--------------------------------------------------------------------------------------------------------------------------------------------------------
   Vehicle test  instrumentation          Output/input                Range                Resolution              Accuracy           Make/model used
--------------------------------------------------------------------------------------------------------------------------------------------------------
Programmable Steering Machine with   Controls Steering       Max 40-60Nm (29.5-44.3  .....................  .....................  Automotive Testing
 Steering Angle Encoder.              Wheel Angle Input.      lb-ft) torque at a                                                    Inc. (ATI) Model:
                                                              hand wheel rate up to                                                 Spirit.\3\
                                                              1200 deg/sec.
                                     Handwheel Angle.......  800 deg...  0.25 deg.............  0.25 deg.
--------------------------------------------------------------------------------------------------------------------------------------------------------
Multi-Axis Inertial Sensing System.  Longitudinal, Lateral   Accelerometers: 2 g.              ug.                    <=0.05% of full        Model: MP-1.
                                      Acceleration.                                                          range
                                     Roll, Yaw, and Pitch    Angular rate sensors:   Angular Rate Sensors:  Angular Rate Sensors:
                                      Rate.                   100 deg/    <=0.004 deg/s.         0.05% of full range.
                                                              sec.
--------------------------------------------------------------------------------------------------------------------------------------------------------
Speed Sensor.......................  Vehicle Speed to DAS    0-201 km/h (0-125 mph)  .014 km/h (.009 mph).  0.1 km/h full scale..  Make: RaceLogic
                                      and Steering Machine.                                                                         Model: VBox.
--------------------------------------------------------------------------------------------------------------------------------------------------------
Infrared Distance Measuring Sensor.  Left and Right Side     350-850 mm (14-35       0.3-8.0 mm (0.01-0.3   1%...................  Sensor Make: Wenglor.
                                      Vehicle Height (For     inches).                inches).                                      Model: HT66MGV80.
                                      calculated vehicle
                                      roll angle).
--------------------------------------------------------------------------------------------------------------------------------------------------------

    During research additional instrumentation was used for collecting
data outside the scope of the proposed standard and that
instrumentation is not discussed here. Furthermore, this table does not
include a discussion of non-critical instrumentation like the brake
pedal load cell used to ensure the test driver does not apply the brake
during the maneuver, or the thermocouples used to monitor brake
temperatures.
(a) Outriggers
    Throughout the agency's research program, truck tractors and buses
were equipped with outrigger devices to prevent vehicle rollover.
During the program, the agency encountered many instances of wheel lift
and outrigger contact with the ground indicating that it was probable
that rollover could occur during testing. Over many years of research
of ESC systems, it has been proven that outriggers are essential to

ensure driver safety and to prevent vehicle and property damage during
NHTSA's compliance testing. Although NHTSA conducted some of its
testing with ESC systems disabled, thereby increasing the need for
outriggers, outriggers are still necessary as a safety measure during
testing of vehicles equipped with an ESC system in case the system
fails to activate.
    The agency proposes that outriggers be used on all truck tractors
and buses tested. Nevertheless, the agency acknowledges, as it did
during the development of the light vehicle ESC system testing program,
that outriggers have the potential to influence the dynamics of a
vehicle during performance testing. For light vehicles, the agency
determined that outrigger influence could be noticeable. However, we
believe that outrigger influence on heavy vehicles is minimal because
of the higher vehicle weight and test load. The agency has invested
significant effort in outrigger designs that are both functional and
minimize the impact to the test vehicle dynamic performance. To reduce
test variability and increase the repeatability of the test results,
the agency proposes to specify a standard outrigger design for the
outriggers that will be used for compliance testing. The agency used
this same approach in FMVSS No. 126 for compliance testing of light
vehicle ESC systems. The agency also made available the detailed design
specifications by reference to a design document located in the agency
public docket.
    For truck tractors, the document detailing the outrigger design to
be used in testing has been placed in a public docket.\51\ This
document provides detailed construction drawings, specifies materials
to be used, and provides installation guidance. For truck tractor
combinations, the outriggers would be mounted on the trailer. The
outriggers are mounted mid-way between the center of the kingpin and
the center of the trailer axle (in the fore and aft direction of
travel), which is generally near the geometric center of the trailer.
They will be centered geometrically from side-to-side and bolted up
under the traditional flatbed control trailer. Total weight of the
outrigger assembly, excluding the mounting bracket and fasteners
required to mount the assembly to the flatbed trailer, is approximately
1,490 pounds. The bulk of the mass, over 800 pounds, is for the
mounting bracket which is located under the trailer near the vehicle's
lateral and longitudinal center of gravity so that its inertial effects
are minimized. The width of the outrigger assembly is 269 inches and
the contact wheel to ground plane height is adjustable to allow for
various degrees of body roll. A typical installation on a flatbed type
trailer involves clamping and bolting the outrigger mounting bracket to
the main rails of the flatbed.
---------------------------------------------------------------------------

    \51\ Docket No. NHTSA-2010-0034-0010.
---------------------------------------------------------------------------

    For buses, the outrigger installations will not be as
straightforward as the outrigger installations on the control trailers,
and we desire comments on bus outrigger design. This is because
outriggers cannot be mounted under the flat structure, but instead must
extend through the bus. NHTSA used outriggers on the three large buses
tested during its research program and proposes using outriggers for
testing buses for compliance with this rule. The agency will use the
same outrigger arms of the standard outrigger design that it plans to
use for truck tractor testing. Therefore, the size, weight, and other
design characteristics will be similar.
    The location and manner of mounting the outriggers on buses cannot
be identical to truck tractors. Nonetheless, there are a limited number
of large bus manufacturers, which results in a limited number of unique
chassis structural designs. Also, the agency understands that large bus
structural designs do not change significantly from year-to-year. We
believe that once outrigger mounts have been constructed for several
different bus designs, those mountings can be modified and reused
during subsequent testing. The agency has, in the document described
above, provided additional engineering design drawings and further
installation guidelines for installing the standard outrigger assemble
to large buses.
(b) Automated Steering Machine
    As part of the heavy vehicle ESC system research programs, the
agency performed testing that compared multiple runs with test-driver-
generated steering inputs, and found that test drivers cannot provide
the same repeatable results as those obtained with an automated
steering machine. Therefore, this NPRM proposes that an automated
steering machine be used for the test maneuvers on the truck tractors
and large buses in an effort to achieve highly repeatable and
reproducible compliance test results.
    An essential element of any compliance test program is for the test
being executed to be reproducible, a test that can be easily executed
the same way by different testing facilities, and repeatable, test
results from repeated tests of the same vehicle are identical. The
proposed 0.5 Hz SWD maneuver is a complex test maneuver where the
steering must follow an exact sinusoidal pattern over a three-second
time period. For the SWD maneuver, each test vehicle is subjected to as
many 22 individual test runs all requiring activation at a specific
vehicle speed, each of which will require a different peak steering
wheel angle and corresponding steering wheel turning rate. To ensure
the agency has an effective compliance program that will not vary from
one test laboratory to another, from one test driver to another, or
from one test vehicle to another, each maneuver must be repeatable and
reproducible. The agency has extensive experience with execution of
these and other steering maneuvers utilizing both human drivers and
automated steering controllers. Based upon this experience, the agency
has determined that a test driver cannot consistently execute these
kinds of dynamic maneuvers exactly as required repeatedly. We note
that, for the same reasons, the agency currently requires that
automated steering machines be used for execution of the steering
maneuvers performed under both the NCAP Rollover program and the FMVSS
No. 126 light vehicle ESC program.
(c) Anti-Jackknife Cables
    The agency proposes using anti-jackknife cables when testing truck
tractors. Anti-jackknife cables would prevent the trailer from striking
the tractor during testing in the event that a jackknife event occurs
during testing. This would prevent damage to the tractor that may occur
during testing. We do not believe that the use of anti-jackknife cables
would affect test results, nor have we observed any damage to test
vehicles, including vehicle finishes, caused by anti-jackknife cables.
Nevertheless, we request comment on the necessity of the use of anti-
jackknife cables during agency compliance testing.
(d) Control Trailer
    The agency proposes using a control trailer to evaluate the
performance of a tractor in its loaded condition. A control trailer
would not be used when testing buses. In FMVSS No. 121, the agency
specifies the use of an unbraked control trailer for compliance testing
purposes. An unbraked control trailer minimizes the effect of the
trailer's brakes when testing the braking performance of a tractor in
its loaded condition.
    The agency has also considered using a braked control trailer in
ESC performance testing for truck tractors because the tractor-based
stability control systems have the capability to apply the trailer
brakes during stability

control intervention. This ability provides a slightly greater vehicle
retardation that could further help prevent an impending rollover or
reduce yaw instabilities.
    As described in section IV.C above, the agency conducted numerous
vehicle research test maneuvers using six different trailers. For each
trailer, a test series was conducted collecting data for each trailer
in a braked and unbraked condition. The effects of stability control,
trailer brakes, and trailer type were analyzed using a logistical
regression model to predict if wheel lift occurred during the test. A
test was conducted to determine the effects of trailer brakes when
stability control systems were enabled. With stability control systems
enabled and trailer braking in the ``off'' position, the trailer was
found not to be a significant factor in predicting wheel lift. Hence,
the results indicate that the current FMVSS No. 121 unbraked control
trailer can be used effectively in the stability control system testing
to determine the capability of the tractor-based stability control
system.
    NHTSA's compliance tests must be objective, repeatable and
reproducible. The goal of the testing program is to ensure that the ESC
system takes the necessary actions of reducing engine torque and
applying brakes to prevent yaw and roll instability. To achieve this
goal any trailer type could be used as long as that trailer type
becomes the ``standard'' trailer or ``control trailer'' used for all
tractor trailer testing. Because it is the tractor performance that is
being evaluated, the use of a standardized trailer will allow the test
to distinguish the performance differences between different ESC
systems and tractor types.
    We believe that the current FMVSS No. 121 unbraked control trailer
can be used effectively in the stability control testing to determine
the capability of an ESC system. However, as discussed in section
IV.D.5.(b) earlier, NHTSA's testing of EMA's Vehicle J revealed that
the specifications for the control trailer in FMVSS No. 121 were not
sufficient to ensure test repeatability.\52\
---------------------------------------------------------------------------

    \52\ The FMVSS No. 121 control trailer specifications, set forth
in S<IP_ADDRESS> and S<IP_ADDRESS> of FMVSS No. 121 provide that the center
of gravity of the ballast on the loaded control trailer be less than
24 inches above the top of the tractor's fifth wheel and that the
trailer have a single axle with a GAWR of 18,000 pounds and a
length, measured from the transverse centerline of the axle to the
centerline of the kingpin, of 258  6 inches.
---------------------------------------------------------------------------

