values for the class of non-ICE sounds as a whole. Rather, the
equivalent detectability sound pressure level value for a particular
non-ICE sound must initially be determined experimentally by a jury
process that rates detectability. As psychoacoustic models improve, it
may be possible to use them in place of jury testing to determine
minimum sound pressure level specifications for these sounds, but that
approach is not yet sufficiently accurate.
    In this concept sound generation systems with signal processing
capabilities would be used to continuously and monotonically vary the
pitch and amplitude of sounds as appropriate to operating conditions
according to vehicle inputs (e.g. vehicle speed sensors, throttle
sensors, etc.). The appropriate relationship between sound amplitude
and throttle position would need to be determined. The detectability of
a specific non-ICE sound can be best determined only through human
subjects testing, at the present state of the art.
Hybrid of Options Discussed Above
    A third concept to designing countermeasure sounds, explored in the
Phase II report, would be a combination of the concepts (i.e. using
ICE-like or non-ICE-like sounds) discussed above, with the goal of
gaining the benefits of each, while minimizing the disadvantages.
Simulated ICE sound could be generated which would vary pitch and
loudness depending on vehicle inputs. This system could simultaneously
generate both ICE-like sounds at a lower sound pressure level than the
concepts based on ICE sounds discussed above, and synthetic sounds
designed for optimal alerting potential with minimal annoyance. The
ICE-like sound components may not be heard in higher urban ambient-
noise conditions, but their association with the alerting sound would
be learned over time from when the pedestrian is exposed to the sound
in lower ambients. This method would most likely depend on jury testing
of human subjects to set the sound level for detection.

Human Subject Evaluation of Detectability
    A human subject study was conducted to compare the auditory
detectability of potential sounds for hybrid and electric vehicles
operating at a low speed. The sounds evaluated included: (1) Sounds
produced by vehicles with integrated sound systems rented from
manufacturers, and (2) sounds produced by prototype systems rented from
manufacturers, and played back by loudspeakers temporarily mounted on
HVs rented separately. Five vendors, motor vehicle manufacturers or
suppliers of automotive electronics, provided prototypes of synthetic
sound generators for EVs or HVs. The five systems were labeled ``A'' to
``E''. A total of nine sounds were evaluated: A1, A2, A5, B, C, D, E1,
E3, and E4. Sounds were evaluated at two sound pressure levels typical
of ICE vehicles at low speeds (i.e., A-weighted SPL of 59.5 dB and 63.5
dB).\55\ An ICE vehicle that produced A-weighted SPL of 60 dB in the 6
mph pass-by test was used as a reference in this evaluation. The ICE
vehicle was labeled `R'.
---------------------------------------------------------------------------

    \55\ As measured by the SAE J-2889 draft test procedure (SAE J-
2889, draft, 2009).
---------------------------------------------------------------------------

    Sound A1 was an engine like sound with a turbine-like whine that
had a prominent peek that varied from 150 Hz to 300 Hz based on vehicle
speed. Sound A2 was an engine sound with enhanced valve noise with
prominent signal content between 100 Hz and 200 Hz. Sound A5 was a
whirring sound with a diesel engine sound. The fundamental signal
content of the whirring part of the sound for sound A5 was between 400
Hz and 600 Hz based on vehicle speed. Sound B emulated the exhaust note
(the fundamental of the combustion noise) of an engine. The sound did
not contain appreciable components above 250 Hz. Sound C was a Wavy,
turbo-like sound with most of its energy as broadband noise in the 200
Hz to 5000 Hz range. Sound D was a broadband sound designed to suggest
an electric motor coupled to other rotating machinery. Sound E1 was a
pure engine noise with most of its energy below 300 Hz. Sound E3 was an
engine-like sound with a `whirring' character and a flatter spectral
distribution than Sound E1 and had none of the prominent harmonics of
the combustion note. Sound E4 contained short bursts of predominantly
high-frequency sound with the peak amplitude of the fundamental varying
in frequency from about 450 Hz to 700 Hz based on speed.
    Data was collected outdoors during three independent sessions
conducted on three days in July and August 2010. The first session
included four operating modes: idle (stationary), acceleration from
stop, start-up and 6 mph forward pass-by. The following two sessions
included the 6 mph forward pass-by. The HVs used in the study were
operated in electric mode during the pass-by trials. The sample
included 79 participants 34 of which were sighted and 45 of which were
legally blind. The legally blind participants were independent
travelers and all participates had self-reported normal hearing.
    The study took place in a parking lot located on the USDOT/Volpe
Center campus in Cambridge, Massachusetts. The test site has the
acoustic characteristic of an urban area with a typical ambient noise
of approximately A-weighted sound pressure level of 58-61 dB. The
dependent variables examined in the study included raw detection
distance, proportion of detection, time-to-vehicle arrival, and
detection distance. Raw detection distance is the number of feet the
vehicle was from the participant when the participant indicated she or
he heard the sound. A failure to detect the sound before the vehicle
passed was treated as missing data. Proportion of detection is the
proportion of trials of a given condition in which the participant
detected the sound anytime before the vehicle passed the participant.
Time-to-vehicle-arrival is the time, in seconds, from detection of a
target vehicle sound to the instant the vehicle passes the pedestrian
location. Detection distance is the calculated distance, feet, to the
target vehicle at the moment each subject responded.
    Each subject had a push button device which they used to indicate
when they detected a nearby vehicle. Participants were asked to press a
response button when they detected and recognized a vehicle that would
affect their decision about when to start crossing the street.
    Table 8 shows the mean detection distances for the sounds evaluated
in the human-subject studies for the 6 mph pass-by; sounds at the top
of the list can be described as sounds designed according to
psychoacoustic principles and sounds at the end of the list can be
described as ICE-like sounds with only the fundamental combustion noise
or otherwise lacking in the qualities that support detectability. The
results show that high amplitude sounds (A-weighted SPL of 63.5 dB)
were detected more often and at greater distances than low amplitude
sounds (A-weighted SPL of 59.5 dB).

 Table 8--Mean Detection Distance (ft) for All Sounds at Two Amplitudes
                    and for the Reference ICE Vehicle
------------------------------------------------------------------------
                                              Average         Average
                                             detection       detection
                                             distance        distance
              Sound number                  (feet) for      (feet) for
                                             amplitude       amplitude
                                            equal 59.5      equal 63.5
                                               dB(A)           dB(A)
------------------------------------------------------------------------
E4......................................              72              85
A2......................................              57              77
E3......................................              52              70
A5......................................              50              47
ICE vehicle, 60 dB(A)...................              41              NA
A1......................................              35              44
C.......................................              32              41
E1......................................              30              32
B.......................................              20              25
D.......................................              19              NA
------------------------------------------------------------------------

    Results show that A2, A5, E3, and E4 have significantly better
detectability than the ICE reference sound at 6 mph. These sounds never
have significantly worse detectability in any condition. Thus, these
sounds overall have better detectability than the ICE reference sound.
In contrast, sounds A1, B, C, D, and E1 all have significantly worse
detectability than the reference sound for the 6 mph forward pass-by.
These sounds never have significantly better detectability in any of
the conditions presented to subjects. Thus, these sounds overall have
worse detectability than the reference sound.
    The analysis also indicated significant main effects of sound and a
significant three-way interaction of session, sound, and direction.
This implies that the relative performance of each sound, including the
reference sound, is jointly contingent on the direction it comes from
and the session it was presented in. The directional effect results
primarily from the fact that the roof-top fans on buildings to the west
were the predominant source of ambient noise, which can mask vehicles
approaching from the west compared with vehicles approaching from the
east. The detectability of each sound relative to the reference was
evaluated by comparing each sound to the reference vehicle for the
corresponding session and direction condition of each.
    To compare the detectability of the sounds to each other, a mixed
design ANOVA was performed on detectability with session and vision as
between-subjects independent variables, and sound, direction, and
amplitude as within-subject independent variables.\56\ Sounds were
ranked by comparing each to the other (t-tests) for each session by-
direction-by-amplitude condition. To assist in the control for family-
wise error rate, the analyses only included the four sounds shown to be
superior to the reference sound. Results show that E4 has overall
significantly better detectability than the other sounds, and within
each condition it is never worse than any other sound, except for one
condition when compared to A2. Sounds A2 and E3 are overall not
significantly different than each other, showing only a difference in a
single condition. Sound A5 has overall significantly worse
detectability than the other sounds, and within each condition is it
never better, except for one condition when compared to E3. The overall
ranking of the sounds from most to least detectable is therefore: E4,
A2 and E3, and A5.\57\
---------------------------------------------------------------------------

    \56\ The reference sound `R' and sound `D' were excluded from
this analysis since they did not differ in amplitude.
    \57\ The acoustic characteristics of these sounds are discussed
in Section 5.2 of NHTSA Report No. DOT HS 811 496.
---------------------------------------------------------------------------

    In summary, the human subject testing in Phase 2 suggest that
synthetic sounds that resemble those of an ICE produce similar
detection distances as actual ICE vehicles. In some instances,
synthetic sounds designed according to psychoacoustic principles can
produce double the detection distances relative to the reference
vehicle. The results also suggest that synthetic sounds that contain
only the fundamental combustion noise are relatively ineffective. None
of the analyses found a significant effect of vision ability.\58\
Participants who are legally blind, on average, were no better or worse
than sighted participants in detecting the approach sounds.
---------------------------------------------------------------------------

    \58\ All participants were required to wear a blindfold during
the study.
---------------------------------------------------------------------------

C. NHTSA Phase 3 Research

    The third phase of NHTSA's research involving quiet vehicles
consisted of developing an objective, repeatable test procedure and
objective specifications for minimum sound requirements for hybrid and
electric vehicles. NHTSA's Vehicle Research and Test Center (VRTC)
conducted acoustic measurements and recordings of several HVs and EVs
and those vehicle's ICE pair vehicles. Volpe used these recordings as
well as data from the Phase 1 and Phase 2 research to identify
parameters and criteria for sounds to be detectable and recognizable as
a motor vehicle.
VRTC Acoustic Measurements
    The primary focus of Phase 3 research conducted by VRTC was to
evaluate the new SAE J2889-1 test method and several variations used to
test operating conditions that were not included in SAE J2889-1 and
provide data to establish performance criteria. The research was
conducted using 3 HVs, 1 EV, and 4 ICE vehicles.
    SAE J2889-1 was still in draft form at the start of the project,
but the final version published in September of 2011 was not
significantly different from the draft. The vehicles were used to
gather sample data on the difference in sound pressure levels between
ICE sounds and EV or HV sounds as well as directivity and sound quality
levels using eleven test scenarios developed for this program (4 static
and 7 pass-by). Some of the hybrid and electric vehicles were tested
with multiple alert sounds. Some the hybrid and electric vehicles were
also tested with no alert sound at all to determine crossover levels.
    A significant modification to the SAE procedure was the addition of
a laser at the microphone line-labeled as PP' in SAE J2889-1. This
addition enabled recording the time at which the leading edge of the
vehicle reached the microphone location.
Test Scenarios \59\
---------------------------------------------------------------------------

    \59\ Diagrams showing the microphone setup for all the scenarios
are contained in the Phase 3 report from VRTC.
---------------------------------------------------------------------------

