[Federal Register Volume 80, Number 120 (Tuesday, June 23, 2015)]
[Rules and Regulations]
[Pages 36049-36110]
[FR Doc No: 2015-14127]

Vol. 80

Tuesday,

No. 120

June 23, 2015

Part II

Department of Transportation

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National Highway Traffic Safety Administration

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49 CFR Part 571

Federal Motor Vehicle Safety Standards; Electronic Stability Control
Systems for Heavy Vehicles; Final Rule

Federal Register / Vol. 80 , No. 120 / Tuesday, June 23, 2015 / Rules
and Regulations

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DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

49 CFR Part 571

[Docket No. NHTSA-2015-0056]
RIN 2127-AK97

Federal Motor Vehicle Safety Standards; Electronic Stability
Control Systems for Heavy Vehicles

AGENCY: National Highway Traffic Safety Administration (NHTSA),
Department of Transportation (DOT).

ACTION: Final rule.

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SUMMARY: This document establishes a new Federal Motor Vehicle Safety
Standard No. 136 to require electronic stability control (ESC) systems
on truck tractors and certain buses with a gross vehicle weight rating
of greater than 11,793 kilograms (26,000 pounds). ESC systems in truck
tractors and large buses are designed to reduce untripped rollovers and
mitigate severe understeer or oversteer conditions that lead to loss of
control by using automatic computer-controlled braking and reducing
engine torque output.
    In 2018, we expect that, without this rule, about 34 percent of new
truck tractors and 80 percent of new buses affected by this final rule
would be equipped with ESC systems. We believe that, by requiring that
ESC systems be installed on the rest of truck tractors and large buses,
this final rule will prevent 40 to 56 percent of untripped rollover
crashes and 14 percent of loss-of-control crashes. As a result, we
expect that this final rule will prevent 1,424 to 1,759 crashes, 505 to
649 injuries, and 40 to 49 fatalities at $0.1 to $0.6 million net cost
per equivalent life saved, while generating positive net benefits.

DATES: The effective date of this rule is August 24, 2015. The
incorporation by reference of certain publications listed in the rule
is approved by the Director of the Federal Register as of August 24,
2015.
    Petitions for reconsideration: Petitions for reconsideration of
this final rule must be received not later than August 7, 2015.

ADDRESSES: Petitions for reconsideration of this final rule must refer
to the docket and notice number set forth above and be submitted to the
Administrator, National Highway Traffic Safety Administration, 1200 New
Jersey Avenue SE., Washington, DC 20590.

FOR FURTHER INFORMATION CONTACT: For technical issues, you may contact
Patrick Hallan, Office of Crash Avoidance Standards, by telephone at
(202) 366-9146, and by fax at<PHONE_NUMBER>. For legal issues, you may
contact David Jasinski, Office of the Chief Counsel, by telephone at
(202) 366-2992, and by fax at<PHONE_NUMBER>. You may send mail to both
of these officials at the National Highway Traffic Safety
Administration, 1200 New Jersey Avenue SE., Washington, DC 20590.

SUPPLEMENTARY INFORMATION:

