---------------------------------------------------------------------------

    \57\ This research was documented in a report, ``Development and
Validation of Functional Definitions and Evaluation Procedures for
Collision Warning/Avoidance Systems,'' Kiefer, R., et al., DOT HS
808 964, August 1999. Additional NHTSA FCW research is described in
Zador, P.L., et al., ``Final Report--Automotive Collision Avoidance
System (ACAS) Program,'' DOT HS 809 080, August 2000; and Ference,
J.J., et al., ``Objective Test Scenarios for Integrated Vehicle-
Based Safety Systems,'' Paper No. 07-0183, Proceedings of the 20th
International Conference for the Enhanced Safety of Vehicles, 2007.
    \58\ Najm, W.G., Stearns, M.D., Howarth, H., Koopmann, J., and
Hitz, J., ``Evaluation of an Automotive Rear-End Collision Avoidance
System,'' DOT HS 810 569, April 2006 and Najm, W.G., Stearns, M.D.,
and Yanagisawa, M., ``Pre-Crash Scenario Typology for Crash
Avoidance Research,'' DOT HS 810 767, April 2007.
    \59\ Forkenbrock, G., O'Harra, B., ``A Forward Collision Warning
(FCW) Program Evaluation, Paper No. 09-0561, Proceedings of the 21st
International Technical Conference for the Enhanced Safety of
Vehicles, 2009.
---------------------------------------------------------------------------

    NHTSA's research and test track performance evaluations of AEB
began around 2010. The agency began a thorough examination of the state
of forward-looking advanced braking technologies, analyzing their
performance and identifying areas of concern or uncertainty, to better
understand their safety potential. NHTSA issued a report \60\ and a
request for comments (RFC) seeking feedback on its CIB and DBS research
in July 2012.\61\ Specifically, NHTSA wanted to enhance its knowledge
further and help guide its continued efforts pertaining to AEB
effectiveness, test operation (including how to ensure repeatability
using a target or surrogate vehicle), refinement of performance
criteria, and exploration of the need for ``false positive'' tests to
minimize the unintended negative consequences of automatic braking in
non-critical driving situations where a crash was not imminent.
---------------------------------------------------------------------------

    \60\ The agency's initial research and analysis of CIB and DBS
systems were documented in a report, ``Forward-Looking Advanced
Braking Technologies: An analysis of current system performance,
effectiveness, and test protocols'' (June 2012). http://www.regulations.gov, NHTSA 2012-0057-0001.
    \61\ 77 FR 39561.
---------------------------------------------------------------------------

    NHTSA considered feedback it received on the RFC and conducted
additional testing to support further development of the test
procedures. The agency's work was documented in two additional reports,
``Automatic Emergency Braking System Research Report'' (August 2014)
\62\ and ``NHTSA's 2014 Automatic Emergency Braking (AEB) Test Track
Evaluations'' (May 2015),\63\ and in accompanying draft CIB and DBS
test procedures.\64\
---------------------------------------------------------------------------

    \62\ https://www.regulations.gov, NHTSA 2012-0057-0037.
    \63\ DOT HS 812 166.
    \64\ https://www.regulations.gov, NHTSA 2012-0057-0038.
---------------------------------------------------------------------------

    In 2016, NHTSA published a report identifying the most recurrent
AEB-relevant pre-crash scenarios for heavy vehicles. NHTSA identified
the three most recurrent situations as a heavy vehicle moving toward a
stopped lead vehicle, a heavy vehicle moving toward a slower moving
lead vehicle, and a heavy vehicle moving toward a lead vehicle that is
decelerating.\65\ These were the same three crash scenarios that had
been identified as the most prevalent AEB-relevant crash scenarios for
light vehicles.
---------------------------------------------------------------------------

    \65\ Boday, C., et al., ``Class 8 Truck-Tractor and Motorcoach
Forward Collision Warning and Automatic Emergency Braking Test Track
Research--Phase I,'' Washington, DC: National Highway Traffic Safety
Administration (June 2016). Docket No. NHTSA[hyphen]2015-0024-0004.
---------------------------------------------------------------------------

2. Phase I Testing of Class 8 Truck-Tractors and Motorcoach
    In 2016, NHTSA published its first report on track-testing of AEB
for heavy vehicles. The previous studies describing the test procedures
for light vehicles provided a framework for the establishment of heavy
vehicle test procedures. Since test procedures were not yet developed
for heavy vehicles, the goal of the research was to first adapt
existing testing protocols for light vehicle AEB and then follow these
adapted test procedures to quantify the performance of FCW and AEB
systems on heavy vehicles. The research was conducted in two phases.
    NHTSA's Phase I work began with using a combination of the specific
test situations established for NHTSA's NCAP for assessment of FCW and
AEB systems and a modified version of the light vehicle test procedures
to create heavy vehicle draft research test procedures. NCAP tests
involved use of a strikable surrogate vehicle; however, for early heavy
vehicle Phase I work, NHTSA used a surrogate lead vehicle comprised of
canvas-covered foam to exhibit geometric and reflective features of the
rear of a passenger car. The testing for Phase I was performed with
four heavy vehicles outfitted with FCW and AEB, including three Class 8
truck-tractors and one Class 8 motorcoach. Specifically, the four Class
8 vehicles were a 2006 Volvo VNL 64T630 6x4 tractor, a 2006
Freightliner Century Class 6x4 tractor, a 2012 Freightliner Cascadia
6x4 tractor, and a 2007 MCI 56-passenger motorcoach (bus). Each vehicle
was equipped with ABS, ESC, FCW, and AEB systems. The 2006 and 2012
Freightliners and the MCI motorcoach employed a Meritor WABCO system,
and the 2006 Volvo was equipped with a Bendix Wingman Advanced system.
In general, the FCW and AEB systems utilized a front bumper mounted
sensor to detect objects in front of the vehicle and a display to warn
the driver with audio and visual alerts.
    For each vehicle, NHTSA planned to run ten tests that are
summarized in Table 8. These situations covered the three most common
AEB-relevant pre-crash scenarios, as well as two false positive tests
and two tests performed at different weighted conditions.

                                         Table 8--Phase I Test Scenarios
----------------------------------------------------------------------------------------------------------------
                                        Lead vehicle    Subject vehicle     Lightly loaded      Loaded at GVWR
               Scenario                 speed (km/h)      speed (km/h)    (number of trials)  (number of trials)
----------------------------------------------------------------------------------------------------------------
Lead vehicle Stopped.................               0                 40                  10  ..................
Lead Vehicle Moving..................              16                 40                  10                  10
Lead Vehicle Moving..................              32                 72                  10                  10
Lead Vehicle Decelerating............              40                 40                  10                  10
Lead Vehicle Decelerating............              48                 48  ..................                  10
Lead Vehicle Decelerating............              56                 56                   5                   5
Steel Trench Plate False Positive....             N/A                 40                   5                   5

Steel Trench Plate False Positive....             N/A                 72                   5                   5
----------------------------------------------------------------------------------------------------------------

    The test scenarios were defined by the initial speeds of the
subject vehicle and lead vehicle, and the starting headway distance
between the vehicle was monitored. For all the tested scenarios, the
test driver was instructed to modulate the accelerator pedal to
maintain the desired test speed until FCW initiated, upon which the
accelerator pedal input was removed. Steering was applied to maintain
lateral position test tolerances to the lead vehicle. Manual brake
pedal applications were only applied in certain scenarios where AEB was
not designed to activate, or an impact occurred with the leading
surrogate vehicle. Additionally, the previously described test
situations were conducted under both a lightly loaded condition and a
fully loaded vehicle weight condition (i.e., loaded up to the vehicle's
GVWR). Based upon potential damage to the subject vehicle, the
feasibility of completing each test scenario with the specific load,
and the fact that there was no discernable difference between the
performance under the lightly loaded and GVWR loaded conditions in the
trials executed, some of the speed combinations were not investigated
under both loads. The false positive tests were conducted by driving
the selected vehicles toward and over a steel trench plate to determine
if these commonly used road construction covers would trigger false
alerts or unintentional automatic braking.
    Stationary lead vehicle testing was limited to the 2006 Volvo, as
it was equipped with the only system that would trigger an FCW on
stationary vehicles. At the time these evaluations were performed, none
of the systems tested were designed to activate AEB on stationary
vehicles. During every slower moving lead vehicle test, FCW was
activated. Additionally, every vehicle's AEB activated and avoided
collision during each slower moving test performed with a subject
vehicle speed of 40 km/h, and a lead vehicle speed of 16 km/h.
    The lead vehicle decelerating test was used to evaluate all four
heavy vehicles, but multiple test adjustments had to be applied. For
the lead vehicle decelerating test performed with both the subject and
lead vehicle speeds of 40 km/h, the lead vehicle was slowed to 8 km/h
instead of a stop to account for the failure of the subject vehicles to
activate AEB for stopped vehicles. Once the change was implemented,
both the FCW and the AEB systems were activated, and speeds were
reduced. Collisions between the subject and lead vehicle did occur, but
testing of this scenario mainly led to the observation that the test
procedure's headway would also have to be adjusted since heavy vehicles
have different braking capabilities than light vehicles.
    The steel trench plate false positive test was performed using the
2006 Volvo, 2006 Freightliner, and 2007 MCI at 40 km/h and 72 km/h.\66\
For both velocities examined, the 2006 Freightliner and 2007 MCI
exhibited no false positives in all five trials. However, the 2006
Volvo triggered unnecessary auditory warnings in all five trials for
both velocities. None of the false positive testing trials resulted in
AEB system activation.
---------------------------------------------------------------------------

    \66\ The 2012 Freightliner was not evaluated with steel trench
plate scenario due to the short window that the vehicle was
available for testing.
---------------------------------------------------------------------------

    During this early testing, the surrogate lead vehicle was towed
onto the test track and fixed laterally in the test lane via a low-
profile plastic monorail track. Initially, the test system employed a
low-stretch rope to pull the surrogate lead vehicle by a tow vehicle.
This configuration performed well in the slower moving lead vehicle
situation because the lead vehicle moves at a constant velocity,
allowing the tow rope to stay in tension. In contrast, when testing the
lead vehicle decelerating scenario, the tension in the tow rope was not
maintained once the tow vehicle decelerated, and subsequently the tow
rope was prone to becoming stuck under the surrogate lead vehicle. This
issue resulted in a loss of surrogate lead vehicle lateral stability
and consequently decreased the test repeatability.
    To address this shortcoming, the foam surrogate lead vehicle was
replaced with a vertical cylinder wrapped with a layer of radar
reflective material secured to the top of a movable platform with more
consistent and stable deceleration properties. However, because the
cylinder was not representative of a real vehicle, this was identified
as needing further development and modification of the test protocols.
    A significant portion of this early AEB testing focused on
developing draft research test procedures that could be used to safely
and objectively assess AEB performance. The development history of test
protocols is important for two reasons. First, it explains how NHTSA
came to the conclusion to propose the performance parameters described
in the notice and its basis that the performance requirements are
objective and practicable. Second, it provides some context as to some
of the limitations of early performance evaluations of AEB for heavy
vehicles. In general, this initial phase of research demonstrated that
the scenarios were generally repeatable and practical, and the tests
showed additional development would potentially result in better
controlled deceleration and stability of the lead vehicle.
3. Phase II Testing of Class 8 Truck-Tractors
    NHTSA's primary objectives of the Phase II efforts were to continue
to develop the FCW and AEB test procedures executed in Phase I such
that they could be effectively utilized on a closed-course track test
to assess performance of heavy vehicle FCW and AEB systems. For this
testing, NHTSA used four Class 8, truck-tractors, three of which were
from Phase I. The fourth vehicle from Phase I, the MCI motorcoach, was
replaced with a 2016 Freightliner. Specifically, these subject vehicles
were a 2016 Freightliner, a 2012 Freightliner, a 2006 Volvo, and a 2006
Freightliner. Like in Phase I, all vehicles were outfitted with ABS,
ESC, FCW, and AEB systems. Both the 2006 and 2012 Freightliners
employed the Meritor WABCO system, the 2016 Freightliner had the
Detroit Assurance Safety System, and the 2006 Volvo utilized the Bendix
Wingman Advance system. All AEB systems on the selected vehicles
utilized radar installed on the front bumper and each AEB system
provided auditory and visual alerts. For Phase II testing, NHTSA used
the test scenarios from Phase I; however, a second false positive test
scenario was added. Specifically, NHTSA investigated a pass-through
test from

Europe's AEB requirements \67\ involving a subject vehicle being driven
in a central lane between two parked vehicles.
---------------------------------------------------------------------------

    \67\ United Nations, ``Uniform provisions concerning the
approval of motor vehicles with regard to the Advanced Emergency
Braking Systems (AEBS)'' 2013. Available at https://unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/2013/R131e.pdf (last accessed
February 10, 2023).
---------------------------------------------------------------------------

    While other standards \68\ were considered for this research study,
the use of United States collision data and different testing goals led
to establishment of specific test procedures. While vehicle test speeds
were similar, with some overlap, NHTSA's test procedures included
higher velocity tests to be executed at 55 km/h with more
specifications governing the test conditions and test completion.
NHTSA's Phase II test scenario matrix is summarized in Table 9.
---------------------------------------------------------------------------

    \68\ The following were among the standards considered:
International Organization for Standardization (ISO) 22839:2013,
``Intelligent transport systems--Forward vehicle collision
mitigation systems--Operation, performance, and verification
requirements; ISO 15623:2013, ``Intelligent transport systems--
Forward vehicle collision warning systems--Performance requirements
and test procedures,'' and SAE International recommended practice
J3029, ``Forward collision warning and mitigation vehicle test
procedure--Truck and bus.''
---------------------------------------------------------------------------

    Phase II also further enhanced the testing of Phase I by
implementing a new strikable surrogate vehicle (SSV) system as the lead
vehicle. The SSV system was created for NHTSA's light vehicle AEB
assessment and was engineered to enhance test repeatability and lateral
stability in higher velocity tests.