    VRTC measured the vehicle sound output for the operating scenarios
listed below for ICE vehicles, hybrid and electric vehicles with an
alert sound active, and hybrid and electric vehicles with no alert
sound active. The overall goal of the research was to capture as much
acoustic data as possible for both ICE sounds and artificial sounds
added to hybrid and electric vehicles as alert sounds so that the
sounds could be analyzed when the agency was the establishing acoustic
specifications contained in this proposal.
     Scenario 1: SAE J2889-1 modified Startup (8 microphones).
This set up was used to generate a 360 degree sound or directivity
profile for the vehicle.
     Scenario 2: SAE J2889-1 modified Stationary but active (8
microphones). This scenario was the same as Scenario 1 except that the
sound of the vehicle while stationary was recorded.
     Scenario 3: SAE J2889-1 modified Startup (5 microphones).
Data from this recording can be used can be used to generate a 180
degree sound or directivity profile for the vehicle.
     Scenario 4: SAE J2889-1 modified Stationary but active (5
microphones). This scenario was the same as Scenario 3 except that the
sound of the vehicle while stationary was recorded.
     Scenario 5: SAE J2889-1 10 km/h Forward Constant Speed (2
microphones). This test produced result from 2 microphones on either
side of the vehicle centerline.
     Scenario 6: SAE J2889-1 20 km/h Forward Constant Speed (2
microphones). This test produced result from 2 microphones on either
side of the vehicle centerline.
     Scenario 7: SAE J2889-1 30 km/h Forward Constant Speed (2
microphones). This test produced result from 2 microphones on either
side of the vehicle centerline.
     Scenario 8: SAE J2889-1 10 km/h Reverse Constant Speed (2
microphones). This test was pass-by noise test with data being recorded
as the vehicle is driven backwards though the noise test pad with two

microphones on either side of the vehicle centerline.
     Scenario 9: 0 to 10 km/h Forward Acceleration to Constant
Speed (2 microphones) The vehicle was positioned 2 meters before the
PP' line and accelerated at 0.1 g from 0 to 10 km/h pass-by noise test
with data being recorded by two microphones on either side of the
vehicle centerline as the vehicle is accelerated though the remainder
of the noise test pad.
     Scenario 10: 30 to 10 km/h Forward Deceleration to
Constant Speed (2 microphones). The vehicle was driven at 30 km/h into
the test zone and began deceleration at 0.1 g to 10 km/h at the PP'
line.
     Scenario 11: 0 to 10 km/h Reverse Acceleration to Constant
Speed (2 microphones). The vehicle was positioned 2 meters before the
PP' line and accelerated from 0 to 10 km/h with data being recorded by
microphones on both sides of the vehicle centerline as the vehicle was
accelerated though the remainder of the noise test pad.
    When testing the vehicle in the scenarios described above VRTC
identified some challenges. The test drivers found that it was
difficult to reliably maintain a low travel speed for some vehicles
during the 10 km/hr forward pass-by test as these vehicles tried to
shift gears or the electric controls energized or de-energized. During
the pass-by tests conducted in reverse at 10 km/hr the test drivers
experienced some of the same difficulties experienced during the
forward pass-by testing. Also, it was very difficult to maintain the
vehicle in the center of the lane. Testing in reverse could only be
done during daylight hours due to difficulty in driving backwards,
drifting in the lane and possible equipment damage. During the testing
of the vehicle accelerating from 0 to 10 km/hr the test drivers
encountered difficulty in maintaining a consistent acceleration rate.
Positioning the vehicle for this test and starting the data acquisition
was very labor intensive
    When testing the vehicle decelerating from 30 to 10 km/hr the test
drivers encountered difficulty in maintaining a consistent deceleration
rate. Determining the starting point of deceleration was difficult.
Some vehicle braking rates were difficult to maintain the 0.1 g rate.
During braking the vehicles' regenerative braking systems transitioned
back and forth from mechanical to regenerative braking. When testing
the vehicles while accelerating in reverse the test drivers encountered
difficulty in maintaining a consistent acceleration rate and
maintaining the center of the lane for the remainder of the test pad.
Positioning the vehicle and starting the data acquisition was very
labor intensive for this test.
Interpretation of Results
    One of the purposes of the Phase 3 acoustic measurements was to
gather additional data on the difference in sound levels between EVs
and HVs operating in electric mode and ICE vehicles. For the pass-by
tests in Phase 3 the ICE vehicles were 6.2 to 8.5 A-weighted dB louder
than the EV/HVs without added sound at 10 km/h. At 20 km/h the
difference between the HV/HVs and ICE vehicles varied, but the average
level was 3.5 A-weighted dB louder for the ICE vehicles. At 30 km/h the
sound levels of the HV/HVs approached the levels of the ICE vehicles
and the individual measurements for the two types of vehicles have
considerable overlap. Table 9 shows the results of HEV/EV vehicles with
no sound alert system as compared to their ICE counterpart.

   Table 9--Pass-By Sound Level for HEV/EV Vehicles Without Alert Sound Active Versus Counterpart ICE Vehicles
----------------------------------------------------------------------------------------------------------------
                                                                   HEV/EV Sound      ICE Sound    ICE minus HEV/
                  Manufacturer                      Speed, km/h      level, dB       level, dB        EV, dB
----------------------------------------------------------------------------------------------------------------
Nissan..........................................              10            50.5            56.6             6.2
                                                              20            60.0            62.3             2.2
                                                              30            66.5            68.1             1.5
Prototype Vehicle G.............................              10            51.4            59.9             8.5
                                                              20            60.5            63.1             0.6
                                                              30            67.0            67.5             0.5
Prototype Vehicle H.............................              10            51.2            59.7             8.5
                                                              20            59.3            64.5             5.2
                                                              30            65.3            69.2             3.9
Average.........................................              10            51.0            58.7             7.7
                                                              20            59.9            63.3             3.5
                                                              30            66.3            68.3             2.0
----------------------------------------------------------------------------------------------------------------

    The measurements from the startup and stationary but active
scenarios were used to measure the directivity of the vehicles' sound.
The purpose of measuring the directivity pattern of the vehicles was to
compare the directivity pattern of ICE vehicles to those hybrid and
electric vehicles equipped with a speaker system. For the ICE vehicles
the sound pressure level behind the vehicle was from 6 to 10 dB less
than that directly in front of the vehicle. For the vehicles with an
speaker system the sound level behind the vehicle was 12 to 15 dB lower
behind the vehicle, and in some cases the sound level at the microphone
behind the vehicle was not distinguishable from a quiet background
sound level of 40 dB. There was a systematic difference from left to
right for some vehicles, particularly with an artificial sound.
Acoustic Analysis Performed by Volpe
    As part of the Phase 3 research Volpe examined the frequency range,
minimum sound level for selected one-third octave bands, and
requirements for broadband noise and tones as possible criteria for
vehicle sound using a loudness model to determine when the sounds might
be detectable in a given ambient. Also considered were the relative
proportions of acoustical energy emitted from a vehicle as a function
of direction (directivity) and ways to denote changes in vehicle speed.
Two approaches were used to identify potential detectability
specifications for alert sounds to be included in the NPRM: (a) sound
parameters based on a loudness model and detection distances and (b)
sound parameters based on the sound of ICE vehicles.

    Volpe's work in developing the acoustic specifications based on a
loudness model and detection distances was guided by several aspects of
the agency's Phase 1 and Phase 2 research. Volpe analyzed the acoustic
data of the sounds used in the human factors research in Phase 2 from a
psychoacoustic perspective to determine the loudness of the sounds and
whether the sounds would be detectable in several different ambient
environments. Of the several different loudness models examined by
Volpe, Moore's Loudness provided the most pertinent information about
the perceived loudness and detectability of a sound.
    Because the response of the study participants in the human subject
experimentation in Phase 2 varied significantly due to variations in
the ambient, Volpe determined that any analysis of sounds using a
loudness model should use a synthetic ambient that did not vary with
respect to the frequency profile or overall sound pressure level. Volpe
used a synthetic ambient sound with the loudness model during Phase 3
in developing the specifications contained in this proposal. Volpe also
observed during the human factors research that sounds with strong
tonal components were more detectable.
    Volpe developed the specifications based on the sound of ICE
vehicles using measurements of ICE vehicles captured in Phase 2 and
acoustic data provided by representatives of auto manufacturers.
    Before presenting these two approaches, it is important to explain
how background noise, critical frequency range, and loudness models
relate to the detectability of a sound.
Background Noise
    When talking about the detectability of a sound, it is important to
understand masking and background noise (ambient noise). Masking occurs
when the perception of one sound is affected by the presence of an
unrelated sound. Background noise can affect the extent to which
masking occurs. Two characteristics of background sounds are of primary
importance: overall sound pressure level and the frequency content or
shape of the frequency spectrum. Masking depends on the signal-to-noise
ratio in the different frequency bands and therefore cannot be
estimated from the overall A-weighted sound level alone. Acoustic data
for background noise can be obtained from recordings of background
noise made at various locations. Recordings of actual traffic may
include peaks (e.g., passage of nearby loud vehicles) that can
introduce variability when using human subjects for testing or when
applying detectability models. An alternative to recordings of the
actual traffic is to use standardized synthetic background noise.
Synthetic background noise consists of, for example, white noise
filtered to have the same spectrum as what a pedestrian would hear in
real traffic but without the variations in amplitude over time (e.g.,
those caused by the passage of a particular loud vehicle or aircraft).
This broadband noise creates masking while reducing the issues
associated with fluctuations or peaks. The standardized noise is an
advantage for repeatability. For more information about this, see
Pedersen et al. 2011.\60\
---------------------------------------------------------------------------

    \60\ Pedersen et al. (2011). White paper on external sounds for
electric cars--Recommendations and guidelines. Delta-Senselab.
Copenhagen.
---------------------------------------------------------------------------

    A standardized background noise was used in Phase 3 in the
implementation of Moore's Loudness model to compute minimum sound
levels for detection in a given one-third octave band and to identify
frequency ranges relevant for alert sounds.\61\ The ambient selected
for these analyses is representative of many common urban ambients.\62\
Being detectable in this ambient would mean that the alert sound would
be detectable in other ambients with lower overall levels and similar
spectral shapes. The spectral shape is given in Figure 2. The overall
A-weighted level for detection computations was 55 dB). Results for 60
A-weighted dB can be accurately estimated by adding 5 dB to the results
from the 55 A-weighted dB analysis. Similarly, results for 50 A-
weighted dB can be accurately estimated by subtracting 5 dB from the
results from the 55 A-weighted dB analysis.
---------------------------------------------------------------------------

    \61\ For a discussion of loudness models see page 67.
    \62\ See footnote 59.
    [GRAPHIC] [TIFF OMITTED] TP14JA13.030

Critical Frequency Range
    Critical frequency regions, defined by a set of one-third octave
bands, are determined by applying psychoacoustic principles for a given
ambient condition. The purpose of identifying a critical frequency
region(s) is to ensure that a sound signal is emitted from the vehicle
such that it would be expected to be detectable at a reasonable
distance away from a pedestrian. Due to masking effects of the ambient
and potential hearing loss of the pedestrian, opportunities for
detection will be maximized if the alert signal contains detectable
components over a wide frequency range.
    Frequencies in the audible range for children and most young adults
are from about 20 to 20,000 Hz. Human

hearing is more sensitive in the 500-5,000 Hz range than it is at low
frequencies or very high frequencies.\63\ Exposure to loud noise and
age-related factors often diminish a person's sensitivity to sound at
higher frequencies. Mid-range frequencies (approximately 320--5120 Hz)
are perceived with greater loudness than lower (20 to 320 Hz) or higher
frequencies (5000 to 20,000 Hz). Frequencies below 300 Hz are commonly
masked by urban background noise.\64\
---------------------------------------------------------------------------

    \63\ Fletcher, H. and Munson, W. A. (1933). Loudness, its
definition, measurement, and calculation. Journal of the Acoustic
Society of America. 5 (1), 82-108.
    \64\ See footnote 11 Chapter 6.
---------------------------------------------------------------------------

    Localization of sounds is accomplished through multiple
neurophysiological processes, each of which is most effective in a
different range of frequencies. Above 1600 Hz, inter-aural level
differences (caused by the shadowing effect of the head) become the
primary directional cues. For some combinations of frequency and
angular orientation between sound source and listener, cancellation of
the direction cues can occur. Hence, an accurate localization of a
sound source is most likely to occur when it contains multiple high-
frequency components that are audible above the background noise.\65
66\
---------------------------------------------------------------------------

    \65\ Feddersen et al. (1957). Localization of high frequency
tones. Journal of the Acoustical Society of America. 5, 82-108.
    \66\ Yost, W.A. (1994) Fundamentals of Hearing: An Introduction.
San Diego: Academic Press.
---------------------------------------------------------------------------

    A person's relative sensitivity to different frequencies varies
with loudness. Loudness is a numerical designation of the strength,
expressed in units called ``sones,'' of a sound that is proportional to
the subjective magnitude as estimated by listeners having normal
hearing (ANSI S3.4 2007).\67\ Loudness models predict this strength by
accounting for how the human auditory system processes both the
amplitude and frequency characteristics of a sound.
---------------------------------------------------------------------------

    \67\ American National Standard (1995). Procedure for the
computation of loudness of steady sound (ANSI S1.13). New York, New
York: Secretariat, Acoustical Society of America.
---------------------------------------------------------------------------