Table of Contents

I. Executive Summary
II. Statutory Authority
III. Background
IV. Safety Need
    A. Heavy Vehicle Crash Problem
    B. Contributing Factors in Rollover and Loss-of-Control Crashes
    C. NTSB Safety Recommendations
    D. Motorcoach Safety Plan
    E. International Regulation
V. Summary of the May 2012 NPRM
VI. Overview of the Comments
VII. Key Differences Between the Final Rule and the NRPM
VIII. ESC Requirement
    A. Whether To Require Stability Control
    B. Whether To Require ESC or RSC
    C. Definition of ESC
    D. Technical Documentation
IX. Vehicle Applicability and Phase-In
    A. Trucks
    1. Summary of the NPRM
    2. Exclusions From ESC Requirement
    3. Single-Unit Trucks
    4. Compliance Dates
    B. Buses
    1. Summary of the NPRM
    2. Buses Built on Truck Chassis
    (a) Summary of NPRM
    (b) Summary of Comments
    (c) NHTSA's Response to Comments
    3. Hydraulic-Braked Buses
    4. School Buses
    5. Transit Buses
    6. Minimum Seating Capacity and Seating Configuration
    7. Compliance Dates
    8. Class 3 Through 6 Buses
    C. Retrofitting
X. Performance Testing
    A. NHTSA's Proposed Performance Tests
    1. Characterization Test--SIS
    2. Roll and Yaw Stability Test--SWD
    3. Lateral Displacement
    B. Comments on SIS and SWD Maneuvers
    C. Alternative Maneuvers Considered in the NPRM
    D. Comments on Alternative Test Maneuvers
    E. NHTSA Examination and Testing of EMA Maneuvers
    F. Roll Stability Performance Test--J-Turn Test
    1. Rationale for Using J-Turn Test
    2. Test Procedure and Performance Requirements
    3. System Responsiveness
    4. Engine Torque Reduction
    5. Roll Stability Performance Requirements
    G. Yaw Stability
    H. Understeer
XI. Test Conditions and Equipment
    A. Outriggers
    B. Automated Steering Machine
    C. Anti-Jackknife System
    D. Control Trailer
    E. Sensors
    F. Ambient Conditions
    G. Road Test Surface
    H. Vehicle Test Weight
    I. Tires
    J. Mass Estimation Drive Cycle
    K. Brake Conditioning
    L. Compliance Options
    M. Data Collection
    XII. ESC Disablement
    A. Summary of Comments
    B. Response to Comments
XIII. ESC Malfunction Detection, Telltale, and Activation Indicator
    A. ESC Malfunction Detection
    B. ESC Malfunction Telltale
    C. Combining ESC Malfunction Telltale With Related Systems
    D. ESC Activation Indicator
XIV. Benefits and Costs
    A. Target Crash Population
    B. System Effectiveness
    1. Summary of the NPRM
    2. Summary of Comments and Response
    (a) ATRI Study
    (b) Bendix Study
    3. Effectiveness Estimate
    C. Benefits Estimates
    1. Safety Benefits
    2. Monetized Benefits
    D. Cost Estimate
    Truck Tractors
    Large Buses
    E. Cost Effectiveness
    F. Comparison of Regulatory Alternatives
XV. Regulatory Analyses and Notices
    A. Executive Order 12866, Executive Order 13563, and DOT
Regulatory Policies and Procedures
    B. Regulatory Flexibility Act
    C. Executive Order 13132 (Federalism)
    D. Executive Order 12988 (Civil Justice Reform)
    E. Protection of Children From Environmental Health and Safety
Risks
    F. Paperwork Reduction Act
    G. National Technology Transfer and Advancement Act
    H. Unfunded Mandates Reform Act
    I. National Environmental Policy Act
    J. Incorporation by Reference
    K. Regulatory Identifier Number (RIN)
    L. Privacy Act

I. Executive Summary

    This final rule establishes a new Federal Motor Vehicle Safety
Standard (FMVSS) No. 136, Electronic Stability Control Systems for
Heavy Vehicles, to reduce rollover and loss of directional control of
truck tractors and large buses. The standard requires that truck
tractors and certain large buses with a gross vehicle weight rating
(GVWR) of greater than 11,793 kilograms (26,000 pounds) to be equipped
with an electronic stability control (ESC) system that meets the
equipment and performance criteria of the standard. ESC systems use
engine torque control and computer-controlled