                                        Table 9--Phase II Test Scenarios
----------------------------------------------------------------------------------------------------------------
                                        Lead vehicle    Subject vehicle     Lightly loaded      Loaded at GVWR
               Scenario                 speed (km/h)      speed (km/h)    (number of trials)  (number of trials)
----------------------------------------------------------------------------------------------------------------
Lead Vehicle Stopped.................               0                 40                   6                   8
Lead Vehicle Moving..................               0                 40                   8                   8
Lead Vehicle Moving..................              35                 75                   8                   8
Lead Vehicle Decelerating............              40                 40                   8                   8
Lead Vehicle Decelerating............              55                 55              6 or 8              6 or 8
Steel Trench Plate False Positive....             N/A                 40                   8                   8
Steel Trench Plate False Positive....             N/A                 75                   8                   8
Stationary Vehicle False Positive....             N/A                 50                   8                   8
----------------------------------------------------------------------------------------------------------------

    The SSV served as the lead vehicle or the vehicle test device (VTD)
in the AEB tests. The rear of the SSV was designed to depict features
of a typical passenger car. The carbon fiber surrogate exemplified
these aspects, considering physical measurements, reflective
properties, and visual characteristics. Its structure was not only
developed to be detected as a real vehicle by the AEB systems, but it
was also intended to endure wind gusts and recurrent impacts up to
approximately 40 km/h. The required surrogate test velocities and
deceleration of the VTD were achieved by a tow vehicle equipped with a
brake controller in conjunction with a towed two-rail track used to
move the SSV during the test.
    NHTSA implemented changes in the test procedures from Phase I to
Phase II. The Phase II test procedures contained more detail as input
from within NHTSA and data collected during both phases of heavy
vehicle research were used to develop and refine the procedures. For
example, the test procedures contained structure for test scenario
descriptions, minimum data channels to collect, and general testing
requirements (e.g., ambient temperature range, wind, speed, brake
burnish, etc.). Definitions were added for when the initial test
conditions started, and more detail was added to the definition of when
a test trial ended. The test conditions were established to be on dry,
straight roadways in the daylight, based on a previous analysis of
crash data and observed safety critical events in field operation
testing. FCW activation, AEB activation, collision detection, and
accelerator pedal release time were measured in the tests. Similar to
Phase I, the testing of each scenario occurred under two different load
conditions.
    After reviewing the Phase I test outcomes, NHTSA determined that
the lead vehicle stopped scenario could only be assessed by the latest
model year test vehicle outfitted with a capable AEB system. In Phase
II, the subject vehicle traveled 40 km/h and approached a stationary
lead vehicle in the same lane. Valid trials required the driver to
remain centered in the traveling lane and continue driving at the
target velocity until AEB was triggered. Once AEB was triggered, the
test driver fully released the accelerator pedal, and the driver was
not allowed to use the brake pedal of the test vehicle unless the
vehicle collided with the lead vehicle or if the AEB system completely
stopped the vehicle. The results showed that FCW was activated,
followed by automatic braking by the AEB system in all 8 trials
performed under the GVWR condition.
    The lead vehicle moving test situation was evaluated at multiple
velocity combinations for all four test vehicles. During this test, the
subject test vehicle traveled at 40 km/h or 75 km/h and approached a
slower-moving lead vehicle traveling at 15 km/h or 35 km/h,
respectively, in the same lane. Valid trials required the driver to
remain centered in the traveling lane and continue driving at the
target velocity until AEB was triggered. Once AEB was triggered, the
test driver fully released the accelerator pedal. Testing for this
scenario was conducted for both lightly loaded and GVWR conditions. All
of the vehicles tested consistently issued FCW alerts and activated the
AEB systems; however, impacts occurred.
    The lead vehicle decelerating situation was executed with all the
test vehicles except the 2006 Volvo due to its Phase I performance. Two
initial velocity and initial headway combinations of the subject and
lead vehicles were tested (i.e., 40 km/h and 80 m; 55 km/h and 23 m).
After a short period of steady state driving using constant speeds and
a constant headway, the lead vehicle was braked at approximately 0.3g
while traveling in the same lane as the subject vehicle. The subject
vehicle driver kept the subject vehicle centered in the traveling lane
and continued driving until AEB was triggered. Under both the lightly
loaded and GVWR load conditions testing was completed.
    The lead vehicle decelerating test scenario with initial test
speeds of 55 km/h and 23 m of headway presented the greatest challenges
when compared to other tests. In Phase II, the initial headway was
changed from 30.5 m to 23

m to keep the lead vehicle from transitioning to a stopped lead vehicle
test scenario near the end of a test trial, as it did in Phase I
testing with a headway of 30.5 m. Testing for this scenario was
conducted for both lightly loaded and GVWR conditions and all four
vehicles. All of the vehicles consistently issued FCW alerts and
activated the AEB systems; however, most tests resulted in impact.
    Two false positive test types were also conducted. The steel trench
plate scenario was executed at 40 km/h and 75 km/h for all test
vehicles. Each vehicle was evaluated in the GVWR load condition, but
only the 2016 Freightliner was also assessed in the lightly loaded
condition. Most of the vehicles did not exhibit any FCW or AEB
activations in these tests. However, one vehicle's FCW/AEB system
perceived the steel trench plate as a stationary object on the path of
travel and the reaction to this false positive detection was not
consistent in terms of warning time, brake initiation time, and
deceleration level. The second test involved two stationary vehicles in
lanes on either side of the test vehicle's travel lane; and only the
2012 Freightliner and the 2016 Freightliner were evaluated under the
GVWR load condition. Neither vehicle exhibited any false FCW or AEB
activations in this test.
    Overall, the Phase II test results demonstrated the ability of the
vehicles and AEB systems tested to avoid contact in the lead vehicle
stopped and lead vehicle moving test scenarios at the different
velocities and achieve no collisions. These capabilities extended to
the lead vehicle decelerating tests performed at 40 km/h and a headway
of 80 m. In contrast, there was a much lower likelihood of these
vehicles avoiding contact with the lead vehicle using an initial speed
of 55 km/h and a headway of 23 m.
4. NHTSA's 2018 Heavy Vehicle AEB Testing
    NHTSA conducted test track research in 2017 and 2018 on heavy
vehicles equipped with FCW and AEB. This section describes the third
phase of NHTSA's heavy vehicle testing and the results from three
single-unit trucks. These trucks included a class 3 2016 Freightliner
3500 Sprinter, a class 6 2017 International 4300 SBA 4x2, and a class 7
2018 Freightliner M2-106. The main goal of this third phase was to
develop objective test procedures for evaluating the performance of
heavy vehicles equipped with FCW and AEB systems on a closed course
test track.

                                       Table 10--Phase III Test Scenarios
----------------------------------------------------------------------------------------------------------------
                                                                   Lead vehicle    Subject vehicle     Initial
                            Scenario                               speed (km/h)      speed (km/h)    headway (m)
----------------------------------------------------------------------------------------------------------------
Lead Vehicle Stopped............................................               0                 40           55
Lead Vehicle Moving.............................................              15                 40           35
Lead Vehicle Moving.............................................              35                 75           56
Lead Vehicle Decelerating.......................................              40                 40           80
Lead Vehicle Decelerating.......................................              55                 55           23
Steel Trench Plate False Positive...............................             N/A                 40           56
Steel Trench Plate False Positive...............................             N/A                 75          105
Stationary Vehicle Pass-Through False Positive..................             N/A                 50           60
----------------------------------------------------------------------------------------------------------------

    In this third phase of research, the newly developed heavy vehicle
AEB test procedures included test conditions where the driver applies
the subject vehicle brakes while approaching a lead vehicle, but with
an input insufficient to prevent a rear-end crash, to complement the
previously developed scenarios.
    The 2017 International 4300 was outfitted with a Bendix system
which includes FCW and AEB. This system was enhanced since Phase II of
NHTSA's research where, in Phase III, it used camera and radar to
engage automatic emergency braking and demonstrated the ability to
respond to traveling and stationary vehicles. The FCW provided alerts
at velocities greater than 8 and 15 km/h for moving and stationary
objects, respectively. For the AEB system to be engaged, the vehicle
had to travel above 25 km/h.
    The 2018 Freightliner M2-106 was outfitted with an OnGuardACTIVE
Collision Mitigation system which features FCW and AEB. This system
used radar to engage automatic emergency braking and displayed the
ability to respond to traveling and stationary vehicles. The FCW
provided alerts with visual and auditory cues and a braking warning was
issued when the AEB was activated. In order for the AEB system to be
engaged, the vehicle had to travel above 25 km/h.
    The study concluded that the test procedures were reproducible and
appropriate for heavy vehicles outfitted with FCW and AEB systems.
After Phase II, the test procedures and scenarios were updated and
applied to heavy vehicles with different weight classifications. The
inclusion of heavy vehicles with updated AEB systems in Phase III
allowed for evaluation of more systems in the lead vehicle stopped
scenario; during the lead vehicle stopped evaluations with no driver
braking, at least one vehicle experienced no collisions for all trials
tested. This showed improvement in comparison to the prior phase, which
was only able to test lead vehicle stopped on one vehicle and resulted
in multiple collisions. The lead vehicle moving scenario test results
also displayed improvement where the percentage of collisions decreased
in comparison to Phase II. Overall, the outcomes showed that the FCW/
AEB systems have the capacity for being able to decrease rear-end
collisions by exhibiting velocity reductions before a collision or
avoiding contact with a lead vehicle entirely. While some FCW false
positives were observed, the overall results depicted that the systems
have the ability to avoid collision on the test track.
    The results of this research show that the test procedures are
applicable to many heavy vehicles and indicate that performance
improvements in heavy vehicles equipped with these safety systems can
be objectively measured.\69\ Further, this was the first phase of the
series that was able to apply the test procedures to single-unit trucks
across multiple weight classifications; and new test scenarios were
added.
---------------------------------------------------------------------------

    \69\ Salaani, M.K., Elsasser, D., Boday, C., ``NHTSA's 2018
Heavy Vehicle Automatic Emergency Braking Test Track Research
Results,'' SAE International. J Advances & Current Practices in
Mobility 2(3):1685-1704, 2020, doi:10.4271/2020-01-1001.
---------------------------------------------------------------------------

5. NHTSA's Research Test Track Procedures
    NHTSA's most recently published heavy vehicle AEB research test
track

procedures were published in March 2019 and evaluate AEB performance in
crash-imminent scenarios both with and without manual brake pedal
applications.\70\ These procedures, with some modification, form the
basis for the proposed test procedure in this NPRM.
---------------------------------------------------------------------------

    \70\ Elsasser, D., Salaani, M.K., & Boday, C., ``Test track
procedures for heavy-vehicle forward collision warning and automatic
emergency braking systems,'' Report No. DOT HS 812 675, Washington,
DC: National Highway Traffic Safety Administration (March 2019).
Available at https://rosap.ntl.bts.gov/view/dot/42186/dot_42186_DS1.pdf (last accessed June 28, 2022).
---------------------------------------------------------------------------