Loudness Models
    Sound-pressure-level-based metrics, such as, the A-weighted level,
provide a first estimate of the perceived loudness of a sound. These
metrics fail to account for several factors that affect the perceived
loudness including: the level dependence of the frequency sensitivity,
level dependence on frequency selectivity, and frequency based masking
effects. The level dependence of the frequency sensitivity refers to
the fact that for the same change in sound pressure level for a low
frequency sound and a high frequency sound, the low frequency sound
will be perceived as increasing in loudness more than the high
frequency sound. The level dependence of the frequency selectivity
refers to how the human auditory system separates frequency components
of a complex sound's signal. Frequency-based masking is used to
describe how a high-energy component can prevent or reduce the
perception of a lower-energy component at a different frequency. That
is, for example, an ambient with a high level of low-frequency sound
can mask a signal with components in a higher frequency range.
    Several psychoacoustic models exist that relate sound pressure
level data to the perceived loudness of the signal or its
detectability/audibility. Moore's Loudness model \68 69\ was used in
Phase 3 to estimate the minimum sound level needed for a sound to be
detectable in the presence of an ambient. This model is useful for the
prediction of thresholds in quiet ambients and for thresholds in the
presence of a masker,\70\ as well as for computing equal loudness
contours.\71\ This model was developed for use with ISO 226, Normal
Equal-Loudness Contours, (1987) and the absolute thresholds found in
ISO 389-7, Acoustics--Reference zero for the calibration of audiometric
equipment--Part 7: Reference threshold of hearing under free-field and
diffuse-field listening conditions, (1996). Since the model's original
development, both of these standards have been updated to ISO 226
(2003) and ISO 389-7 (2005). There are newer implementations of Moore's
model that reflect these new data. However, we are not aware of any
implementations that include these updates as well as provide for
computing thresholds in the presence of a masker. Since computing
thresholds in the presence of a masker is of fundamental importance for
the work in Phase 3, and since the updates represent ``fine tuning'' of
the model, the 1997 model was identified as the most suitable choice.
---------------------------------------------------------------------------

    \68\ Moore et al. (1997). A model for the prediction of
thresholds, loudness, and partial loudness, J. Audio Eng. Soc.
45(5).
    \69\ Moore and Glasberg (1997). A model of loudness perception
applied to cochlear hearing loss. Auditory Neuroscience, 3, 289-311.
    \70\ A value of 0 sones is approximately the threshold of
perception. Moore models threshold to be at 0.003 sones to match ISO
389-7:2005 to within 0.2 dB over the frequency range from 50 to
12,500 Hz (ANSI S3.4-2007).
    \71\ Loudness contours is a graphical representation of
frequency (x-axis) versus levels (y-axis) such that tones of
different frequency and different level are judged to be equally
loud.
---------------------------------------------------------------------------

    Moore's Loudness model, as described in Moore and Glasberg
(1997),\72\ accounts for the following factors: how the sound is
presented to the subject (free field, diffuse field, via headphones);
transmission through the pinna (outer ear) and the middle ear;
frequency sensitivity and selectivity; excitation compression/
amplification; the transformation of pressure entering the cochlea to
an excitation pattern (determined from the magnitude of auditory filter
output); transformation from an excitation pattern to specific loudness
for sounds in quiet ambient environments and in the presence of a
masker (specific loudness is analog to power spectral density); and
integration of specific loudness (integrating the area under the curve
of a power spectral density function gives the total power of that
function).
---------------------------------------------------------------------------

    \72\ See footnote 67, 289-311.
---------------------------------------------------------------------------

    The general procedure for running the model is to provide un-
weighted one-third octave band levels for both the signal and the
masker and to provide information on how the signal is presented. For
the purposes of the Phase 3 work, free-field, frontal presentation was
used, which is both accurately and conservatively compared to diffuse
field or headphones. The model provides several levels of detail in the
results, including the specific loudness as a function of the number of
equivalent rectangular bandwidths. It is the integral of this function,
or simply Loudness in sones that was utilized in Phase 3.
    This model was adequate for the needs of Phase 3. However, since
this is a time-invariant model, it does not take into account
differences in duration (sounds with very short durations are perceived
differently than long duration sounds due to the temporal windows
associated with the auditory system). Nor does it account for periodic
modulations including the effect of co-modulation masking release.
    As part of the Phase 3 research, in addition to exploring the
detectability of sounds, the agency examined acoustic characteristics
that make sounds recognizable. Recognition includes two aspects: 1)
recognition that the sound is emanating from a motor vehicle, and, 2)
recognition of the type of operation that the vehicle is conducting so
that the pedestrian can take appropriate measures. Our research has
shown that sounds that contain both broadband components and tones are
more likely to be recognized as vehicles. Sounds that contain only high
frequencies have a synthetic (and unpleasant) character.

Sounds with lower frequency tones and broadband components have a more
closely resemble the sound produced by an ICE vehicle. In the Phase 2
human factors research Volpe observed that sounds with strong tonal
components were more detectable.
    While developing the acoustic parameters contained in this proposal
during Phase 3, parameters that were critical to recognition were
determined by simulating sounds. Sound simulations were developed for
the following vehicle operating scenarios: stationary but activated,
constant speed pass-bys, and accelerating pass-bys. Pass-bys included
Doppler shifts and accelerations also included a pitch shifting tied to
vehicle speed. The sound pressure levels changed as a function of speed
and as a function of position relative to the receiver during the
vehicle pass-by sound simulations. Roughly two hundred sounds were
generated and evaluated. Based on initial assessment of these sounds
and engineering judgment, at least one tone (and preferably more)
should be included in the acoustic specifications for HVs and EVs for
the purpose of recognition. The lowest tone should have a frequency no
greater than 400 Hz. A component is considered to be a tone if the
Tone-to-Noise ratio according to ANSI S1.13-1995 \73\ is greater than
or equal to 6 dB. (Note: the methodology in ANSI S1.13-1995 appears to
be overly conservative for the Phase 3 work. It may be better to: a)
either reduce the bandwidth, or b) include all tones within the band
for this calculation for the current application. Comments are
specifically sought on this issue).
---------------------------------------------------------------------------

    \73\ Secretariat, Acoustical Society of America (1995).
Procedure for the computation of loudness of steady sound, American
National Standard ANSI S1.13. New York, NY.
---------------------------------------------------------------------------

    Broadband components, which may be modulated, should be in each
one-third octave band from 160 Hz to 5000 Hz. Tones at frequencies
above 2000 Hz do not contribute to recognition. To aid in recognition
of vehicle acceleration and deceleration, the pitch (as measured by the
fundamental frequency) should increase and decrease by at least one
percent per km/hr of speed over the range from 0 km/hr to 30 km/hr.
Additional cues for recognition will be obtained by the movement of the
vehicle relative to the pedestrian, and were not considered for
potential acoustic specifications.
    The following are recommendations to increase recognition based on
the Phase 3 research:
     No greater than 50 percent amplitude modulation at
stationary but activated, at a frequency equal to the modeled
combustion frequency.
     Ratios of the total tonal power to the total broadband
power should not exceed 15 dB. (Note: this is not the same as the Tone-
to-Noise Ratio).
     Multiple harmonics with a fundamental equal to a
hypothetical combustion frequency.
     The lowest harmonic included should be as low in frequency
as the countermeasure system can reliably produce.
     The first or second harmonic present should have the
highest amplitude with higher harmonics generally decreasing in
amplitude.
     Amplitude should increase as a function of speed beyond
the required change for minimum detection (but not beyond the maximum
level).
    The agency solicits comments regarding the specific values, e.g. 50
percent, 15 dB, etc., as well as why characteristics should be
included/excluded from this list.
    In addition to the recommendations for the recognition of HV and EV
sounds contained above, the Phase 3 research found the acoustic
requirements for HVs and EVs should include pitch shifting as an
element to enhance recognition. A pitch shifting requirement would keep
out melodies or sounds that change over time. The low-frequency
requirement would convey the sound of rotating machinery. Limiting
amplitude modulation would reduce annoyance and help with recognition,
as will excluding frequency modulation and the noise component of the
sound filter shapes with high roll-off rates.

D. International Approach to Pedestrian Alert Sounds

    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.
    The MLIT included the following guidelines for the type and volume
for the sound generator system:
     ``The sound shall be continuous sound associating motor
vehicles running condition.''
     ``Siren, chime, bells, melody, horns sounds, animals,
insects, and sound of natural phenomenon such as wave, wind, river
current, etc., are not allowed.''
     ``The sounds generated shall be automatically altered in
volume or tone depending on the vehicle speed for easier recognition of
the movement of the vehicle.''
     ``Sound volume shall not exceed a level of the sound
generated when vehicles driven by internal combustion only run at speed
of 20 km/h.''
    The use of `add-on' devices, generating sound continuously for five
seconds or longer, have been approved in order to increase AVAS
penetration. MLIT will look into social acceptability and verification
of technology implementation issues before moving from a voluntary
process to a mandate.\74\
---------------------------------------------------------------------------

    \74\ MLIT and JASIC (2010). Guidelines for Measure Against
Quietness Problem of HV. GRB Informal group on Quiet Road Transport
Vehicles (QRTV) Working papers of the 3rd informal meeting. Tokyo,
13-15 July 2010. Available at: http://www.unece.org/trans/main/wp29/wp29wgs/wp29grb/QRTV_3.html.
---------------------------------------------------------------------------

    In addition to the actions taken in Japan the United Nations
Economic Commission for Europe (UNECE) World Forum for Harmonization of
Vehicle Regulation has an informal group on Quiet Road Transport
Vehicles (QRTV). The objective of the QRTV is to ``[d]etermine the
viability of `quiet vehicle' audible acoustic signaling techniques and
the potential need for their global harmonization.'' The QRTV's program
plan includes: review the available research; determine human factors
needed for pedestrians; develop technical performance parameters for
vehicles based on human factors needs; determine audible sound
characteristics and ways to convey desired vehicle performance
information to pedestrians; and determine technical and

economical feasibility of potential audible warning techniques.\75\
---------------------------------------------------------------------------

    \75\ QRTV (2010). Terms of Reference and Rules of Procedure for
the GRB Informal Group on Quiet Road Transport Vehicles (QRTV).
Available at: http://www.unece.org/trans/main/wp29/wp29wgs/wp29grb/QRTV_1.html.
---------------------------------------------------------------------------

    UNECE has adopted guidelines substantially similar to the MLIT
guidelines discussed above with the same requirements and
recommendations.\76\ The guidelines are intended to provide
manufacturers with recommendations to follow in developing alert sound
systems for adding sound to quiet vehicles.
---------------------------------------------------------------------------

    \76\ http://www.unece.org/fileadmin/DAM/trans/main/wp29/wp29wgs/wp29gen/wp29fdoc/ECE-TRANS-WP29-78-r2e.pdf.
---------------------------------------------------------------------------

E. SAE Sound Measurement Procedure

    SAE J2889-1 SEP2011, Measurement of Minimum Noise Emitted by Road
Vehicles,\77\ is a performance-based and technology neutral test
standard. The standard specifies an objective method for measuring the
minimum noise emitted by road vehicles. The standard reflects the
development of engine and propulsion technologies that cannot be
correctly tested under other SAE standards. SAE J2889-1 SEP2011
specifies test site and meteorological conditions, as well as the
ambient noise level under which the sound should be recorded. The
standard includes provisions for outdoor and indoor (hemi-anechoic)
testing. The test procedure includes specifications for microphone
position, condition of vehicles (e.g., battery state, tires, warning
signals), operating condition (i.e., 10 km/hr (6 mph) and stopped),
measurement readings, and reporting requirements. SAE J2889-1 is
derived from SAE 2805, Measurement of Noise Emitted by Accelerating
Road Vehicles, and therefore some of the requirements related to
ambient, equipment, and facilities are the same.
---------------------------------------------------------------------------

    \77\ See footnote 2.
---------------------------------------------------------------------------

    The standard also includes procedures to evaluate external vehicle
sound generator systems for alerting pedestrians about a vehicle's
operating conditions. The outcome includes various acoustic metrics for
the external vehicle sound generators such as sound pressure level,
frequency content, and changes in sound pressure level and frequency as
a function of vehicle speed. SAE J2889-1 SEP2011 does not account for
psychoacoustic factors such as annoyance, recognizability, or
detectability.
    SAE published a second version of SAE J2899-1 in May of 2012. This
version, SAE J2889-1 MAY2012, in addition to the provisions described
above, contains a bench test to allow the alert sound's shift in pitch
to be measured on a component level and a procedure to measure the
alert sound's shift in pitch on a vehicle level indoors. SAE J2889-1
MAY2012 also contains a procedure for measuring a ``commencing motion''
sound.
    The International Organization for Standardization (ISO) is
cooperating with SAE in its efforts to develop a vehicle minimum noise
measurement standard. The ISO document ISO/NP 16254 Measurement of
Minimum Noise Emitted by Road Vehicles \78\ and SAE J2889-1 are
reportedly technically identical but this has not yet been confirmed by
NHTSA because the ISO document is still in draft form.
---------------------------------------------------------------------------

