each OEM's HV and
EV production in compliance by September 1, 2015; 60 percent by
September 1, 2016; 90 percent by September 1, 2017; and 100 percent by
September 1, 2018. The proposed phase-in schedule was intended to be
applicable to all manufacturers of HVs and EVs, except small volume and
final stage manufacturers. The latter were allowed to postpone
compliance until the date on which other manufacturers were required to
have all their vehicles brought into compliance, i.e., September 1,
2018.
    The NPRM also included amendments to Part 585 Reporting
Requirements to allow for OVSC verification of each manufacturer's
phase-in of pedestrian alert systems.
    With the exception of two advocacy groups, all commenters opposed
the phase-in requirements as proposed in

the NPRM. The NFB and NCSAB supported the phase-in schedule as
proposed. The NCSAB stated that the rule should be completed by January
2014, according to the PSEA. Neither commenter suggested an alternative
phase-in schedule.
    All other commenters requested that NHTSA provide more lead time
for compliance with the new safety standard. Some favored eliminating
the phase-in altogether and establishing a single date for full
compliance for all production hybrid and electric vehicles.
Alternatively, commenters requested that NHTSA begin the phase-in at a
later date, unless changes were made in the final rule to adopt
performance requirements much less stringent than those in the NPRM.
Honda and Alliance/Global requested that NHTSA allow for carry-forward
credits which would give a manufacturer credit for meeting one of the
phase-in stages prior to the deadline for that stage, and the
manufacturer could use that credit if it did not fully meet a deadline
of a later stage.
    A heavy vehicle OEM commented that the proposed Part 585 phase-in
reporting should not apply to a manufacturer that achieves 100 percent
early compliance, and also stated that paragraph S9.5 of the NPRM,
regarding phase-in for multi-stage vehicles, is unnecessary because
only a final stage manufacturer would be responsible for meeting the
phase-in requirements.
    Porsche, a light vehicle manufacturer that produces only one hybrid
model, provided proprietary production estimates through September 2018
indicating that they would not meet the 90 percent level by the third
year of the proposed phase-in.
    The EDTA commented that, due to the complexity of the proposal, as
well as the technology needed to implement it, substantial lead time
will be needed to design, develop, test and certify new alert systems.
EDTA stated that it joined with Alliance/Global in recommending that,
if the final rule is substantially the same as the proposal, the phase-
in specified in the final rule should be limited to a single 100-
percent compliance date that is set in accordance with the PSEA (i.e.,
September 1st of the calendar year that begins three years after the
date on which the final rule is issued).
    Honda commented that, if the final rule must be complied with
starting in September 2015, it would need more time to meet all the
requirements proposed in the NPRM (modification of speakers, control
unit, vehicle structural modifications, etc.). Therefore, Honda
requested at least two or more years from the date that the final rule
is issued before the phase-in requirements begin. As mentioned above,
Honda also requested that a credit system be established as part of the
phase-in.
    Toyota stated that it is committed to pedestrian safety, and as
such, has already equipped every hybrid and electric vehicle it
produced since model year 2012 under the Toyota and Lexus brands
(currently, there is no Scion HV or EV) with a pedestrian alert sound
meeting the existing Japanese guidelines. However, Toyota noted that
the proposed requirements of the NPRM would require significant
redesign of Toyota's current production alert system, which will in
turn require substantial development and test time. Therefore, Toyota
recommended elimination of the phase-in requirements and suggested that
NHTSA consolidate the schedule by simply requiring full compliance for
all HVs and EVs by September 1, 2018 (assuming the final rule is
published in calendar year 2014 or earlier).
    Alliance/Global commented that it would not be possible for
manufacturers to meet a phase-in beginning September 1, 2014. If the
requirements of the final rule were to be substantially similar to the
NPRM, they recommend foregoing the phase-in and going directly to full
implementation on September 1, 2018. However, if the final rule instead
were to approximate the Alliance/Global recommendations, then a phase-
in period is feasible beginning with vehicles built on or after
September 1, 2015, and ending with vehicles built on or after September
1, 2018 (those dates would need to be adjusted should the final rule be
significantly delayed beyond the original January 2014 deadline).
    Alliance/Global also commented that currently there are no EVs or
HVs produced by their member companies that are capable of meeting the
requirements proposed by NHTSA. They stated that several strategies had
been considered, including reprogramming an existing alert sound
control module. They also stated they had interviewed suppliers who
currently manufacture alert systems in an effort to explore all
possible solutions for meeting the NPRM. They concluded that
considerably more time would be needed than a September 1, 2014 start
of phase-in would allow to package/repackage components, develop new
systems, source the components, and certify the new systems.
    However, Alliance/Global commented that such a phase-in schedule as
the one they suggested still would need assistance from carry-forward
credits (including early carry-forward credits). They recommended full
credits for EVs and HVs that comply with their suggested sound
specifications (assuming those were implemented in the NHTSA final
rule) and half-credit (i.e., two vehicles equal one credit) for EVs and
HVs that are equipped with pedestrian alert systems that do not meet
the Alliance/Global suggested requirements, but that nevertheless
comply with the spirit and purpose of the PSEA. If NHTSA specifies a
phase-in, Alliance/Global stated that carry-forward credits are
necessary for their member companies to avoid needless compliance
expenditure on vehicle models imminently due to be phased out of
production.
    Alliance/Global commented that small manufacturers should not be
required to comply until the end of the phase-in period. Because no
current EV or HV pedestrian alert sound voluntarily implemented by
vehicle manufacturers meets NHTSA's proposed requirements, if the
agency proceeds to a final rule that is substantially similar to the
NPRM, Alliance/Global would prefer that NHTSA does not specify a phase-
in, and instead allows all manufacturers the maximum amount of time to
comply with the requirements of the new safety standard.
    Finally, Alliance/Global stated that phase-in language needs to
clarify that requirements pertain only to vehicles described in the
Applicability section of the regulation and not to every type of
vehicle that a full-line manufacturer produces.
    The MIC commented that, if NHTSA does decide to establish minimum
sound requirements for motorcycles, it should extend the phase-in
exemption for small manufacturers, including motorcycle manufacturers,
indefinitely.
    Nissan requested that the phase-in begin at least two years
following the issuance of a final rule. Nissan also requested that
NHTSA provide for the use of advanced credits for vehicles that comply
before the final date for compliance.
    Denso commented that vehicle manufacturers, as well as equipment
suppliers, need three years of lead time before beginning phase-in of
complying vehicles.
    Navistar questioned how the proposed phase-in meshes with Parts 567
and 568 regarding certification of multistage vehicles.
    OICA commented that the Phase-in should include only those vehicles
to which the performance requirements are meant to apply, i.e., certain
hybrid and electric vehicles.