    There were three specifications, not set forth in FMVSS No. 121,
which could affect test performance and prevent repeatable, consistent
test results using different control trailers. First, the track width
of the control trailer is not specified. A trailer with a wider track
width would be more stable than a trailer with a narrower track width,
potentially affecting test results. Second, the center of gravity of
the control trailer is not specified in FMVSS No. 121. The center of
gravity of the trailer may be affected by the height of the load deck.
A trailer with a higher load deck height would be less stable than a
trailer with a lower load deck height. Third, the center of gravity of
the load in FMVSS No. 121 testing is only specified to be less than 24
inches above the top of the tractor's fifth wheel. However, a load with
a lower center of gravity (for example 12 inches) would be more stable
than a load with a higher center of gravity (for example 24 inches).
    The performance measures specified in this proposal were based upon
NHTSA's testing using the control trailer used by VRTC researchers.
Although the track width and center of gravity of the trailer are not
specified in the proposed regulatory text and the center of gravity of
the load is specified only by an upper bound, we request comment on
possible specifications and appropriate levels of variability in
trailer track width, trailer CG height, and load CG height for a
control trailer to be used during ESC system testing.
(e) Sensors
    A multi-axis inertial sensing system would be used to measure
longitudinal, lateral, and vertical linear accelerations and roll,
pitch, and yaw angular rates. The position of the multi-axis inertial
sensing system must be measured relative to the center of gravity of
the tractor when loaded. To simplify testing, the vertical center of
gravity location is assumed to be at the top of the frame rails for
tractors. For buses, the center of gravity height is assumed to be at
the height of the main interior floor of the bus. The measured lateral
acceleration and yaw rate data are required for determining the lateral
displacement, LAR and YRR performance criteria. All six of the sensing
system signals are utilized in the equations required to translate the
motion of the vehicle at the measured location to that which occurred
at the actual center of gravity to remove roll, pitch, and yaw effects.
    The vehicle speed would be measured with a non-contact GPS-based
speed sensor. Accurate speed data is required to ensure that the SWD
maneuver is executed at the required 72.4  1.6 km/h (45.0
 1.0 mph) test speed. Sensor outputs are available to allow
the driver to monitor vehicle speed and data are provided as input to
the automated steering machine for maneuver activation.
    Infrared height sensors would be used to collect left and right
side vertical ride height or displacement data for calculating vehicle
roll angle. One sensor would be mounted on each side of the vehicle.
With these data, roll angle is calculated during post-processing using
trigonometry and would be used for correcting the measured lateral
acceleration data due to the effects caused by body roll.
6. Test Conditions
(a) Ambient Conditions
    The ambient temperature range specified in other FMVSSs for outdoor
brake performance testing is 0 [deg]C to 38 [deg]C (32 [deg]F to 100
[deg]F). However, when the agency proposed a range of 0 [deg]C to 40
[deg]C (32 [deg]F to 104 [deg]F) for FMVSS No. 126, the issue of tire
performance at near freezing temperatures was raised. The agency
understood that near freezing temperatures could impact the variability
of compliance test results. As a result, the agency increased the lower
bound of the temperature range to 7 [deg]C (45 [deg]F) to minimize test
variability at lower ambient temperatures. For the same reasons, this
NPRM proposes an ambient temperature range of 7 [deg]C to 40 [deg]C (45
[deg]F to 104 [deg]F) for testing.
    The agency proposes that the maximum wind speed for conducting the
compliance testing for be no greater than 5 m/s (11 mph). This is the
same value specified for testing multi-purpose passenger vehicles
(MPVs), buses, and trucks under FMVSS No. 126. This is also the same
value used for compliance testing for FMVSS No. 135, Light Vehicle
Brake Systems. For FMVSS No. 126, the agency initially proposed a
maximum wind speed of 10 m/s (22 mph) for all vehicles. However, the
agency decided to reduce the speed for MPVs, buses, and trucks because
of a concern that the higher wind speeds could impact the performance
of certain vehicle configurations (e.g., cube vans, 15 passenger vans,
vehicles built in two or more stages).\53\ Commenters to the proposed
rule had estimated that a cross wind of 22 mph could reduce lateral
displacement by 0.5 feet, compared to the same test conducted under
calm conditions. The agency agreed that wind speed could have some
impact on the lateral displacement for certain vehicle configurations
and believes that the same argument is applicable testing truck
tractors and large buses.

Nevertheless, the agency notes that specifying such a low maximum wind
speed can impose additional burdens on testing by restricting the
environmental conditions under which testing can be conducted.
---------------------------------------------------------------------------

    \53\ See 72 FR 17286 (Apr. 6, 2007).
---------------------------------------------------------------------------

(b) Road Test Surface
    The SWD maneuver executed on a high friction surface is a
dynamically challenging maneuver that evaluates the effectiveness of an
ESC system. Low friction surfaces, such as wet Jennite, are well known
for producing a high degree of braking and handling tests variability
compared to similar tests on high friction surfaces. The variability is
exacerbated by the difficulty in ensuring a consistent water depth
across the test surface. Therefore, this NPRM proposes conducting the
SWD test on a dry test surface with a PFC of 0.9, which is typical of a
dry asphalt surface or a dry concrete surface. As in other standards
where the PFC is specified, we propose that the PFC be measured using
an ASTM E1136 standard reference test tire in accordance with ASTM
Method E1337-90, at a speed of 64.4 km/h (40 mph), without water
delivery. We are proposing incorporating these ASTM provisions into the
Standard.
(c) Vehicle Test Weight
    The agency proposes that the combined weight of the truck tractor
and control trailer be equal to 80 percent of the tractor's GVWR. To
achieve this load condition the tractor is loaded with the fuel tanks
filled to at least 75 percent capacity, test driver, test
instrumentation and ballasted control trailer with outriggers. Center
of gravity of all ballast on the control trailer is proposed to be
located directly above the kingpin. When possible, load distribution on
non-steer axles is in proportion to the tractor's respective axle
GAWRs. Load distribution may be adjusted by altering fifth wheel
position, if adjustable. In the case where the tractor fifth wheel
cannot be adjusted so as to avoid exceeding a GAWR, ballast is reduced
so that axle load equals specified GAWR, maintaining load proportioning
as close as possible to specified proportioning.
    The agency is proposing that liftable axles be in the down position
for testing. This is because we are conducting our proposed performance
test in a loaded condition. Typically, in real world use, we believe
that a truck tractor loaded to 80% of its GVWR would operate with the
liftable axle in the down position. Consequently, we propose to conduct
compliance testing in that configuration.
    For testing large buses, the agency proposes loading the vehicle to
a simulated multi-passenger configuration. For this configuration the
bus is loaded with the fuel tanks filled to at least 75 percent
capacity, test driver, test instrumentation, outriggers and simulated
occupants in each of the vehicle's designated seating positions. The
simulated occupant loads are obtained by securing a 68 kilogram (150
pound) water dummy in each of the test vehicle's designated seating
positions without exceeding the vehicle's GVWR and GAWR. The 68
kilogram (150 pound) occupant load was chosen because that is the
occupant weight specified for use by the agency for evaluating a
vehicle's load carrying capability under FMVSS Nos. 110 and 120. During
loading, if any rating is exceeded the ballast load would be reduced
until the respective rating or ratings are no longer exceeded.
(d) Tires
    We propose testing the vehicles with the tires installed on the
vehicle at time of initial vehicle sale. The agency's compliance test
programs generally evaluate new vehicles with new tires. Therefore, we
are proposing as a general rule that a new test vehicle have less than
500 miles on the odometer when received for testing.
    For testing, the agency proposes that tires be inflated to the
vehicle manufacturer's recommended cold tire inflation pressure(s)
specified on the vehicle's certification label or the tire inflation
pressure label. No tire changes would occur during testing unless test
vehicle tires are damaged before or during testing. We are not
proposing using inner tubes for testing because we have not seen any
tire debeading in any test.
    Before executing any SIS and SWD maneuvers, the agency is proposing
to condition tires to wear away mold sheen and achieve operating
temperatures. To begin the conditioning the test vehicle would be
driven around a circle 46 meters (150 feet) in radius at a speed that
produces a lateral acceleration of approximately 0.1g for two clockwise
laps followed by two counterclockwise laps.
(e) Mass Estimation Drive Cycle
    Both truck tractors and large buses experience large changes in
payload mass, which affects a vehicle's roll and yaw stability
thresholds. To adjust the activation thresholds for these changes,
stability control systems estimate the mass of the vehicle after
ignition cycles, periods of static idling, and other driving scenarios.
To estimate the mass, these systems require a period of initial
driving.
    The agency proposes to include a mass estimation drive cycle as a
part of pre-test conditioning. To complete this drive cycle the test
vehicle is accelerated to a speed of 64 km/h (40 mph), and then, by
applying the vehicle brakes, decelerated at 0.3g to 0.4g to a stop.
(f) Brake Conditioning
    Heavy vehicle brake performance is affected by the original
conditioning and temperatures of the brakes. We believe that
incompletely burnished brakes and excessive brake temperatures can have
an effect on ESC system test results, particularly in the rollover
performance testing, because a hard brake application may be needed for
the foundation brakes to reduce speed to prevent rollover.
    FMVSS No. 126 uses a simple conditioning procedure by executing ten
stops from 35 mph followed by three stops at 45 mph. Subsequently, a
cool down period of between 90 seconds and 5 minutes is required
between each SWD maneuver allowing sufficient time for the brakes to
cool down but not so long that the brakes lose all their retained heat.
However, for heavy vehicles, brake conditioning and operating
temperatures are more critical to brake performance than for light
vehicles primarily because the vast majority of heavy vehicles use drum
brakes, which require more conditioning than disc brakes. We believe
that conditioning needs to be more extensive and a brake temperature
range is preferable to a specified cool-down period because each
vehicle may have different cooling rates based on its configuration.
    The agency is proposing that the brakes be burnished before any
testing is executed. We believe that the burnish procedure specified in
S6.1.8 of FMVSS No. 121, Air Brake Systems, provides the brake
conditioning needed for the stability control system testing. The
burnish procedure is performed by conducting 500 brake snubs \54\
between 40 mph and 20 mph at a deceleration of 10 fp \2\. If the
vehicle has already completed testing to FMVSS No. 121, we are not
proposing to require the procedure be repeated. Instead, the brakes
would be conditioned for the ESC with 40 snubs. The agency proposes
that the brake temperatures be in the range of 65 [deg]C to 204 [deg]C
(150 [deg]F to 400 [deg]F) at the beginning of each test maneuver. We
also propose that the

brake temperature be measured by plug-type thermocouples installed on
all brakes and that the hottest brake be used for determining whether
cool-down periods are required.
---------------------------------------------------------------------------

    \54\ A snub is a brake application where the vehicle is not
braked to a stop but to a lower speed.
---------------------------------------------------------------------------

    After the brakes are burnished, immediately prior to executing any
SIS or SWD maneuvers, the agency would perform 40 brake application
snubs from a speed of 64 km/h (40 mph), with a target deceleration of
approximately 0.3g. At end of the 40 snubs, the hottest brake
temperature would be confirmed within the temperature range of 65
[deg]C to 204 [deg]C (150 [deg]F to 400 [deg]F). If the hottest brake
temperature is above 204 [deg]C (400 [deg]F) a cool-down period would
be provided until the hottest brake temperature is measured within that
range. If the hottest brake temperature is below 65 [deg]C (150 [deg]F)
individual brake stops would be repeated to increase any one brake
temperature to within the target temperature range before the
compliance testing can be continued.
7. Data Filtering and Post Processing
    To determine if a test vehicle meets the performance requirements
of the proposed standard, data needs to be measured and processed and
ultimately used to calculate the lateral displacement, lateral
acceleration ratio and yaw rate ratio performance measures. The agency
understands that filtering and post processing methods, if not defined,
can have a significant impact on the final test results used for
determining vehicle compliance. When developing FMVSS No. 126 the
agency received several comments recommending that filtering and
processing methods be defined and included in the regulatory text. The
agency decided to add to the test procedures section of the final
rule's regulatory text a section that specified the critical test
filtering protocols and techniques to be used for test data processing.
We propose to include the same information in this standard. In
addition, the agency proposes to make available on NHTSA's Web site the
actual MATLAB code used for post-processing the critical lateral
acceleration, yaw rate and lateral displacement performance data.
    During post-processing the following data signals will be filtered
and conditioned as follows:
    1. Filter raw steering wheel angle data with a 12-pole phaseless
Butterworth filter and a cutoff frequency of 10 Hz. Zero the filtered
data to remove sensor offset utilizing static pretest data.
    2. Filter raw yaw, pitch and roll rate data with a 12-pole
phaseless Butterworth filter and a cutoff frequency of 3 Hz. Zero the
filtered data to remove sensor offset utilizing static pretest data.
    3. Filter raw lateral, longitudinal and vertical acceleration data
with a 12-pole phaseless Butterworth filter and a cutoff frequency of 3
Hz. Zero the filtered data to remove sensor offset utilizing static
pretest data.
    4. Filter raw speed data with a 12-pole phaseless Butterworth
filter and a cutoff frequency of 2 Hz.
    5. Filter left side and right side ride height data with a 0.1-
second running average filter. Zero the filtered data to remove sensor
offset utilizing static pretest data.
    6. The J1939 torque data collected as a digital signal does not get
filtered. J1939 torque data collected as an analog signal is to be
filtered with a 0.1-second running average filter.
    There are several events in the calculation of performance metrics
that require determining the time and/or level of an event, including:
Beginning of steer, 1.5 seconds after beginning of steer, completion of
steer, 0.75 second after completion of steer, and 1.50 seconds after
completion of steer. The agency proposes using interpolation \55\ for
all of these circumstances because interpolation provides more
consistent results than other approaches, such as choosing the sample
that is closest in time to the desired event.
---------------------------------------------------------------------------

    \55\ Interpolation is a way of computing data values at the
exact time that any of these events occur, even though the digital
samples did not coincide with the exact event point. Rather, one
sample is collected slightly before the time of the event and a
second sample slightly after the time of the event.
---------------------------------------------------------------------------