    \78\ ISO/NP 16254 Measurement of Minimum Noise Emitted by Road
Vehicles. http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=56019.
---------------------------------------------------------------------------

F. Alert Sounds Currently Provided by Manufacturers

    Automotive manufacturers that produce EVs for the U.S. market have
recently developed various pedestrian alert sounds. At the time that
PSEA was enacted, most manufacturers of HVs had not typically been
equipping those vehicles with alert sounds for the U.S. market. As of
the date of this writing, we have detailed knowledge of only one system
developed by Nissan. We know that others are under development and that
several manufacturers plan to equip their vehicles with these systems
in the near future. Nissan has developed a system called Approaching
Vehicle Sound for Pedestrians (VSP) for the 2011 Nissan Leaf.\79\ The
system consists of a digital sound synthesizer connected to a speaker
mounted under the hood of the vehicle and a sound control system. The
sound controller gets three inputs: Vehicle speed, gear position, and
brake signal. The VSP has an on/off switch located in the instrument
panel for temporary deactivation by the driver. A forward sound
activates at low speeds, fades off as the vehicle reaches 30 km/hr (18
mph) and fades back on as the vehicle speed reduces to 25 km/hr. The
pitch increases proportionally with vehicle speed. A unique sound is
activated when the gear is in ``reverse'' and when the vehicle starts
from a stopped position. No sound is emitted when the vehicle is in
``drive'' gear but stationary, but the vehicle does emit a sound when
stationary in ``reverse'' gear. The sounds emitted from the vehicle are
digitally generated as opposed to being a recording of an ICE vehicle,
and plays through speakers.
---------------------------------------------------------------------------

    \79\ Konet et al. (2011) Development of Approaching Vehicle
Sound for Pedestrians (VSP) for Quiet Electric Vehicles. SAE
International. Paper No. 2011-01-0928. Abstract available at: http://saeeng.saejournals.org/content/4/1/1217.abstract.
---------------------------------------------------------------------------

    Nissan indicates that the sound was designed to achieve the same
detectability as ICE sound while maintaining a quiet cabin for the
driver and without being intrusive to communities. The VSP was
developed based on three design guidelines. First, increase peak
frequency content between 600 and 800 Hz to improve detectability for
aging pedestrians with high frequency hearing loss. Second, increase
peak frequency content between 2000 and 5000 Hz to improve
detectability of pedestrians with normal hearing. Lastly, reduce
frequency content at around 1000 Hz to avoid noise intrusion. The VSP
was set to have a similar sound pressure level as a Nissan Versa 1.8L
at 10 km/hr (6 mph) while having two peaks at 630 Hz and 2500 Hz, and a
valley at 1000 Hz.

G. The Notice of Intent To Prepare an Environmental Assessment

    On July 12, 2011, the agency published a Notice of Intent to
Prepare an Environmental Assessment (NOI) seeking comment on the
alternatives that the agency should consider when analyzing the
environmental consequences of a proposed quiet vehicle rule. The NOI
stated that the purpose and need of the rulemaking was to ``require EVs
and HVs, which tend to be quieter than the ICE vehicles, to be equipped
with a pedestrian alert sound system that would activate in certain
vehicle operating conditions to aid blind and other pedestrians in
detecting the presence, direction, location, and operation of those
vehicles.'' \80\
---------------------------------------------------------------------------

    \80\ 76 FR 40860 (July 12, 2011). The agency intends this
proposal to be technology neutral. The statement of purpose and need
in the NOI acknowledges, for the purposes of the agency's NEPA
analysis of the environmental impacts of this rulemaking action,
that many manufacturers will choose to install speaker systems on
their vehicles in order to meet the minimum sound requirements in
this proposal. This proposal establishes minimum sound requirements
that HVs and EVs must meet. It does not specify that vehicles must
be equipped with a speaker system.
---------------------------------------------------------------------------

    The NOI discussed the following five alternatives that the agency
planned on considering in its analysis of the environmental
consequences of the rule and requested that the commenters propose
other alternatives for the agency to consider: (1) Taking no action;
(2) requiring alert sounds based on recordings of ICE vehicles; (3)
specifying acoustic requirements for synthetic sounds that would
closely resemble sounds produced by ICE vehicles; (4) setting
requirements for alert sounds that possess aspects of both

sounds produced by ICE vehicles and acoustic elements that contribute
to detectability; and (5) using psychoacoustic principals to develop
requirements for alert sounds that would have enhanced detectability
but would not necessarily have a reference to sounds produced by ICE
vehicles. The NOI stated that it was likely that a rule that allowed
alternatives 4 and 5 would need to include a jury testing procedure to
ensure that the sounds were recognizable to pedestrians as a motor
vehicle in operation.
Comments Received in Response to NOI
    In response to the NOI, NHTSA received 33 comments from state
governments and Indian tribes, advocacy organizations for individuals
who are blind, national and international standards organizations, auto
manufacturers, heavy vehicle manufacturers, trade organizations that
represent motor vehicle manufacturers, component manufacturers,
environmental groups and private individuals. The agency received
comments on both the technical and environmental aspects of the NOI.
    Most of the commenters expressed support for all of the
alternatives, except the no action alternative. All the commenters that
commented on possible methods for determining compliance with the
various alternatives stated that the performance criteria for alert
sounds should be based on objective factors and that jury testing was
not an appropriate method for determining compliance with an FMVSS.
    Several of the commenters requested that the agency set the minimum
sound level requirements for EVs and HVs to the sound levels produced
by quiet ICE vehicles rather than the average sound pressure level
produced by ICEs. These commenters expressed concerns that if NHTSA set
the minimum sound pressure level requirements for EVs and HVs to the
average sound level produced by ICE vehicles, this would stop noise
reduction trends in vehicle design. Commenters that stated that the
minimum sound level requirements for EVs and HVs should be tied to
quiet ICE vehicles were also concerned about minimizing the
environmental effects of adding sound to EVs and HVs and driver
acceptance of the added sounds. One commenter stated that the acoustic
specifications developed by the agency should include a dB level dip in
the mid-range frequencies around 1000 Hz to limit the community noise
impact of adding sound to hybrid and electric vehicles.
    Several commenters also questioned whether there was a safety need
for the agency to set minimum sound level requirements for the
stationary but activated operating condition. Most motor vehicle
manufacturers stated that the agency should only require that EVs and
HVs produce sound until the vehicle reaches a speed of 20 km/hr (12
mph) while advocacy groups for individuals who are blind stated that
EVs and HVs should produce sound until 32 km/hr (20 mph).
    Light vehicle manufacturers stated that the agency should not be
overly concerned with writing the acoustic specifications for the alert
sound to prevent the use of annoying noises. These manufacturers stated
that they did not believe it was necessary to try to prevent annoying
sounds because manufacturers would not use annoying sounds as alert
sounds because they do not want to annoy their customers.
    Several commenters stated that the agency should adopt the ECE
guidelines for alert sound systems (the ECE guidelines are based on the
Japanese guidelines discussed in Section VIII.E), as the agency's
requirements for alert sounds for HVs and EVs. These commenters
believed that the ECE guidelines provide manufacturers with flexibility
in developing sounds while appropriately balancing the needs of
pedestrians and concerns about environmental noise impact. In
discussions with the agency manufacturers have stated that they believe
that the ECE guidelines would address the agency's concerns about
annoying alert sounds.\81\
---------------------------------------------------------------------------

    \81\ See Section VIII. E. for a discussion of why we are not
proposing to adopt the Japanese or ECE guidelines.
---------------------------------------------------------------------------

    Several commenters pointed out potential drawbacks in requiring an
alert sound that was a recording of an ICE vehicle.
    The commenters requested that the agency maintain a significant
degree of flexibility in developing acoustic specifications for alert
sounds. Several commenters stated they did not believe that all of the
characteristics that the agency used to describe sounds comprising
alternative 5 were necessary to provide effective pedestrian alert
sounds. Advocacy groups for individuals who are blind also stated that
the agency should not allow alert sounds with none of the acoustic
characteristics of current ICE vehicles and that the agency should not
consider alternative 5 in specifying acoustic requirements for an alert
sound.
    Some of the manufacturers of heavy vehicles stated that heavy-duty
hybrid vehicles that are not capable of electric propulsion should be
exempt from the requirements of the standard because these vehicles
produce sufficient sound for pedestrians to detect them in all
operating conditions, including stationary but activated. Several
commenters also stated that motorcycles should be exempt from the
requirements of the proposal.
    A few of the commenters questioned whether adding sound to HVs and
EVs was an appropriate means of addressing the increased rate of
collisions between HVs and EVs and pedestrians. Three of these
commenters believed that avoiding pedestrian collisions was the
responsibility of the driver. One commenter believed that NHTSA should
address crashes between HVs and EVs and pedestrians by adding advanced
pedestrian crash avoidance technology to these vehicles.

VII. NHTSA's Proposal

    NHTSA has considered three different viable alternatives for
ensuring that HVs and EVs provide detectable, recognizable sound cues
for pedestrians on which the agency seeks comments. These alternatives
include setting the minimum sound levels for EVs and HVs based on the
sound level required for a safe detection distance which is the
agency's preferred alternative, setting the minimum sound levels for
EVs and HVs based on the sound levels produced by light ICE vehicles
and using a jury testing procedure instead of acoustic specifications
to ensure that sounds produced by HVs and EVs are recognizable. The
alternatives differ in the manner in which they balance
recognizability, regulatory feasibility, and manufacturer flexibility.
In this section, we propose the alternative that we believe is the best
approach. The other two alternatives that are not being proposed, jury
testing for recognizability and acoustic profiles designed around
sounds produced by ICE vehicles, are discussed in detail in Section
VIII of this notice.
    Under our proposal EVs and HVs would be required to produce sounds
that conform to the specifications listed in S5 of the Proposed
Regulatory Text (see Section XIII of this notice). Our proposal is
similar to Alternative 4 described in the previously referenced NOI as
it contains acoustic elements designed to enhance detection and to aid
with recognition of motor vehicle operation. Through a compliance test,
the agency would be able to easily measure the sound produced by an EV
or HV and determine whether that sound conforms to the requirements in
S5 of the proposed regulatory text. The

agency developed the acoustic specifications contained in this proposal
using a loudness model and a representative urban ambient sound level
to ensure that sounds fitting the specifications would be detectable in
a wide range of ambient noise conditions.
    The agency has included specifications for low frequency because
the agency believes that the low frequency one-third octave band
requirements contained in S5 will assist pedestrians in recognizing
sounds that conform to the requirements as being produced by a motor
vehicle. The low frequency content of the sounds produced by current
ICE engines is the spectral component that pedestrians hear and
associate with these sounds. While the agency believes that the
specifications in S5 provide manufacturers a significant degree of
flexibility to develop vehicle sounds, the specifications do place some
constraints on the sounds that manufacturers are able to use as
countermeasure sounds. These constraints will ensure that
countermeasure sounds will be recognizable and provide the needed
auditory cues to be useful to pedestrians, while avoiding unnecessary
environmental impact.
    The agency also developed and is seeking comment on a set of
minimum sound requirements for HVs and EVs using an analysis of sounds
produced by ICE vehicles. The proposed requirements include minimum
sound pressure level specifications in different one-third octave bands
so the frequency content of sounds produced by HVs and EVs would
resemble the spectral content of ICE vehicles. Sounds that meet these
proposed requirements would resemble sounds described in Alternative 3
of the NOI. Relative to the other two viable alternatives, this
approach would place primary emphasis on feasibility and
recognizability.