Agency Response to Comments
    Given that this final rule is being published in calendar year 2016
and, furthermore, given that the PSEA stipulates full compliance on and
after September 1st of the calendar year that begins three years after
the date on which the final rule is issued, NHTSA is requiring
compliance for 100 percent of HVs and EVs produced for sale in the U.S.
by all manufacturers by no later than September 1, 2019. This
compliance date is set forth in the Applicability section of the
regulatory text of this final rule.
    In addition, after review of the comments submitted, NHTSA is
adopting a one-year, 50 percent phase-in. Under this phase-in, 50
percent of the total production volume of each manufacturer's hybrid
and electric vehicles to which the safety standard applies, and which
are produced by the manufacturer for sale in the United States., must
comply by no later than September 1, 2018.
    This phase-in does not apply to multi-stage and small volume
manufacturers. Those manufacturers would have until September 1, 2019,
to comply. This should not have any significant effect on traffic
safety because of the relatively small number of vehicles they produce.
    Because the phase-in period will have a duration of only one year,
carry-forward credits would not be of any benefit. Therefore, NHTSA is
not making any provisions in this rule for carry-forward credits.
    The agency's decision on the phase-in issues is a compromise that
responds to comments about reducing the phase-in or eliminating it
altogether. The one year phase-in addresses the mandatory PSEA
requirements and ensures that any delay in getting complying vehicles
to market will be minimized. At the same time, it responds to
commenters' requests for additional lead time to comply and to their
suggestions that the NPRM phase-in should be consolidated and
simplified. A one-year phase-in provides additional flexibility for
manufacturers as to when they bring their model lines into compliance.
    Furthermore, NHTSA has reviewed current model lines of vehicle
manufacturers using OVSC annual compliance information and has
determined that several of the OEMs that produce HVs and/or EVs have
only one or two such models among their vehicle lines. This is one
factor that we have considered in choosing an appropriate phase-in
period. These manufacturers will benefit from a shortened phase-in
schedule that provides additional lead time prior to the initial date
on which the phase-in begins.