braking of individual wheels to assist the driver in maintaining
control of the vehicle and maintaining its heading in situations in
which the vehicle is becoming roll unstable (i.e., wheel lift
potentially leading to rollover) or experiencing loss of control (i.e.,
deviation from driver's intended path due to understeer, oversteer,
trailer swing or any other yaw motion leading to directional loss of
control). In such situations, intervention by the ESC system can assist
the driver in maintaining control of the vehicle, thereby preventing
fatalities and injuries associated with vehicle rollover or collision.
    This final rule is made pursuant to the authority granted to NHTSA
under the National Traffic and Motor Vehicle Safety Act (``Motor
Vehicle Safety Act''). Under 49 U.S. C. Chapter 301, Motor Vehicle
Safety (49 U.S. C. 30101 et se.), the Secretary of Transportation is
responsible for prescribing motor vehicle safety standards that are
practicable, meet the need for motor vehicle safety, and are stated in
objective terms. The responsibility for promulgation of Federal motor
vehicle safety standards is delegated to NHTSA. This rulemaking also
completes NHTSA's rulemaking pursuant to a directive in the Moving
Ahead for Progress in the 21st Century Act (MAP-21) that the Secretary
consider requiring stability enhancing technology on motorcoaches.\1\
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    \1\ Pub. L. 112-141 (July 6, 2012).
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    There have been two types of stability control systems developed
for heavy vehicles. A roll stability control (RSC) system is designed
to prevent rollover by decelerating the vehicle using braking and
engine torque control. The other type of stability control system is
ESC, which includes all of the functions of an RSC system plus the
ability to mitigate severe oversteer or understeer conditions by
automatically applying brake force at selected wheel-ends to help
maintain directional control of a vehicle. To date, ESC and RSC systems
for heavy vehicles have been developed for air-braked vehicles. Truck
tractors and buses covered by today's final rule make up a large
proportion of air-braked heavy vehicles and a large proportion of the
heavy vehicles involved in both rollover crashes and total heavy
vehicle crashes.
    As a result of the data analysis research, we determined that ESC
systems can be 40 to 56 percent effective in reducing first-event
untripped rollovers and 14 percent effective in eliminating loss-of-
control crashes caused by severe oversteer or understeer conditions.
This estimate is based on an update of the estimate presented in a 2011
research note analyzing the effectiveness of ESC systems discussed in
the Final Regulatory Impact Analysis (FRIA) accompanying this final
rule.\2\
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    \2\ See Wang, Jing-Shiam, ``Effectiveness of Stability Control
Systems for Truck Tractors'' (January 2011) (DOT HS 811 437); Docket
No. NHTSA-2010-0034-0043.
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    The agency considered requiring truck tractors and large buses to
be equipped with RSC systems. When compared to the ESC requirement in
this final rule, RSC systems would cost less than ESC systems, be
slightly more cost-effective, but would produce net benefits that are
much lower than the net benefits from this final rule. This is because
RSC systems are less effective at preventing rollover crashes and much
less effective at preventing loss-of-control crashes. We also
considered requiring trailers to be equipped with RSC systems. However,
this alternative would save many fewer lives, would not be cost-
effective, and would not result in net benefits.
    This final rule requires ESC systems to meet both definitional