A. Acoustic Specifications Developed To Enhance Detection and
Recognition

    This NPRM proposes performance requirements for sounds produced by
HVs and EVs so that pedestrians can detect, recognize, and locate these
vehicles. While NHTSA acknowledges that many manufacturers will choose
to install a speaker system to comply with the requirements of this
proposal, this is a technology neutral proposal, so manufacturers would
be able to choose any means of compliance they wish so long as the
vehicle produces a sound that complies with the acoustic specifications
in Section XIII of this notice.
    The agency has sought to balance community noise impact with the
safety of pedestrians in developing the acoustic specifications
contained in this proposal. For people living in communities near
highways and along busy streets, elevated noise levels can be annoying
and diminish quality of life. The agency recognizes the contributions
motor vehicles make to ambient sound levels in urban areas and near
highways. The DOT's Federal Highway Administration has previously
conducted studies (not part of this rulemaking) that examine noise-
reducing pavements in an attempt to reduce tire noise produced by
vehicles. We note the research on noise reduction that is being
conducted by other operating administrations within DOT in order to
emphasize that this proposal is not contrary to, and will not interfere
with, noise reduction efforts. In setting a minimum requirement for
sound produced by HVs and EVs, the agency has sought to ensure these
sound level requirements would not contribute to transportation noise
pollution. A majority of transportation noise is caused by vehicles
traveling at high speed. In this proposal, the agency would set minimum
sound requirements for vehicles traveling at lower speeds. The proposal
would not affect vehicle noise output during the high speed scenarios
that contribute to noise pollution. Furthermore, as required by the
PSEA, the agency considered the maximum noise emission requirements for
heavy vehicles and motorcycles issued by the Environmental Protection
Agency (EPA) in setting the minimum sound requirements contained in
this proposal.\82\
---------------------------------------------------------------------------

    \82\ 40 CFR parts 201-211.
---------------------------------------------------------------------------

    In developing this proposal, NHTSA sought to maintain the current
situation involving ICE vehicles in which the pedestrian and the driver
share responsibility for avoiding pedestrian vehicle collisions. Thus,
a pedestrian must be able to hear a vehicle from the point at which the
vehicle would no longer be able to safely stop if the pedestrian
decided to walk into an intersection. A pedestrian must be able to
initiate a street crossing with the knowledge that there are no
vehicles present that would be unable to stop before colliding with the
pedestrian. At distances farther than the vehicle's stopping distance,
the driver would be able to respond to the presence of a pedestrian and
avoid a collision. At distances within which the driver would not be
able to respond to the presence of a pedestrian and stop the vehicle,
the pedestrian must be able to hear the vehicle so the pedestrian can
share responsibility for avoiding a crash by not stepping into the
street.

B. Critical Operating Scenarios

    The PSEA states that the required safety standard must allow
pedestrians ``to reasonably detect a nearby electric or hybrid vehicle
in critical operating scenarios including, but not limited to constant
speed, accelerating, or decelerating.'' \83\ The PSEA defines alert
sound as ``a vehicle-emitted sound to enable pedestrians to discern
vehicle presence, direction, location and operation.'' \84\ Thus, in
order for a vehicle to satisfy the requirement in the PSEA to provide
an ``alert sound,'' the sound emitted by the vehicle must satisfy that
definition. In addition to the critical operating conditions mentioned
above, the agency believes that the definition of ``alert sound'' in
the PSEA requires the agency to establish minimum sound requirements
for when a vehicle is in a stationary but activated condition and while
operating in reverse.
---------------------------------------------------------------------------

    \83\ Public Law 111-373, 124 Stat. 4086 (January 4, 2011).
    \84\ Id.
---------------------------------------------------------------------------

1. Stationary But Activated
    It is NHTSA's position that the scenario in which the vehicle is
stationary, but its starting system is activated \85\ is a critical
operating scenario because the definition of ``alert sound'' contained
in the PSEA requires that a pedestrian be able to locate a nearby
vehicle that is running; it is the agency's position that including
this scenario satisfies that provision of the PSEA. Furthermore, sound
provided by idling ICE vehicles is essential to assisting visually-
impaired pedestrians in making safe travel decisions. Sounds made by
vehicles that are stationary but activated address collisions between
pedestrians and HVs and EVs starting from a stopped position.
---------------------------------------------------------------------------

    \85\ This condition is commonly referred to as an ``idling''
vehicle for vehicles with internal combustion engines. However, the
term ``idle'' technically refers to an engine state, not a vehicle
state, and has no relevance to electric motors. The description used
here ``stationary but activated'' means the vehicle is not moving,
but its starting system is activated.
---------------------------------------------------------------------------

    The agency has concluded that the requirement in the PSEA that the
alert sound required by the agency should allow pedestrians to
``discern vehicle presence, direction, location, and operation,'' \86\
requires the agency to establish minimum sound requirements for the
stationary but activated operating

condition. As discussed in Section III of this notice, when read
together the terms ``presence'' and ``operation'' in the definition of
alert sound in PSEA require the agency to establish minimum sound
requirements when the vehicle is stationary, but the starting system is
activated.
---------------------------------------------------------------------------

    \86\ Public Law 111-373, Sec.  2(2), 124 Stat. 4086 (2011).
---------------------------------------------------------------------------

    As discussed in Section V of this notice, sound cues produced by
idling ICE vehicles are critical for the safety of blind pedestrians.
The sound produced by vehicles idling while waiting to pass through an
intersection provides a reference to visually-impaired pedestrians so
they are able to cross a street in a straight line and arrive safely at
the other side. The reference provided by idling vehicles is especially
important to provide auditory cues for visually-impaired pedestrians
crossing streets at complex intersections where the streets intersect
at non-perpendicular angles. The sound of vehicles idling on the far
side of the street while waiting to pass through an intersection also
provides visually-impaired pedestrians with a reference of how wide a
street is so they can accurately gauge the amount of time needed to
safely cross.
    A sound emitted by an HV or EV when stationary but activated is
analogous to the ICE vehicle idling and ensures that the responsibility
to avoid a crash between a vehicle and a pedestrian is shared between
the driver of the vehicle and the pedestrian by providing pedestrians
with an acoustic cue that a vehicle may begin moving at any moment.
While there are some scenarios in which a driver starting from stop
should be able to see a pedestrian in front of the vehicle and thus
avoid a crash, the driver may not always be able to be relied upon,
especially in situations where the driver may have an obstructed view.
A driver pulling out of a parking space in a parking lot is an example
of a situation in which a driver might not be able to see a pedestrian
and the pedestrian may step into the path of a vehicle just as the
vehicle is beginning to move. If the pedestrian is able to hear the
vehicle before it begins to move the pedestrian would be able to
exercise caution and avoid a collision with the vehicle by not stepping
in front of the vehicle.
    In deciding to include a sound requirement for HVs and EVs at the
stationary but activated condition, we also relied on the experiences
of agency staff when attempting to navigate street crossings while
blindfolded. NHTSA staff traveled to the national headquarters of the
National Federation of the Blind in Baltimore, Maryland to receive
training on white cane travel techniques used by individuals who are
blind. The meeting included a class room session and a session in which
the participants from NHTSA were blindfolded and trained on navigation
using a white cane outside on city streets with blind and visually
impaired individuals as guides. The participants from NHTSA attempted
to navigate city streets and cross at non-signaled intersections while
blindfolded. When approaching intersections, NHTSA staff found the
sound of idling vehicles necessary for determining whether there was a
vehicle present at the intersection and whether it was safe to cross.
    Our October 2011 statistical report on the incidence rates of
crashes between HVs and pedestrians \87\ also supports stationary but
activated as a critical operating scenario for pedestrians. The report
shows six incidents of collisions when the vehicle was starting from a
stopped position. While the difference in HV and ICE vehicle crashes
with pedestrians for vehicles starting from a stopped position is not
statistically significant, this can be partially attributed to the
limited penetration of HVs in the fleet. There were no EV collisions
with pedestrians documented in NHTSA's report because electric vehicles
were not widely available in 2008, the last year for which data is
available. Overall, EVs and HVs represent a small percentage of the
total vehicle fleet and fully electric vehicles have yet to be
introduced to the U.S. fleet in significant numbers. Therefore, the
sample size of HVs represented in the State Data System, and the number
of HV pedestrian collisions, remains extremely small. The limited
available crash data does show that HVs have collided with pedestrians
when starting from a stopped position even though the sample size is
not large enough to prove a statistically significant incidence rate.
The growing penetration of HVs and EVs into the vehicle fleet means
that vehicle collisions with pedestrians when an HV or EV is starting
from a stopped position represents a safety concern that is rising to a
level of significance, for which the agency believes it is appropriate
to require that vehicles provide adequate sound cues while stationary
but activated. In passing the PSEA, Congress directed NHTSA to be
proactive in addressing the risk to pedestrians posed by HVs and EVs.
Congress did not intend for NHTSA to wait until crashes between
pedestrians and HVs and EVs starting from a stop rise to the level
where NHTSA has a data set that shows that a sound for the stationary
but activated condition is needed.
---------------------------------------------------------------------------

    \87\ See footnote 36.
---------------------------------------------------------------------------

    The agency does not believe that establishing minimum sound
requirements for EVs and HVs operating in the stationary but active
condition will have any noticeable impact on ambient noise levels. As
discussed in Section X.D, NHTSA has conducted an Environmental
Assessment (EA) to analysis the environmental effects of this
rulemaking. The EA shows that the difference in ambient sound levels if
the agency issues minimum sound requirements for the stationary but
active condition compared to if the agency did not require sound at
that condition would be negligible.
    The agency does not believe that there would be any incremental
cost to requiring a sound at the stationary but active operating
condition to a vehicle that is already equipped with an alert sound
system. Rather, as with all other required operating scenarios, a
vehicle with an alert sound system could be reconfigured to play a
sound at the stationary but active condition through a simple software
modification, which would not require any additional equipment to be
installed on the vehicle.
    In comments on the NOI and in meetings between representatives from
various auto manufacturers and NHTSA staff, several manufacturers
stated that the agency should not establish minimum sound requirements
for the stationary but activated condition. These manufacturers do not
believe there is a safety need for an alert sound when vehicles are
stationary but activated. They were concerned that the sound of EVs and
HVs standing in highway traffic and other scenarios in which
pedestrians would not be expected to be present would unnecessarily
contribute to increases in environmental noise impact.
    Advocacy organizations for individuals who are blind or visually
impaired believe that the agency should establish minimum sound
requirements for the stationary but active condition. In meetings with
agency rulemaking staff, representatives from NFB have stated that a
sound at the stationary but active operating scenario is necessary for
the safety of blind or visually impaired pedestrians in avoiding
collisions with EVs and HVs operating at low speeds. Representatives
from NFB stated that blind individuals exercise greater caution when
they hear a nearby idling ICE vehicle because they know that the
vehicle could begin moving at any moment. Representatives from NFB
stated that a nearby vehicle that made no sound that could start

moving at any moment presents a safety hazard to blind or visually
impaired pedestrians because the vehicle could collide with a blind or
visually impaired pedestrians without the pedestrian even knowing that
the vehicle posed a danger to them. The agency believes that minimum
sound levels for EVs and HVs operating when stationary but activated
are necessary from a safety perspective for the reasons previously
discussed. The agency believes that it is important to establish
minimum sound requirements for the stationary but activated condition
so that the sound will alert nearby pedestrians of the presence of a
vehicle without unduly contributing to overall ambient noise levels.
The agency believes that the safety interest in assisting pedestrians
with detecting nearby vehicles and providing the visually-impaired with
acoustic cues necessary to make safe travel decisions justifies
establishing minimum sound level requirements for EVs and HVs operating
when stationary but activated.
    The agency acknowledges that with the technology under
consideration today for adding sound to HVs and EVs, most vehicles that
would be subject to this proposed rule (should it become final) will
establish compliance by means of adding a sound generating system that
includes at least one speaker. Requiring a sound at this condition may
result in manufacturers adding speakers to some vehicles (for example
motorcycles or some heavy vehicles) that may not otherwise need a
speaker to meet the requirements of the other operating conditions in
today's proposal (because the vehicle operation in those conditions
makes enough sound without adding an artificial sound). However, we
believe that the definition of alert sound in the PSEA requires the
agency to establish minimum sound requirements for this condition. We
seek comment on the number of vehicles to which this proposal would
apply that would only require speakers to meet the acoustic
requirements in this proposal at the stationary but active condition.
    Also, the agency solicits comment on possible configurations of the
alert sound that would lower or deactivate the alert sound in
situations in which pedestrians would not be present. One of the
methods proposed for mitigating the noise caused by stationary EVs and
HVs would be to allow the vehicle to reduce or turn off its sound after
the vehicle had been stationary for a period of five to ten minutes.
The agency does not believe that a switch that would allow the driver
to turn off the vehicle's sound is a viable option for controlling the
noise impact of EVs and HVs when stationary but activated because the
PSEA specifically forbids the agency from allowing the driver to
deactivate the sound; in addition, the agency believes that allowing
drivers to deactivate the sound would compromise pedestrian safety.
    As an alternative to requiring a sound when the vehicle is
activated but not moving, Mercedes-Benz USA, LLC (Mercedes) stated that
the agency should instead include acoustic specifications for a
``commencing motion sound'' that would be activated as soon as the
vehicle starts moving.\88\ Mercedes stated that the specifications for
such a sound should be the same as the specifications for the sound at
10 km/hr (6 mph). Mercedes stated that the sound pressure level of the
``commencing motion sound'' should be noticeably higher than the sound
pressure level required for low speeds. Volkswagen Group of America,
Inc. also stated that the agency should require a ``commencing motion
sound'' instead of a sound when the vehicle is activated but
stationary. We seek comment on whether requiring a ``commencing motion
sound'' is as an effective approach to implementing the requirements in
the PSEA that an alert sound allow pedestrians to discern the
``presence, direction, location and operation'' of the vehicle as
establishing minimum sound requirements for when the vehicle is
activated but stationary.
---------------------------------------------------------------------------