IV. International Harmonization and Stakeholder Consultation

    NHTSA is required by the PSEA to consult with the following
organizations as part of this rulemaking: The Environmental Protection
Agency (EPA) to assure that any alert sound required by the rulemaking
is consistent with noise regulations issued by that agency; consumer
groups representing visually-impaired individuals; automobile
manufacturers and trade associations representing them; technical
standardization organizations responsible for measurement methods such
as the Society of Automotive Engineers, the International Organization
for Standardization (ISO), and the UNECE World Forum for Harmonization
of Vehicle Regulations (WP.29).
    The agency has established three dockets to enhance and facilitate
cooperation with outside entities including international
organizations. The first docket (No. NHTSA-2008-0108) was created after
the 2008 public meeting was held; it contains a copy of the notice of
public meeting in the Federal Register, a transcript of the meeting,
presentations prepared for the meeting and comment submissions. It also
includes NHTSA's research plan, our ``Notice of Intent to Prepare an
Environmental Assessment for the Pedestrian Safety Enhancement Act of
2010'' published on July 12th 2011 in the Federal Register, and the
agency's Phase 1 and 2 research reports. (The Notice of Intent [NOI]
and the agency's research are discussed more fully in other parts of
this document.) The second docket (No. NHTSA-2011-0100) was created to
collect comments on the NOI; it also includes a copy of that notice.
The third docket (No. NHTSA-2011-0148) was created in September 2011 to
include materials related to the rulemaking process (``The Pedestrian
Safety Enhancement Act of 2010,'' Phase 1 and 2 research reports,
statistical reports, meeting presentations, etc.), and outside
comments.
    On June 25, 1998, the United States signed the 1998 Global
Agreement, which entered into force on August 25, 2000. This agreement
was negotiated under the auspices of the United Nations Economic
Commission for Europe (UNECE) under the leadership of the U.S., the
European Community (EC) and Japan. The 1998 Agreement provides for the
establishment of Global Technical Regulations (GTRs) regarding the
safety, emissions, energy conservation and theft prevention of wheeled
vehicles, equipment and parts. By establishing GTRs under the 1998
Agreement, the Contracting Parties seek to pursue harmonization in
motor vehicle regulations not only at the national and regional levels,
but worldwide as well.
    As a general matter, governments, vehicle manufacturers, and
ultimately, consumers, both here and abroad, can expect to achieve cost
savings through the formal harmonization of differing sets of standards
when the contracting parties to the 1998 Global Agreement implement new
GTRs. Formal harmonization also improves safety by assisting us in
identifying and adopting best safety practices from around the world
and reducing diverging and unwarranted regulatory requirements. The
harmonization process also allows manufacturers to focus their
compliance and safety resources on regulatory requirements whose
differences government experts have worked to converge as narrowly as
possible. Compliance with a single standard will enhance design
flexibility and allow manufacturers to design vehicles that better meet
safety standards, resulting in safer vehicles. Further, we support the
harmonization process because it allows the agency to leverage scarce
resources by consulting with other governing bodies and international
experts to share data and knowledge in developing modernized testing
and performance standards that enhance safety.
    Under the 1998 Agreement, countries voting in favor of establishing
a GTR, agree in principle to begin their internal implementation
processes for adopting the provisions of the GTR, e.g., in the U.S., to
issue an NPRM or Advanced NPRM, within one year. The ultimate decision
whether or not to adopt the GTR is at each contracting party's
discretion, however, based on its determination that the GTR meets or
does not meet its safety needs. The UNECE World Forum for Harmonization
of Vehicle Regulations (WP.29) administers the 1998 Agreement.
    In 2009, the Ministry of Land, Infrastructure, Transport and
Tourism (MLIT) of Japan assembled a committee to study the issue of the
quietness of HVs. The committee concluded that an Approaching Vehicle
Audible System (AVAS) was a realistic alternative to allow pedestrians
who are blind or visually-impaired to detect quiet vehicles. In 2010,
MLIT announced guidelines for AVAS based on the recommendations of the
study committee. Although several vehicles were considered in the
initial scope, MLIT concluded that AVAS should be