criteria and performance requirements. It is necessary to include
definitional criteria and require compliance with them because
developing separate performance tests to cover the wide array of
possible operating ranges, roadways, and environmental conditions would
be impractical. The definitional criteria are consistent with those
recommended by SAE International and used by the United Nations (UN)
Economic Commission for Europe (ECE), and similar to the definition of
ESC in FMVSS No. 126, the agency's stability control standard for light
vehicles. This definition describes an ESC system for heavy vehicles as
one that will enhance both the roll and yaw stability of a vehicle
using a computer-controlled system that can receive inputs such as the
vehicle's lateral acceleration and yaw rate, and use the information to
apply brakes individually, including trailer brakes, and modulate
engine torque.
    This final rule is applicable to all new typical three-axle truck
tractors manufactured on or after August 1, 2017. We believe that two
years of lead time is sufficient for these vehicles to be equipped with
ESC, given that this is a common platform for which ESC systems are
readily available today. We are allowing four years of lead time for
all other truck tractors. These vehicles include two-axle vehicles,
which have been more recently required to satisfy new, reduced minimum
stopping distance requirements, and severe-service tractors, for which
we believe two additional years of lead time is necessary to design and
test ESC systems.
    This final rule is applicable to buses over 14,969 kilograms
(33,000 pounds) GVWR manufactured more than three years after the date
of this final rule. Although we proposed a two-year lead time for buses
in the NPRM, the Motorcoach Enhanced Safety Act mandates that new
rules, including stability enhancing technology, be applicable to all
buses manufactured more than three years after publication of a final
rule. However, for buses with a GVWR greater than 11,793 kilograms
(26,000 pounds) but not more than 14,969 kilograms (33,000 pounds), we
believe that three years of lead time is not feasible. Some of these
buses include vehicles with body-on-frame construction and hydraulic
brakes, for which ESC system availability is not as widespread.
Therefore, we are allowing four years of lead time for buses with a
GVWR greater than 11,793 kilograms (26,000 pounds) but not more than
14,969 kilograms (33,000 pounds). We believe that including buses with
body-on-frame construction and hydraulic brakes in this final rule will
spur development of ESC systems for other hydraulic-braked vehicles,
including vehicles with a GVWR of greater than 4,536 kilograms (10,000
pounds) but not more than 11,793 kilograms (26,000 pounds), which are
not covered by this rulemaking.
    We have chosen an alternative performance test to demonstrate an
ESC system's ability to mitigate roll instability to what was proposed.
After considering the public comments and conducting additional track
testing, we have determined that a 150-foot-radius J-turn test maneuver
is an efficient means to ensure vehicles maintain roll stability. Like
the test maneuver in the NPRM, the J-turn test maneuver is among those
available to manufacturers to demonstrate compliance with the UNECE
mandate for ESC on trucks and buses.
    The J-turn test maneuver, based on an alternative test discussed in
the NPRM, involves accelerating to a constant speed on a straight
stretch of high-friction track before entering into a 150-foot radius
curve. After entering the curve, the driver attempts to maintain the
lane. At a speed that is at up to 1.3 times the speed at which the ESC
system activates, but in no case below 48.3 km/h (30 mph), an ESC
system must activate the vehicle's service brakes to slow the vehicle's
speed to 46.7 km/h (29 mph) within 3 seconds