    The beginning of steer is a critical moment during the maneuver
because the lateral displacement performance measure is determined at
exactly 1.5 seconds after the beginning of steer. For compliance
purposes it is essential that the beginning of steer be determined
accurately and consistently during each maneuver and each test. The
process proposed in this NPRM to identify the beginning of steer uses
three steps. The first step identifies when the steering wheel velocity
exceeds 40 degrees per second. From this point, steering wheel velocity
must remain greater than 40 degrees per second for at least 200 ms. If
the condition is not met, the next time steering wheel velocity exceeds
40 degrees per second is identified and the 200 ms validity check is
applied. This iterative process continues until the conditions are
satisfied. In the second step, a zeroing range defined as the 1.0
second time period prior to the instant the steering wheel velocity
exceeds 40 degrees per second. In the third step, the first instance
the filtered and zeroed steering wheel angle data reaches minus 5
degrees (when the initial steering input is counterclockwise) or plus 5
degrees (when the initial steering input is clockwise) after the end of
the zeroing range is identified. The time identified is taken to be the
beginning of steer.
    The agency understands that an unambiguous reference point to
define the start of steering is necessary in order to ensure
consistency when computing the performance metrics measured during
compliance testing. The practical problem is that typical ``noise'' in
the steering measurement channel causes continual small fluctuations of
the signal about the zero point, so departure from zero with very small
steering angles does not reliably indicate that the steering machine
has started the test maneuver. NHTSA's extensive evaluation of zeroing
range criteria has confirmed that the method successfully and robustly
distinguishes the initiation of the SWD steering inputs from the
inherent noise present in the steering wheel angle data channel. The
value for time at the beginning of steer used for calculating the
lateral displacement metric is interpolated.
    The completion of steer is a critical moment during the maneuver
because the LAR and YRR metrics are determined at specific time
intervals after the completion of steer. The agency believes that an
unambiguous point to define the completion of steer is also necessary
for consistency in computing the required performance metrics during
compliance testing. The agency proposes considering the first
occurrence of the ``zeroed'' steering wheel angle crossing zero degrees
after the second peak of steering wheel angle during the sine maneuver
to be the completion of steer. Although signal noise results in
continual zero crossings as long the data is being sampled, the first
zero crossing after the steering wheel has begun to return to the zero
position is a logical end to the steering maneuver.
    Given the potential for the accelerometers used in the measurement
and determination of lateral acceleration and lateral displacement to
drift over time, the agency uses the data one second before the start
of steering to ``zero'' the accelerometers and roll signal. Prior to
the test maneuver, the driver must orient the vehicle to the desired
heading, position the steering wheel angle to zero, and be coasting
down (i.e., not using throttle inputs) to the target test speed of 45
mph. This process, known as achieving a ``quasi steady-state,''
typically occurs a few seconds prior to initiation of the maneuver, but
can be influenced by external factors such as test track traffic,

differences in vehicle deceleration rates, etc. Any zeroing performed
on test data must be performed after a quasi-steady-state condition has
been satisfied, but before the maneuver is initiated. The proposed
zeroing duration of one second provides an adequate combination of
sufficient time (i.e., enough data is present so as to facilitate
accurate zeroing of the test data) and performability (i.e., the
duration is not so long that it imposes an unreasonable burden on the
driver).
    The lateral acceleration data are collected from an accelerometer,
corrected for roll angle effects, and resolved to the vehicle's CG
using coordinate transformation equations. The use of accelerometers is
commonplace in the vehicle testing community, and installation is
simple and well understood. However, in most cases, it is not possible
to install a lateral acceleration sensor at the location of the
vehicle's exact center of gravity. For this reason, it is important to
provide a coordinate transformation to resolve the measured lateral
acceleration values to the vehicle's center of gravity location. The
specific equations proposed to perform this operation, as well as those
used to correct lateral acceleration data for the effect of chassis
roll angle, will be incorporated into the laboratory test procedure and
are included in the MATLAB post processing routines used by the agency.
    The equations used for coordinate transformation and vehicle body
roll are as follows:

Equation 1: x''corrected = x''accel-([Theta]' \2\
+ [Psi]' \2\)xdisp + ([Theta]'[Phi]'-
[Psi]'')ydisp + ([Psi] '[Phi]' + [Theta]'')zdisp
Equation 2: y''corrected = y''accel +
([Theta]'[Phi]' + [Psi] '')xdisp-([Phi]' \2\ + [Psi] '
\2\)ydisp + ([Psi] '[Theta]'-[Phi]'')zdisp
Equation 3: z''corrected = z''accel + ([Psi]
'[Phi]'-[Theta]'')xdisp + ([Psi] '[Theta]' +
[Phi]'')ydisp-([Phi]' \2\ + [Theta]' \2\)zdisp

Where:

x''corrected, y''corrected, and
z''corrected = longitudinal, lateral, and vertical
accelerations, respectively, at the vehicle's center of gravity
x''accel, y''accel, and z''accel =
longitudinal, lateral, and vertical accelerations, respectively, at
the accelerometer location
xdisp, ydisp, and zdisp =
longitudinal, lateral, and vertical displacements, respectively, of
the center of gravity with respect to the accelerometer location
[Phi]' and [Phi]'' = roll rate and roll acceleration, respectively
[Theta]' and [Theta]'' = pitch rate and pitch acceleration,
respectively
[Psi] ' and [Psi] '' = yaw rate and yaw acceleration, respectively

    If the sensors used to measure the vehicle responses are of
sufficient accuracy, and have been installed and configured correctly,
use of the analysis routines provided by NHTSA are expected to minimize
the potential for performance discrepancies among NHTSA and industry
test efforts. The equations utilized are the same equations used by the
agency for its NCAP rollover program and the FMVSS No. 126 light
vehicle ESC program, and were derived from equations of general
relative acceleration for a translating reference frame utilizing the
SAE convention for Vehicle Dynamics Coordinate Systems.
    Furthermore, NHTSA does not propose using inertially stabilized
accelerometers for this test procedure. Therefore, lateral acceleration
must be corrected for vehicle roll angle during data post processing.
Non-contact displacement sensors are used to collect left and right
side vertical displacements for the purpose of calculating vehicle roll
angle. One sensor is mounted on each side of the vehicle, and is
positioned at the longitudinal CG. With these data, roll angle is
calculated during post-processing using trigonometry as follows:

Equation 4: ayc = aymcos [Phi] -
azmsin [Phi]

Where:
ayc is the corrected lateral acceleration (i.e., the
vehicle's lateral acceleration in a plane horizontal to the test
surface)
aym is the measured lateral acceleration in the vehicle
reference frame
azm is the measured vertical acceleration in the vehicle
reference frame
[Phi] is the vehicle's roll angle

    Note:  The z-axis sign convention is positive in the downward
direction for both the vehicle and test surface reference frames.

G. Compliance Dates and Implementation Schedule

    The agency proposes that all new typical 6x4 truck tractors and all
buses covered by this proposal would be required to meet this proposed
standard effective two years after the final rule is published. The
current annual installation rate for stability control systems on new
truck tractors is approximately 18 percent. Because there are currently
only two suppliers of truck tractor and large bus stability control
systems, Bendix and Meritor WABCO, we believe that the industry will
need lead time to ensure that the necessary production stability
control systems are available to manufacturers.
    For severe service tractors and tractors with four axles or more,
the agency believes that manufacturers of these atypical truck
tractors, which represent about 5 percent of annual truck tractor
sales, may need additional lead time to develop, test and equip these
vehicles with a stability control system. Therefore, we are proposing
to require that severe service tractors and other atypical tractors be
equipped with ESC systems beginning four years after the final rule is
published. We note that we made a similar distinction between typical
6x4 tractors and other tractors in specifying the lead time for
amendments to FMVSS No. 121 mandating improved stopping distance
performance.\56\
---------------------------------------------------------------------------

    \56\ See 49 CFR 571.121, Table IIA.
---------------------------------------------------------------------------

    However, in our stopping distance rulemaking, we allowed extra time
for two-axle tractors to comply because shorter wheelbase tractors
(i.e., two-axle tractors) showed a risk of instability resulting from
the improved stopping distance requirements. However, the increased
risk of instability in shorter wheelbase vehicles led us to the
opposite tentative conclusion in this rulemaking. Because two-axle
tractors have a particular risk of instability, we do not believe
extending lead time for two-axle tractors is warranted.
    The vast majority of new truck tractors are three-axle (6x4)
vehicles, which facilitates standardization of ESC for these vehicles.
The available test data for typical three-axle (6x4) tractors with
stability control systems show that the existing ESC technology should
enable these vehicles to readily comply with stability control
requirements proposed by the agency. In addition, the agency's benefit
analysis indicates that ESC provides substantial safety benefits to
truck tractors. Hence, we believe that it is important that the
implementation date for ESC on these vehicles be as early as
practicable so that these safety benefits could be achieved.
    Several manufacturers of Class 8 buses are already offering ESC as
standard equipment on their vehicles but we are not aware of any Class
7 bus that is available with ESC. We believe that the manufacturers of
Class 7 buses would need some lead time to have the ESC systems
developed, tested and installed on their vehicles. Hence, for large
buses, the agency proposes an effective date of two years after the
final rule is published, primarily to accommodate manufacturers of
Class 7 buses.

VI. Benefits and Costs

A. System Effectiveness

    As discussed above, direct data that would show the effectiveness
of stability control systems is not available

because stability control system technology on heavy vehicles is so
new. Accordingly, NHTSA sponsored a research program with Meritor WABCO
and UMTRI to examine the potential effectiveness of stability control
systems on the fleet of truck tractors. A copy of UMTRI's report has
been placed in the docket.
    However, for NHTSA to calculate the effectiveness of stability
control systems for truck tractors, two modifications were necessary.
First, the UMTRI study based its effectiveness estimates on a simple
aggregation of cases rather than weighting the likelihood of occurrence
of each case. Second, based on NHTSA's independent review of the 159
cases, two cases were incorrectly categorized as loss of control rather
than untripped rollover and the effectiveness rating of six cases were
revised downward.
    The results of UMTRI's study and the agency's revised effectiveness
estimates were published in a January 2011 research note entitled
``Effectiveness of Stability Control Systems For Truck Tractors'' (DOT
HS 811 437).\57\ The effectiveness estimates from that research note
are summarized in the following table.
---------------------------------------------------------------------------

    \57\ Docket No. NHTSA-2010-0034-0043.

                         Table 4--Effectiveness Rates for ESC and RSC by Target Crashes
                                            [Current NHTSA estimates]
----------------------------------------------------------------------------------------------------------------
                                        Overall  effectiveness     Untripped rollover        Loss of control
              Technology                         (%)               effectiveness  (%)       effectiveness  (%)
----------------------------------------------------------------------------------------------------------------
ESC..................................                    28-36                    40-56                       14
RSC..................................                    21-30                    37-53                        3
----------------------------------------------------------------------------------------------------------------

    For large buses, it was not feasible to conduct a similar
statistical analysis because of limited crash data. However, NHTSA's
testing revealed that an identical set of test maneuvers could be used
to evaluate truck tractor and large bus systems' ability to prevent
rollover and loss-of-control crashes. Therefore, for the purpose of
this proposal, the effectiveness of ESC and RSC systems on large buses
was assumed to be identical to the performance of systems on truck
tractors.

B. Target Crash Population

    The initial target crash population for estimating benefits
includes all crashes resulting in occupant fatalities, MAIS 1 and above
nonfatal injuries, and property damage only crashes that were the
result of either (a) first-event untripped rollover crashes and (b)
loss-of-control crashes (e.g., jackknife, cargo shift, avoiding,
swerving) that involved truck tractors or large buses and might be
prevented if the subject vehicle were equipped with a stability control
system. For this analysis, particularly in multi-vehicle crashes, the
subject vehicle is the at-fault or striking vehicle. The initial target
crash populations were retrieved from the 2006-2008 Fatality Analysis
Reporting System (FARS) and General Estimate System (GES). The FARS
data were used for evaluating fatal crashes and the GES data were used
for evaluating nonfatal crashes. The injury data were converted to MAIS
format and the following number of crashes, fatalities, injuries, and
deaths were estimated.

     Table 5--Initial Target Crashes, MAIS Injuries, and Property Damage Only Vehicle Crashes by Crash Type
----------------------------------------------------------------------------------------------------------------
                                                                                MAIS 1-5
                   Crash type                         Crashes       Fatalities       Injuries          PDOVs
----------------------------------------------------------------------------------------------------------------
Rollover........................................           5,510             111           2,217           3,297
Loss of control.................................           4,803             216           1,141           3,935
                                                 ---------------------------------------------------------------
      Total.....................................          10,313             327           3,358           7,332
----------------------------------------------------------------------------------------------------------------
Source: 2006-2008 FARS, 2006-2008 GES.
PDOVs: property damage only vehicles.