installed only on HVs that can run on electric motors, EVs and fuel-
cell vehicles. In terms of the activation condition, the MLIT
recommended that AVAS automatically generate sound at least in a speed
range from the start of a vehicle until reaching 20 km/h (12 mph) and
when moving in reverse. The AVAS would not be required when a vehicle
is stopped. The system may include a switch to temporarily halt the
operation of the AVAS. The reason for including this switch is because
the committee believes that the system is not needed on expressways
where there are no pedestrians and to reduce other issues such as
drivers deliberately increasing vehicle speed in order to stop the
AVAS.
    In its March 2011 session, WP.29 determined that vehicles propelled
in whole or in part by electric means, present a danger to pedestrians
and consequently adopted Guidelines covering alert sounds for electric
and hybrid vehicles that are closely based on the Japanese Government's
guidelines. The Guidelines were published as an annex to the UNECE
Consolidated Resolution on the Construction of Vehicles (R.E.3).
Considering the international interest and work in this new area of
safety, the U.S. decided to lead the efforts on the new GTR, with Japan
as co-sponsor, and develop harmonized pedestrian alert sound
requirements for electric and hybrid-electric vehicles under the 1998
Global Agreement. Development of the GTR for pedestrian alert sound has
been assigned to the Group of Experts on Noise (GRB), the group most
experienced with vehicle sound emissions. GRB is in the process of
assessing the safety, environmental and technological concerns to
develop a GTR that leverages expertise and research from around the
world and feedback from consumer groups. The U.S. is the co-chair (with
Japan) of the informal working group on Quiet Road Transport Vehicles
(QRTV) assigned to develop the GTR and, therefore, will guide the
informal working group's development of the GTR. GRB will meet
regularly and report to WP.29 until the establishment of the new GTR.
NHTSA has been participating in the QRTV's meetings since its
foundation and has kept the group informed about ongoing agency
research activities as well as the results from completed research
studies. At the time the NPRM was issued, the QRTV informal group had
held five sessions to discuss development of a GTR on quiet vehicles.
    NHTSA has also hosted roundtable meetings with industry, technical
organizations and groups representing people who are visually-impaired
for the purpose of consulting with these groups on topics related to
this rulemaking. Participating in these meetings were representatives
from the Alliance of Automotive Manufacturers, the Global Automakers
(formerly Association of International Automobile Manufacturers
(AIAM)), American Council of the Blind, The American Foundation of the
Blind (AFB), the National Federation of the Blind (NFB), The
International Organization for Standardizations (ISO), The Society of
Automotive Engineers (SAE), the International Organization of Motor
Vehicles Manufacturers (OICA), The Environmental Protection Agency
(EPA) and Japan Automobile Manufacturers Association (JAMA).
    Representatives of the EPA have also been included in our
activities with outside organizations. They have been kept updated on
our research activities and have actively participated in our outreach
efforts. NHTSA has also kept up to date on EPA activities on the
international front through the activities of the UNECE Working Party
of Noise (GRB).
    The American Foundation of the Blind, the American Council of the
Blind and the National Federation of the Blind have provided NHTSA with
invaluable information about visually-impaired pedestrian safety needs
since the 2008 Public Meeting was held.
    The Alliance of Automobile Manufacturers and Global Automakers have
met separately with the agency to discuss our research findings and
their ideas regarding this rulemaking. Members of both organizations
have also met separately with the agency to discuss their own research
findings and ideas for a potential regulatory approach to address the
safety issues of interest to the agency.
    Automotive manufacturers that produce EVs for the U.S. market have
developed various pedestrian alert sounds, recognizing that these
vehicles, when operating at low speeds, may pose an elevated safety
risk to pedestrians. They have made vehicles with sound alert systems
available for lease by NHTSA for research purposes. This information
has been helpful in the agency decision making process.
    The Society of Automotive Engineers (SAE) established the Vehicle
Sound for Pedestrians (VSP) subcommittee in November 2007 with the
purpose of developing a recommended practice to measure sounds emitted
by ICE vehicles and alert sounds for use on EVs and HVs. Their efforts
resulted in recommended practice SAE J2889-1, Measurement of Minimum
Noise Emitted by Road Vehicles. The agency had been sending a liaison
to VSP meetings starting in 2008. SAE is the U.S. technical advisory
group to the International Organization for Standardization (ISO), and
they both have cooperated in the development of the industry safety
standard. The ISO document (ISO/NP 16254, Measurement of Minimum Noise
Emitted by Road Vehicles) and the SAE document are technically
identical. The agency used SAE J2889-1 and ISO 16254 as references in
the NHTSA test procedure development. Other international
organizations, such as the International Organization of Motor Vehicle
Manufacturers (OICA) and Japan Automobile Manufacturers Association
(JAMA) have provided NHTSA with research findings and also have
attended various quiet vehicle meetings.
    In the NPRM, the agency concluded that the voluntary guidelines
adopted by the Japanese government, and subsequently by the UNECE WP.29
Committee, did not have the level of detail necessary for NHTSA to
establish objective minimum performance requirements for creation of an
FMVSS. We did not believe that the agency would be able to tell if a
sound fell within one of the exclusions by means of an objective
measurement, nor would we be able to adequately ensure that sound
levels would be detectable by pedestrians or provide manufacturers with
a set of requirements that they would be able to meet. The NPRM noted
that the WP.29 QRTV work was scheduled to be completed in 2014, and a
draft GTR adopted in November 2014.
    OICA, EU, Chrysler, EDTA, VW, and Alliance/Global all suggested
delaying the development of a U.S. regulation on minimum noise levels
until WP.29 has had sufficient time to develop a globally harmonized
set of regulations via the GTR process. They stated that establishment
of separate requirements that may or may not be harmonized with the
recommendations under negotiation through WP.29 would harm development
of electric drive vehicles globally and constrain the growth of the
market as a whole.
    OICA, EU, VW, and Alliance/Global commented that the PSEA statute
does not provide enough time for WP.29 to address all remaining
technical issues in development of a globally harmonized standard that
the U.S. could then adopt. EU commented that if the agency is unable to
delay publication of a final rule that would harmonize with the
international community, it should at a minimum ensure that any U.S.
regulations are consistent with the recommendations of the WP.29
Informal