    The test procedures were based upon prior research and include the
lead vehicle stopped, lead vehicle moving, and lead vehicle
decelerating test scenarios, as well as the steel trench plate and
stationary vehicles false positive scenarios. The testing was divided
into three phases. First, the subject vehicle and the lead vehicle are
situated on the test track to the proper location and test velocity.
The second stage involves determining whether the vehicles have met the
proper starting test conditions to achieve valid and reproducible test
outcomes. The third and final stage serves to assess test validity and
system performance as well as response to any FCW or AEB triggers. In
the research test procedure, if an invalid test is detected, the test
is repeated until at least seven valid test attempts are completed.
Testing was executed during daylight, avoiding inclement weather and
irrelevant obstructions such as overhead signs, bridges, overpasses,
etc. For test procedures that include manual brake pedal applications,
the pedal was displaced at a rate of 254 mm/s to achieve a target
longitudinal acceleration of -3.0 m/s\2\, simulating a manual brake
pedal application of a panicked driver. Test procedures for brake pedal
input characterization and verification assessment are described for
checking uniformity and to ensure the set braking magnitude and
response can be achieved.
    The lead vehicle stopped test scenario requires the test subject
vehicle to be driven toward the stationary lead vehicle at 40 km/h. The
subject vehicle is to maintain its velocity and relative lateral
position to the straight testing path as it advances toward the lead
vehicle. When the time to collision is equal to 5 seconds there is a
nominal separation distance of 56 m between the front of the subject
vehicle and the rear of the lead vehicle. Once braking is initiated,
the accelerator pedal input of the subject vehicle is discontinued
fully within 0.5 seconds after the start of braking. For lead vehicle
stopped tests performed with insufficient brake pedal applications, the
brake pedal is applied at a time to collision of 1.51 seconds. The
point at which the brake pedal rate exceeds 50 mm/s is used to define
the beginning event of brake pedal input. The conclusion of testing is
marked by a collision between the subject and lead vehicle or the
subject vehicle stopping prior to colliding with the lead vehicle. The
test procedures are repeated until seven valid test trials are obtained
for each lead vehicle stopped test with and without brake pedal
applications, to obtain a total of 14 valid tests.
    The test procedure for the lead vehicle moving scenario is similar
for its two vehicle speed combinations. The subject vehicle travels to
reach the target speed of 40 or 75 km/h for a minimum of 1 second; and
the lead vehicle travels at 15 or 35 km/h, respectively. Prior to
approaching the lead vehicle there should be a separation distance of
at least 100 m. Additionally, by a time to collision equal to 5
seconds, the separation range is 35 m for 40 km/h and 56 m for 75 km/h.
Once the subject vehicle encounters the lead vehicle and braking is
automatically initiated, the subject vehicle accelerator pedal was
fully released within 0.5 seconds.
    The lead vehicle decelerating test procedure starts with the
subject vehicle traveling toward the lead vehicle while maintaining an
80 m separation distance. Both the subject vehicle and the lead vehicle
are required to reach and maintain a velocity of 40 km/h for at least 1
second while keeping the headway distance. Once the subject vehicle
encounters the lead vehicle and braking is initiated, the subject
vehicle accelerator pedal was fully released within 0.5 seconds. This
test procedure is repeated with similar steps for a 55 km/h velocity
and a 23 m separation distance.
    In order to evaluate false positives, the steel trench plate test
scenario was executed at 40 and 75 km/h, and the stationary vehicles
test was completed at 50 km/h. For the seven test trials performed at
40 and 75 km/h, a short edge of the rectangular steel trench plate was
centered on the roadway about the x-axis. The subject vehicle was
driven toward the steel trench plate such that an initial 110.0 m
headway existed, and a nominal velocity of 40 or 75 km/h was maintained
for at least 1.0 second. The test initial test condition began when the
separation distance between the subject vehicle and steel trench plate
was 56 m and 105 m for 40 and 75 km/h, respectively. Once the subject
vehicle encountered the steel trench plate at a headway of 16.83 or
40.88 m for 40 and 75 km/h, respectively, the brakes of the subject
vehicle were engaged. The test ends when either the subject vehicle
drives over the steep trench plate or the subject vehicle stops before
crossing over the steel trench plate.
    The preliminary conditions of the stationary vehicles test involved
two vehicles parked with a lateral separation of 4.5 m. These two
vehicles were faced in the forward direction of the test track and were
aligned. The subject vehicle was driven along the test track with a
100.0 m headway from the stationary vehicles. The subject vehicle was
then driven to maintain a velocity of 50 km/h for at least 1.0 second.
The starting test condition is a headway of 60 m where the steering
wheel of the subject vehicle was controlled to center the vehicle along
the test track. Once the subject vehicle encountered the stationary
vehicles at a range of approximately 23.74 m the subject vehicle
accelerator pedal was fully released within 0.5 seconds of the
initiation of braking.
6. 2021 VRTC Testing
    The test track data that follows represents vehicle performance
with the latest generation AEB systems and the procedures and
conditions proposed in this NPRM largely match the procedures and
conditions used for this testing.
2021 Freightliner Cascadia
    The 2021 Freightliner Cascadia was tested under the lead vehicle
stopped, lead vehicle moving, and lead vehicle decelerating scenarios
at the NHTSA VRTC in 2021. The GVT was used as the lead vehicle in
these test scenarios. The lead vehicle stopped scenario was executed at
multiple initial subject vehicle velocities from 20 km/h up to 95 km/h.
While contact with the VTD occurred at 20, 25, 30, and 35 km/h, there
were measurable speed reductions. At test velocities between 40 and 85
km/h, no collisions were observed. Collisions also occurred at 90 and
95 km/h, but the FCW at both speeds was issued earlier than 2 seconds
before contact. Ten additional test trials were conducted at 40 km/h,
and only one trial resulted in contact. Four additional test trials
were executed at 50, 60, 70, 80, and 85 km/h; in all four trials, there
were no collisions at three speeds and one collision at two speeds
(i.e., 80 and 85 km/h, respectively) which ultimately resulted in a
speed reduction when compared to the other trials.
    The lead vehicle moving scenario was performed at several
combinations of subject vehicle and lead vehicle initial speeds. The
first set of eight trials

involved the subject vehicle at a range of velocities of 30 km/h to 90
km/h and the initial speed of the lead vehicle was 20 km/h for each.
Contact occurred only at the 30 and 60 km/h test velocities. The
initial speeds for the subject vehicle and lead vehicle for the second
set of eight trials was 40 and 15 km/h, respectively. One of these
trials ended in a collision and this run exhibited a notably lower
speed reduction when compared to the other trials. The third and fourth
sets of trials included subject vehicle and lead vehicle initial
velocity combinations of 75 and 35 km/h and 80 and 12 km/h,
respectively, and contact was avoided in all trials. For the lead
vehicle decelerating scenario collision was avoided for all trials
during the 40 km/h test. Impact occurred during four out of five runs
in the 50 km/h test with an initial headway of 18 m. However, at the
longer headway lengths of 21, 23, 25, and 40 m there were no collisions
during the 50 km/h tests. Additionally, contact was avoided for the 80
km/h test with headway lengths of 23, 25, 28, 40, and 45 m.

        Table 11--2021 Freightliner Cascadia Test Track Scenarios
------------------------------------------------------------------------
                                        Lead vehicle    Subject vehicle
               Scenario                 speed  (km/h)    speed  (km/h)
------------------------------------------------------------------------
Lead Vehicle Stopped.................               0              20-95
Lead Vehicle Moving..................              20              30-90
Lead Vehicle Moving..................              15                 40
Lead Vehicle Moving..................              35                 75
Lead Vehicle Moving..................              12                 80
Lead Vehicle Moving..................              32                 80
Lead Vehicle Decelerating............              40                 40
Lead Vehicle Decelerating............              50                 50
Lead Vehicle Decelerating............              55                 55
Lead Vehicle Decelerating............              80                 80
------------------------------------------------------------------------

2021 Ram 5500
    The class 5 2021 Ram 5500 was tested under the lead vehicle
stopped, lead vehicle moving, and lead vehicle decelerating scenarios
at the NHTSA VRTC in 2022. The tests performed for these scenarios
involved no manual brake application; and the GVT was used as the lead
vehicle. For the lead vehicle stopped scenario, the Ram truck avoided
collisions at 10, 20, 30, 40 km/h, while impact occurred during two of
the five trials in the 50 km/h test, although there was an
approximately 80 percent reduction in speed. In general, these results
seemed to align with limitations described in the vehicle owner's
manual that indicated that the system works up to 50 km/h. Testing up
to 80 km/h was not completed to avoid damage to the subject vehicle and
test equipment. During the lead vehicle moving scenario, the truck
avoided contact at 30, 40, 50, 60, 70, and 80 km/h. Impact did occur at
90 km/h, though there was a speed reduction of 63 percent. At 50 km/h,
the lead vehicle decelerating scenario resulted in consecutive impacts
with some speed reduction. Due to the repeated collisions, testing was
discontinued to prevent damage to the subject vehicle and the GVT.
    NHTSA also tested The Ram 5500 under the three scenarios with
manual brake application. The lead vehicle stopped scenario resulted in
avoidance of contact for all trials at 30, 40, and 60 km/h. Collision
did occur at 50 km/h, though there was a speed reduction of
approximately 80 percent. The lead vehicle moving scenario resulted in
impact avoidance for all 40 to 90 km/h trials, but impact did occur
during the 100 km/h test. For the lead vehicle decelerating scenario,
impact occurred during the 50 km/h test with an initial headway of 40,
32, and 23 m. Collision also occurred for the 80 km/h test with a
headway of 40 m.

              Table 12--2021 Ram 5500 Test Track Scenarios
------------------------------------------------------------------------
                                        Lead vehicle    Subject vehicle
               Scenario                 speed (km/h)      speed (km/h)
------------------------------------------------------------------------
Lead Vehicle Stopped.................               0              10-60
Lead Vehicle Moving..................              20             30-100
Lead Vehicle Decelerating............              50                 50
Lead Vehicle Decelerating............              80                 80
------------------------------------------------------------------------

    In general, no single vehicle avoided collisions at all speeds in
the tested scenarios. While one vehicle may have performed better at
lower speeds and the other better at higher speeds, the combination of
results from the individual vehicles showed positive results over a
range of speeds. Overall, the performance demonstrated that the AEB
technology has improved over time, as shown in Tables 13 and
14.71 72 73 74
---------------------------------------------------------------------------

    \71\ Phase 1--Boday, C., et al., ``Class 8 Truck-Tractor and
Motorcoach Forward Collision Warning and Automatic Emergency Braking
Test Track Research--Phase I,'' Washington, DC: National Highway
Traffic Safety Administration (June 2016). Docket No.
NHTSA[hyphen]2015-0024-0004.
    \72\ Phase II- U.S. DOT/NHTSA- Class 8 Truck- Tractor and
Motorcoach Forward Collision Warning and Automatic Emergency Braking
System Test Track Research- Draft Report. Docket No. NHTSA-2015-
0024-0006.
    \73\ Phase III--Salaani, M.K., Elsasser, D., Boday, C.,
``NHTSA's 2018 Heavy Vehicle Automatic Emergency Braking Test Track
Research Results,'' SAE International. J Advances & Current
Practices in Mobility 2(3):1685-1704, 2020, doi:10.4271/2020-01-
1001.
    \74\ This information is available in the report titled ``NHTSA
Heavy Vehicle AEB Test Track Performance Data Summary Report--
2022,'' placed in the docket identified in the heading of this NPRM.

                                   Table 13--Technology Improvement Over Time
                                                   [Class 7-8]
----------------------------------------------------------------------------------------------------------------
                                            1st period--             2nd period--2nd
 Class 7-8 heavy vehicle capability         introduction           generation  (2015)         Current  (2022)
----------------------------------------------------------------------------------------------------------------
FCW and AEB activate for moving      Yes......................  Yes.....................  Yes.
 vehicles.
AEB can avoid contact at test        No.......................  Yes.....................  Yes.
 speeds up to 80 km/h in lead
 vehicle moving scenarios.
AEB can avoid contact at test        No.......................  N/A.....................  Yes.
 speeds greater than 80 km/h in
 lead vehicle moving scenarios.
FCW alerts for stopped vehicles....  Yes......................  Yes.....................  Yes.
AEB activates for stopped vehicles.  No.......................  Yes.....................  Yes.
AEB can avoid contact at test        No.......................  No......................  Yes.
 speeds up to 80 km/h in lead
 vehicle stopped scenarios.
AEB can avoid contact at test        No.......................  No......................  Yes.
 speeds greater than 80 km/h.
----------------------------------------------------------------------------------------------------------------

               Table 14--Technology Improvement Over Time
                               [Class 3-6]
------------------------------------------------------------------------
  Class 3-6 heavy vehicle AEB
          capability                 Up to 2015            2016-2022
------------------------------------------------------------------------
FCW and AEB activate for        Yes.................  Yes.
 moving vehicles.
AEB can avoid contact at test   No..................  Yes.
 speeds up to 80 km/h in lead
 vehicle moving scenarios.
AEB can avoid contact at test   No..................  Yes.
 speeds greater than 80 km/h
 in lead vehicle moving
 scenarios.
FCW alerts for stopped          Yes.................  Yes.
 vehicles.
AEB activates for stopped       No..................  Yes.
 vehicles.
AEB can avoid contact at test   No..................  No.
 speeds up to 80 km/h in lead
 vehicle stopped scenarios.
AEB can avoid contact at test   No..................  No.
 speeds greater than 80 km/h.
------------------------------------------------------------------------

C. NHTSA Field Study of a New Generation Heavy Vehicle AEB System

    NHTSA has an ongoing field study with VTTI that aims to collect
naturalistic driving data of at least 150 heavy vehicles over a one-
year timeframe. The goal is to collect data from each driver
participant for a three-month segment of the year. This research has
very similar parameters and objectives as those described above for the
``Field Study of Heavy-Vehicle Crash Avoidance Systems'' study.
However, several years have elapsed since the data were collected for
the prior study; and the trucks included in this ongoing research
project are equipped with newer generation AEB systems, including
stationary object braking and system integration into instrument
clusters.
    The data acquisition systems installed on the heavy vehicles will
allow VTTI to sample various system activations including AEB,
stationary object alerts and FCWs. The focus of the study's real-world
data collection and analysis is to ascertain an understanding of
vehicle performance, driver behavior, and driver adaptation. VTTI is
evaluating Bendix Commercial Vehicle Systems and Detroit Assurance
(Daimler) systems and the five objectives include evaluation of system
reliability, assessment of driver performance over time, assessment of
overall driving behavior, collection of data on real-world conflicts,
and generation of inputs to a safety benefits simulation model.
    Preliminary results from the driver survey responses indicate that
many drivers agree that collision mitigation technology makes drivers
safer. Approximately 50 percent of drivers surveyed at least slightly
agree that AEB is beneficial and helps drivers avoid a crash.\75\
---------------------------------------------------------------------------