    \88\ Docket No. NHTSA-2011-0148-0029.
---------------------------------------------------------------------------

2. Reverse
    The agency believes that reverse is a critical operating scenario
for which the agency should issue minimum sound level requirements for
HVs and EVs to provide acoustic cues to pedestrians to prevent
pedestrian collisions and to satisfy the requirements of the PSEA.
Requirements for the reverse operation of EVs and HVs will ensure that
these vehicles provide sound cues to pedestrians so pedestrians will be
able to avoid these vehicles when the vehicles are backing out of
parking spaces or driveways.
    Several manufacturers in meetings with NHTSA staff stated that
minimum sound requirements for EVs and HVs operating in reverse were
not necessary because the agency's proposed amendments to FMVSS No.
111, Rear Visibility, as required by the Cameron Gulbransen Kids
Transportation Safety Act, would allow drivers to see pedestrians while
backing and thus avoid collisions. NHTSA's proposed amendments to FMVSS
No. 111, while intended to address vehicle collisions with pedestrians
while backing, do not fully ensure that EVs and HVs will not experience
higher rates of pedestrian collisions than ICE vehicles while backing.
Establishing minimum sound level requirements for reverse operation
will ensure that both the pedestrian and the driver continue to have
the ability to avoid pedestrian vehicle collisions. If EVs and HVs do
not produce audible sound levels during reverse operations,
pedestrians, especially those who are blind and visually impaired,
would not have the opportunity to avoid collisions with backing
vehicles because they would not be able to tell that they are being
threatened by a backing vehicle.
    NHTSA's report on the incidence rates of crashes between HVs and
pedestrians found 13 collisions with pedestrians when a HV is backing.
The difference between the incidence rates of HVs involved in
pedestrian crashes while backing and the incidence rate of ICE vehicles
involved in pedestrian crashes while backing was not statistically
significant. We do not believe that the lack of a statistically
significant difference in incidence rates between ICE vehicles and HVs
involved in pedestrian crashes while backing can be attributed to the
absence of a safety problem related to a vehicle's noise level during
this operating condition. As discussed above, the absence of a
difference in the incidence rates in backup pedestrian crashes between
ICE vehicles and HVs is, the agency believes, due to the low
penetration of these vehicles into the fleet and the sample size of HVs
and EVs in the State Data System. Also, backing incidents with
pedestrians may tend to be underreported because they occur in parking
lots, garages, and drive ways, as well as other ``off roadways'' that
traditionally have not been captured by existing data collection
systems.
    NHTSA believes that the PSEA requires the agency to set minimum
sound requirements for the backing scenario for the same reason that
the agency believes that minimum sound requirements are necessary for
the stationary but activated condition. The PSEA requires minimum sound
level requirements promulgated by NHTSA to allow pedestrians to discern
vehicle presence and operation. A vehicle moving in reverse is
unquestionably operating, thus a minimum sound level is required for
this condition.
    The PSEA also requires that the minimum sound level requirements
promulgated by NHTSA allow pedestrians to discern the direction of the
vehicle. This language also indicates that the PSEA requires any
standard to establish minimum sound requirements

for when the vehicle is operating in reverse.
3. Acceleration and Deceleration
    Section 5 of the proposed regulatory text would ensure that sounds
produced by EVs and HVs that meet the requirements of this proposal
will allow pedestrians to determine when a vehicle is accelerating or
decelerating. Pitch shifting is the sound characteristic that
pedestrians currently associate with an accelerating vehicle based on
the sounds produced by an ICE vehicle. The agency included requirements
for pitch shifting in S5 to ensure that components of the sounds
produced by EVs and HVs moved along the frequency spectrum in a manner
similar to those of ICE vehicles as vehicle speed increases. Pitch
shifting will also denote that the vehicle is decelerating. The sound
pressure level in each one-third octave band required in S5 changes as
speed increases, leading to an increasing overall sound pressure level
that corresponds to the behavior of an ICE vehicle. Thus, in addition
to the acoustic cues provided by pitch shifting, pedestrians will be
able to tell if an EV or HV is accelerating or decelerating based on
the increase or decrease in sound emitted from the vehicle, just as
they would be able to in the case of an ICE vehicle.
    The agency did not include a separate acoustic measurement
procedure for acceleration and deceleration because we believe that the
requirements for pitch shifting and the increase in overall sound level
as the vehicle increases speed (or the decrease in sound level as the
vehicle decelerates) will provide enough information so that
pedestrians will be able to determine when EVs and HVs are accelerating
and decelerating. The agency also decided not to include acoustic
measurement procedures for acceleration and deceleration because of
concerns about the feasibility of testing in these conditions. It is
difficult for even an experienced test driver to repeatedly achieve and
maintain a specific rate of acceleration or deceleration over the
distance used in the proposed test procedure. Given the difficulty of
ensuring repeatable results of an acoustic test measuring acceleration
and the fact that information about changes in vehicle speed is
provided by pitch shifting and increases and decreases in sound
pressure level corresponding to changes in vehicle speed, NHTSA decided
that the test procedure did not need to include a dynamic test for
acceleration or deceleration.
4. Constant Speed
    The agency is proposing to ensure that EVs and HVs produce a
minimum sound level necessary for safe pedestrian detection at constant
speeds by measuring vehicle sound output at 10 km/hr (6 mph), 20 km/hr
(12 mph) and 30 km/hr (18 mph). The agency's proposal would ensure EVs
and HVs produce sound that is sufficient to allow pedestrians to detect
these vehicles at all speeds between 0 and 10 km/hr (6 mph), 10 km/hr
(6 mph), 20 km/hr (12 mph), and 30 km/hr (18 mph) by requiring that the
minimum sound levels be attained for all speeds between these test
speeds. The proposal contains minimum acoustic requirements up to the
speed of 30 km/hr (18 mph) because, for the reasons discussed in
Section VII.E.3 of this notice, the agency believes that this is the
appropriate cross over speed. Manufacturers have suggested in meetings
with the agency that the test procedure for sound measurement should
only specify a pass by test at 10 km/hr (6 mph) because, according to
manufacturers, this is the speed at which the sound levels produced by
ICE vehicles and EVs and HVs differ the most. The agency believes that
it is necessary to include pass by tests at speeds up to and including
the crossover speed to ensure that EVs and HVs meet the minimum sound
level requirements for all speeds for which requirements are specified.

C. Application

1. The Definition of Hybrid Vehicle
    The PSEA defines hybrid vehicle as a vehicle with more than one
means of propulsion. The agency has concluded that the definition in
the PSEA requires the agency to apply the standard only to hybrid
vehicles that are capable of propulsion in any forward or reverse gear
without the vehicle's ICE operating. Under the agency's interpretation
of the definition of hybrid vehicle in the PSEA, more than one means of
propulsion means more than one independent means of propulsion. This
proposed definition of hybrid vehicle would exclude from the
application of the proposed standard those vehicles that are equipped
with an electric motor that runs in tandem with the vehicle's ICE to
provide additional motive power when the vehicle is accelerating.\89\
---------------------------------------------------------------------------

    \89\ The agency is aware that a vast majority of vehicles that
are equipped with an electric motor to provide additional motive
power when the vehicle is accelerating are equipped with idle-stop.
For a discussion of why the agency has chosen not to require
vehicles equipped with idle-stop that are not capable of propulsion
by a means other than the vehicle's ICE to meet the minimum sound
level requirements in this proposed standard see Section VII.C.5.
---------------------------------------------------------------------------

    Because the ICE is always running when these vehicles are in motion
on hybrids that employ the electric engine to provide additional power
when accelerating, the fact that these vehicles may not provide
sufficient sound for pedestrians to detect them cannot be attributed to
the vehicle's propulsion source. If a pedestrian cannot hear this type
of vehicle it is because of the quietness of the vehicle's ICE.
Therefore, we believe that it is most appropriate to address vehicles
that are equipped with an electric motor that provides assistance to
the ICE when the vehicle is accelerating in the report to Congress
regarding the safety need to establish minimum sound requirements for
quiet ICE vehicles required by the PSEA.
    The agency would also like to note that the definition of ``hybrid
vehicle'' in the PSEA is not limited to hybrid-electric vehicles. Thus,
the standard would apply to hybrid vehicles that operate using
hydraulic propulsion independently of the vehicle's ICE.
2. Vehicles With a GVWR Over 10,000 Pounds
    NHTSA is proposing that the acoustic specifications in Section XIII
apply to all hybrid and electric motor vehicles covered by the PSEA,
including all hybrid and electric passenger cars, multipurpose
vehicles, trucks, buses, low-speed vehicles and motorcycles.\90\
---------------------------------------------------------------------------

    \90\ The PSEA specifically excludes trailers from the scope of
the required rulemaking.
---------------------------------------------------------------------------

    Across the entire fleet (ICE, hybrid, and electric vehicles
included), heavy vehicles have a lower pedestrian crash rate than light
vehicles (10,000 pounds and less). Only 0.3 percent of all heavy
vehicle crashes involved pedestrians while 0.59 percent of all light
vehicle crashes involve pedestrians. The pedestrian crash rate of heavy
vehicles involved in low-speed maneuvers is also lower than that of
light vehicles. Only 0.42 percent of all heavy vehicle crashes at low
speeds involved pedestrians while 0.80 percent of all low speed light
vehicle crashes involve pedestrians.
    NHTSA was not able to determine a separate pedestrian crash rate
for hybrid and electric heavy duty vehicles based on the data available
in the State Data System. The sample of all crashes of hybrid and
electric heavy vehicles in the State Data System is extremely limited
and the State Data System did not, when it was examined, contain any
incidents of hybrid or electric heavy vehicle pedestrian crashes. The
agency

believes that the lack of crash data on hybrid and electric heavy
vehicles is due to the very low market penetration of these vehicles at
the present time. Therefore, the agency attributes the lack of any
hybrid or electric heavy vehicle pedestrian crashes not to the fact
that these vehicles provide sufficient sounds levels to allow safe
pedestrian detection but instead to the fact that these vehicles are
not present in the fleet in any significant numbers. The agency
believes that it is reasonable to assume that as hybrid and electric
heavy vehicles achieve a higher penetration into the vehicle fleet that
the difference between the crash rates for hybrid and electric heavy
vehicles and ICE heavy vehicles will be similar to the difference in
crash rates between light hybrid and electric vehicles and light ICE
vehicles.
    We note that the PSEA did not exclude vehicles with a GVWR over
10,000 pounds from the scope of the required rulemaking. We believe
Congress intended the agency to be proactive in addressing the safety
problem posed by quiet hybrid and electric heavy vehicles before hybrid
and electric heavy vehicle pedestrian crashes begin to show up in crash
data bases in significant numbers. In other words, through the passage
of the PSEA, Congress has determined that there is a safety need for
HVs and EVs of various sizes to produce a minimum sound level.
    The agency recognizes that there are some challenges in including
vehicles with GVWR over 10,000 lbs in the current rulemaking. The
agency has not determined the extent to which hybrid heavy vehicles
produce less sound than their traditional ICE peer vehicles. The agency
also is not aware of the extent to which hybrid electric vehicles with
a GVWR of over 10,000 lbs are capable of propulsion using only electric
power without the ICE running.\91\ Heavy vehicle manufacturers, in
their comments on our NOI, stated that to the extent that heavy
vehicles are not capable of propulsion solely by some means other than
the vehicle's ICE, they should be exempt from the requirements of this
proposal.
---------------------------------------------------------------------------