Working Group on Quiet Road Transport Vehicles.
    The EU questioned to what extent NHTSA had taken into consideration
the conclusions and results of the QRTV-IWG. They believed a delay in
the NPRM process and the finalization of the new FMVSS until the new
GTR has been drafted would contribute towards a common approach and an
overall consensus at the international level with respect to EVs and
HEVs.
    VW and Alliance/Global commented that if NHTSA is unable to delay
the enactment based on statutes within the PSEA, NHTSA should inform
the United States Congress that additional time to complete this
rulemaking is required in order to allow for completion of the GTR so
that a harmonized regulation can be achieved.
    Alliance/Global commented that in accordance with the QRTV Terms of
Reference, the development of the GTR should be concluded in the fall
of 2014, with status reports provided along the way so that the public
can monitor the status of the activity. Alliance/Global explained that
the benefits of having consensus on a global technical regulation are
enormous and any potential downside related to allowing an accelerated
GTR process to conclude prior to finalizing the NHTSA regulation will
be negligible given that a majority of current production EVs and HVs
are already voluntarily equipped with audible pedestrian alert systems.
    EU, VW, Chrysler, and Alliance/Global all supported using the GTR
process to finalize any remaining technical issues towards a globally
harmonized standard.
    WBU and MB supported using the NPRM as a basis for development of
the WP.29 GTR.
Agency Response to Comments
    The NPRM stated that the recommendations of the QRTV informal
working group do not include objective criteria with which the agency
could ensure vehicles comply with an FMVSS. The agency maintains that
this is still the case. Further, as discussed above, the agency has
determined that a crossover speed of 30 km/h is necessary because our
conclusion from the data we have acquired to date from all sources
(i.e., from commenters and from our own vehicle evaluations) is that
some hybrid and electric vehicles continue to need sound enhancement at
speeds above 20 km/h in order to ensure that they are adequately
detectable.
    Most of the commenters recommended that the agency wait until the
WP.29 World Forum can complete development of a GTR for minimum sound
levels, or, at a minimum, work closely with the QRTV in development of
requirements that could be recognized globally. The agency, through its
leadership role in the QRTV informal group, continues to work with the
international community in development of criteria that are technically
sound and objective. We note that the WP.29 QRTV work has been extended
until late 2015, at the earliest, with expected eventual adoption of a
GTR on minimum noise requirements for electrically driven vehicles.
Adoption of the GTR is only the beginning of the process of regulating
minimum noise levels by signatories of the 1998 UN agreement. After a
GTR on minimum noise requirements is adopted, NHTSA would still need to
issue an NPRM or an SNPRM (Supplemental Notice of Proposed Rulemaking)
to begin the process of adopting the GTR as an FMVSS. This could result
in several additional years of delay before an FMVSS mandating sound
for EVs and HVs could be issued. We do not believe that a delay of this
length is justified from a safety perspective. We believe the agency's
approach in development of this final rule to be consistent with both
the mission and safety goals of the agency and with the PSEA and Safety
Act.
    We agree with WBU and MB that development of U.S. regulations for
minimum noise levels might aid WP.29 in addressing some of the
technical issues that hinder development of a global regulation that is
both measurable and enforceable. We note that the leadership role of
the U.S. delegation in development of a global regulation for minimum
noise levels is consistent with the comments regarding using the GTR
process to refine a harmonized regulation. In that light, we believe
that development of a U.S. regulation would aid WP.29 in drafting a
global regulatory framework that is both measureable and enforceable.
    The agency has also continued to actively monitor the work that has
been done internationally by SAE and ISO. The SAE recently issued an
updated version of J2889-1 dated December 2014. The ISO recently
submitted the latest draft of ISO 16254 to the agency's docket.\164\
The agency has taken into consideration these documents to the extent
possible for the development of this final rule.
---------------------------------------------------------------------------