    \75\ This information is available in a report titled ``HV AEB
Driver Exit Survey Summary as of August 31, 2022,'' which has been
placed in the docket for this rulemaking.
---------------------------------------------------------------------------

V. Need for This Proposed Rule and Guiding Principles

A. Estimating AEB System Effectiveness

    In developing this NPRM, NHTSA has examined the effectiveness of
AEB, proposing only those amendments that contribute to improved crash
safety, and have considered the principles for regulatory decision-
making set forth in Executive Order 12866 (as amended), Regulatory
Planning and Review.
    The effectiveness of AEB indicates the efficacy of the system in
avoiding a rear-end crash. This NPRM proposes to require heavy vehicles
to have AEB systems that enable the vehicle to completely avoid an
imminent rear-end collision under a set of test scenarios. One method
of estimating effectiveness would be to perform a statistical analysis
of real-world crash data and observe the differences in statistics
between heavy vehicles equipped with AEB and those not equipped with
AEB. However, this approach is not feasible currently due to the low
penetration rate of AEB in the on-road vehicle fleet. Consequently,
NHTSA estimated effectiveness of AEB systems using performance data
from the agency's vehicle testing. The agency assessed effectiveness
against all crash severity levels collectively, rather than for
specific crash severity levels (i.e., minor injury versus fatal).
    The performance data derived from four different test vehicles was
used to estimate AEB effectiveness,\76\ and the agency is continuing
its effort to test a larger variety of vehicles to further evaluate AEB
system performance. These vehicles were subject to the same test
scenarios (stopped lead vehicle, slower-moving lead vehicle,
decelerating lead vehicle) that are proposed in this NPRM, and
effectiveness estimates are based on each vehicle's capacity to avoid a
collision during a test scenario. For example, if a vehicle avoided
colliding with a stopped lead vehicle in four out of five test runs,
its effectiveness in that scenario would be 80 percent. The test
results for each vehicle were combined
---------------------------------------------------------------------------

    \76\ This information is available in the report titled ``NHTSA
Heavy Vehicle AEB Test Track Performance Data Summary Report--
2022,'' placed in the docket identified in the heading of this NPRM.

---------------------------------------------------------------------------

into an aggregate effectiveness value by vehicle class range and crash
scenario, as displayed in Table 15.

                                 Table 15--AEB Estimated Effectiveness (Percent)
                                   [By vehicle class range and crash scenario]
----------------------------------------------------------------------------------------------------------------
                                                                  Stopped lead    Slower-moving    Decelerating
                      Vehicle class range                            vehicle       lead vehicle    lead vehicle
----------------------------------------------------------------------------------------------------------------
7-8............................................................            38.5             49.2            49.2
3-6............................................................            43.0             47.8            47.8
----------------------------------------------------------------------------------------------------------------

    As shown in Table 15, after aggregating class 7 and class 8
together, the agency has estimated AEB would avoid 38.5 percent of
rear-end crashes for the stopped lead vehicle scenario, and 49.2
percent of slower-moving and decelerating lead vehicle crashes. For
class 3-6, AEB is estimated to be 43.0 percent effective against
stopped lead vehicle crashes and 47.8 percent against slower-moving and
decelerating lead vehicle crashes. These effectiveness values are the
values NHTSA used for assessing the benefits of this proposed rule.

B. AEB Performance Over a Range of Speeds Is Necessary and Practicable

    The performance requirements proposed in this NPRM are designed
around the goal of realizing as much of the safety potential of AEB
systems, while remaining realistic and practicable both economically
and technically. AEB performance guidelines created outside of the
agency's rulemaking process appear not to have been created with these
same goals, and thus may not represent the optimal balance of safety
and practicability. Several AEB performance tests developed in the
private sector are limited to a maximum test speed of around 40 km/h
(25 mph), and do not test the capability of AEB system at highway
speeds.77 78
---------------------------------------------------------------------------

    \77\ IIHS Autonomous Emergency Braking Test Protocol (Version
I). Available at https://www.iihs.org/media/a582abfb-7691-4805-81aa-16bbdf622992/REo1sA/Ratings/Protocols/current/test_protocol_aeb.pdf.
(last accessed August 5, 2022).
    \78\ SAE International Forward Collision Warning and Mitigation
Vehicle Test Procedure--Truck and Bus J3029_201510. (For more
details, see https://www.sae.org/standards/content/j3029_201510)
(last accessed August 5, 2022).
---------------------------------------------------------------------------

    NHTSA considered two primary factors in selecting the proposed test
speed ranges. The first factor is the practical ability of AEB
technology to consistently operate and avoid contact with a lead
vehicle at the widest reasonable range of speeds. A larger range of
speeds would likely yield more safety benefits and would more
thoroughly test the capabilities of the AEB system. Furthermore, as
observed in vehicle testing for NHTSA research, AEB performance during
testing at higher speeds does not necessarily indicate what the same
system's performance will be at lower speeds. For example, NHTSA's
testing of the 2021 Freightliner Cascadia truck showed that the AEB
system was able to avoid a collision with the lead vehicle at test
speeds of 40 to 85 km/h, but not at speeds below 40 km/h. Thus, testing
over a range of speeds is necessary to more fully assess AEB
performance.\79\
---------------------------------------------------------------------------

    \79\ This information is available in the report titled ``NHTSA
Heavy Vehicle AEB Test Track Performance Data Summary Report--
2022,'' placed in the docket identified in the heading of this NPRM.
---------------------------------------------------------------------------

    The second factor is the practical limit of safely conducting
vehicle tests of AEB systems. Test data indicates that AEB performance
is less consistent, becoming less likely to avoid a collision when test
speeds approach or exceed the proposed upper limits, indicating that
testing at higher speeds than proposed would be beyond technological
feasibility.\80\
---------------------------------------------------------------------------

    \80\ More detail on test data is discussed in the NHTSA and
FMCSA Research and Testing section.
---------------------------------------------------------------------------

    NHTSA's testing must be safe and repeatable as permitted by track
conditions and testing equipment. For example, if the AEB system does
not intervene as required, or if test parameters inadvertently fall
outside of the specified limits, it should be possible to safely abort
the test. In the event the subject vehicle does collide with the lead
vehicle, it should not injure the testing personnel nor cause excessive
property damage. Additionally, test tracks may be constrained by
available space and there may be insufficient space to accelerate a
heavy vehicle up to a higher speed and still have sufficient space to
perform a test. Many types of heavy vehicles are not capable of
accelerating as quickly as lighter vehicles and reaching higher test
speeds may require longer stretches that exceed available testing
facilities. At approximately 100 km/h, the agency found that
constraints with available test track length, in conjunction with the
time required to accelerate the vehicle to the desired test speed, made
performing these higher speed tests with heavy vehicles logistically
challenging.\81\ The agency has tentatively concluded that at this time
the maximum practicable test speed is 100 km/h.
---------------------------------------------------------------------------

    \81\ During testing of a 2021 Freightliner Cascadia at speeds
approaching 100 km/h, NHTSA experienced difficulty establishing
valid test conditions due to test facility use restrictions.
Facility use restrictions limited where emergency braking tests by
heavy vehicles and automated lead vehicle robots could co-operate,
thereby reducing the effective useable track length to less than
1100 meters.
---------------------------------------------------------------------------

    The maximum speed of 100 km/h is included in the test speed range
when manual braking is present; the manual braking will reduce impact
speed if the FCW issues a warning and the AEB system does not activate
before reaching the lead vehicle. This would limit potential damage to
the test equipment and avoid injury to testing personnel. With no
manual braking, the maximum test speed is 80 km/h so that in the event
that the AEB system does not provide any braking at all, damage to the
subject vehicle and test equipment is reduced and potential injuries
avoided.
    The stopped lead vehicle test scenario uses a no-manual-braking
test speed range of 10-80 km/h and a manual-braking test speed range of
70-100 km/h. Similarly, the slower-moving lead vehicle test scenario
uses subject vehicle speed ranges of 40-80 km/h for no manual-braking
and 70-100 km/h for manual braking, while the lead vehicle travels
ahead at a constant speed of 20 km/h. The lower end of the subject
vehicle test speed range is 40 km/h so that the subject vehicle is
traveling faster than the lead vehicle. The decelerating lead vehicle
tests are run at either 80 or 50 km/h. This latter test is performed at
two discreet speeds rather than at ranges of speeds because the main
factors that test AEB performance are the variation of headway, or the
distance between the subject vehicle

and lead vehicle, and how hard the lead vehicle brakes. Also, because
these tests contain a larger number of variables requiring more complex
test choreography, limiting the test to two discreet test speeds
reduces the number of potential test conditions and reduces potential
test burden. Together, these test speed ranges provide good coverage of
the travel speeds at which heavy vehicle rear-end crashes occur in the
real world, while reducing the potential risk and damage to test
equipment and vehicles and not exceeding the practical physical size
limits of test tracks.
    Additionally, the agency is proposing that these requirements would
not apply at speeds below 10 km/h. NHTSA believes that there are real-
world cases where heavy vehicles are being maneuvered intentionally in
proximity of other objects at low-speed, and AEB intervention could be
in conflict with the vehicle operator's intention. For example, if an
operator intends to drive towards the rear of another vehicle in a
parking lot in order to park the vehicle near the other, automatic
braking during this parking maneuver would be unwanted. The agency
tentatively concluded that excluding speeds below 10 km/h from the AEB
requirement would allow these types of low-speed maneuvers. This
proposal does not require AEB systems to be disabled below 10 km/h.
However, publicly available literature from at least one manufacturer
shows that some or all of the AEB system functions are not available
below 15 mph (24 km/h), indicating that current manufacturers may have
similar considerations about low-speed AEB functionality.\82\ A lower
bound for FCW and AEB activation speed of 10 km/h is also consistent
with the lower bound testing proposed for light vehicle AEB and the
Euro NCAP rating program.\83\
---------------------------------------------------------------------------

    \82\ Bendix Wingman Fusion Brochure, or SD-61-4963 Service Data
manual for Bendix Wingman Fusion Driver Assistance System. Available
at https://www.bendix.com/media/documents/technical_documentsproduct_literature/bulletins/SD-61-4963_US_005.pdf (last accessed August 23, 2022).
    \83\ Euro NCAP Test Protocol--AEB Car-to-Car systems v3.0.3
(April 2021). See https://cdn.euroncap.com/media/62794/euro-ncap-aeb-c2c-test-protocol-v303.pdf.
---------------------------------------------------------------------------

    During each test run in any of the test scenarios, the vehicle test
speed will be held constant until the test procedure specifies a
change. NHTSA is proposing that vehicle speed would be maintained
within a tolerance range of 1.6 km/h of the specified test value. In
NHTSA's experience, both the subject vehicle and lead vehicle speeds
can be reliably controlled within the 1.6 km/h tolerance range, and
speed variation within that range yields consistent test results. A
tighter speed tolerance is unnecessary for repeatability and burdensome
as it may result in a higher test-rejection rate, without any greater
assurance of accuracy of the test track performance.
    NHTSA's vehicle testing suggested that the selected speed ranges
for the various scenarios are within the capabilities of at least some
recent model year AEB-equipped production vehicles.\84\ While these
current AEB systems perform a bit differently depending on the vehicle,
given that this notice proposes a lead time for manufacturers to come
into compliance with the proposed performance requirement, the agency
expects that future model year performance in accordance with a final
rule schedule will be achievable.
---------------------------------------------------------------------------

    \84\ This information is available in the report titled ``NHTSA
Heavy Vehicle AEB Test Track Performance Data Summary Report--
2022,'' placed in the docket identified in the heading of this NPRM.
---------------------------------------------------------------------------