    The 2006-2008 crash data were then adjusted to take account of ESC
and RSC system installation rates in 2006-2008 and in model year 2012.
To determine the number of crashes that could be prevented by requiring
that ESC systems be installed on new truck tractors, the agency had to
consider two subsets of the total crash population--those vehicles that
would not be equipped with stability control systems (Base 1
population) and those vehicles that would be equipped with RSC systems
(Base 2 population). The Base 1 population would benefit fully from
this proposal. However, the Base 2 population would benefit only from
the incremental increased effectiveness of ESC systems over RSC
systems.
    Based upon data obtained from industry, the agency estimates that
about 1.9 percent of truck tractors in the on-road fleet in 2008 were
equipped with ESC systems and 3.3 percent were equipped with RSC
systems. Based upon manufacturer production estimates, about 26.2
percent of truck tractors manufactured in model year 2012 would be
equipped with ESC systems and 16.0 percent would be equipped with RSC
systems. Adjusting the initial target crash populations using these
estimates, the agency was able to estimate the Base 1 and Base 2
populations and the projected target crash population (Base 1 + Base 2)
expressed in the following table.

    Table 6--Projected Crashes, MAIS Injuries, and Property Damage Only Vehicle Crashes by Crash Type, Crash
                           Severity, Injury Severity, and Vehicle Type for 2012 Level
----------------------------------------------------------------------------------------------------------------
                                                                                MAIS 1-5
                   Crash type                         Crashes       Fatalities       Injuries          PDOVs
----------------------------------------------------------------------------------------------------------------
                                                     Base 1
----------------------------------------------------------------------------------------------------------------
Rollover........................................           3,263              66           1,313           1,952
Loss of Control.................................           2,786             125             662           2,283
                                                 ---------------------------------------------------------------
    Total.......................................           6,049             191           1,975           4,235
----------------------------------------------------------------------------------------------------------------
                                                     Base 2
----------------------------------------------------------------------------------------------------------------
Rollover........................................             903              18             364             540
Loss of Control.................................             771              35             183             632
                                                 ---------------------------------------------------------------
    Total.......................................           1,674              53             547           1,172
----------------------------------------------------------------------------------------------------------------
                                  Base 1 + Base 2 (Projected Target Population)
----------------------------------------------------------------------------------------------------------------
Rollover........................................           4,166              84           1,677           2,492
Loss of Control.................................           3,557             160             845           2,915
                                                 ---------------------------------------------------------------
    Total.......................................           7,723             244           2,522           5,407
----------------------------------------------------------------------------------------------------------------
Source: 2006-2008 FARS, 2006-2008 GES.
PDOVs: property damage only vehicles.

    The agency has also examined the same crash data sources for large
buses. Based upon this examination, the agency estimates that an
average of one target bus rollover and one target bus loss-of-control
crash occurs per year that would be affected by this proposal.

C. Benefits Estimate

    ESC systems are crash avoidance countermeasures that would mitigate
and even prevent crashes. Preventing a crash not only would save lives
and reduce injuries, it also would alleviate crash-related travel
delays and property damage. Therefore, the estimated benefits include
both injury and non-injury components. The injury benefits are the
estimated fatalities and injuries that would be mitigated or eliminated
by ESC. The non-injury benefits include the travel delay and property
damage savings from crashes that were avoided by ESC. Savings from
reducing property-damage-only vehicle crashes also were included in the
non-injury benefits.
    The benefits estimates for rollover crashes are presented in a
range in this analysis. This is the result of a range of ESC
effectiveness figures in addressing rollover crashes that were used for
the analysis. In contrast, at the publication, there is only one
effectiveness estimate for addressing loss-of-control crashes.
    The benefits of this proposal were derived by multiplying the
projected target population by the corresponding effectiveness rates.
As shown in Table 7, this proposal would prevent 1,807 to 2,329 target
crashes, 49 to 60 fatalities, and 649 to 858 MAIS 1-5 injuries.
Furthermore, the proposal would eliminate 1,187 to 1,499 property-
damage-only crashes. Table 7 presents the benefits by target crash
type.

                                   Table 7--Estimated Benefits of the Proposal
----------------------------------------------------------------------------------------------------------------
                                                                                MAIS 1-5
                   Crash type                         Crashes       Fatalities       Injuries          PDOVs
----------------------------------------------------------------------------------------------------------------
                                                 Base 1 Benefits
----------------------------------------------------------------------------------------------------------------
Rollover........................................     1,305-1,827           26-37         526-735       781-1,093
Loss of Control.................................             390              18              93             320
                                                 ---------------------------------------------------------------
Total...........................................     1,695-2,217           44-55         619-828     1,101-1,413
----------------------------------------------------------------------------------------------------------------
                                                 Base 2 Benefits
----------------------------------------------------------------------------------------------------------------
Rollover........................................              27               1              11              16
Loss of Control.................................              85               4              19              70
                                                 ---------------------------------------------------------------
    Total.......................................             112               5              30              86
----------------------------------------------------------------------------------------------------------------
                                   Benefits of the Proposal (Base 1 + Base 2)
----------------------------------------------------------------------------------------------------------------
Rollover........................................     1,332-1,854           27-38         537-746       797-1,109
Loss of Control.................................             475              22             112             390
                                                 ---------------------------------------------------------------
    Total.......................................     1,807-2,329           49-60         649-858     1,187-1,499
----------------------------------------------------------------------------------------------------------------
Source: 2006-2008 FARS, 2006-2008 GES.
PDOVs: property damage only vehicles.

    The non-injury benefits also include savings from the elimination
of crash-related travel delay and vehicle property damage. Table 8
shows the total travel delay and property damage savings from this
proposal, broken down by target crash type. These benefits were derived
by determining the unit cost of property damage and travel delay for
each level of crash severity (e.g., fatal, MAIS 1-5, or property damage
only) and multiplying that cost by the number of incidents of each type
of crash prevented. As shown in Table 8, this proposal would save
(undiscounted) $17.1 to $22.0 million from travel delays and property
damage as a result of crashes that would be prevented by this proposal.

                             Table 8--Total Travel Delay and Property Damage Savings
                                              [Undiscounted 2010 $]
----------------------------------------------------------------------------------------------------------------
                                                                                Property damage +
                                                        Property damage      Travel delay        travel delay
----------------------------------------------------------------------------------------------------------------
Rollover--Lower Bound...............................          $7,713,841          $4,655,187         $12,369,028
Rollover--Upper Bound...............................          10,735,872           6,475,446          17,211,318
Loss of Control.....................................           3,006,977           1,765,804           4,772,781
                                                     -----------------------------------------------------------
Total--Lower Bound..................................          10,720,818           6,420,991          17,141,809
                                                     -----------------------------------------------------------
Total-Upper Bound...................................          13,742,849           8,241,250          21,984,099
----------------------------------------------------------------------------------------------------------------

D. Cost Estimate

    The cost of this proposal is derived from the product of the
average unit cost of an ESC system and the number of vehicles affected
by this proposal. The number of vehicles affected by this proposal
would include vehicles that would have no stability control systems and
vehicles that would be equipped with RSC systems. Therefore, when
considering vehicles equipped with RSC systems, the average cost would
be the difference between the cost of an ESC system and the cost of an
RSC system.
    Based upon data received from manufacturers, the agency estimates
that the average unit cost for an ESC system is $1,160 and the average
unit cost for an RSC system is $640; therefore, the incremental cost of
installing an ESC system instead of an RSC system is $520 per vehicle.
The agency did not receive cost information from large bus
manufacturers. However, because the components used on truck tractors
and buses are nearly identical, the unit cost estimates for truck
tractors are used for buses.
    The agency has estimated that 150,000 truck tractors and 2,200
buses covered by this proposal would be produced in model year 2012. As
stated earlier, the agency estimates that 26.2 percent of truck
tractors and 80 percent of buses covered by this proposal manufactured
in model year 2012 would be equipped with ESC systems. In addition,
16.5 percent of truck tractors would be equipped with RSC systems.
Accordingly, 57.8 percent of truck tractors and 20 percent of buses
would be required to be equipped with an ESC system and 16.5 percent of
truck tractors would be required to upgrade from an RSC system to an
ESC system.
    Table 9 summarizes the costs of this proposal based on the
estimated unit cost of an ESC system and the number of vehicles that
would need to be equipped with ESC systems. As shown in Table 10, the
incremental cost of providing ESC systems compared to manufacturers'
planned production in model year 2012 would cost $113.1 million for
truck tractors and $0.5 million for large buses. Therefore, the total
cost of this proposal is estimated to be $113.6 million.

                                  Table 9--Annual Total Costs for the Proposal
                                                    [2010 $]
----------------------------------------------------------------------------------------------------------------
                                                                       Technology upgrade needed
                                                     -----------------------------------------------------------
                                                             None           Incremental ESC           ESC
----------------------------------------------------------------------------------------------------------------
Truck Tractors:
    % Needing Upgrade...............................               26.2%               16.0%               57.8%
    150,000 Sales Estimated.........................              39,300              24,000              86,700
    Costs per Affected Vehicle......................                   0                $520              $1,160
                                                     -----------------------------------------------------------
        Total Costs.................................                   0             $12.5 M            $100.6 M
Large Buses:
    % Needing Upgrade...............................                 80%                  0%                 20%
    2,200 Sales Estimated...........................               1,760                   0                 440
    Costs per Affected Vehicle......................                   0                $520              $1,160
                                                     -----------------------------------------------------------
        Total Costs.................................                   0                   0              $0.5 M
----------------------------------------------------------------------------------------------------------------
M: million.

                   Table 10--Summary of Vehicle Costs
                                [2010 $]
------------------------------------------------------------------------
                                                     Average
                                                     vehicle     Total
                                                      costs      costs
------------------------------------------------------------------------
Truck Tractors....................................     $753.7   $113.1 M
Large Buses.......................................      232.0      0.5 M
                                                   ---------------------
    Total.........................................      746.1    113.6 M
------------------------------------------------------------------------
M: million.

    We also note that manufacturers may incur costs to certify their
vehicles as compliant with the proposed standard. We have estimated the
cost to conduct the proposed test maneuvers. We believe that the
execution of the proposed SIS and SWD maneuvers would cost
approximately $15,000 per test, assuming access to test facilities,
tracks, and vehicles. Because it is not possible to anticipate how many
tests manufacturers might choose to run to certify a specific make,
model, and configuration, the agency cannot estimate the total
compliance costs for manufacturers. However, compliance costs are
implicitly included in the estimated consumer cost, which includes a
150% markup to account for fixed and overhead costs.

E. Cost Effectiveness

    Safety benefits can occur at any time during the vehicle's
lifetime. Therefore, the benefits are discounted at both 3 and 7
percent to reflect their values in 2010 dollars, as reflected in Table
11. Table 11 also shows that the net cost per equivalent life saved
from this proposal ranged from $1.5 to $2.0 million at a 3 percent
discount rate and from $2.0 to $2.6 million at a 7 percent discount
rate. The net benefits of this proposal are estimated to range from
$228 to $310 million at a 3 percent discount rate and from $155 to $222
million at a 7 percent discount rate.

                    Table 11--Summary of Cost-Effectiveness and Net Benefits by Discount Rate
                                                    [2010 $]
----------------------------------------------------------------------------------------------------------------
                                                      3% Discount                         7% Discount
                                         -----------------------------------------------------------------------
                                                 Low              High               Low              High
----------------------------------------------------------------------------------------------------------------
Fatal Equivalents.......................                51                63                40                50
Injury Benefits.........................      $328,197,087      $405,419,931      $257,409,480      $321,761,850
Property Damage and Travel Delay Savings       $13,862,581       $17,778,541       $11,006,756       $14,115,990
Vehicle Costs *.........................      $113,562,400      $113,562,400      $113,562,400      $113,562,400
Net Costs...............................       $99,699,819       $95,783,859      $102,555,644       $99,446,410
Net Cost Per Fatal Equivalent...........        $1,954,898        $1,520,379        $2,563,891        $1,988,928
Net Benefits............................      $228,497,268      $309,636,072      $154,853,836      $222,315,440
----------------------------------------------------------------------------------------------------------------
* Vehicle costs are not discounted, since they occur when the vehicle is purchased, whereas benefits occur over
  the vehicle's lifetime and are discounted back to the time of purchase.