after entering the curve and 45.1 km/h (28 mph) within 4 seconds after
entering the curve. Additional J-turn tests are conducted to ensure
that an ESC system is able to reduce engine torque.
    The performance metric for the J-turn (reduction in forward speed)
is easy to obtain and serves as a proxy for absolute lateral
acceleration. Lateral acceleration on a fixed-radius curve is a
function of forward velocity. On a 150-foot radius curve, a forward
speed of 48.3 km/h (30 mph) corresponds to a lateral acceleration of
approximately 0.4g. Based on prior NHTSA testing, we have found that
0.4g represents the margin of lateral stability on a typical fully
loaded truck tractor with the loads having a high center of gravity
(CG). That is, lateral acceleration levels greater than 0.4g (or
forward speeds on a 150-foot radius curve of greater than 48.3 km/h (30
mph)) on a typical truck tractor are likely to lead to lateral
instability, wheel lift, and possible rollover. However, lateral
acceleration levels less than 0.4g (or forward speeds on a 150-foot
radius curve of less than 48.3 km/h (30 mph)) on a typical truck
tractor are unlikely to lead to lateral instability, wheel lift, and
rollover.
    This final rule includes a requirement proposed in the NPRM that an
ESC system be able to mitigate yaw instability. This requirement is
similar to one proposed in the NPRM, and adopted in this final rule,
requiring an ESC system be able to mitigate understeer. However, this
final rule does not include any performance test to evaluate the
ability of an ESC system to mitigate yaw instability. Although the NPRM
included the sine with dwell (SWD) maneuver to test both roll and yaw
instability, we have decided not to include it in this final rule. The
SWD maneuver is only a partial test of the ability to mitigate yaw
instability. It tests an ESC system's ability to mitigate loss of
control resulting from oversteer conditions, but not its ability to
mitigate understeer, which is the most common loss-of-control scenario
for heavy vehicles. NHTSA has been unable to develop a test for
understeer mitigation. As argued by many commenters, performing the SWD
maneuver entails substantial time and instrumentation burdens. We do
not believe that this additional time and cost is justified solely to
test an ESC system's ability to mitigate yaw instability caused by
oversteer conditions when a majority of the benefits of this final rule
are derived from rollover prevention and the majority of benefits
attributed to prevented loss-of-control crashes in heavy vehicles are
derived from understeer mitigation, which would not have been tested in
the SWD maneuver. However, we are continuing to examine possible yaw
performance maneuvers, including the SWD maneuver, to test yaw
stability performance in the future.
    The decision to adopt the J-turn test maneuver as the performance
test in this final rule has caused us to reconsider test conditions and
equipment. However, many aspects of testing remain identical to the
proposal. For example, we will conduct performance testing on a high-
friction surface. We believe that the potential for variance in surface
friction on a low-friction surface may introduce variabilities in ESC
testing that may lead to inconsistent results. We are still equipping
all test vehicles with outriggers and truck tractors with anti-
jackknife systems for the safety of test drivers.
    On the other hand, many proposed aspects of testing had to be
modified to accommodate the J-turn test maneuver. Because the J-turn
test maneuver is a path-following maneuver, we are not using a steering
wheel controller that was proposed in the NPRM. We noted potential
variabilities in the proposed specification for the control trailer.
However, because the performance metric for the J-turn test maneuver is
different than the proposed SWD requirements, those variabilities
identified in the NPRM that were related to the SWD maneuver are no
longer relevant. We have modified the loading condition to load the
vehicle to its GVWR because that is the most severe test condition with
the J-turn test maneuver. Finally, the number of sensors used in
testing is substantially reduced because the vehicle's actual lateral
acceleration throughout the maneuver does not need to be measured.
    We have considered comments on the issue of allowing ESC system
disablement. This final rule does not allow the driver to disable the
ESC system at speeds higher than 20 km/h (12.4 mph), which we have
defined as the minimum speed at which an ESC system must operate. Many
of the comments we received arguing in favor of allowing ESC system
disablement were, in fact, arguing for disablement of traction control
to allow a vehicle to start moving on certain surfaces with low
friction such as on snow, ice, or off-road conditions. However, we do
not believe that an ESC system would prevent a heavy vehicle from
moving in these circumstances. Rather, we believe that manufacturers
may wish to disable an automatic traction control system to allow the
vehicle to move. NHTSA does not require traction control systems, nor
does NHTSA prohibit the installation of an on/off switch for a traction
control system. We understand that traction control systems are related
to ESC systems in that they can control engine torque output and
activate the brakes on individual wheel ends. However, we do not find
these arguments to be a compelling reason to allow an ESC system
deactivation switch or automatic deactivation of ESC systems at speeds
above 20 km/h (12.4 mph).
    This final rule requires that an ESC system be able to detect a
malfunction and provide a driver with notification of a malfunction by
means of a telltale. This requirement is similar to the malfunction
detection and telltale requirements for light vehicles in FMVSS No.
126. After considering public comments, we have changed the vehicle
depicted on the telltale to better represent the profile of a
combination vehicle or bus rather than a passenger car.
    Based on the agency's effectiveness estimates, this final rule will
prevent 1,424 to 1,759 crashes per year resulting in 505 to 649
injuries and 40 to 49 fatalities. This final rule will also result in
significant monetary savings as a result of the prevention of property
damage and travel delays.
    Without this final rule, we project that, in 2018, manufacturers
would have equipped 33.9 percent of truck tractors with ESC systems,
21.3 percent of truck tractors would be equipped with RSC systems, and
80.0 percent of large buses would be equipped with ESC systems. Based
on the agency's cost teardown study, the average ESC system cost is
estimated to be $585 for truck tractors and $269 for large buses. The
incremental cost of installing an ESC system in place of an RSC system
on a truck tractor is estimated to be $194. Based upon the agency's
estimate that 150,000 truck tractors and 2,200 buses covered by this
final rule will be manufactured annually, the agency estimates the
total technology cost of this final rule to be approximately $45.6
million.
    This final rule is highly cost effective and beneficial. The net
benefits of this final rule are estimated to range from $412 to $525
million at the 3 percent discount rate and $312 to $401 million at the
7 percent discount rate. The agency estimates that this rule will
result in societal economic savings resulting from preventing crashes,
reducing congestion, and preventing property damage, such that the net
cost of this final rule range from $3.6 to $12.3 million at a 3 percent
discount rate and from $12.3 to $19.2 million at 7 percent discount
rate. As a result, the net cost per equivalent life saved ranges