    \164\ NHTSA-2011-0148-0334.
---------------------------------------------------------------------------

V. Analysis of Costs, Benefits, and Environmental Effects

A. Benefits

    As stated above in the discussion of the statistical analysis of
safety need done for this rulemaking (see Section II.B), the data from
16 states cannot be used to directly estimate the national problem
size. Also, an analysis of pedestrian fatalities rather than injuries
is not appropriate for this rulemaking. The target population analysis
will therefore focus on injuries only.
    The PSEA directs NHTSA to establish minimum sound requirements for
EVs and HVs as a means of addressing the increased rate of pedestrian
crashes for these vehicles. In calculating the benefits of this
rulemaking we have assumed that adding sound to EVs and HVs will bring
the pedestrian crash rates for these vehicles in line with the
pedestrian crash rates for ICE vehicles because the minimum sound
requirements in the proposed rule would ensure that EVs and HVs are at
least as detectable to pedestrians as ICE vehicles. This approach
assumes that EVs and HVs have higher pedestrian crash rates than ICE
vehicles because of the differences in sound levels produced by these
vehicles. Therefore, the target population for this rulemaking is the
number of crashes that would be avoided if the crash rates for hybrid
and electric vehicles were the same as the crash rate for ICE vehicles.
    No quantifiable benefits are estimated for EVs because we assume
that EV manufacturers would have added alert sounds to their cars in
the absence of this proposed rule and the PSEA.
    NHTSA was not able to directly measure the safety differences
between hybrids with and without sound. Although there are now some
hybrids in the market that produce sounds to alert pedestrians and
pedalcyclists, the agency is unable to directly measure the
effectiveness rate of sound by using data from these new hybrid
vehicles because there is not sufficient crash data on new model hybrid
vehicles with sound to be able to make a statistically significant
comparison to hybrids without sound. The agency's data base for low
speed injuries is a sample, and data on crashes involving hybrid
vehicles that emit sound is limited. Furthermore, the data set used to
analyze differences in crash rates for this rulemaking consists of
crash data from 16 states. At this time, only half of the states have
submitted data for the 2012 or later calendar years. Since we believe
that most hybrid vehicles have been equipped with some type of alert
sound only since 2012, any effect that voluntary adoption would