F. Comparison of Regulatory Alternatives

    The agency considered two alternatives to the proposal. The first
alternative was requiring RSC systems be installed on all newly
manufactured truck tractors and buses covered by this proposal. The
second alternative was requiring RSC systems be installed on all newly
manufactured trailers.
    Regarding the first alternative, requiring RSC systems be installed
on truck tractors and large buses, our research has concluded that RSC
systems are less effective than ESC systems. Overall for the target
crash population, our research has indicated that RSC systems have a 21
to 30 percent effectiveness rate, whereas ESC systems have a 28 to 36
percent effectiveness rate. An RSC system is only slightly less
effective at preventing rollover crashes than an ESC system (37 to 53
percent versus 40 to 56 percent effective, respectively), but it is
much less effective at preventing loss of control crashes (3 percent
versus 14 percent). However, RSC systems are only estimated to cost
$640 per unit, whereas ESC systems are estimated to cost $1,160 per
unit. Furthermore, only approximately 57.8% of truck tractors would be
required to install RSC systems based on the data discussed earlier
regarding manufacturers' plans.
    A summary of the cost effectiveness of RSC systems is set forth in
Table 12. When comparing this alternative to the regulatory proposal,
requiring RSC systems rather than ESC systems would be slightly more
cost effective. However, this alternative would save fewer lives and
have lower net benefits than this proposal.

Table 12--Summary of Cost-Effectiveness and Net Benefits by Discount Rate Alternative 1--Requiring Tractor-Based
                                                   RSC Systems
                                                    [2010 $]
----------------------------------------------------------------------------------------------------------------
                                                   3% Discount                           7% Discount
                                     ---------------------------------------------------------------------------
                                             Low                High               Low                High
----------------------------------------------------------------------------------------------------------------
Fatal Equivalents...................                 31                 43                 24                 34
Injury Benefits.....................       $199,492,347       $276,715,191       $154,445,688       $218,798,058
Property Damage and Travel Delay             $9,714,383        $13,649,563         $7,713,126        $10,837,621
 Savings............................
Vehicle Costs *.....................        $55,769,600        $55,769,600        $55,769,600        $55,769,600
Net Costs...........................        $46,055,217        $42,120,037        $48,056,474        $44,931,979
Net Cost Per Fatal Equivalent.......         $1,485,652           $979,536         $2,002,353         $1,321,529
Net Benefits........................       $153,437,130       $234,595,154       $106,389,214       $173,866,079
----------------------------------------------------------------------------------------------------------------
* Vehicle costs are not discounted, since they occur when the vehicle is purchased, whereas benefits occur over
  the vehicle's lifetime and are discounted back to the time of purchase.

    The second alternative considered was requiring trailer-based RSC
systems to be installed on all newly manufactured trailers. Trailer-
based RSC systems would only be expected to prevent rollover crashes.
Based on 2006-2008 GES data, 98 percent of the target truck-tractor
crashes involve truck tractors with trailers attached. Therefore, the
base crash population would be 98 percent of Base 1 discussed above.
    As discussed in the proposal, it became apparent during testing
that trailer-based stability control systems were less effective than
tractor-based systems because trailer-based systems could only control
the trailer's brakes. Based upon the agency's test data, it is
estimated that the effectiveness of trailer-based RSC systems in
preventing rollover crashes is 7 to 10 percent. Therefore, the benefits
of trailer-based RSC systems in preventing rollover are about 17.2
percent of tractor-based ESC systems.
    The agency estimates that about 203,000 new trailers are
manufactured each year. Further, based on information from
manufacturers, the agency estimates that a trailer-based RSC system
would cost $400 per trailer. Available data indicates that less than
0.2 percent of the current annual production of trailers comes with RSC
systems installed. Assuming all new trailers would be required to
install RSC, the cost of this alternative is estimated to be $81.2
million.
    Table 13 sets forth a summary of the cost effectiveness of trailer-
based RSC systems. Because the operational life of a trailer
(approximately 45 years) is much longer than that of a truck tractor,
it would take longer for trailer-based RSC systems to fully penetrate
the fleet than it would for any tractor-based system. Therefore, when
the benefits of trailer-based RSC systems are discounted at a 3 and 7
percent rate, there is a much higher discount factor. As can be seen in
Table 13, this results in this alternative having negative net benefits
and a high cost per life saved. Also, this alternative would have no
effect on buses. Accordingly, the agency does not favor this
alternative.

Table 13--Summary of Cost-Effectiveness and Net Benefits by Discount Rate Alternative 2--Requiring Trailer-Based
                                                   RSC Systems
                                                    [2010 $]
----------------------------------------------------------------------------------------------------------------
                                                 At 3% Discount                        At 7% Discount
                                     ---------------------------------------------------------------------------
                                             Low                High               Low                High
----------------------------------------------------------------------------------------------------------------
Fatal Equivalents...................                  5                  7                  3                  5
Injury Benefits.....................        $30,754,672        $43,935,246        $20,700,937        $29,572,767
Property Damage and Travel Delay             $1,459,169         $2,038,560           $982,165         $1,372,153
 Savings............................
Vehicle Costs *.....................        $81,200,000        $81,200,000        $81,200,000        $81,200,000
Net Costs...........................        $79,740,831        $79,161,440        $80,217,835        $79,827,847
Net Cost Per Fatal Equivalent.......        $15,948,166        $11,308,777        $26,739,278        $15,965,569
Net Benefits........................       -$48,986,159       -$35,226,194       -$59,516,898       -$50,255,080
----------------------------------------------------------------------------------------------------------------
* Vehicle costs are not discounted, since they occur when the vehicle is purchased, whereas benefits occur over
  the vehicle's lifetime and are discounted back to the time of purchase.

    The information in Tables 12 and 13 can be contrasted with this
proposal. A summary of the total costs and benefits and annualized
costs and benefits of this proposal appears in Table 14.

                                              Table 14--Estimated Total Costs and Benefits of the Proposal
                                                              [In millions of 2010 dollars]
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Property damage      Cost per
                                                                   Total costs     Injury benefits  and travel delay   equivalent live    Net benefits
                                                                                savings            saved
--------------------------------------------------------------------------------------------------------------------------------------------------------
At 3% Discount................................................            $113.6         $328-$405       $13.9-$17.8         $1.5-$2.0         $228-$310
At 7% Discount................................................             113.6           257-322         11.0-14.1           2.0-2.6           155-222
--------------------------------------------------------------------------------------------------------------------------------------------------------

VII. Public Participation

How do I prepare and submit comments?

    Your comments must be written and in English. To ensure that your
comments are correctly filed in the Docket, please include the docket
number of this document in your comments.
    Your comments must not be more than 15 pages long (49 CFR 553.21).
We established this limit to encourage you to write your primary
comments in a concise fashion. However, you may attach necessary
additional documents to your comments. There is no limit on the length
of the attachments.
    Please submit two copies of your comments, including the
attachments, to Docket Management at the beginning of this document,
under ADDRESSES. You may also submit your comments electronically to
the docket following the steps outlined under ADDRESSES.

How can I be sure that my comments were received?

    If you wish Docket Management to notify you upon its receipt of
your comments, enclose a self-addressed, stamped postcard in the
envelope containing your comments. Upon receiving your comments, Docket
Management will return the postcard by mail.

How do I submit confidential business information?

    If you wish to submit any information under a claim of
confidentiality, you should submit the following to the NHTSA Office of
Chief Counsel (NCC-110), 1200 New Jersey Avenue SE., Washington, DC
20590: (1) A complete

copy of the submission; (2) a redacted copy of the submission with the
confidential information removed; and (3) either a second complete copy
or those portions of the submission containing the material for which
confidential treatment is claimed and any additional information that
you deem important to the Chief Counsel's consideration of your
confidentiality claim. A request for confidential treatment that
complies with 49 CFR Part 512 must accompany the complete submission
provided to the Chief Counsel. For further information, submitters who
plan to request confidential treatment for any portion of their
submissions are advised to review 49 CFR part 512, particularly those
sections relating to document submission requirements. Failure to
adhere to the requirements of Part 512 may result in the release of
confidential information to the public docket. In addition, you should
submit two copies from which you have deleted the claimed confidential
business information, to Docket Management at the address given at the
beginning of this document under ADDRESSES.

Will the Agency consider late comments?

    We will consider all comments that Docket Management receives
before the close of business on the comment closing date indicated at
the beginning of this notice under DATES. In accordance with our
policies, to the extent possible, we will also consider comments that
Docket Management receives after the specified comment closing date. If
Docket Management receives a comment too late for us to consider in
developing the proposed rule, we will consider that comment as an
informal suggestion for future rulemaking action.

How can I read the comments submitted by other people?

    You may read the comments received by Docket Management at the
address and times given near the beginning of this document under
ADDRESSES.
    You may also see the comments on the Internet. To read the comments
on the Internet, go to http://www.regulations.gov and follow the on-
line instructions provided.
    You may download the comments. The comments are imaged documents,
in either TIFF or PDF format. Please note that even after the comment
closing date, we will continue to file relevant information in the
Docket as it becomes available. Further, some people may submit late
comments. Accordingly, we recommend that you periodically search the
Docket for new material.

VIII. Regulatory Analyses and Notices

A. Executive Order 12866, Executive Order 13563, and DOT Regulatory
Policies and Procedures

    NHTSA has considered the impact of this rulemaking action under
Executive Order 12866, Executive Order 13563, and the Department of
Transportation's regulatory policies and procedures. This rulemaking is
considered economically significant and was reviewed by the Office of
Management and Budget under E.O. 12866, ``Regulatory Planning and
Review.'' The rulemaking action has also been determined to be
significant under the Department's regulatory policies and procedures.
NHTSA has placed in the docket a Preliminary Regulatory Impact Analysis
(PRIA) describing the benefits and costs of this rulemaking action. The
benefits and costs are summarized in section VI of this preamble.
    Consistent with Executive Order 13563 and to the extent permitted
under the Vehicle Safety Act, we have considered the cumulative effects
of the new regulations stemming from NHTSA's 2007 ``NHTSA's Approach to
Motorcoach Safety'' plan and DOT's 2009 Motorcoach Safety Action Plan,
and have taken steps to identify opportunities to harmonize and
streamline those regulations. By coordinating the timing and content of
the rulemakings, our goal is to expeditiously maximize the net benefits
of the regulations (by either increasing benefits or reducing costs or
a combination of the two) while simplifying requirements on the public
and ensuring that the requirements are justified. We seek to ensure
that this coordination will also simplify the implementation of
multiple requirements on a single industry.
    NHTSA's Motorcoach Safety Action Plan identified four priority
areas--passenger ejection, rollover structural integrity, emergency
egress, and fire safety. There have been other initiatives on large bus
performance, such as ESC systems--an action included in the DOT plan--
and an initiative to update the large bus tire standard.\58\ In
deciding how best to initiate and coordinate rulemaking in these areas,
NHTSA examined various factors including the benefits that would be
achieved by the rulemakings, the anticipated vehicle designs and
countermeasures needed to comply with the regulations, and the extent
to which the timing and content of the rulemakings could be coordinated
to lessen the need for multiple redesign and to lower overall costs.
After this examination, we decided on a course of action that
prioritized the goal of reducing passenger ejection and increasing
frontal impact protection because many benefits could be achieved
expeditiously with countermeasures that were readily available (using
bus seats with integral seat belts, which are already available from
seat suppliers) and whose installation would not significantly impact
other vehicle designs. Similarly, we have also determined that an ESC
rulemaking would present relatively few synchronization issues with
other rules, because the vehicles at issue already have the foundation
braking systems needed for the stability control technology and the
additional equipment necessary for an ESC system are sensors that are
already available and that can be installed without significant impact
on other vehicle systems. Further, we estimate that 80 percent of the
affected buses already have ESC systems. We realize that a rollover
structural integrity rulemaking, or an emergency egress rulemaking,
could involve more redesign of vehicle structure than rules involving
systems such as seat belts, ESC, or tires.\59\ Our decision-making in
these and all the rulemakings outlined in the ``NHTSA's Approach to
Motorcoach Safety'' plan and DOT's Motorcoach Safety Action Plan will
be cognizant of the timing and content of the actions so as to simplify
requirements applicable to the public and private sectors, ensure that
requirements are justified, and increase the net benefits of the
resulting safety standards.
---------------------------------------------------------------------------

    \58\ 75 FR 60037 (Sept. 29, 2010).
    \59\ The initiative on fire safety is in a research phase.
Rulemaking resulting from the research will not occur in the near
term.
---------------------------------------------------------------------------

B. Regulatory Flexibility Act

    Pursuant to the Regulatory Flexibility Act (5 U.S.C. 601 et seq.,
as amended by the Small Business Regulatory Enforcement Fairness Act
(SBREFA) of 1996), whenever an agency is required to publish a notice
of rulemaking for any proposed or final rule, it must prepare and make
available for public comment a regulatory flexibility analysis that
describes the effect of the rule on small entities (i.e., small
businesses, small organizations, and small governmental jurisdictions).
The Small Business Administration's regulations at 13 CFR Part 121
define a small business, in part, as a business entity ``which operates
primarily within the United States.'' (13 CFR 121.105(a)).