C. Market Penetration Varies Significantly Among Classes of Heavy
Vehicles

    Though the presence of AEB in heavy vehicles has increased over the
years, many new heavy vehicles sold in the U.S. are not equipped with
AEB. Market data obtained by NHTSA indicates that although AEB is
likely equipped on the majority of class 8 vehicles and is available on
nearly all class 3 and class 4 vehicles, few of class 5 and 6 vehicles
come equipped with any type of AEB system. In addition, though the
capabilities of these AEB systems have also improved over time, there
has been no set of standardized performance metrics in the U.S. that
manufacturers could use as a benchmark to meet. This NPRM proposes
standard performance metrics that would meet a motor vehicle safety
need.
    Among the variety of heavy vehicle types, class 7 and 8 truck
tractors have been the earliest to voluntarily adopt AEB systems. These
vehicles are (with some exceptions) already subject to the electronic
stability control requirement in FMVSS No. 136 and contain fewer
variations in vehicle type, configuration, and operational pattern. It
was estimated that as of 2013 only 8 to 10 percent of class 8 trucks in
the U.S. were equipped with this technology.\85\ In 2017 a FMCSA report
extrapolated available information to estimate that 12.8 percent of the
entire on-road fleet of class 8 trucks in the United States were
equipped with an AEB system,\86\ while the industry estimated that up
to 15 percent of class 8 trucks were equipped with AEB.\87\ More
recently, a survey of public information on AEB availability for heavy
vehicles reveals that this technology is becoming more prevalent on new
trucks. In 2016, Peterbilt announced the option of AEB in its class 8
model 579 truck tractor, and then made the technology standard in
2019.88 89 As of 2017, Volvo Trucks made AEB standard
equipment on all of its class 8 truck tractor models, as a part of its
Volvo Active Driver Assist safety package.\90\ While several fleets or
manufacturers have made AEB standard, it remains an option for some
class 8 vehicles, such as the Peterbilt single-unit truck models 337
and 348.\91\ Data from a recent study indicates that the large majority
of class 8 vehicles sold from 2018 until mid-2022 had AEB as a standard
feature, and that the top ten selling class 8 vehicles all include
standard AEB.\92\
---------------------------------------------------------------------------

    \85\ National Transportation Safety Board. 2015. ``Special
Investigation Report: The Use of Forward Collision Avoidance Systems
to Prevent and Mitigate Rear-End Crashes.'' Report No. NTSB/SIR-15/
01 PB2015-104098. Washington, DC.
    \86\ Grove, K., et al., ``Research and Testing to Accelerate
Voluntary Adoption of Automatic Emergency Braking (AEB) on
Commercial Vehicles,'' VTTI (May 2020). Available at https://rosap.ntl.bts.gov/view/dot/49335 (last accessed June 9, 2022).
    \87\ Cannon, J., ``Automatic emergency braking is the next
generation of driver assist technologies,'' Commercial Carrier
Journal, December 14, 2017. https://www.ccjdigital.com/business/article/14936178/future-of-automatic-emergency-braking-driver-assist-tech.
    \88\ https://www.peterbilt.com/about/news-events/news-releases/peterbilt-introduces-bendix-wingman-fusion-advanced-safety-system
(last accessed August 23, 2022).
    \89\ https://www.peterbilt.com/about/news-events/peterbilt-trucks-introduce-bendix-wingman-fusion-standard (last accessed
August 23, 2022).
    \90\ https://www.volvotrucks.us/news-and-stories/press-releases/
2017/july/volvo-active-driver-assist-now-standard/
#:~:text=Volvo%20Active%20Driver%20Assist%20is%20now%20standard%20equ
ipment,is%20fully%20integrated%20with%20Volvo%E2%80%99s%20Driver%20In
formation%20Display (last accessed August 23, 2022).
    \91\ https://www.peterbilt.com/about/news-events/peterbilt-announces-bendix-wingman-fusion-medium-duty (last accessed August
23, 2022).
    \92\ This information is available in the S&P Global's
presentation titled ``MHCV Safety Technology Study,'' which has been
placed in the docket identified in the heading of this NPRM.
---------------------------------------------------------------------------

    AEB systems are also available on nearly all class 3 and 4 trucks
that are relatively similar in size to light trucks, are manufactured
by companies that also manufacture light vehicles, and likely have
similar component and component suppliers as light vehicles. Although
these vehicles are not required to have ESC systems, many of them are
also available with ESC, likely because these vehicles are similar in
size and use to light trucks. However, while NHTSA has information on
ESC and AEB system availability, NHTSA has no

information on what percentage of class 3 and 4 vehicle purchases are
equipped with ESC and AEB. For classes 5 and 6, there is substantially
lower ESC and AEB system availability. However, NHTSA believes that
this slower pace of voluntary adoption does not imply that these
vehicles are not capable of being deployed with an AEB system. The
system components are largely the same and have little to do with a
vehicle's size. There are also vehicles within these classes that are
available with ESC, and the availability of ESC has increased since
NHTSA issued FMVSS No. 136. This market information indicates that AEB
is practicable for all vehicles included in this proposal.

D. This NPRM Would Compel Improvements in AEB

    This rulemaking is also needed to drive improvements in AEB
systems. The performance requirements proposed in this NPRM are
designed around the goal of realizing as much of the safety potential
of AEB systems as possible, while remaining realistic and practicable.
Some contemporary AEB systems are currently designed to detect and
mitigate collision with a vehicle ahead when travelling at a wide range
of speeds, including interstate speeds.\93\ While the systems are also
functional at lower speeds, the higher speed capabilities indicate that
AEB will be capable of reducing the frequency of interstate rear-end
crashes rather than just slower speed events.
---------------------------------------------------------------------------

    \93\ See https://www.bendix.com/media/documents/technical_documentsproduct_literature/bulletins/SD-61-4963_US_005.pdf (last accessed March 1, 2023).
---------------------------------------------------------------------------

    NHTSA has tentatively concluded that the improvements to AEB
systems by manufacturers in the absence of regulation have
insufficiently addressed the safety problem associated with rear-end
crashes. No individual vehicle's AEB system tested by NHTSA is
currently capable of avoiding a collision over the range of test speeds
that aligns with the majority of the safety problem. However, the range
of speeds included in this proposal is practicable as at least some
vehicles were able to achieve the desired results at each tested speed.
While manufacturers may continue to improve AEB systems, only a
regulation would ensure that all heavy vehicles are equipped with an
AEB system that can avoid a collision at a range of speeds that targets
the majority of the safety problem. Establishing performance criteria
that meet the safety need of preventing fatalities and serious injuries
will also ensure that the systems will be designed to address the
serious safety problem associated with these crashes. This NPRM
proposes that all heavy vehicles be subject to the same performance
requirements such that the entire heavy vehicle fleet benefits from
improvements in AEB technology.

E. BIL Section 23010(b)(2)(B)

    NHTSA is issuing this NPRM in accordance with a statutory mandate
in BIL. Section 23010 of BIL requires the Secretary to prescribe a
Federal motor vehicle safety standard to require all commercial
vehicles subject to FMVSS No. 136 to be equipped with an AEB system.
The FMVSS is required to establish performance standards for AEB
systems. BIL directs the Secretary to prescribe the standard not later
than two years after the date of enactment of the Act.
    Section 23010(b)(2)(B) of BIL states that prior to prescribing the
FMVSS for heavy vehicle AEB, the Secretary shall consult with
representatives of commercial motor vehicle drivers regarding the
experiences of drivers with AEB. Prior to this NPRM, NHTSA and FMCSA
have engaged drivers and the industry more generally in various ways.
NHTSA has published research previously that involved surveying the
driving experiences of 18 drivers driving heavy trucks equipped with a
prototype FCW system over a 10-month period in May 2011.\94\ NHTSA has
also been sponsoring studies seeking input of commercial motor vehicle
drivers. The current ongoing field study with VTTI aims to collect and
analyze performance and operational data on newer generation AEB crash
avoidance technologies on new, class 8 tractors by heavy vehicle
original equipment manufacturers and their suppliers. One year of
naturalistic driving data will be collected by monitoring the
production systems used in real-world conditions as deployed by
multiple fleets across the United States. In addition to the
performance and operational data retrieved from on-board data
acquisition systems for evaluation, the study will also involve
conducting subjective surveys with drivers and fleet managers regarding
performance, satisfaction, and overall acceptance of the crash
avoidance technologies.
---------------------------------------------------------------------------

    \94\ ``Integrated Vehicle-Based Safety Systems Heavy-Truck Field
Operational Test Independent Evaluation,'' DOT HS 811 464.
---------------------------------------------------------------------------

    FMSCA is also engaged consultation with representatives of drivers
through the Tech-Celerate Now program.\95\ This program intends to
accelerate the adoption of advanced crash avoidance technologies by the
trucking industry. The first phase initiatives include national
outreach and education. The outreach element allowed for the successful
creation of training materials for fleets, drivers, and maintenance
personnel related to AEB technology. Additionally, the program features
other avenues to reach drivers including educational videos on braking,
presentations, booth exhibitions, and webinars. As of January 2023,
FMCSA has compiled the findings from drivers and/or representatives of
drivers in a final report that is currently undergoing internal review.
However, planning for the second phase has been initiated and includes
expanding the national outreach and education campaign.
---------------------------------------------------------------------------

    \95\ Tech-Celerate Now. FMCSA. Available at https://www.fmcsa.dot.gov/Tech-CelerateNow (last accessed August 8, 2022).
---------------------------------------------------------------------------

    Building upon this and other research, NHTSA and FMCSA seek comment
from representatives of commercial motor vehicle drivers, and from
drivers themselves, about their experiences with AEB systems, including
whether the AEB system prevented a crash, whether the FCW warnings were
helpful, and whether any malfunctions or unwarranted activations
occurred. Although members of the public should comment on all aspects
of the NPRM they find relevant, NHTSA also request comments on the
following specific issues:
     This proposal includes considerations that automatic
braking is needed for safety and crash prevention. NHTSA seeks comment
from driver experiences with AEB-equipped heavy vehicles on whether AEB
improves heavy vehicle rear-end crash safety.
     This proposal includes warning requirements to the driver
as part of the AEB system that braking is needed in a rear-end crash-
imminent situation. NHTSA seeks comments from driver experiences on
whether AEB is helpful in getting a driver's attention back to the task
of driving.
     This proposal includes requirements that automatic braking
will occur in the event of an imminent collision on a straight testing
path. NHTSA seeks comment on driver experiences with the performance of
AEB when it is applied on curved roads.
     This proposal includes requirements that automatic braking
will be tested under certain weather and roadway pavement conditions.
NHTSA seeks comment on driver experiences when AEB is applied at the
last moment in all weather conditions.
     This proposal includes considerations that automatic
braking is needed because of multiple elements, including driver
misjudgments and distractions. NHTSA seeks comment on driver
experiences on whether the

application of AEB causes drivers to pay less attention to the road; or
whether the application of AEB distracts or annoys drivers.

F. Vehicles Excluded From Braking Requirements

    The result of this proposal would require AEB and ESC on nearly all
heavy vehicles. The only vehicles that would be excluded from AEB and
ESC requirements would be vehicles that are already excluded from
NHTSA's braking requirements for vehicles equipped with pneumatic
brakes in FMVSS No. 121. This braking standard includes requirements
for minimum stopping distance. For those vehicles, there is no
assurance that their foundational brake systems would have the
capability to meet the proposed AEB performance requirements, even if
equipped with sensors capable of detecting another vehicle. These
vehicles are also presently excluded from FMVSS No. 136 and would
continue to be excluded under this proposal. The vehicles excluded from
the proposed AEB and ESC requirements are:
     Any vehicle equipped with an air brake system and equipped
with an axle that has a gross axle weight rating of 13,154 kilograms
(29,000 pounds) or more;
     Any truck or bus that is equipped with an air brake system
and that has a speed attainable in 3.2 km (2 miles) of not more than 53
km/h (33 mph);
     Any truck equipped with an air brake system that has a
speed attainable in 3.2 km (2 miles) of not more than 72 km/h (45 mph),
an unloaded vehicle weight that is not less than 95 percent of its
gross vehicle weight rating, and no capacity to carry occupants other
than the driver and operating crew.
    FMCSA believes that an exemption from its ESC and AEB regulations
is appropriate for vehicles involved in driveaway-towaway operations,
for example, vehicles that are being transported to dealer locations or
that are manufactured exclusively for use outside of the United States.
Although these vehicles are operated on public roads in the United
States when they are being transported from the point of manufacture to
a domestic or foreign destination, these vehicles have not yet entered
commercial service. The economic burden associated with requiring these
vehicles to be equipped with AEB or ESC for the one-way trip out of the
United States would certainly exceed the potential benefits.
    The driveaway-towaway exemption would also be applicable to
vehicles being delivered to the Armed Forces of the United States.
Vehicles operated by the military are exempt from the FMCSRs under
Sec.  390.3(f)(2).\96\
---------------------------------------------------------------------------

    \96\ FMCSA notes that the driveaway-towaway exemption provided
in Sec.  393.56 and Sec.  393.57 is consistent with exceptions
provided by NHTSA. Section 571.7(c) provides an exception for
vehicles and items of equipment manufactured for, and sold directly
to, the Armed Forces of the United States in conformity with
contractual specifications. Section 571.7(d), through a cross-
reference to the United States Code, indicates the FMVSSs do not
apply to motor vehicles or motor vehicle equipment intended only for
export, labeled for export on the vehicle or equipment and on the
outside of any container of the vehicle or equipment, and exported
(49 U.S.C. 30112(b)(2)).
---------------------------------------------------------------------------

    FMCSA seeks comment on other types of operations for which an
exemption from the AEB or ESC requirements may be appropriate. For
example, what types of exemptions may be needed for CMVs with auxiliary
equipment installed that would interfere with the operation of the AEB
system?