have on pedestrian crash rates would not be captured by this data set.
In addition, none of the recently introduced hybrids with sounds were
designed to meet all of the requirements in this rule. Therefore, any
change in crash rate between original quiet HVs and these voluntarily-
equipped HVs would not necessarily be indicative of the full safety
benefits of compliant sounds.
    NHTSA has also been unable to directly measure the pedestrian and
pedalcyclist crash rates per mile travelled for HVs and EVs to the
rates for ICEs because the agency does not have data on VMT for HVs and
EVs. To calculate the difference in crash rates between HVs and ICEs
NHTSA computes the ratio of the number of pedestrian and pedalcyclist
crashes involving HVs to the number of other types of accidents
involving HVs and compares it to a similar ratio for ICEs. While this
is a standard technique in analyzing crash risk, it does raise a
problem in this case because NHTSA was not able to control for VMT.
NHTSA assumes that any difference in these ratios is attributable to
the lack of sound in HVs. However, it is possible that there are other
explanations for differences. For example, there may be reasons other
than sound for why HVs have higher numbers of pedestrian and
pedalcyclist accidents. Or there may be reasons why ICEs have higher
numbers of other types of accidents.\165\ This could result in a lower
ratio for ICEs even if the two types of vehicles had similar pedestrian
and pedalcyclist crash rates.
---------------------------------------------------------------------------

    \165\ For example, HLDI compared overall rates of injury for
hybrid vehicles and their ICE non-hybrid twins and found that crash
rates are lower for hybrids. HLDI concluded that the heavier weight
of hybrids was an important factor in this lower overall crash rate
for hybrids. Highway Loss Data Institute. ``Injury Odds and Vehicle
Weight Comparison of Hybrids and Conventional Counterparts.'' HLDI
Bulletin 28(10). Arlington, VA, 2011.
---------------------------------------------------------------------------

    The first step in NHTSA's analysis was to use injury estimates from
the 2006-2012 National Automotive Sampling System--General Estimates
System (NASS-GES) and both 2007 and 2008-2011 Not in Traffic
Surveillance (NiTS) database to provide an average estimate for
combined in-traffic and relevant not-in-traffic crashes. In order to
combine the GES and NiTS data in a meaningful way, it was assumed that
the ratio of GES to NiTS will be constant for all years 2006 to 2012.
    Because both the GES and NiTS databases rely on police-reported
crashes, these databases do not accurately reflect all vehicle crashes
involving pedestrians because many of these crashes are not reported to
the police. The agency estimates that the number of unreported crashes
for pedestrians is equal to 100.8 percent of the reported crashes. That
is to say, for every 100 police-reported pedestrian crashes, there
exist 100.8 additional unreported pedestrian crashes.
    Table 20 shows the reported and unreported crashes by injury
severity. Only injury counts will be examined for the purpose of
benefits calculations and, as such, fatalities and uninjured (MAIS 0)
counts are not included.

     Table 20--Estimated Annual Quiet Cars Target Population Injuries Reported (GES 2006-2012, NiTS 2007, 2008-2011) and Unreported Pedestrians and
                                                                Pedalcyclists, by Vehicle
--------------------------------------------------------------------------------------------------------------------------------------------------------
                       MAIS level                                1               2               3               4               5           TOTAL 1-5
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                 Reported (GES+NiTS) and Unreported Injured Pedestrians
--------------------------------------------------------------------------------------------------------------------------------------------------------
Passenger Car (PC)......................................          69,453          11,093           2,249             529             214          83,538
Light Trucks & Vans (LTV)...............................          47,604           7,852           1,629             387             156          57,626
                                                         -----------------------------------------------------------------------------------------------
    Total Light Vehicles (PC+LTV).......................         117,056          18,945           3,877             916             370         141,164
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                Reported (GES+NiTS) and Unreported Injured Pedalcyclists
--------------------------------------------------------------------------------------------------------------------------------------------------------
MAIS level..............................................               1               2               3               4               5       TOTAL 1-5
Passenger Car (PC)......................................          42,943           6,148           1,082             239              84          50,495
Light Trucks & Vans (LTV)...............................          26,932           3,957             715             160              56          31,820
                                                         -----------------------------------------------------------------------------------------------
    Total Light Vehicles (PC+LTV).......................          69,875          10,105           1,796             400             140          82,315
--------------------------------------------------------------------------------------------------------------------------------------------------------