No regulatory flexibility analysis is required if the head of an agency
certifies the rule will not have a significant economic impact on a
substantial number of small entities. SBREFA amended the Regulatory
Flexibility Act to require Federal agencies to provide a statement of
the factual basis for certifying that a rule will not have a
significant economic impact on a substantial number of small entities.
    NHTSA has considered the effects of this NPRM under the Regulatory
Flexibility Act. I certify that this NPRM will not have a significant
economic impact on a substantial number of small entities. This
proposed rule would directly impact manufacturers of truck-tractors,
large buses, and stability control systems for those vehicles. NHTSA
believes these entities do not qualify as small entities.

C. Executive Order 13132 (Federalism)

    NHTSA has examined today's final rule pursuant to Executive Order
13132 (64 FR 43255, August 10, 1999) and concluded that no additional
consultation with States, local governments or their representatives is
mandated beyond the rulemaking process. The agency has concluded that
the rulemaking would not have sufficient federalism implications to
warrant consultation with State and local officials or the preparation
of a federalism summary impact statement. The final rule would not have
``substantial direct effects on the States, on the relationship between
the national government and the States, or on the distribution of power
and responsibilities among the various levels of government.''
    NHTSA rules can preempt in two ways. First, the National Traffic
and Motor Vehicle Safety Act contains an express preemption provision:
When a motor vehicle safety standard is in effect under this chapter, a
State or a political subdivision of a State may prescribe or continue
in effect a standard applicable to the same aspect of performance of a
motor vehicle or motor vehicle equipment only if the standard is
identical to the standard prescribed under this chapter. 49 U.S.C.
30103(b)(1). It is this statutory command by Congress that preempts any
non-identical State legislative and administrative law addressing the
same aspect of performance.
    The express preemption provision described above is subject to a
savings clause under which ``[c]ompliance with a motor vehicle safety
standard prescribed under this chapter does not exempt a person from
liability at common law.'' 49 U.S.C. 30103(e). Pursuant to this
provision, State common law tort causes of action against motor vehicle
manufacturers that might otherwise be preempted by the express
preemption provision are generally preserved. However, the Supreme
Court has recognized the possibility, in some instances, of implied
preemption of such State common law tort causes of action by virtue of
NHTSA's rules, even if not expressly preempted. This second way that
NHTSA rules can preempt is dependent upon there being an actual
conflict between an FMVSS and the higher standard that would
effectively be imposed on motor vehicle manufacturers if someone
obtained a State common law tort judgment against the manufacturer,
notwithstanding the manufacturer's compliance with the NHTSA standard.
Because most NHTSA standards established by an FMVSS are minimum
standards, a State common law tort cause of action that seeks to impose
a higher standard on motor vehicle manufacturers will generally not be
preempted. However, if and when such a conflict does exist--for
example, when the standard at issue is both a minimum and a maximum
standard--the State common law tort cause of action is impliedly
preempted. See Geier v. American Honda Motor Co., 529 U.S. 861 (2000).
    Pursuant to Executive Order 13132 and 12988, NHTSA has considered
whether this rule could or should preempt State common law causes of
action. The agency's ability to announce its conclusion regarding the
preemptive effect of one of its rules reduces the likelihood that
preemption will be an issue in any subsequent tort litigation.
    To this end, the agency has examined the nature (e.g., the language
and structure of the regulatory text) and objectives of today's rule
and finds that this rule, like many NHTSA rules, prescribes only a
minimum safety standard. As such, NHTSA does not intend that this rule
preempt state tort law that would effectively impose a higher standard
on motor vehicle manufacturers than that established by today's rule.
Establishment of a higher standard by means of State tort law would not
conflict with the minimum standard announced here. Without any
conflict, there could not be any implied preemption of a State common
law tort cause of action.

D. Executive Order 12988 (Civil Justice Reform)

    With respect to the review of the promulgation of a new regulation,
section 3(b) of Executive Order 12988, ``Civil Justice Reform'' (61 FR
4729; Feb. 7, 1996), requires that Executive agencies make every
reasonable effort to ensure that the regulation: (1) Clearly specifies
the preemptive effect; (2) clearly specifies the effect on existing
Federal law or regulation; (3) provides a clear legal standard for
affected conduct, while promoting simplification and burden reduction;
(4) clearly specifies the retroactive effect, if any; (5) specifies
whether administrative proceedings are to be required before parties
file suit in court; (6) adequately defines key terms; and (7) addresses
other important issues affecting clarity and general draftsmanship
under any guidelines issued by the Attorney General. This document is
consistent with that requirement.
    Pursuant to this Order, NHTSA notes as follows. The issue of
preemption is discussed above. NHTSA notes further that there is no
requirement that individuals submit a petition for reconsideration or
pursue other administrative proceedings before they may file suit in
court.

E. Protection of Children From Environmental Health and Safety Risks

    Executive Order 13045, ``Protection of Children from Environmental
Health and Safety Risks'' (62 FR 19855, April 23, 1997), applies to any
rule that: (1) Is determined to be ``economically significant'' as
defined under Executive Order 12866, and (2) concerns an environmental,
health, or safety risk that the agency has reason to believe may have a
disproportionate effect on children. If the regulatory action meets
both criteria, the agency must evaluate the environmental health or
safety effects of the planned rule on children, and explain why the
planned regulation is preferable to other potentially effective and
reasonably feasible alternatives considered by the agency.
    This notice is part of a rulemaking that is not expected to have a
disproportionate health or safety impact on children. Consequently, no
further analysis is required under Executive Order 13045.

F. Paperwork Reduction Act

    Under the Paperwork Reduction Act of 1995 (PRA), a person is not
required to respond to a collection of information by a Federal agency
unless the collection displays a valid OMB control number. There is not
any information collection requirement associated with this NPRM.

G. National Technology Transfer and Advancement Act

    Section 12(d) of the National Technology Transfer and Advancement
Act (NTTAA) requires NHTSA to evaluate and use existing voluntary
consensus standards in its regulatory activities unless doing so would
be inconsistent with applicable law (e.g., the statutory provisions
regarding NHTSA's vehicle safety authority) or otherwise impractical.
Voluntary consensus standards are technical standards developed or
adopted by voluntary consensus standards bodies. Technical standards
are defined by the NTTAA as ``performance-based or design-specific
technical specification and related management systems practices.''
They pertain to ``products and processes, such as size, strength, or
technical performance of a product, process or material.''
    Examples of organizations generally regarded as voluntary consensus
standards bodies include ASTM International, the Society of Automotive
Engineers (SAE), and the American National Standards Institute (ANSI).
If NHTSA does not use available and potentially applicable voluntary
consensus standards, we are required by the Act to provide Congress,
through OMB, an explanation of the reasons for not using such
standards.
    This NPRM proposes to require truck tractors and large buses to
have electronic stability control systems. In the proposed definitional
requirement, the agency adapted the criteria from the light vehicle ESC
rulemaking, which was based on (with minor modifications) SAE Surface
Vehicle Information Report on Automotive Stability Enhancement Systems
J2564 Rev JUN2004 that provides an industry consensus definition of an
ESC system. In addition, SAE International has a Recommended Practice
on Brake Systems Definitions--Truck and Bus, J2627 AUG2009 that has
been incorporated into the agency's definition. The agency has also
incorporated by reference two ASTM standards in order to provide
specifications for the road test surface. These are: (1) ASTM E1136-93
(Reapproved 2003), ``Standard Specification for a Radial Standard
Reference Test Tire,'' and (2) ASTM E1337-90 (Reapproved 2008),
``Standard Test Method for Determining Longitudinal Peak Braking
Coefficient of Paved Surfaces Using a Standard Reference Test Tire.''

H. Unfunded Mandates Reform Act

    Section 202 of the Unfunded Mandates Reform Act of 1995 (UMRA)
requires federal agencies to prepare a written assessment of the costs,
benefits, and other effects of proposed or final rules that include a
Federal mandate likely to result in the expenditure by State, local, or
tribal governments, in the aggregate, or by the private sector, of more
than $100 million annually (adjusted for inflation with base year of
1995). Before promulgating a NHTSA rule for which a written statement
is needed, section 205 of the UMRA generally requires the agency to
identify and consider a reasonable number of regulatory alternatives
and adopt the least costly, most cost-effective, or least burdensome
alternative that achieves the objectives of the rule. The provisions of
section 205 do not apply when they are inconsistent with applicable
law. Moreover, section 205 allows the agency to adopt an alternative
other than the least costly, most cost-effective, or least burdensome
alternative if the agency publishes with the final rule an explanation
of why that alternative was not adopted.
    This NPRM will not result in any expenditure by State, local, or
tribal governments or the private sector of more than $100 million,
adjusted for inflation. When $100 million is adjusted by the implicit
gross domestic product price deflator for the year 2010, the result is
$136 million. This NPRM is not subject to the requirements of sections
202 and 205 of the UMRA because it is not estimated to result in an
expenditure of more than $136 million annually by State, local, or
tribal governments or the private sector.

I. National Environmental Policy Act

    NHTSA has analyzed this rulemaking action for the purposes of the
National Environmental Policy Act. The agency has determined that
implementation of this action will not have any significant impact on
the quality of the human environment.

J. Plain Language

    Executive Order 12866 requires each agency to write all rules in
plain language. Application of the principles of plain language
includes consideration of the following questions:
     Have we organized the material to suit the public's needs?
     Are the requirements in the rule clearly stated?
     Does the rule contain technical language or jargon that
isn't clear?
     Would a different format (grouping and order of sections,
use of headings, paragraphing) make the rule easier to understand?
     Would more (but shorter) sections be better?
     Could we improve clarity by addling tables, lists, or
diagrams?
     What else could we do to make the rule easier to
understand?
    If you have any responses to these questions, please include them
in your comments on this proposal.

K. Regulatory Identifier Number (RIN)

    The Department of Transportation assigns a regulation identifier
number (RIN) to each regulatory action listed in the Unified Agenda of
Federal Regulations. The Regulatory Information Service Center
publishes the Unified Agenda in April and October of each year. You may
use the RIN contained in the heading at the beginning of this document
to find this action in the Unified Agenda.

L. Privacy Act

    Anyone is able to search the electronic form of all comments
received into any of our dockets by the name of the individual
submitting the comment (or signing the comment, if submitted on behalf
of an association, business, labor union, etc.). You may review DOT's
complete Privacy Act Statement in the Federal Register published on
April 11, 2000 (65 FR 19477-78).

List of Subjects in 49 CFR Part 571

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

Proposed Regulatory Text

    In consideration of the foregoing, we propose to amend 49 CFR part
571 to read as follows:

PART 571--FEDERAL MOTOR VEHICLE SAFETY STANDARDS

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

    Authority:  49 U.S.C. 322, 30111, 30115, 30166 and 30177;
delegation of authority at 49 CFR 1.50.

    2. Revise paragraphs (d)(32) and (d)(33) of Sec.  571.5 to read as
follows:

Sec.  571.5  Matter incorporated by reference.

* * * * *
    (d) * * *
    (32) ASTM E1136-93 (Reapproved 2003), ``Standard Specification for
a Radial Standard Reference Test Tire,'' approved March 15, 1993, into
Sec. Sec.  571.105; 571.121; 571.126; 571.135; 571.136; 571.139;
571.500.
    (33) ASTM E1337-90 (Reapproved 2008), ``Standard Test Method for

Determining Longitudinal Peak Braking Coefficient of Paved Surfaces
Using a Standard Reference Test Tire,'' approved June 1, 2008, into
Sec. Sec.  571.105; 571.121; 571.126; 571.135; 571.136; 571.500.
* * * * *
    3. Revise the heading of Sec.  571.126 to read as follows:

Sec.  571.126  Standard No. 126; Electronic stability control systems
for light vehicles.

* * * * *
    4. Add Sec.  571.136 to read as follows:

Sec.  571.136  Standard No. 136; Electronic stability control systems
for heavy vehicles.