    \91\ In its comments to the Notice of Intent to Prepare an
Environmental Assessment (NOI) that the agency issued to solicit
comments on the environmental consequence of this rulemaking, Hino
Motors, Ltd. stated that it is planning on introducing a heavy-duty
hybrid truck that is capable of propulsion using only the electric
motor. Hino, however, stated that even when the truck is being
propelled by the electric motor the ICE will remain on in order to
power auxiliary systems. Comment of Hino Motors Ltd. available at
www.regulations.gov, Docket No. NHTSA-2011-0100-0015.
---------------------------------------------------------------------------

    While the agency is today proposing to include heavy vehicles as
part of this rulemaking, we note that the agency intends to conduct
further research before issuing a final rule to determine the sound
levels produced by heavy-duty hybrid and electric vehicles and to
establish whether the sound requirements for light vehicles are also
appropriate for heavy vehicles.
    The agency is also aware of practical concerns about acoustic
testing of heavy vehicles. The agency is aware that there are a limited
number of noise pads necessary for vehicle acoustics testing that can
accommodate heavy vehicles. We seek comment on whether it is necessary
to test heavy vehicles on a noise pad meeting the requirements of ISO
10844, Acoustics--Specification of test tracks for measuring noise
emitted by road vehicles and their tires. In the alternative the agency
is considering specifying an acoustic testing surface for heavy vehicle
testing that is based on a typical vehicle test track pavement.
    The agency also has not validated whether the sound specifications
that it has developed based on research conducted on light vehicles
would provide appropriate countermeasure sounds for heavy-duty
vehicles. We seek comment on this issue.
    The agency is aware that many heavy and medium duty trucks are
equipped with backup alarms to provide warning when the vehicle is
backing. Because we do not want to require that these vehicles produce
additional sound if they are already producing sound when backing, we
would not require vehicles with a GVWR over 10,000 pounds to meet the
acoustic specifications in S5.1.2 when backing. Instead, these vehicles
would only be required to produce a sound with an overall sound
pressure level of 52 A-weighted dB when backing. We seek comment on
this issue. In addition, the agency also has yet to determine whether
it is necessary from a safety perspective for pedestrians to
differentiate light vehicles from heavy vehicles. The agency is aware,
based on conversations with advocacy groups representing people that
are visually-impaired, that a visually-impaired person may wait a
longer amount of time than normal to cross a street after hearing a
heavy truck pass in order to avoid colliding with a trailer that might
be attached to the truck.
    The agency also seeks comment regarding the appropriateness of
limiting the application of this proposal to vehicles with a gross
vehicle weight rating of 10,000 pounds and less.
    Another regulatory option that the agency considered for heavy-duty
HVs and EVs would require that these vehicles produce only a minimum
sound pressure level rather than the full set of acoustic
specifications in S5. Pending planned research on the sounds emitted by
heavy vehicles, ICE, HV, and EV, the agency has tentatively concluded
that applying the full acoustic specifications that the agency intends
to apply to light vehicles to heavy vehicles would better fulfill the
requirements of the PSEA.
3. Electric Motorcycles
    The agency has tentatively concluded that the minimum sound level
requirements in S5 proposed in this notice should apply to electric
motorcycles (we are not aware of the existence of any hybrid
motorcycles). Motorcycles are not specifically excluded by the PSEA.
Also, the agency has yet to determine that these vehicles provide sound
levels that are sufficient to allow pedestrians to detect these
vehicles in time to avoid collisions.
    Table 10 shows the number of collisions between motorcycles and
pedestrians from 2000 until 2008. This data was obtained from the State
Data System. Because the State Data System does not include any data
regarding the power source used by motorcycles, the agency was not able
to determine if the incidence rate of collisions between pedestrians
and electric motorcycles is different between the incidence rate of
collisions between pedestrians and motorcycles with ICEs.

                               Table 10--Preliminary Results of Motorcycle Crashes
                                           [16 States during 2000-08]
----------------------------------------------------------------------------------------------------------------
                                                                      Backing
                                                                   entering/exit     Straight
                                                                  parking spots,    moving and
                                                                     turning,      other normal        Total
                                                                   starting, and      speeds
                                                                      slowing
----------------------------------------------------------------------------------------------------------------
Pedestrian crashes..............................................              55             438             493
Other crashes and missing data..................................          20,669          90,371         111,040
                                                                 -----------------------------------------------
    Total.......................................................          20,724          90,809         111,533
----------------------------------------------------------------------------------------------------------------

    As with heavy-duty vehicles, there are challenges in establishing
minimum sound levels for electric motorcycles in this rulemaking. The
agency has not determined the extent to which electric motorcycles have
a greater risk of collisions with pedestrians than motorcycles with
ICEs or the extent to which electric motorcycles are quieter than ICE
motorcycles of the same type. The agency has not measured any
motorcycles according to the procedures contained in this proposal so
the agency has yet to determine whether the measurement procedure used
to measure sound emitted by 4-wheeled vehicles would be appropriate for
motorcycles.
    BMW of North America, LLC (BMW), in its comments on the NOI
(discussed in Section VI.G. above), submitted crash data on incidents
of motorcycle collisions with pedestrians. BMW stated that based on the
number of crashes between motorcycles and pedestrians and the
percentage of pedestrian crashes involving motorcycles, there is no
safety need for minimum sound requirements for electric motorcycles.
BMW cited several different sources of data to illustrate the low rates
of crashes between motorcycles and pedestrians. 2009 statistics from
the New York Department of Motor Vehicles show that approximately 0.4
percent of pedestrian/motor vehicle collisions involved
motorcycles.\92\ Data from the FARS for the period between 2005 and
2009 shows that only 0.7 percent of the pedestrian fatalities during
that period involved motorcycles colliding with pedestrians. Data from
the NHTSA's General Estimates System (GES) for the same time period
shows that 1.07 percent of the pedestrians injured in motor vehicle
crashes were injured in crashes involving motorcycles.
---------------------------------------------------------------------------

    \92\ BMW's comments on the NOI. Available at,
www.regulations.gov, Docket No. NHTSA-2011-0100-0020.
---------------------------------------------------------------------------

    Both BMW and the Motorcycle Industry Council (MIC) stated that
because of unique attributes of motorcycles, there is no safety need
for NHTSA to establish minimum sound levels for electric motorcycles.
According to MIC and BMW, motorcycle riders are able to better see and
avoid pedestrians than automobile drivers because their view is
unobstructed by pillars and sun visors and they are more alert because
they themselves are vulnerable road users. BMW and MIC maintained that
because motorcycles are unstable at low speeds, riders are required to
maintain a high level of alertness, which minimizes the likelihood of
collisions with pedestrians during low speed maneuvers.
    Both BMW and MIC stated that adding a speaker system to a
motorcycle could involve technical challenges not present for other
vehicles. MIC and BMW claimed that it would be more difficult to add a
speaker to a motorcycle than a passenger car because there is less
space available on a motorcycle for a speaker system, the weight of the
system would be a larger percentage of the vehicle's weight, which
could affect low-speed stability, energy consumption by the speaker
system would have a greater impact on a vehicle's range, and the price
of installing the system would be higher than that for other vehicles.
MIC and BMW also claimed that electric motorcycles should not be
subject to the minimum sound level requirements in this proposal
because electric motorcycles are not quiet.\93\
---------------------------------------------------------------------------

    \93\ MIC submitted measurements of overall sound pressure level
of two electric vehicle models recorded at 8 km/hr (5 mph) and 16
km/hr (10 mph) in its comments to the NOI. MIC did not provide any
measurements of overall sound pressure level for ICE motorcycles as
a comparison. Available at, www.regulations.gov, Docket No. NHTSA-
2011-0100-0028.
---------------------------------------------------------------------------

    The agency acknowledges that establishing minimum sound
requirements for electric motorcycles raises unique issues that are not
present for other light vehicles. The agency, however, notes that
because this proposal is technology neutral, it would be possible for
electric motorcycles to meet the requirements of this proposal without
the use of a speaker system. The agency seeks comment on whether the
minimum sound level requirements in this proposal should apply to
electric motorcycles. The agency seeks comment on the crash risk to
pedestrians and pedalcyclists posed by electric motorcycles and the
cost of the proposal as applied to these vehicles.
4. Low-Speed Vehicles
    The agency has tentatively concluded that low-speed vehicles (LSVs)
must meet the requirements in this proposal. While the agency expects
that LSVs that run via an electric motor are extremely quiet, the
agency has not conducted any acoustic measurements of these vehicles to
determine the amount of sound they produce. The agency has very limited
real-world data on crashes involving LSVs so the rate at which these
vehicles are involved in pedestrian collisions is unknown. The agency
has not yet determined the extent to which minimum sound levels
developed for light vehicles would be appropriate for LSVs. The agency
seeks comment on whether the requirements in this proposal should apply
to LSVs.
5. Quiet ICE Vehicles
    The agency does not intend to require a minimum sound level for
quiet ICE vehicles in this rulemaking. The agency is aware that,
similar to HVs and EVs, some ICE vehicles may pose a risk to
pedestrians because of the low level of sound that they produce when
operating at low speeds. The PSEA requires the agency to study and
report to Congress whether there is a need for the agency to apply the
minimum sound requirement established for HVs and EVs to ICE vehicles
so that these vehicles can be readily detected by pedestrians. If,
after the study, the agency determines that there is a safety need to
apply these minimum sound requirements to quiet ICE vehicles, NHTSA is
required to initiate a rulemaking to do so. The agency is also aware
that many manufacturers intend

to make idle stop technology available on ICE vehicles in the near
future.\94\ The agency realizes that the introduction of ICE vehicles
equipped with idle stop means that there will be ICE vehicles that will
be effectively silent when the vehicle is not moving. While the agency
does not propose, in this rulemaking, to require that ICE vehicles
equipped with idle stop produce a minimum sound level while at idle,
the agency plans to consider whether vehicles equipped with idle stop
have a greater risk of collision with pedestrians than vehicles that
produce a sound at idle with an eye toward a rulemaking in the future
to address this issue.
---------------------------------------------------------------------------

    \94\ Vehicles equipped with an idle stop function shut down or
slow the vehicle's engine when the vehicle comes to a stop. Because
the vehicle's engine shuts off, the vehicle is no longer providing
any acoustic cues to pedestrians to indicate its presence.
---------------------------------------------------------------------------

D. Requirements

    The agency's preferred method for establishing minimum sound
requirements for EVs and HVs uses a detectability model to determine
the sound that the vehicle needs to produce to allow pedestrians to
detect the vehicle at a given distance. The sounds that meet the
minimum requirements using the detection model would be similar to
those described in Alternative 4 in the NOI.
1. Acoustic Parameters Designed According to a Detectability Model
    The two critical aspects of the minimum sound level requirements in
this proposed approach are that the sound be detectable and
recognizable. This approach addresses the detectability aspect of the
minimum sound level requirements by determining the sound
specifications needed for a pedestrian to detect a vehicle at a safe
distance and by examining the typical ambient sound profile to
determine which one-third octave bands contribute the most to a
pedestrian's ability to detect vehicles.\95\ This proposal addresses
the pedestrian recognition aspect of the minimum sound requirements by
insuring that the sound has aspects that allow pedestrians to recognize
the sound as being produced by a motor vehicle and by allowing the
pedestrian to recognize the mode of operation of the vehicle.
---------------------------------------------------------------------------

    \95\ The agency's research to develop the minimum specifications
for alert sounds for hybrid and electric vehicles is discussed in
greater detail in the agency's report ``Research on Minimum Sound
Specifications for Hybrid and Electric Vehicles.''. Available at
Docket No. NHTSA-2011-0148-0048.
---------------------------------------------------------------------------

    The agency developed the minimum detectability requirements for HVs
and EVs by first determining the distance at which a pedestrian would
need to hear a vehicle in order to make a decision about whether it was
safe to cross the street. Thus, the distance at which a pedestrian
would need to hear a vehicle is at least as long as the vehicle's
stopping distance. At distances shorter than a vehicle's stopping
distance the pedestrian must be able to hear the vehicle, otherwise a
situation might develop in which the pedestrian steps off the curb
(because s/he cannot hear the vehicle) and the driver of the vehicle
would be unable to stop the vehicle in time to avoid a collision with
the pedestrian.
    The agency set the distance at which it believes that the
pedestrian should be able to hear an approaching HV or EV, also
referred to as the detection distance, using stopping sight distances
computed from the guide on highway design \96\ of the American
Association of State Highway Transportation Officials (AASHTO).
Stopping sight distance is the distance that enables a vehicle
traveling at or near the design speed to stop before reaching an object
in its path. The stopping sight distance is the sum of the driver
reaction distance and the braking distance. The driver reaction
distance is the distance traveled by a vehicle from the instant the
object becomes visible to the driver to the instant the driver applies
the brakes. The braking distance is the distance needed to stop the
vehicle once the driver applies the brakes. The sight distance for a
vehicle traveling at the design speed and on a level road can be
computed with the following formula:
---------------------------------------------------------------------------