    The estimates in Table 20 are based on the current make-up of the
fleet for all propulsion types. Next, we make the assumption that
because the hybrid and electric vehicles pose a higher risk of
pedestrian collisions, each hybrid and electric vehicle is producing
more injuries per year than their ICE counterparts. Thus, while the
2006-2012 time period resulted in 141,164 pedestrian injuries annually,
this injury count is the result of the mixed hybrid/electric/ICE fleet
during that period. Based on the odds ratios from our crash analysis,
we can calculate what size of theoretical ICE-only fleet would have
been needed to generate as many injuries during that same time period.
    The estimated injuries in Table 21 and Table 22 are created by
combining the estimated percentage of annual sales of hybrid and
electric vehicles for MY2020 from Table 23 with the odds ratio of 1.18,
representing the increased risk of an HV being involved in a pedestrian
crash, and the odds ratio of 1.51, representing the increased risk of
an HV being involved in a pedalcyclist crash.\166\ Thus, when
considering pedestrians injured by MY2020 vehicles and assuming these
pedestrian crashes occurred because the pedestrians failed to detect
these vehicles by hearing, the rulemaking applies to the 877 injury
difference between that theoretical ICE-only fleet (140,663 injuries)
and the estimated lifetime injuries from the MY2020 fleet (141,567).
Given the effectiveness assumption of 97 percent, the rulemaking
addresses 850 of those 877 injuries. When considering pedalcyclists
injured by MY2020 vehicles, the rulemaking is applied to the 1,514
injury difference between that theoretical fleet (81,455 injuries) and
the estimated lifetime injuries from the MY2020 fleet (83,015). Given
our assumption that the pedestrian and pedalcyclists crash rates for
LSVs without sound is similar to that for other types of light vehicles
without sound, the rule would also reduce pedestrian injuries by 4 over
the lifetime of the MY2020 fleet of LSVs and

pedalcyclist injuries by 7 over the lifetime of the MY2020 fleet of
LSVs.
---------------------------------------------------------------------------

    \166\ Wu, J. (2015). Updated Analysis of Pedestrian and
Pedalcyclist Crashes by Hybrid Vehicles with Larger Samples and
Multiple Risk Factors. Washington, DC: National Highway Traffic
Safety Administration.
    \167\ Table values may not add up to the correct total due to
rounding.
    \168\ Table values may not add up to the correct value due to
rounding.

                                     Table 21--Enhanced Injury Rate (EIR) for Pedestrians for 2020 Model Year \167\
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Injuries   Injuries
                                                         Mild      Strong     EVs +                 Total     assuming   assuming    Injury
                                                       hybrids    hybrids   fuel cell  ICEs  (%)     (%)      100% ICE  predicted  difference   Benefits
                                                         (%)        (%)         (%)                            fleet      fleet
--------------------------------------------------------------------------------------------------------------------------------------------------------
Passenger Car.......................................       6.94       6.86       0.21      87.02     101.03     83,101     83,953         853        827
Light Trucks & Vans.................................       7.97       0.59       0.08      91.45     100.09     57,563     57,614          51         50
                                                     ---------------------------------------------------------------------------------------------------
Total...............................................  .........  .........  .........  .........  .........    140,663    141,567         904        877
--------------------------------------------------------------------------------------------------------------------------------------------------------

                                    Table 22--Enhanced Injury Rate (EIR) for Pedalcyclists for 2020 Model Year \168\
--------------------------------------------------------------------------------------------------------------------------------------------------------