    S1. Scope. This standard establishes performance and equipment
requirements for electronic stability control (ESC) systems on heavy
vehicles.
    S2. Purpose. The purpose of this standard is to reduce crashes
caused by rollover or by directional loss-of-control.
    S3. Application. This standard applies to truck tractors and buses
with a gross vehicle weight rating of greater than 11,793 kilograms
(26,000 pounds). However, it does not apply to:
    (a) Any truck tractor or bus equipped with an axle that has a gross
axle weight rating (GAWR) of 29,000 pounds or more;
    (b) Any truck tractor or bus that has a speed attainable in 2 miles
of not more than 33 mph;
    (c) Any truck tractor that has a speed attainable in 2 miles of not
more than 45 mph, an unloaded vehicle weight that is not less than 95
percent of its gross vehicle weight rating (GVWR), and no capacity to
carry occupants other than the driver and operating crew;
    (d) Any bus with fewer than 16 designated seating positions
(including the driver);
    (e) Any bus with fewer than 2 rows of passenger seats that are
rearward of the driver's seating position and are forward-facing or can
convert to forward-facing without the use of tools;
    (f) School buses; and
    (g) Any urban transit buses sold for operation as a common carrier
in urban transportation along a fixed route with frequent stops.
    S4. Definitions.
    Ackerman Steer Angle means the angle whose tangent is the wheelbase
divided by the radius of the turn at a very low speed.
    Electronic stability control system or ESC system means a system
that has all of the following attributes:
    (1) That augments vehicle directional stability by applying and
adjusting the vehicle brake torques individually at each wheel position
on at least one front and at least one rear axle of the vehicle to
induce correcting yaw moment to limit vehicle oversteer and to limit
vehicle understeer;
    (2) That enhances rollover stability by applying and adjusting the
vehicle brake torques individually at each wheel position on at least
one front and at least one rear axle of the vehicle to reduce lateral
acceleration of a vehicle;
    (3) That is computer-controlled with the computer using a closed-
loop algorithm to induce correcting yaw moment and enhance rollover
stability;
    (4) That has a means to determine the vehicle's lateral
acceleration;
    (5) That has a means to determine the vehicle's yaw rate and to
estimate its side slip or side slip derivative with respect to time;
    (6) That has a means to estimate vehicle mass or, if applicable,
combination vehicle mass;
    (7) That has a means to monitor driver steering inputs;
    (8) That has a means to modify engine torque, as necessary, to
assist the driver in maintaining control of the vehicle and/or
combination vehicle; and
    (9) That, when installed on a truck tractor, has the means to
provide brake pressure to automatically apply and modulate the brake
torques of a towed semi-trailer.
    Initial brake temperature means the average temperature of the
service brakes on the hottest axle of the vehicle immediately before
any stability control system test maneuver is executed.
    Lateral acceleration means the component of the vector acceleration
of a point in the vehicle perpendicular to the vehicle x axis
(longitudinal) and parallel to the road plane.
    Oversteer means a condition in which the vehicle's yaw rate is
greater than the yaw rate that would occur at the vehicle's speed as
result of the Ackerman Steer Angle.
    Peak friction coefficient or PFC means the ratio of the maximum
value of braking test wheel longitudinal force to the simultaneous
vertical force occurring prior to wheel lockup, as the braking torque
is progressively increased.
    Sideslip or side slip angle means the arctangent of the lateral
velocity of the center of gravity of the vehicle divided by the
longitudinal velocity of the center of gravity.
    Understeer means a condition in which the vehicle's yaw rate is
less than the yaw rate that would occur at the vehicle's speed as
result of the Ackerman Steer Angle.
    Yaw Rate means the rate of change of the vehicle's heading angle
measure in degrees per second of rotation about a vertical axis through
the vehicle's center of gravity.
    S5. Requirements. Each vehicle must be equipped with an ESC system
that meets the requirements specified in S5 under the test conditions
specified in S6 and the test procedures specified in S7 of this
standard.
    S5.1 Required Equipment. Each vehicle to which this standard
applies must be equipped with an electronic stability control system,
as defined in S4.
    S5.2 System Operational Capabilities.
    S5.2.1 An electronic stability control system must be operational
over the full speed range of the vehicle except at vehicle speeds less
than 20 km/h (12.4 mph), when being driven in reverse, or during system
initialization.
    S5.2.2 An electronic stability control system must remain capable
of activation even if the antilock brake system or traction control is
also activated.
    S5.3 Performance Requirements.
    S5.3.1 Slowly Increasing Steer Maneuver. During the slowly
increasing steer test maneuver performed under the test conditions of
S6 and the test procedure of S7.6, the vehicle with the ESC system
enabled must satisfy the engine torque reduction criteria of S<IP_ADDRESS>.
    S<IP_ADDRESS> The engine torque reduction when measured 1.5 seconds
after the activation of the electronic stability control system must be
at least 10 percent less than the engine torque requested by the
driver.
    S5.3.2 Sine With Dwell Maneuver. During each sine with dwell
maneuver performed under the test conditions of S6 and the test
procedure of S7.10, the vehicle with the ESC system enabled must
satisfy the roll stability criteria of S<IP_ADDRESS> and S<IP_ADDRESS>, the yaw
stability criteria of S<IP_ADDRESS> and S<IP_ADDRESS>, and the responsiveness
criterion of S<IP_ADDRESS> during each of those tests conducted with a
commanded steering wheel angle of 0.7A or greater, where A is the
steering wheel angle computed in S7.6.2.
    S<IP_ADDRESS> The lateral acceleration measured at 0.75 seconds after
completion of steer of the sine with dwell steering input must not
exceed 30 percent of the peak value of the lateral acceleration
recorded during the 2nd half of the sine maneuver (including the dwell
period), i.e., from time 1 second after the beginning of steer to the
completion of steer during the same test run.
    S<IP_ADDRESS> The lateral acceleration measured at 1.5 seconds after
completion of steer of the Sine With

Dwell steering input must not exceed 10 percent of the peak value of
the lateral acceleration recorded during the 2nd half of the sine
maneuver (including the dwell period), i.e., from time 1 second after
the BOS to the COS during the same test run.
    S<IP_ADDRESS> The yaw rate measured at 0.75 seconds after completion of
steer of the Sine With Dwell steering input must not exceed 40 percent
of the peak value of the yaw rate recorded during the 2nd half of the
sine maneuver (including the dwell period), i.e., from time 1 second
after the BOS to the COS during the same test run.
    S<IP_ADDRESS> The yaw rate measured at 1.5 seconds after completion of
steer of the Sine With Dwell steering input must not exceed 15 percent
of the peak value of the yaw rate recorded during the 2nd half of the
sine maneuver (including the dwell period), i.e., from time 1 second
after the BOS to the COS during the same test run.
    S<IP_ADDRESS> The lateral displacement of the vehicle center of gravity
with respect to its initial straight path must be at least 2.13 meters
(7 feet) for each truck tractor and at least 1.52 meters (5 feet) for
each bus when computed 1.5 seconds after the BOS.
    S<IP_ADDRESS>.1 The computation of lateral displacement is performed
using double integration with respect to time of the measurement of
lateral acceleration at the vehicle center of gravity, as expressed by
the formula:

Lateral Displacement = [int][int] AyCG dt

    S<IP_ADDRESS>.2 Time t = 0 for the integration operation is the instant
of steering initiation, known as the BOS.
    S5.4 ESC System Malfunction Detection. Each vehicle shall be
equipped with an indicator lamp, mounted in front of and in clear view
of the driver, which is activated whenever there is a malfunction that
affects the generation or transmission of control or response signals
in the vehicle's electronic stability control system.
    S5.4.1 The ESC malfunction telltale must illuminate only when a
malfunction exists and must remain continuously illuminated for as long
as the malfunction exists, whenever the ignition locking system is in
the ``On'' (``Run'') position.
    S5.4.2 The ESC Malfunction telltale must be identified by the
symbol shown for ``Electronic Stability Control System Malfunction'' or
the specified words or abbreviations listed in Table 1 of Standard No.
101 (49 CFR 571.101).
    S5.4.3 The ESC malfunction telltale must be activated as a check of
lamp function either when the ignition locking system is turned to the
``On'' (``Run'') position when the engine is not running, or when the
ignition locking system is in a position between the ``On'' (``Run'')
and ``Start'' that is designated by the manufacturer as a check
position.
    S5.4.4 The ESC malfunction telltale need not be activated when a
starter interlock is in operation.
    S5.4.5 The ESC malfunction telltale lamp must extinguish at the
next ignition cycle after the malfunction has been corrected.
    S5.5 ESC System Technical Documentation. To ensure that a vehicle
is equipped with an ESC system that meets the definition of ``ESC
System'' in S4, the vehicle manufacturer must make available to the
agency, upon request, the following documentation:
    S5.5.1 A system diagram that identifies all ESC system hardware.
The diagram must identify what components are used to generate brake
torques at each controlled wheel, determine vehicle lateral
acceleration and yaw rate, estimate side slip or the side slip
derivative, monitor driver steering inputs, and for a tractor, generate
the towed vehicle brake torques.
    S5.5.2 A written explanation describing the ESC system basic
operational characteristics. This explanation must include a discussion
of the system's capability to apply brake torques at each wheel, how
the system estimates vehicle mass, and how the system modifies engine
torque during ESC system activation. The explanation must also identify
the vehicle speed range and the driving phases (acceleration,
deceleration, coasting, during activation of ABS or traction control)
under which the ESC system can activate.
    S5.5.3 A logic diagram that supports the explanation provided in
S5.5.2.
    S5.5.4 Specifically for mitigating, avoiding, and preventing
vehicle rollover, oversteer, and understeer conditions, a discussion of
the pertinent inputs to the computer or calculations within the
computer and how its algorithm uses that information and controls ESC
system hardware to limit these loss of control conditions.
    S6. Test Conditions. The requirements of S5 shall be met by a
vehicle when it is tested according to the conditions set forth in the
S6. On vehicles equipped with automatic brake adjusters, the automatic
brake adjusters must remain activated at all times.
    S6.1 Ambient conditions.
    S6.1.1 The ambient temperature is between 7 [deg]C (45[emsp14]
[deg]F) and 40 [deg]C (104[emsp14] [deg]F).
    S6.1.2 The maximum wind speed is no greater than 5 m/s (11mph).
    S6.2 Road test surface.
    S6.2.1 The tests are conducted on a dry, uniform, solid-paved
surface. Surfaces with irregularities and undulations, such as dips and
large cracks, are unsuitable.
    S6.2.2 The road test surface produces a peak friction coefficient
(PFC) of 0.9 when measured using an American Society for Testing and
Materials (ASTM) E1136-93 (Reapproved 2003) standard reference test
tire (incorporated by reference,, in accordance with ASTM Method E
1337-90 (Reapproved 2002), at a speed of 64.4 km/h (40 mph), without
water delivery (both documents incorporated by reference, see Sec.
571.5).
    S6.2.3 The test surface has a consistent slope between 0% and 1%.
    S6.3 Vehicle conditions.
    S6.3.1 The ESC system is enabled for all testing, except for the
ESC Malfunction test in S7.11.
    S6.3.2 Test Weight.
    S<IP_ADDRESS> Truck tractors. The combined total weight of the truck
tractor and control trailer (specified in S6.3.4) is 80 percent of the
tractor GVWR. The tractor is loaded with the fuel tanks filled to at
least 75 percent capacity, test driver, test instrumentation, and a
ballasted control trailer with outriggers. Center of gravity of all
ballast on the control trailer is located directly above the kingpin.
The load distribution on non-steer axles is adjusted so that it is
proportional to the tractor's respective rear axles GAWRs by adjusting
the fifth wheel position, if adjustable. If the fifth wheel of the
truck tractor cannot be adjusted without exceeding a GAWR, ballast is
reduced so that axle load is equal to or less than the GAWR,
maintaining load proportioning as close as possible to specified
proportioning.
    S<IP_ADDRESS> Buses. A bus is loaded to a simulated multi-passenger
configuration. For this configuration the bus is loaded with the fuel
tanks filled to at least 75 percent capacity, test driver, test
instrumentation and simulated occupants in each of the vehicle's
designated seating positions. The simulated occupant loads are attained
by securing a 68-kg (150-lb) water dummy in each of the test vehicle's
designated seating positions without exceeding the vehicle's GVWR and
each axle's GAWR. If any rating is exceeded the ballast load is reduced
until the respective rating or ratings are no longer exceeded.
    S6.3.3 Transmission selector position. The transmission selector