VI. Heavy Vehicles Not Currently Subject to ESC Requirements

A. AEB and ESC Are Less Available on These Vehicles

    NHTSA is proposing to include nearly all vehicles with a GVWR
greater than 4,536 kg (10,000 lbs.). This includes vehicles that are
currently exempted from FMVSS No. 136 such as trucks other than truck
tractors, school buses, perimeter-seating buses, transit buses,
passenger cars, and multipurpose passenger vehicles because about half
of the fatalities and serious injuries brought about by heavy vehicles
are caused by class 3 through 6 vehicles.
    The FMVSSs do not currently require ESC on class 3 through 6
vehicles or on class 7 and 8 single unit trucks, school buses, and
certain bus types such as transit buses. ESC has not been commercially
available for as long on class 3 through 6 vehicles as it has been for
class 7 and 8 vehicles. However, examples can be found of manufacturers
who offer ESC as an option on their class 3 through 6 vehicles.
Kenworth has made AEB optional for the T880 vocational truck as well as
for their T270 and T370 conventional class 6 trucks. Ford made ESC
standard on its F-650 model in the 2018 model year and has made AEB
optional on model year 2022 F-650 and F-750 class 6 trucks. A number of
school bus manufacturers have made ESC standard on certain models,
including ones that fall into classes 3 through 6. For example, Thomas
Built offers ESC as standard equipment on its type C school buses,
which can be configured to be in class 6. In some cases, ESC technology
originating in hydraulic-brake passenger cars has moved up into the
lower classes of heavy vehicles. For example, the 2019 Mercedes
Sprinter, a cargo van which can be configured as a class 3 heavy
vehicle, has ESC as standard equipment. Other class 3 and 4 vehicles
that resemble light vehicles, such as pickup trucks, are available with
ESC.
    The availability of ESC as an option across multiple brands and
models within class 3 through 6 leads NHTSA tentatively to conclude
that providing ESC is technically and economically feasible. NHTSA
believes it is reasonable and practicable to require that ESC to be
installed on class 3 through 6 vehicles.

B. This NPRM Proposes To Require ESC

    NHTSA has tentatively determined that ESC is necessary for safety
to include as a foundation for an AEB requirement. Historically, the
two technologies have been thought of as supplement or complementary
rather joined technologies. That is, while ESC and AEB share hardware
fundamental to both technologies, such as brake actuators, ESC is
generally not described or advertised as a component of AEB.
    That said, despite this theoretical separation, in a survey NHTSA
has conducted on the availability of ESC and AEB systems, NHTSA was
unable to identify any heavy vehicle that could currently be purchased
with an AEB system, other than an FCW-only system (i.e., not capable of
automatic brake application), that did not also have an ESC system.\97\
In a 2017 white paper Bendix indicated that collision mitigation
technology is built on a foundation of full stability. Bendix stated
that as we look to more automated, autonomous functionality in the
future, all of this is likely to be built on an ESC foundation as
well.\98\ In a 2018 news release, Bendix stated that ESC provides the
necessary platform for more advanced driver assistance systems (ADAS),
including collision mitigation technologies.\99\ Manufacturers such as
Ford have ESC as a must-have system for installing driver assist
technology on the stripped commercial chassis, including AEB.\100\

Also, Ford has ESC and AEB as standard equipment on other chassis
models such as the E-series models, F-650, and F-750 truck series. Ram
Trucks also offers ESC and AEB for Chassis Cab models like RAM 3500
trucks.101 102 Based upon these factors and its own
understanding of the capabilities of AEB and ESC systems, NHTSA has
tentatively concluded that there may be safety risks associated with
the installation of an AEB system without an ESC system. For example, a
driver who responds to an imminent collision by steering to avoid a
collision while an AEB system is simultaneously applying braking may
induce a lateral instability event that is not addressed by ABS, but
that may be prevented with an ESC system. Thus, this NPRM proposes to
require both AEB and ESC for the class 3 through 8 vehicles not
currently subject to FMVSS No. 136.
---------------------------------------------------------------------------

    \97\ This information is available in NHTSA's VRTC class 3 to 6
market scan for ESC-FCW-AEB spreadsheet, which has been placed in
the docket identified in the heading of this NPRM.
    \98\ Full Stability and the Road Map to The Future- Are we still
on the Right Road? https://www.bendix.com/media/documents/products_1/absstability/BW8055_US_000.pdf (last accessed March 3,
2023).
    \99\ October 16, 2018. Bendix News Release, ``WORKING TOGETHER,
BENDIX AND NORTH AMERICA'S SCHOOL BUS MANUFACTURERS ENHANCE STUDENT
TRANSPORTATION SAFETY''.
    \100\ 2022 Ford Commercial Vehicles, F-59 Commercial Stripped
Chassis. ESC is required for the stripped chassis Driver Assist
Technology Package.
    \101\ ESC equipped standard on E-Series models, and F-650/F-750
trucks, available at this link https://www.ford.com/cmslibs/content/dam/vdm_ford/live/en_us/ford/nameplate/f-650-750/2022/brochures/BRO_SUF_130E80EB-C9B2-936F-6F54-72CA6F5472CA.pdf (last viewed March
3, 2023).
    \102\ https://www.ramtrucks.com/gab.html, ESC equipped standard
on the RAM Chassis cab models and RAM 3500 trucks, available at this
link (last accessed March 3, 2023).
---------------------------------------------------------------------------

    NHTSA requests comment on this tentative conclusion that ESC is
necessary to ensure safe AEB operation or whether ESC systems are
necessary prerequisites for AEB systems for any other reason. NHTSA
further requests comments on specific safety scenarios where ESC
systems would be necessary for safe operation of an AEB system.
    Currently, pursuant to FMVSS No. 136, only class 7 and 8 truck
tractors and certain large buses are required to have ESC systems.
FMVSS No. 136 includes both vehicle equipment requirements and
performance requirements. This proposal would require nearly all heavy
vehicles to have an ESC system that meets the equipment requirements,
general system operational capability requirements, and malfunction
detection requirements of FMVSS No. 136. The general ESC system
operational capability requirements are the nine capabilities that are
specified in the definition of ESC system in S4 of FMVSS No. 136, which
include a means to augment directional stability and enhance rollover
stability by having control over the brake systems individually at each
wheel position and the means to control engine torque. However, NHTSA
is not proposing test track performance requirements at this time
because NHTSA is conscious of the potential testing burden on small
businesses and the multi-stage vehicle manufacturers involved in class
3 through 6 vehicle production.
    NHTSA's proposed approach would provide vehicle manufacturers the
ability to ascertain the ESC system design most appropriate for their
vehicles. The approach recognizes that ESC system design is dependent
on vehicle dynamics characteristics, such as the total vehicle weight
and location of that weight (center of gravity), which would differ
depending on the final vehicle configuration. Vehicles not subject to
FMVSS No. 136 include a large variety of vehicle configurations, which
can result in numerous variations of ESC system design. The approach
provides maximum flexibility to vehicle manufacturers to evaluate the
characteristics of their vehicles and design an ESC system.
    In Europe, ESC was predicted to prevent about 3,000 fatalities (14
percent), and about 50,000 injuries (6 percent) per year.\103\ In
Europe, ESC has been mandatory for new types of vehicles since 2011,
and for all new vehicles is mandatory since 2014.\104\ More information
about international regulations can be found in Appendix B.
---------------------------------------------------------------------------

    \103\ Iombiller, S.F., Prado, W.B., Silva M.A. (September 15,
2019). Comparative Analysis between American and European
Requirements for Electronic Stability Control (ESC) Focusing on
Commercial Vehicles. SAE International.
    \104\ July 31, 2009, Official Journal of the European Union,
Regulation (EC) No. 661/2009, Articles 12 & 13, and Annex V.
---------------------------------------------------------------------------

C. BIL Section 23010(d)

    Section 23010 of BIL requires the Secretary to prescribe a Federal
motor vehicle safety standard to require any commercial vehicle subject
to FMVSS No. 136, that is manufactured after the effective date of an
AEB standard, to be equipped with an AEB system that meets established
performance standards. In addition, Section 23010(d) of BIL requires
NHTSA to study equipping AEB on a variety of commercial motor vehicles
not subject to FMVSS No. 136, including an assessment of the
feasibility, benefits, and costs associated with installing AEB systems
on a variety of newly manufactured commercial motor vehicles with a
GVWR greater than 10,000 pounds. Section (d)(3) states that the
Secretary shall issue a notice in the Federal Register containing the
findings of the study and provide an opportunity for public comment.
After completion of this study, the Secretary must determine whether a
motor vehicle safety standard would meet the requirements and
considerations described in paragraphs (a) and (b) of section 30111 of
the Safety Act, and if the Secretary finds that an FMVSS would meet
such requirements, initiate a rulemaking to prescribe such an FMVSS.
    This NPRM and the accompanying PRIA fulfils the mandate of section
23010(d)(1) concerning a study on equipping commercial vehicles not
subject to FMVSS No. 136 with AEB. Pursuant to the mandate section
23010(d)(3) of BIL, NHTSA seeks comment on the tentative conclusions in
this NPRM and the PRIA regarding the feasibility, benefits, and costs
associated with installing AEB on all heavy vehicles, particularly
class 3-6 vehicles and class 7 and 8 single-unit trucks. Further, as
part of this rulemaking, the agency has considered whether proceeding
with an AEB mandate for these vehicles meet the necessary provisions of
the Safety Act, and will continue to do so in any final rule. Finally,
although the agency notes that paragraph (d) concerns when the agency
would be mandated to initiate a rulemaking to require AEB for these
vehicles, that section does not affect the agency's discretionary
ability to issue an FMVSS when it believes doing so is compelled by the
Safety Act.

D. Multi-Stage Vehicle Manufacturers and Alterers

    Heavy vehicles include many specialty or vocational vehicles such
as work trucks, delivery box trucks, motorhomes, and school buses, and
the complexities within this large variety of special purpose vehicles
make installation of ESC and AEB more challenging. These specialized
vehicles may be produced in lower volumes with customized features to
suit the specific needs of individual customers and in multiple stages
by several manufacturers. Concepts and terminology relating to the
certification of vehicles built in two or more stages (multi-stage
vehicles) and alters are described below.
    In the typical situation, a vehicle built in two or more stages is
one in which an incomplete vehicle, such as a chassis-cab or cut-away
chassis built by one manufacturer, is completed by another manufacturer
who adds work-performing or cargo-carrying components to the vehicle.
For example, the incomplete vehicle may have a cab, but nothing built
on the frame behind the cab. As completed, it may be a dry freight van
(box truck), dump truck, tow truck, or plumber's truck. Like all
vehicles that are manufactured for sale in the United States, a multi-
stage vehicle must be certified as complying with all applicable
Federal motor