from $0.1 to $0.3 million at the 3 percent discount rate and from $0.3
to $0.6 million at the 7 percent discount rate. The costs and benefits
of this rule are summarized in Table 1.

                                      Table 1--Estimated Annual Cost, Benefits, and Net Benefits of the Final Rule
                                                              [In millions of 2013 dollars]
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                                                                             Societal                          Total         Cost per
                                                           Vehicle costs     economic       VSL savings      monetized      equivalent     Net benefits
                                                                              savings                         savings       live saved
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At 3% Discount..........................................           $45.6     $33.3-$42.1       $424-$528       $458-$571       $0.1-$0.3       $412-$525
At 7% Discount..........................................            45.6       26.4-33.3         332-413         358-446         0.3-$.6         312-401
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II. Statutory Authority

    NHTSA is issuing this final rule under the National Traffic and
Motor Vehicle Safety Act (``Motor Vehicle Safety Act''). Under 49
U.S.C. Chapter 301, Motor Vehicle Safety (49 U.S.C. 30101 et seq.), the
Secretary of Transportation is responsible for prescribing motor
vehicle safety standards that are practicable, meet the need for motor
vehicle safety, and are stated in objective terms. ``Motor vehicle
safety'' is defined in the Motor Vehicle Safety Act as ``the
performance of a motor vehicle or motor vehicle equipment in a way that
protects the public against unreasonable risk of accidents occurring
because of the design, construction, or performance of a motor vehicle,
and against unreasonable risk of death or injury in an accident, and
includes nonoperational safety of a motor vehicle.'' ``Motor vehicle
safety standard'' means a minimum performance standard for motor
vehicles or motor vehicle equipment. When prescribing such standards,
the Secretary must consider all relevant, available motor vehicle
safety information. The Secretary must also consider whether a standard
is reasonable, practicable, and appropriate for the types of motor
vehicles or motor vehicle equipment for which it is prescribed and the
extent to which the standard will further the statutory purpose of
reducing traffic accidents and associated deaths. The responsibility
for promulgation of Federal motor vehicle safety standards is delegated
to NHTSA.
    On July 6, 2012, President Obama signed MAP-21, which incorporated
in Subtitle G the ``Motorcoach Enhanced Safety Act of 2012.'' Section
32703(b)(3) of the Act states that, not later than two years after the
date of enactment of the Act, the Secretary shall consider requiring
motorcoaches to be equipped with stability enhancing technology, such
as electronic stability control and torque vectoring, to reduce the
number and frequency of rollover crashes of motorcoaches. The Secretary
was directed to prescribe regulations that address stability enhancing
technology if the Secretary determines that such standards meet the
requirements and considerations set forth in subsections (a) and (b) of
49 U.S.C. 30111. These requirements are discussed in the preceding
paragraph.
    The Motorcoach Enhanced Safety Act directs the Secretary to
consider various other motorcoach rulemakings, in provided timeframes,
related to safety belts,\3\ improved roof support standards, advanced
glazing standards and other portal improvements to prevent partial and
complete ejection of motorcoach passengers, tire pressure monitoring
systems, and tire performance standards. The Act also includes
provisions on fire research, interior impact protection, enhanced
seating designs, and collision avoidance systems, and the consideration
of rulemaking based on such research. There also are provisions in the
Motorcoach Enhanced Safety Act relating to improved oversight of
motorcoach service providers, including enhancements to driver
licensing and training programs and motorcoach inspection programs.
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    \3\ Pursuant to the Motor Vehicle Safety Act and the Motorcoach
Enhanced Safety Act, NHTSA published a final rule requiring lap/
shoulder seat belts for each passenger seating position on all new
over-the-road buses, and in new buses other than over-the-road buses
with a GVWR greater than 11,793 kilograms (26,000 pounds) beginning
on November 26, 2016. 78 FR 70415 (Nov. 25, 2013).
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    In section 32702, ``Definitions,'' of the Motorcoach Enhanced
Safety Act, the Act states at section 32702(6) that ``the term
`motorcoach' has the meaning given the term `over-the-road bus' in
section 3038(a)(3) of the Transportation Equity Act for the 21st
Century (TEA-21) (49 U.S.C. 5310 note), but does not include a bus used
in public transportation provided by, or on behalf of, a public
transportation agency; or a school bus, including a multifunction
school activity bus.'' Section 3038(a)(3) states: ``The term `over-the-
road bus' means a bus characterized by an elevated passenger deck
located over a baggage compartment.''
    Under section 32703(e)(1) of the Motorcoach Enhanced Safety Act,
any regulation prescribed in accordance with section 32703(b) (and
several other subsections) shall apply to all motorcoaches manufactured
more than three years after the date on which the regulation is
published as a final rule, take into account the impact to seating
capacity of changes to size and weight of motorcoaches and the ability
to comply with State and Federal size and weight requirements, and be
based on the best available science.
    Prior to enactment of the Motorcoach Enhanced Safety Act, the
agency's May 23, 2012 NPRM proposed requiring truck tractors and large
buses with a GVWR of greater than 11,793 kg (26,000 lb.) to be equipped
with stability enhancing technology. Thus, the agency had already
considered requiring motorcoaches to have stability enhancing
technology, and had proposed requiring the same, prior to the enactment
of the Motorcoach Enhanced Safety Act.
    The agency does not interpret the Motorcoach Enhanced Safety Act on
its own as a mandate to require stability enhancing technology on over-
the-road buses. With respect to rollover crash avoidance, section
32703(b)(3) of the Motorcoach Enhanced Safety Act directs the agency to
``consider requiring'' stability enhancing technology such as
electronic stability control or torque vectoring on over-the-road
buses. However, the agency was also directed in section 32703(b) to
prescribe a regulation if the Secretary determines that such standards
meet the requirements and considerations for issuing a motor vehicle
safety standard under the Motor Vehicle Safety Act. The Motorcoach
Enhanced Safety Act does not provide independent statutory authority to
require stability enhancing technologies on over-the-road buses.\4\