control is in a forward gear during all maneuvers.
    S6.3.4 Control Trailer.
    S<IP_ADDRESS> The control trailer is an unbraked flatbed semi-trailer
that has a single axle with a GAWR of 8,165 kilograms (18,000 pounds)
and a length of 655 + 15 cm (258 + 6 inches) when measured from the
transverse centerline of the axle to the centerline of the kingpin.
    S<IP_ADDRESS> The center of gravity height of the ballast on the loaded
control trailer is less than 61 cm (24 inches) above the top of the
tractor's fifth wheel.
    S6.3.5 Tires. The vehicle is tested with the tires installed on the
vehicle at time of initial vehicle sale. The tires are inflated to the
vehicle manufacturer's recommended cold tire inflation pressure(s)
specified on the vehicle's certification label or the tire inflation
pressure label.
    S6.3.6 Outrigger. An outrigger is used for testing each vehicle.
The outrigger is designed with a maximum weight of 726 kg (1,600 lb),
excluding mounting fixtures.
    S6.3.7 Automated steering machine. A steering machine programmed to
execute the required steering pattern is used during the slowly
increasing steer and sine with dwell maneuvers. The steering machine is
capable of supplying steering torques between 40 to 60 Nm (29.5 to 44.3
lb-ft). The steering machine is able to apply these torques when
operating with steering wheel velocities up to 1200 degrees per second.
    S6.3.8 Truck Tractor Anti-jackknife System. The truck tractor is
equipped with anti-jackknife cables that allow a minimum articulation
angle of 45 degrees between the tractor and the control trailer.
    S6.3.9 Special drive conditions. A vehicle equipped with an
interlocking axle system or a front wheel drive system that is engaged
and disengaged by the driver is tested with the system disengaged.
    S6.3.10 Liftable axles. A vehicle with a liftable axle is tested
with the liftable axle down.
    S6.3.11 Initial brake temperature. The initial brake temperature is
not less than 65 [deg]C (150 [deg]F) and not more than 204 [deg]C (400
[deg]F).
    S6.3.12 Thermocouples. The brake temperature is measured by plug-
type thermocouples installed in the approximate center of the facing
length and width of the most heavily loaded shoe or disc pad, one per
brake. A second thermocouple may be installed at the beginning of the
test sequence if the lining wear is expected to reach a point causing
the first thermocouple to contact the rubbing surface of a drum or
rotor. The second thermocouple is installed at a depth of 0.080 inch
and located within 1.0 inch circumferentially of the thermocouple
installed at 0.040 inch depth. For center-grooved shoes or pads,
thermocouples are installed within 0.125 inch to 0.250 inch of the
groove and as close to the center as possible.
    S6.4 Selection of compliance options. Where manufacturer options
are specified, the manufacturer shall select the option by the time it
certifies the vehicle and may not thereafter select a different option
for the vehicle. Each manufacturer shall, upon request from the
National Highway Traffic Safety Administration, provide information
regarding which of the compliance options it has selected for a
particular vehicle or make/model.
    S7. Test Procedure.
    S7.1 Tire inflation. Inflate the vehicle's tires to the cold tire
inflation pressure(s) provided on the vehicle's certification label or
tire information label.
    S7.2 Telltale lamp check. With the vehicle stationary and the
ignition locking system in the ``Lock'' or ``Off'' position, activate
the ignition locking system to the ``On'' (``Run'') position or, where
applicable, the appropriate position for the lamp check. The ESC system
must perform a check of lamp function for the ESC malfunction telltale,
as specified in S5.3.3.
    S7.3 Mass Estimation Cycle. While driving in a straight line, one
stop is performed from a speed of 65 km/h (40 mph), with a target
longitudinal deceleration between 0.3-0.4g.
    S7.4 Tire Conditioning. Condition the tires using the following
procedure to wear away mold sheen and achieve operating temperature
immediately before beginning the Brake Conditioning, SIS and SWD
maneuver test runs.
    S7.4.1 The test vehicle is driven around a circle 46 meters (150
feet) in radius at a speed that produces a lateral acceleration of
approximately 0.1g for two clockwise laps followed by two
counterclockwise laps.
    S7.5 Brake Conditioning. Conditioning and warm-up the vehicle
brakes must be completed before and during execution of the SIS and SWD
maneuver test runs.
    S7.5.1 Prior to executing the first series of SIS maneuvers for a
test vehicle, the brakes are burnished according to the procedure in
S6.1.8 of Standard No. 121, Air brake systems.
    S7.5.2 After the brakes are burnished in accordance with S7.5.1,
initiate the vehicle compliance test according to S7.6. For a vehicle
on which a full FMVSS No. 121 compliance test was performed,
immediately prior to executing any slowly increasing steer or sine with
dwell maneuvers, the brakes are burnished using 40 brake application
snubs from a speed of 64 km/h (40 mph) to a speed of 32 km/h (20 mph),
with a target deceleration of approximately 0.3g. After each brake
application, accelerate to 64 km/h (40 mph) and maintain that speed
until making the next brake application at a point 1 mile from the
initial point of the previous brake application. At end of the 40
snubs, the hottest brake temperature is confirmed to be within the
temperature range of 65 [deg]C-204 [deg]C (150 [deg]F-400 [deg]F). If
the hottest brake temperature is above 204 [deg]C (400 [deg]F) a cool
down period is performed until the hottest brake temperature is
measured within that range. If the hottest brake temperature is below
65 [deg]C (150 [deg]F) individual brake stops shall be repeated to
increase any one brake temperature to within the target temperature
range of 65 [deg]C-204[deg]C (150 [deg]F-400 [deg]F) before the subject
maneuver can be performed.
    S7.6 Slowly Increasing Steer Test. The vehicle is subjected to two
series of runs of the slowly increasing steer test using a constant
vehicle speed of 48.3  1.6 km/h (30.0  1.0 mph)
and a steering pattern that increases by 13.5 degrees per second until
ESC system activation is confirmed. Three repetitions are performed for
each test series. One series uses counterclockwise steering, and the
other series uses clockwise steering. During each run ESC activation is
required for the Engine Torque Reduction test and is confirmed as
specified in S7.7.
    S7.6.1 The slowly increasing steer maneuver sequence is started
using a commanded steering wheel angle of 270 degrees. If ESC
activation did not occur during the maneuver then the commanded
steering wheel angle is increased by 270 degree increments up to the
vehicle's maximum allowable steering angle or until ESC activation is
confirmed.
    S7.6.2 From the slowly increasing steer tests, the quantity ``A''
is determined. ``A'' is the steering wheel angle in degrees that is
estimated to produce a lateral acceleration of 0.5g for the test
vehicle. Utilizing linear regression on the lateral acceleration data
recorded between 0.05g and 0.3g, and then linear extrapolation out to a
lateral acceleration value of 0.5g, A is calculated, to the nearest 0.1
degrees, from each of the six satisfactory slowly increasing steer
tests. If ESC activation occurs prior to the vehicle experiencing

a lateral acceleration of 0.3g then the data used during the linear
regression will be that data recorded between 0.05g and the lateral
acceleration measured at the time of ESC activation. The absolute value
of the six A's calculated is averaged and rounded to the nearest 0.1
degrees to produce the final quantity, A, used during the sine with
dwell maneuvers below.
    S7.7 Engine Torque Reduction Test. During each of the six completed
slowly increasing steer test maneuvers, ESC activation is confirmed by
comparing the engine torque output and driver requested torque data
collected from the vehicle J1939 communication data link. During the
initial stages of each maneuver the two torque signals with respect to
time will parallel each other. Upon ESC activation, the two signals
will diverge when ESC system activation causes a commanded engine
torque reduction and the driver attempts to accelerate the vehicle
maintaining the required constant test speed causing an increased
driver requested torque.
    S7.7.1 During each of the six slowly increasing steer test runs,
verify the commanded engine torque and the driver requested torque
signals diverge at least 10 percent 1.5 seconds after the beginning of
ESC activation occurs as defined in S7.12.15.
    S7.7.2 If ESC activation does not occur in all of the six slowly
increasing steer test maneuvers the test is terminated.
    S7.8 After the quantity A has been determined in S7.6, without
replacing the tires, the tire and brake conditioning procedures
described in S7.4 and S7.5 are performed immediately prior to
conducting the sine with dwell test.
    S7.9 Check that the ESC system is enabled by ensuring that the ESC
malfunction telltale is not illuminated.
    S7.10 Sine With Dwell Test. The vehicle is subjected to two series
of test runs using a steering pattern of a sine wave at 0.5 Hz
frequency with a 1.0 sec delay beginning at the second peak amplitude
as shown in Figure 1 (sine with dwell maneuver). One series uses
counterclockwise steering for the first half cycle, and the other
series uses clockwise steering for the first half cycle. Before each
test run brake temperatures are monitored and the hottest brake is
confirmed to be within the temperature range of 65 [deg]C-204 [deg]C
(150 [deg]F-400 [deg]F).
[GRAPHIC] [TIFF OMITTED] TP23MY12.008

    S7.10.1 For manual transmissions, the steering motion is initiated
with the vehicle coasting (dropped throttle) with the clutch disengaged
at 72.4  1.6 km/h (45.0  1.0 mph). For
automatic transmissions, the steering motion is initiated with the
vehicle coasting and the transmission in the ``drive'' selection
position.
    S7.10.2 In each series of test runs, the steering amplitude is
increased from run to run, by 0.1A, provided that no such run will
result in steering amplitude greater than that of the final run
specified in S7.10.4.
    S7.10.3 The steering amplitude for the initial run of each series
is 0.3A where A is the steering wheel angle determined in S7.6.
    S7.10.4 The steering amplitude of the final run in each series is
the lesser of 1.3A or 400 degrees. If any 0.1A increment, up to 1.3A,
is greater than 400 degrees, the steering amplitude of the final run
shall be the 0.1A amplitude that is closest or equal to, but not
exceeding, 400 degrees.
    S7.10.5 Upon completion of the two series of test runs, post
processing of the yaw rate and lateral acceleration data to determine
Lateral Acceleration Ratio (LAR), Yaw Rate Ratio (YRR) and lateral
displacement, is done as specified in S7.12.
    S7.11 ESC Malfunction Detection.
    S7.11.1 Simulate one or more ESC malfunction(s) by disconnecting
the power source to any ESC component, or disconnecting any electrical
connection between ESC components (with the vehicle power off). When
simulating an ESC malfunction, the electrical connections for the
telltale lamp(s) are not to be disconnected.
    S7.11.2 With the vehicle initially stationary and the ignition
locking system in the ``Lock'' or ``Off'' position, activate the
ignition locking system to the ``Start'' position and start the engine.
Place the vehicle in a forward gear and obtain a vehicle speed of 48.3
 8.0 km/h (30.0  5.0 mph). Drive the vehicle
for at least two minutes including at least one left and one right
turning maneuver and at least one service brake application. Verify
that within two minutes of obtaining this vehicle speed the ESC
malfunction indicator illuminates in accordance with S5.3.
    S7.11.3 Stop the vehicle, deactivate the ignition locking system to
the ``Off'' or ``Lock'' position. After a five-minute period, activate
the vehicle's ignition locking system to the ``Start'' position and
start the engine. Verify that the ESC malfunction indicator again
illuminates to signal a malfunction and remains illuminated as long as
the engine is running or until the fault is corrected.
    S7.11.4 Deactivate the ignition locking system to the ``Off'' or
``Lock'' position. Restore the ESC system to

normal operation, activate the ignition system to the ``Start''
position and start the engine. Verify that the telltale has
extinguished.
    S7.12 Post Data Processing--Calculations for Performance Metrics.
Engine torque reduction, lateral acceleration and yaw rate decay
calculations, and lateral responsiveness checks must be processed
utilizing the following techniques:
    S7.12.1 Raw steering wheel angle data is filtered with a 12-pole
phaseless Butterworth filter and a cutoff frequency of 10Hz. The
filtered data is then zeroed to remove sensor offset utilizing static
pretest data.
    S7.12.2 Raw yaw, pitch and roll rate data is filtered with a 12-
pole phaseless Butterworth filter and a cutoff frequency of 3 Hz. The
filtered data is then zeroed to remove sensor offset utilizing static
pretest data.
    S7.12.3 Raw lateral acceleration data is filtered with a 12-pole
phaseless Butterworth filter and a cutoff frequency of 6Hz. The
filtered data is then zeroed to remove sensor offset utilizing static
pretest data. The lateral acceleration data at the vehicle center of
gravity is determined by removing the effects caused by vehicle body
roll and by correcting for sensor placement via use of coordinate
transformation. For data collection, the lateral accelerometer shall be
located as close as possible to the position of the vehicle's
longitudinal and lateral centers of gravity.