    \96\ American Association of State Highway and Transportation
Officials, A Policy on Geometric Design of Highways and Streets,
Chapter 3 Elements of Design (2004).
[GRAPHIC] [TIFF OMITTED] TP14JA13.031

---------------------------------------------------------------------------
Where:

t = brake reaction time, s
V = design speed, km/hr
a = deceleration rate, m/s\2\
Drivers typically brake at an average emergency deceleration of about
5.4 m/s\2\ on dry roads. A comfortable deceleration for most drivers
braking on wet surfaces is 3.4 m/s\2\. Drivers' expectation plays a
role in driver reaction time. Mean reaction time to unexpected, but
common, events is about 1.25 seconds. Mean reaction time for surprise
events, such as an object suddenly moving into the drivers' path is
about 1.5 seconds. A longer reaction time, of 2.5 seconds would
consider the capabilities of almost all drivers, including older
drivers and distracted drivers.
    The values used as the basis for this proposal are 5.4 m/s\2\ for
deceleration and 1.5 seconds for brake reaction time. We chose the 5.4
m/s\2\ deceleration rate corresponding to dry pavement braking because
most of the pedestrian crashes that the agency identified occurred in
clear conditions \97\ and the slower deceleration rate for wet
pavement, we believe, would result in a sound profile that is
unnecessarily loud for most conditions. The agency believes that 1.5
seconds is an appropriate value to use for driver reaction time (to
stopped objects) because this represents the reaction time of most
drivers for surprise events.\98\
---------------------------------------------------------------------------

    \97\ See footnote 5.
    \98\ Green (2000) How Long Does It Take to Stop? Methodological
Analysis of Driver Perception-Brake Times.'' Transportation Human
Factors 2(3) 195-216.
---------------------------------------------------------------------------

    Based on calculations using these values, the agency determined
that the desired detection distances were 2 meters in front of the
vehicle for stationary but activated, 5 m in front of the vehicle for
the 10 km/hr (6 mph) pass by, 11 m for the 20 km/h (12 mph) pass-by
operation, and 19 m for 30 km/h (18 mph) pass-by operation. The results
of this computation were rounded up to the nearest meter. Levels were
increased by 0.5 dB to provide a small safety factor and rounded to the
nearest integer for simplicity. This small increase was deemed
sufficient due to other conservative aspects of the estimation, e.g.
multiple detection opportunities due to the multiple components. The
agency solicits comment on the appropriateness of a 1.5 second reaction
time and 5.4 m/s\2\ declaration rate in determining the desired
detection distances.
    Due to a variety of factors that affect the manner in which sound
moves through an environment, it is not practical to measure sound with
the specificity that the agency desires from the distances at which
pedestrians need to be able to detect the sound. Atmospheric
absorption, ground conditions and divergence of sound all affect sound
measurements conducted at distances greater than the two meters
specified in SAE J2889-1. Acoustic measurements conducted at distances
greater than two meters are not able to accurately record a sound's
frequency profile at the one-third octave band level. Furthermore,
because of attenuation, a sound's decibel level decreases the further a
measurement is taken from the sound source. At the detection distances
that the agency

believes are necessary for pedestrians to be able to hear vehicles, the
sound pressure level sounds produced by vehicles begin to approach the
ambient. As the sound pressure level begins to approach that of the
ambient sound level, it is more difficult to measure the frequency
composition of the sound. Based on the factors discussed above, the
agency determined that the best approach for determining the minimum
sound level HVs and EVs need to produce to ensure safe detectability
would be to determine what the sound level would need to be at two
meters from the vehicle in order to allow the pedestrian to hear the
sound at the desired detection distance.
    Using the method below, it is possible to determine what the sound
levels of the vehicle will need to be at a distance of two meters from
the vehicle so that pedestrians will be able to detect the sound at the
desired detection distance. The table below depicts how the sound
produced by the vehicle attenuates when measured using the procedure in
SAE J2889-1.

        Table 11--Computation of Adjustment of SPL (A-Weighted dB) From Source to SAE Microphone Location
----------------------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------------------
Speed, km/hr.................................................             10               20               30
X source, meters.............................................              5               11               19
Y source,* meters............................................              2                2                2
r0,** meters.................................................              2.3              2.3              2.3
r1,** meters.................................................              5.5             11.2             19.1
r doubling...................................................              1.2              2.3              3.0
Attenuation, dB..............................................             -6.0            -12.2            -16.8
----------------------------------------------------------------------------------------------------------------
* Assume effective source is at center of vehicle since propagation is forward.
** Assume Z = 1.2.

X represents the distance from the source while Y is the distance from
the source to the microphones in SAE J2889-1. Z represents the height
of the microphone in meters specified in SAE J2889-1. The values in the
Table 11, above, were calculated using the formula below assuming a 1.2
meters value for Z.
[GRAPHIC] [TIFF OMITTED] TP14JA13.032

    A critical factor for establishing a minimum sound for pedestrians
based on a desired detection distance is the ambient noise environment
in which the pedestrian is attempting to detect the vehicle. The agency
selected an ambient of 55 A-weighted dB to develop the minimum sound
level specifications. The agency choose an ambient sound pressure level
of 55 A-weighted dB because that is a level representative of a
moderate suburban ambient where pedestrians would be expected to be
able to detect vehicles based on hearing alone. In conversations with
the agency during Phase 1 research, visually-impaired individuals
indicated that in noisier suburban ambient conditions, they would not
try to cross streets unassisted. The ambient levels that the agency
measured during Phase 1 research for which visually-impaired
pedestrians would be expected to cross using hearing alone were 49.5 A-
weighted dB and 49.8 A-weighted dB.
    In selecting an ambient at which the agency expects that
pedestrians should be able to detect an approaching vehicle using their
hearing, the agency relied on recommendations for quiet vehicle alert
sound specifications developed by Danish acoustics experts.\99\ In
developing the recommendations the Danish researchers measured
different ambient levels around Copenhagen. The ambient levels in
residential areas where pedestrians would be expected to detect an
approaching vehicle using their hearing was 55 A-weighted dB.
---------------------------------------------------------------------------

    \99\ Pedersen et al. White Paper on External Sounds of Electric
Cars-Guidelines and Recommendations. Available at http://
media.wix.com/ugd/64a49a--
43313ad70e7c40f43150cf747b2e5c44.pdf?dn=A520040+-+DSTN+-
+White+paper+electric+cars+-+av122410+-+ECT+LR.pdf.
---------------------------------------------------------------------------

    In a presentation to NHTSA staff, Honda Motor Company (Honda)
stated that the ambient at which pedestrians would reasonably be able
to detect vehicles using hearing alone is around 52.5 A-weighted
dB.\100\ Honda based this conclusion on a human factors approach in
which recordings of three different ambient sound levels (quiet
residential, moderate suburban, and urban) were played and participants
were asked whether they would rely on hearing alone to detect an
approaching vehicle. While the study did not include any visually-
impaired participants, the agency agrees that pedestrians--those that
are visually impaired and others that are not--could not be reasonably
expected to detect approaching vehicles in ambient conditions near 60
A-weighted dB.
---------------------------------------------------------------------------

    \100\ The Presentation that Honda gave at the meeting is
available on regulations.gov. Docket No. NHTSA-2011-0100-0038.
---------------------------------------------------------------------------

    The agency believes that a 55 A-weighted dB ambient represents a
reasonable level below the 60 A-weighted dB ambient (in which
pedestrians would no longer be able to reasonably rely on hearing to
detect approaching vehicles).
    The spectral distribution of the ambient is another factor that
affects the detectability of an alerting sound. Tonal components of an
alerting sound in portions of the ambient spectrum that are not strong
contribute to detectability. Using a loudness model and synthetic
ambient that represent a typical urban ambient profile in which a
pedestrian would be attempting to detect a vehicle, the agency
developed minimum sound level requirements for selected one-third
octave bands.
    In order to aid pedestrian detection and recognition of sounds
produced by EVs and HVs, the agency has tentatively concluded that the
sound level produced by a vehicle will increase with an increase in
vehicle speed. The agency has two goals in increasing the vehicle's
sound level as the vehicle increases speed. First, increasing the
vehicle's sound level as the vehicle increases speed will allow
pedestrians to detect the vehicle from a greater distance to correspond
to the vehicle's increased sight stopping distance at higher speeds and
the greater distance necessary to stop the vehicle. Second, ICE
vehicles produce increasing sound levels as they accelerate so the
sound produced by HVs and EVs will mimic the behavior of ICE sounds to
enhance recognition.
    In developing the acoustic specifications in this proposal, the
agency considered one-third octave bands from 160 Hz to 5000 Hz. When
all one-third octave bands from 160 Hz to 5000 Hz are set to a minimum
audible level, it can be demonstrated that, relative to the overall
sound level, some

bands are less efficient at providing a detectable signal. That is,
bands below 315 Hz and bands from 630 to 1600 Hz increase the overall
levels more for the same contribution to detection. The levels of these
bands are indicated by arrows in Figure 3. The arrows in the figure
point to the regions of the spectrum that are most effective for
warning sounds, i.e., those where the threshold is not too high and the
ambient is not too high to mask sounds at the threshold.
[GRAPHIC] [TIFF OMITTED] TP14JA13.033

    Due to masking effects of the ambient and potential hearing loss of
the pedestrian, opportunities for detection will be maximized if the
countermeasure signal contains detectable components over a wide
frequency range; therefore, a minimum level is proposed for a set of
one-third octave bands that includes mid-frequency one-third octave
bands (315, 400, and 500 Hz) as well as high frequency one-third octave
bands (2000, 2500, 3150, 4000, and 5000 Hz). Low frequency bands (below
315 Hz) were not considered due to the expected strong masking effects
of the ambient at low frequencies. The agency chose these one-third
octave bands because these bands contributed the most to detection
without increasing the overall levels of the sound. Specifying minimum
sound pressure level requirements for a wide range of one-third octave
bands means that sounds meeting the specifications will be detected in
a wider range of ambient conditions with different acoustic profiles.
Specifications for the mid-range frequency bands between 315 and 500 Hz
will assist pedestrians in detecting HVs and EVs in ambient noise
environments such as areas near construction activity with a
significant degree of high frequency signal content. Low-frequency
bands (below 315 Hz) are omitted because they do not contribute to
detection and the likelihood that many practical countermeasure devices
may not be able to produce high level, low-frequency sounds.
    In consideration of community noise impact, the agency omitted mid-
frequency bands from 630 to 1600 Hz from the acoustic specifications
because, for the ambient considered, these bands contributed more to
the overall sound level than other bands for the same increase in
detectability. By omitting minimum sound level requirements for the
one-third octave bands in the 630 to 1600 Hz frequency range, the
agency is able to ensure that the alert sounds allow pedestrians to
safely detect nearby EVs and HVs without contributing unnecessarily to
an increase in overall ambient noise levels.
    Table 12 shows the one-third octave band frequency requirements for
vehicle emitted sounds for all of the test conditions in S7 of the
proposed regulatory text.

                                  Table 12--Minimum Sound Levels for Detection
----------------------------------------------------------------------------------------------------------------
  One-third octave band center    Stationary but
          frequency, Hz              activated        Backing         10 km/h         20 km/h         30 km/h
----------------------------------------------------------------------------------------------------------------
315.............................              42              45              48              54              59
400.............................              43              46              49              55              59
500.............................              43              46              49              56              60
2000............................              42              45              48              54              58
2500............................              39              42              45              51              56

3150............................              37              40              43              49              53
4000............................              34              36              39              46              50
5000............................              31              34              37              43              48
Overall A-weighted SPL Measured               49              52              55              62              66
 at SAE J2889-1 PP' line........
----------------------------------------------------------------------------------------------------------------

    The agency is not including requirements for overall sound pressure
level in the proposed standard. Because each one-third octave band
contributes to the overall sound pressure level of a sound it is
possible to determine what the sound pressure level of sounds meeting