vehicle safety standards (FMVSS) before the vehicle is introduced into
interstate commerce.
    Manufacturers involved in the production of multi-stage vehicles
can include, in addition to the incomplete vehicle manufacturer, one or
more intermediate manufacturers, who perform manufacturing operations
on the incomplete vehicle after it has left the incomplete vehicle
manufacturer's hands, and a final-stage manufacturer who completes the
vehicle so that it is capable of performing its intended function.
    In some circumstances, a manufacturer at an earlier stage in the
chain of production for a multi-stage vehicle can certify that the
vehicle will comply with one or more FMVSS when completed, provided
specified conditions are met. This allows what is commonly referred to
as ``pass-through certification.'' As long as a subsequent manufacturer
meets the conditions of the prior certification, that subsequent
manufacturer may rely on this certification and pass it through when
certifying the completed vehicle.
    NHTSA requests comments on how this proposal may impact multi-stage
manufacturers and alterers. The agency seeks comment on the specific
challenges that would be faced by the manufacturers in certifying to
the proposed AEB or ESC or in altering a vehicle certified to the
proposed requirements, and on whether and how NHTSA could revise this
proposal to minimize any disproportionate impact.
    We believe that small-volume vehicle manufacturers are not likely
to certify compliance with the proposed AEB and ESC requirements
through their own testing but will use a combination of component
testing by brake system suppliers and engineering judgment. Already
much of the braking development work, including for ABS and ESC, for
these small-volume vehicle manufacturers is done by brake suppliers.
That is, small-volume manufacturers already must certify their vehicles
to FMVSS Nos. 136, 105, and 121. NHTSA believes that small-volume
manufacturers would certify to the proposed ESC and AEB requirements
using the means they use now to certify to those braking requirements,
which involves collaborating with their brake system suppliers, first
and second stage manufacturers, etc. This NPRM would also provide one
year after the last applicable date for manufacturer certification of
compliance, in accordance with 49 CFR 571.8(b).
    NHTSA's regulations governing vehicles manufactured in two or more
stages at 49 CFR part 568 require incomplete vehicle manufacturers to
provide with each incomplete vehicle an incomplete vehicle document
(IVD). This document details, with varying degrees of specificity, the
types of future manufacturing contemplated by the incomplete vehicle
manufacturer and must provide, for each applicable safety standard, one
of the following three statements that a subsequent manufacturer can
rely on when certifying compliance of the vehicle, as finally
manufactured, to some or all of all applicable FMVSS.
    First, the IVD may state, with respect to a particular safety
standard, that the vehicle, when completed, will conform to the
standard if no alterations are made in identified components of the
incomplete vehicle. This representation, which is referred to as a
``Type 1 statement,'' is most often made with respect to chassis-cabs,
since a significant portion of the occupant compartment in incomplete
vehicles of that type is already complete.
    Second, the IVD may provide a statement of specific conditions of
final manufacture under which the completed vehicle will conform to a
particular standard or set of standards. This statement, which is
referred to as a ``Type 2 statement,'' is applicable in those instances
in which the incomplete vehicle manufacturer has provided all or a
portion of the equipment needed to comply with the standard, but
subsequent manufacturing might be expected to change the vehicle such
that it may not comply with the standard once finally manufactured. For
example, the incomplete vehicle could be equipped with a brake system
that would, in many instances, enable the vehicle to comply with the
applicable brake standard once the vehicle was complete, but that would
not enable it to comply if the completed vehicle's weight or center of
gravity height were altered from those specified in the IVD.
    Third, the IVD may identify those standards for which no
representation of conformity is made because conformity with the
standard is not substantially affected by the design of the incomplete
vehicle. This is referred to as a ``Type 3 statement.'' A statement of
this kind could be made, for example, by a manufacturer of a stripped
chassis who may be unable to make any representations about conformity
to any crashworthiness standards if the incomplete vehicle does not
contain an occupant compartment. When it issued the original set of
regulations regarding certification of vehicles built in two or more
stages, the agency indicated that it believed final-stage manufacturers
would be able to rely on the representations made in the IVDs when
certifying the completed vehicle's compliance with all applicable
FMVSS.
    Although the final-stage manufacturer normally certifies the
completed vehicle's compliance with all applicable FMVSS, this
responsibility can be assumed by any other manufacturer in the
production chain. To take on this responsibility, the other
manufacturer must ensure that it is identified as the vehicle
manufacturer on the certification label that is permanently affixed to
the vehicle. The identified manufacturer also has legal responsibility
to provide NHTSA and vehicle owners with notification of any defect
related to motor vehicle safety or noncompliance with an FMVSS that is
found to exist in the vehicle, and to remedy any such defect or
noncompliance without charge to the vehicle's owner.
    An altered vehicle is one that is completed and certified in
accordance with the agency's regulations and then altered, other than
by the addition, substitution, or removal of readily attachable
components, such as mirrors or tire and rim assemblies, or by minor
finishing operations such as painting, before the first retail sale of
the vehicle, in such a manner as may affect the vehicle's compliance
with one or more FMVSS or the validity of the vehicle's stated weight
ratings or vehicle type classification. The person who performs such
operations on a completed vehicle is referred to as a vehicle
``alterer.'' An alterer must certify that the vehicle remains in
compliance with all applicable FMVSS affected by the alteration.
    NHTSA seeks comment on the impacts of this NPRM on multi-stage
manufacturers and alterers and requests comments on the following
questions.
     Are certain multi-stage or altered vehicles manufactured
or altered in a manner that makes it impracticable to comply with this
proposed rule? If so, please explain which vehicles and why it is
impracticable.
     If an incomplete vehicle were equipped with sensors for
AEB that could become obstructed by equipment added in later
manufacturing steps, how should NHTSA apply an AEB requirement to that
vehicle?
     Are there any changes needed to 49 CFR part 567 or part
568 to facilitate certification to the proposed requirements? If so,
what would those changes be? Would a final-stage manufacturer be able
to certify a vehicle based on the information provided by an
intermediate or incomplete vehicle manufacturer, or is additional
information needed in IVDs? If

additional information is needed, please describe the needed
information.
     Are there any requirements in this proposal that ought not
to apply to multi-stage vehicles or altered vehicles? Are there
proposed requirements that should be lowered in stringency to better
enable pass-through certification? Please provide details on those
requirements and provide associated rationale.
     Would intermediate manufacturers, final-stage
manufacturers, and alterers have sufficient information to identify
when an impermissible change has been made? Please explain why or why
not.
     Assuming there would be cases where it may not be
practical to comply with the proposed requirements, are the existing
exemption processes detailed in 49 CFR 555, ``Temporary exemption from
motor vehicle safety and bumper standards,'' sufficient to accommodate
unique vehicles, or should NHTSA explicitly consider applicability
exclusions for certain multi-stage vehicles? If applicability
exclusions are needed, please explain what they include and why the
exclusion is needed. For example, should there be exclusions for
vehicles with permanently installed work-performing equipment installed
on the front of or extending past the front of the vehicle (e.g., auger
trucks, bucket trucks, cable reel trucks, certain car carriers, etc.)
or vehicles with a GVWR equal to or greater than 120,000 pounds (i.e.,
heavy haulers)?

VII. Proposed Performance Requirements

    This NPRM proposes that all heavy vehicles, class 3-8, are subject
to the same performance requirements such that the entire heavy vehicle
fleet benefits from improvements in AEB technology. The proposed set of
requirements would compel AEB technology to operate at its highest
safety potential, while at the same time being objective and
practicable. In order to establish these requirements, the agency
considered the key aspects of the technology and how they would best be
applied to address the safety problem. For example, requiring AEB
systems to perform only at lower speeds may address a significant
portion of the rear-end crash problem, but it would not address the
rear-end crash fatalities that mostly occur at higher speeds. Thus,
NHTSA is proposing that AEB systems must be capable of activating
across a wide spectrum of speeds. Similarly, the agency is aware that
some current AEB systems may occasionally cause unwarranted braking
events, or ``false activations,'' which could lead to unwanted
consequences; we are thus proposing two test scenarios which vehicles
must pass without false activation of the AEB system.
    While creating the proposed performance requirements, NHTSA
considered the capabilities and limitations of current AEB
technologies. Using information from vehicle testing, this proposal
includes test scenarios and parameters that the agency found to be
within the potential of current production vehicles. This means that at
least one vehicle model demonstrated the ability to avoid impacting a
lead vehicle, represented by a vehicle test device, or that it so
nearly avoided the impact that we expect that the additional
development time allowed by this proposal would enable the required
improvement in performance.
    While certain requirements can be assessed without vehicle tests, a
large portion of this proposal has performance requirements that are
evaluated through vehicle tests. These tests, discussed in this
section, simulate real-world scenarios and are run according to
specified conditions and test parameters. NHTSA believes that these
test scenarios will realistically evaluate how AEB systems perform
while the vehicle is travelling at normal driving speeds.
    Several of the vehicle test scenarios test involve multiple moving
vehicles. In these test scenarios, the heavy vehicle being evaluated
with AEB is referred to as the ``subject vehicle.'' Other vehicles
involved in the test are represented by a vehicle test device. When a
vehicle test device is used ahead of the subject vehicle in the same
lane, in the path of the moving subject vehicle, it is referred to as a
``lead vehicle.'' When moving, a lead vehicle moves in the same
direction as the subject vehicle. The speeds and relative motions of
the subject vehicle and lead vehicle are choreographed in a variety of
ways to represent the most common scenarios which lead to heavy vehicle
rear-end crashes, and the test procedures measure whether the AEB
system is able to avoid impacting the lead vehicle.
    The other vehicle tests are two false activation scenarios. A false
activation refers to an unwarranted brake activation by the AEB system
when there is no object present in the path of the vehicle with which
the vehicle would collide. These two test scenarios use objects,
including VTDs and a steel trench plate, arranged in realistic ways in
or near the travel path but without obstructing the path. In these
scenarios, the subject vehicle and AEB system are required to move past
these objects without making a substantial automatic application of the
service brakes.
    This proposal also includes system requirements that are not
accompanied by vehicle tests. Vehicles with AEB systems must mitigate
collision at speeds beyond the those covered by the track testing,
ensuring robustness of the system's range of performance. The AEB
system must include a forward collision warning (FCW) system that
alerts the vehicle operator of an impending collision with a lead
vehicle. Also, the system must indicate an AEB malfunction to the
vehicle operator.

A. Proposed Requirements When Approaching a Lead Vehicle

1. Automatic Emergency Brake Application Requirements
    The agency is proposing that vehicles be required to have a forward
collision warning system and an automatic emergency braking system that
are able to function continuously to apply the service brakes
automatically when a collision with a vehicle or object is imminent.
The system must operate when the vehicle is traveling at any forward
speed greater than 10 km/h (6.2 mph). This is a general system
equipment requirement with no associated performance test. No specific
speed reduction or crash avoidance would be required. However, this
requirement is included to ensure that AEB systems are able to function
at all times, including at speeds above those NHTSA is proposing as
part of the performance test requirements.
    This requirement complements the performance requirements in
several ways. While the track testing described below provides a
representation of real-world crash events, no amount of track testing
can fully duplicate the real world. This requirement ensures that the
AEB's perception system identifies and automatically detects a vehicle,
warns the driver, and applies braking when a collision is imminent.
This requirement also ensures that AEB systems continue to function in
environments that are not as controlled as the test track environment.
For example, unlike during track testing, other vehicles, road users,
and buildings may be present within the view of the sensors. Finally,
track test equipment limitations and safety considerations limit the
ability to test at high speeds. However, crashes still occur at higher
travel speeds. Although generally the number of rear-end crashes
decreases at higher travel speeds, these high-speed crashes are the
ones that more often result in fatalities, as shown in Figure 3. The
automatic braking requirement

ensures that AEB systems continue to provide safety benefits at speeds
above those for which a track-testing requirement is currently not
practicable, either because of performance capabilities or track test
limitations. Where a performance standard is not practical or does not
sufficiently meet the need for safety, NHTSA may specify an equipment
requirement as part of an FMVSS.\105\
---------------------------------------------------------------------------

    \105\ See 72 FR 17235, 17299 (Apr. 6, 2007) (discussing the
understeer requirement in FMVSS No. 126); Chrysler Corp. v. DOT, 515
F.2d 1053 (6th Cir. 1975) (holding that NHTSA's specification of
dimensional requirements for rectangular headlamps constitutes an
objective performance standard under the Safety Act).
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BILLING CODE 4910-59-P
[GRAPHIC] [TIFF OMITTED] TP06JY23.003

BILLING CODE 4910-59-C
    These requirements would not apply at speeds below 10 km/h. NHTSA
believes that there are real-world cases where heavy vehicles are being
maneuvered at low-speed and intentionally in proximity of other
objects, and AEB intervention could be in conflict with the vehicle
operator's intention. For example, if an operator intends to drive
towards the rear of another vehicle in a parking lot in order to park
the vehicle near the other, automatic braking during this parking
maneuver would be unwanted. Publicly available literature from at least
one AEB manufacturer shows that some or all of the AEB system functions
are not available below 15 mph (24 km/h), indicating that current
manufacturers may have similar considerations about low-speed AEB
functionality.\106\ NHTSA tentatively concludes that a minimum
operational speed of 10 km/h would allow these types of low-speed
maneuvers. This proposal would not require AEB systems to be disabled
below 10 km/h.
---------------------------------------------------------------------------

    \106\ SD-61-4963 Bendix Wingman Fusion Driver Assistance System
Brochure, available at https://www.bendix.com/media/documents/technical_documentsproduct_literature/bulletins/SD-61-4963_US_005.pdf (last accessed June 21, 2023).
---------------------------------------------------------------------------

    Enforcement of such a performance requirement can be based on
evidence obtained by engineering investigation that might include a
post-crash investigation and/or system design investigation. For
instance, if a crash occurs in which the vehicle under examination has
collided with a lead vehicle, NHTSA could investigate the details
surrounding the crash to determine if a warning was provided and the
automatic emergency braking system applied the service brakes
automatically. In appropriate cases in the context of an enforcement
proceeding, NHTSA could also use its information-gathering authority to
obtain information from a manufacturer on the basis for its
certification that its FCW and AEB systems meet this proposed
requirement.
2. Forward Collision Warning Requirement
    NHTSA is proposing that AEB-equipped vehicles must have forward
collision warning functionality that provides a warning to the vehicle
operator if a forward collision with a lead vehicle is imminent. The
proposal defines FCW as an auditory and visual warning provided to the
vehicle operator that is designed to elicit an immediate crash
avoidance response by the vehicle operator. The system must operate
when the vehicle is traveling at any forward speed greater than 10 km/h
(6.2 mph).
    While some vehicles are equipped with alerts that precede the FCW
and research has examined their use, NHTSA's proposal is not specifying
an advisory or preliminary alert that would