Thus, any mandate requiring stability enhancing technology pursuant to
the Motorcoach Enhanced Safety Act is dependent on satisfying the
considerations and requirements of the Motor Vehicle Safety Act.
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    \4\ In contrast, the Motorcoach Enhanced Safety Act specifically
mandated that the agency prescribe regulations requiring safety
belts to be installed at each designated seating position on all
over-the-road buses.
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    In issuing this final rule, we took into account the considerations
of section 32703(e)(1) of the Motorcoach Enhanced Safety Act regarding
the implementation of regulations prescribed in accordance with
subsection (b)(3). Unlike subsection (b)(3), subsection (e)(1) does not
use permissive language. Because this final rule is issued in
accordance with subsection (b)(3), we believe the considerations
regarding the application of regulations in subsection (e)(1) must be
addressed in this rulemaking. Nonetheless, because the Motorcoach
Enhanced Safety Act contains no independent statutory authority in
support of a mandate for stability enhancing technology, the
considerations in subsection (e)(1) are constrained by the agency's
authority to issue standards under the Motor Vehicle Safety Act.
Therefore, where the considerations in subsection (e)(1) conflict with
any requirements and considerations set forth in subsections (a) and
(b) of 49 U.S.C. 30111, the requirements of the Motor Vehicle Safety
Act supersede the Motorcoach Enhanced Safety Act.\5\
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    \5\ See section IX.B below for such a finding with respect to
the application of this final rule to buses with a GVWR of 14,969
kilograms (33,000 pounds) or less.
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    This final rule is practicable, meets a need for motor vehicle
safety, and is stated in objective terms. With respect to the
considerations of the Motorcoach Enhanced Safety Act, we believe that
Congress intended that a final rule based on the 2012 NPRM would
complete the rulemaking proceeding specified in section 32703(b)(3) of
the Act. Electronic stability control will reduce the number and
frequency of rollover crashes of motorcoaches. This rulemaking is based
on the best available science. Further, we have considered the impact
to seating capacity and changes to size and weight of motorcoaches, and
we believe that this rule will have no effect on these considerations.
ESC systems will add less than 10 pounds of additional weight to over-
the-road buses.\6\
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    \6\ ``Report: Cost and Weight Analysis of Electronic Stability
Control (ESC) and Roll Stability Control for Heavy Trucks,'' Docket
No. NHTSA-2011-0066-0034.
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    Although the Motorcoach Enhanced Safety Act also suggested torque
vectoring as a possible technology to consider requiring on
motorcoaches, we did not propose requiring torque vectoring in the May
2012 NPRM, and it is beyond the scope of this rulemaking proceeding.
Even if it was within scope to require torque vectoring, the agency
would not do so in this rulemaking. The agency's understanding of
torque vectoring is that it is a technology that allows a vehicle's
differential or brakes to vary the power supplied to the drive axle
wheel end. In contrast, ESC systems activate the vehicle's service
brakes to vary the braking on each wheel end combined with the ability
to reduce engine torque (which reduces power on drive axle wheel ends).
In the May 2012 NPRM, we noted that, all things being equal, a vehicle
entering a curve at a higher speed is more likely to roll over than a
vehicle entering a curve at a lower speed.\7\ Once a vehicle is about
to enter a curve at a high enough speed that would generate sufficient
lateral acceleration to cause a possible rollover, the most effective
manner to vary the individual wheel speeds in an attempt to prevent the
rollover is primarily through the activation of a vehicle's service
brakes along with the decrease in engine power and the use of engine
braking. Torque vectoring systems that are differential-based would not
provide adequate braking power and would be less effective than ESC at
slowing a vehicle down to allow it to maneuver a curve without rolling
over. Likewise, brake-based torque vectoring systems would be less
effective than ESC for braking in a curve. In brake-based systems, the
inside wheels are braked during cornering in order to prevent any loss
of traction, which could result because there is less weight on those
wheel during cornering. ESC provides braking to both the inside and
outside wheels of the vehicle resulting in better brake performance.
---------------------------------------------------------------------------