precede the FCW. Lerner, Kotwal, Lyons, and Gardner-Bonneau (1996b)
differentiated between an imminent alert, which ``requires an immediate
corrective action'' and a cautionary alert, which ``alerts the operator
to a situation which requires immediate attention and may require a
corrective action.'' \107\ A 2004 NHTSA report titled ``Safety Vehicles
using adaptive Interface Technology (Task 9): A Literature Review of
Safety Warning Countermeasures,'' examined the question of whether to
include a cautionary alert level in an FCW system. Although the two FCW
algorithms in the Automotive Collision Avoidance System Field
Operational Test algorithms included a cautionary phase, the Collision
Avoidance Metrics Partnership (1999) program recommended that only
single (imminent) stage warnings be used.
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    \107\ Lerner, Kotwal, Lyons, and Gardner-Bonneau (1996).
Preliminary Human Factors Guidelines for Crash Avoidance Warning
Devices. DOT HS 808 342. National Highway Traffic Safety
Administration.
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    Unlike the FCW required as part of the track testing, NHTSA is not
specifically requiring that FCW presentation occur prior to the onset
of braking in instances that are not tested on the track. This is to
provide manufacturers with the flexibility to design systems that are
most appropriate for the complexities of various crash situations, some
of which may provide very little time for a driver to take action to
avoid a crash. A requirement that FCW occur prior to automatic braking
could suppress the automatic braking function in some actual driving
scenarios, such as a lead vehicle cutting immediately in front of an
AEB-equipped vehicle, where immediate automatic braking should not wait
for a driver warning.
i. FCW Modalities
    Since approximately 1994, NHTSA has completed research and
published related reports for more than 35 research efforts related to
crash avoidance warnings or forward collision warnings. These research
efforts, along with other published research and existing ISO standards
(15623 and 22839) and SAE International (SAE) documents (J3029 and
J2400) provide a basis for the proposed requirements.\108\
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    \108\ ISO 15623--Forward vehicle collision warning systems--
Performance requirements and test procedures; ISO 22839--Forward
vehicle collision mitigation systems--Operation, performance, and
verification requirements (applies to light and heavy vehicles); SAE
J3029: Forward Collision Warning and Mitigation Vehicle Test
Procedure and Minimum Performance Requirements--Truck and Bus (2015-
10; WIP currently); SAE J2400 2003-08 (Information report). Human
Factors in Forward Collision Warning Systems: Operating
Characteristics and User Interface Requirements.
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    NHTSA NCAP and Euro NCAP information relating to FCW was also
considered. Since model year 2011, the agency has included FCW as a
recommended technology in NCAP and identifies to consumers which light
vehicles have FCW systems that meet NCAP's performance tests. NHTSA's
March 2022 request for comments notice on proposed changes to NCAP
sought comment on which FCW modalities or modality combinations should
be necessary to receive NHTSA's NCAP recommendation.\109\ Commenters
generally supported the use of a multimodal FCW strategy. The Alliance
for Automotive Innovation and Intel both advocated allowing credit for
any effective FCW signal type. Multiple commenters supported allowing
NCAP credit for FCW having either auditory or haptic signals. BMW and
Stellantis supported use of FCW auditory or haptic signals in addition
to a visual signal. NTSB and Advocates for Highway and Auto Safety
recommended that NHTSA conduct research examining the human-machine
interface and examine the effectiveness of haptic warning signals
presented in different locations (e.g., seat belt, seat pan, brake
pulse). Dynamic Research, Inc. advocated allowing NCAP credit for
implementation of a FCW haptic brake pulse, while ZF supported use of a
haptic signal presented via the seat belt. Bosch warned that use of a
haptic signal presented via the steering wheel for lane keeping or
blind spot warning and FCW should be avoided as it may confuse the
driver. The Alliance for Automotive Innovation raised the potential
benefits of standardizing the warning characteristics to improve
effectiveness as individuals move from vehicle to vehicle.
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    \109\ 87 FR 13452 (Mar. 9, 2022).
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    All current U.S. vehicle models with FCW systems appear to provide
auditory and visual FCW signals, while only a few manufacturers also
provide a haptic signal (e.g., seat pan vibration or a brake pulse).
Visual FCW signals in current models consist of either a symbol or word
(e.g., ``BRAKE!''), presented on the instrument panel or head-up
display, and most are red.
    For this NPRM, NHTSA proposes that the FCW be presented to the
vehicle operator via at least two sensory modalities, auditory and
visual. Use of a multimodal warning ensures that most drivers will
perceive the warning as soon as its presented, allowing the most time
for the driver to take evasive action to avoid a crash. As a vehicle
operator who is not looking toward the location of a visual warning at
the time it is presented may not see it, NHTSA's proposal views the
auditory warning signal as the primary modality and the visual signal
as a secondary, confirmatory indication that explains to the driver
what the warning was intended to communicate (i.e., a forward crash-
imminent situation). However, because hearing-impaired drivers may not
perceive an FCW auditory signal, a visual signal is important for
presenting the FCW to hearing-impaired individuals.
    A multimodal FCW strategy is consistent with recommendations of
multiple U.S. and international organizations including ISO, SAE
International, and Euro NCAP. ISO recommends a multimodal approach in
both ISO 15623, ``Forward vehicle collision warning systems--
Performance requirements and test procedures'' and ISO 22839, ``Forward
vehicle collision mitigation systems--Operation, performance, and
verification requirements'' (which applies to light and heavy
vehicles). SAE addresses the topic of a multimodal FCW strategy in both
information report J2400 2003-08, ``Human Factors in Forward Collision
Warning Systems: Operating Characteristics and User Interface
Requirements,'' and J3029, ``Forward Collision Warning and Mitigation
Vehicle Test Procedure and Minimum Performance Requirements--Truck and
Bus (2015-10; Work in Progress currently).'' Most of these
recommendations specify an FCW consisting of auditory and visual
signals, while ISO 15623 specifies that an FCW include a visual
warning, as well as an auditory or haptic signal.
ii. FCW Auditory Signal Characteristics
    The proposed FCW auditory signal would be the primary means used to
direct the vehicle operator's attention to the forward roadway and
should be designed to be conspicuous to quickly capture the driver's
attention, convey a high level of urgency, and be discriminable from
other auditory signals presented within the vehicle.\110\ Some
specifications from NHTSA's ``Human Factors Design Guidance For
Driver--Vehicle Interfaces'' are proposed as forward collision warning
specifications to meet these criteria.\111\

As the FCW auditory signal would be the primary warning mode, this
signal would not be permitted to be disabled.
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    \110\ DOT HS 810 697, Crash Warning System Interfaces: Human
Factors Insights and Lessons Learned--Final Report.
    \111\ Campbell, J.L., Brown. J.L., Graving, J.S., Richard, C.M.,
Lichty, M.G., Sanquist, T., . . . & Morgan, J.L. (2016, December).
Human factors design guidance for driver-vehicle interfaces (Report
No. DOT HS 812 360). Washington, DC: National Highway Traffic Safety
Administration.
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    To be conspicuous and quickly capture the driver's attention, the
FCW auditory signal must ensure that the driver will readily detect the
warning under typical driving conditions (e.g., ambient noise). The
auditory signal must be clearly perceptible and quickly focus the
driver's attention on the forward roadway. To ensure that the FCW
auditory signal is conspicuous to the vehicle operator, any in-vehicle
system or device that produces sound that may conflict with the FCW
presentation would be required to be muted, or substantially reduced in
volume, during the presentation of the FCW.\112\ In order for the
warning to be detectable, a minimum intensity of 15-30 dB above the
masked threshold (MT) should be used.113 114 115 116 Because
sound levels inside a vehicle can vary based on any number of different
factors, such as vehicle speed and pavement condition, NHTSA is not
proposing a specific sound level at this time, but requests comments on
suitable and reasonable approaches for ensuring that the FCW auditory
signal can be detected by drivers under typical driving conditions.
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    \112\ DOT HS 810 697, Crash Warning System Interfaces: Human
Factors Insights and Lessons Learned--Final Report.
    \113\ Campbell, J.L., Brown. J.L., Graving, J.S., Richard, C.M.,
Lichty, M.G., Sanquist, T., . . . & Morgan, J.L. (2016, December).
Human factors design guidance for driver-vehicle interfaces (Report
No. DOT HS 812 360). Washington, DC: National Highway Traffic Safety
Administration. ``The amplitude of auditory signals is in the range
of 10-30 dB above the masked threshold (MT), with a recommended
minimum level of 15 dB above the MT (e.g., [1, 2, 3]).
Alternatively, the signal is at least 15 dB above the ambient noise
[3].''
    \114\ Campbell, J.L., Richman, J.B., Carney, C., and Lee, J.D.
(2002). In-vehicle display icons and other information elements.
Task F: Final in-vehicle symbol guidelines (FHWA-RD-03-065).
Washington, DC: Federal Highway Administration.
    \115\ International Organization for Standardization. (2005).
Road vehicles--Ergonomic aspects of in-vehicle presentation for
transport information and control systems--Warning systems (ISO/TR
16532). Geneva, Switzerland: International Organization of
Standards.
    \116\ MIL-STD-1472F. (1998). Human engineering. Washington, DC:
Department of Defense.
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    For communicating urgency and ensuring comprehension of auditory
messages, fundamental frequency, the lowest frequency in a periodic
signal, is a key design parameter.\117\ Research has shown that
auditory warning signals with a high fundamental frequency of at least
800 Hz more effectively communicate urgency.118 119 Greater
perceived urgency of a warning is associated with faster reaction
times, which would mean a quicker crash avoidance response by the
driver.120 121 122 Therefore, NHTSA proposes that the FCW
auditory signal's fundamental frequency must be at least 800 Hz.\123\
Additional proposed FCW auditory signal requirements that support
communication of the urgency of the situation include a duty
cycle,\124\ or percentage of time sound is present, of 0.25-0.95, and
faster auditory signals with a tempo in the range of 6-12 pulses per
second to be perceived as urgent and elicit rapid driver response.\125\
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    \117\ Campbell, J.L., Brown. J.L., Graving, J.S., Richard, C.M.,
Lichty, M.G., Sanquist, T., . . . & Morgan, J.L. (2016, December).
Human factors design guidance for driver-vehicle interfaces (Report
No. DOT HS 812 360). Washington, DC: National Highway Traffic Safety
Administration.
    \118\ Campbell, J.L., Brown. J.L., Graving, J.S., Richard, C.M.,
Lichty, M.G., Sanquist, T., . . . & Morgan, J.L. (2016, December).
Human factors design guidance for driver-vehicle interfaces (Report
No. DOT HS 812 360). Washington, DC: National Highway Traffic Safety
Administration.
    \119\ Guilluame, A., Drake, C., Rivenez, M., Pellieux, L., &
Chastres, V. (2002). Perception of urgency and alarm design.
Proceedings of the 8th International Conference on Auditory Display.
    \120\ Campbell, J.L., Brown. J.L., Graving, J.S., Richard, C.M.,
Lichty, M.G., Sanquist, T., . . . & Morgan, J.L. (2016, December).
Human factors design guidance for driver-vehicle interfaces (Report
No. DOT HS 812 360). Washington, DC: National Highway Traffic Safety
Administration.
    \121\ Campbell, J.L., Richman, J.B., Carney, C., & Lee, J.D.
(2004). In-vehicle display icons and other information elements,
Volume I: Guidelines (Report No. FHWA-RD-03-065). Washington, DC:
Federal Highway Administration. Available at www.fhwa.dot.gov/publications/research/safety/03065/index.cfm.
    \122\ Suied, C., Susini, P., & McAdams, S. (2008). Evaluating
warning sound urgency with reaction times. Journal of Experimental
Psychology: Applied, 14(3), 201-212.
    \123\ Campbell, J.L., Brown. J.L., Graving, J.S., Richard, C.M.,
Lichty, M.G., Sanquist, T., . . . & Morgan, J.L. (2016, December).
Human factors design guidance for driver-vehicle interfaces (Report
No. DOT HS 812 360). Washington, DC: National Highway Traffic Safety
Administration.
    \124\ Duty cycle, or percentage of time sound is present, is
equal to the total pulse duration divided by the sum of the total
pulse duration and the sum of the inter-pulse intervals.
    \125\ Gonzalez, C., Lewis, B.A., Roberts, D.M., Pratt, S.M., &
Baldwin, C.L. (2012). Perceived urgency and annoyance of auditory
alerts in a driving context. Proceedings of the Human Factors and
Ergonomics Society Annual Meeting, 56(1), 1684-1687.
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    The FCW auditory signal needs to be easily discriminable from other
auditory signals in the vehicle. Therefore, vehicles equipped with more
than one crash warning type should use FCW auditory signals that are
distinguishable from other warnings.\126\ This proposed requirement is
consistent with ISO 15623 <IP_ADDRESS>.\127\ Standardization of FCW auditory
signals would likely be beneficial in ensuring driver comprehension of
the warning condition across vehicle makes and models. NHTSA invites
comments on the feasibility of specifying a common FCW auditory signal.
While this proposal contains no specific requirements ensuring that the
FCW auditory signal is distinguishable from other auditory warnings in
the vehicles, NHTSA believes that industry is likely to consider this
in their vehicle designs as part of their due diligence and safety
assurance.
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    \126\ DOT HS 810 697, Crash Warning System Interfaces: Human
Factors Insights and Lessons Learned--Final Report.
    \127\ ISO 15623--Forward vehicle collision warning systems--
Performance requirements and test procedures.
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iii. FCW Visual Signal Characteristics
    Current FCWs in the U.S. vehicle fleet use a mix of symbols and
words as a visual forward collision warning. Use of a common FCW symbol
across makes and models would help to improve consumer understanding of
the meaning of FCWs and encourage more appropriate driver responses in
forward crash-imminent situations.
    ISO 7000, ``Graphical symbols for use on equipment--Registered
symbols'' \128\ and the SAE J2400 (2003-08) \129\ information report,
``Human Factors in Forward Collision Warning Systems: Operating
Characteristics and User Interface Requirements,'' contain recommended
FCW symbols shown in Figure 4. These symbols are similar as they both
communicate a forward impact, while the ISO symbol portrays the forward
impact as being specifically with another vehicle.
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