    \7\ 77 FR 30771.
---------------------------------------------------------------------------

III. Background

    In the NPRM, we provided a detailed explanation of how rollovers
occur, how stability control technologies such as roll stability
control and electronic stability control function and reduce rollover,
examples of situations in which stability control systems may not be
effective, and the differences between stability enhancing technology
on light vehicles and heavy vehicles.\8\ This section is a summary of
that information.
---------------------------------------------------------------------------

    \8\ 77 FR 30771-74.
---------------------------------------------------------------------------

    A turning maneuver initiated by the driver's steering input results
in a vehicle response that can be broken down into two phases. As the
steering wheel is turned, the displacement of the front wheels
generates a slip angle at the front wheels and a lateral force is
generated. That lateral force leads to vehicle rotation, and the
vehicle starts rotating about its center of gravity. Then, the
vehicle's yaw causes the rear wheels to experience a slip angle. That
causes a lateral force to be generated at the rear tires, which causes
vehicle rotation. All of these actions establish a steady-state turn in
which lateral acceleration and yaw rate are constant. In combination
vehicles, which typically consist of a tractor towing a trailer, an
additional phase is the turning response of the trailer, which is
similar to, but slightly delayed, when compared to the turning response
of the tractor.
    If the lateral forces generated at either the front or the rear
wheels exceed the friction limits between the road surface and the
tires, the result will be a vehicle loss-of-control in the form of
severe understeer (loss of traction at the steer tires) or severe
oversteer (loss of traction at the rear tires). In a combination
vehicle, a loss of traction at the trailer wheels would result in the
trailer swinging out of its intended path. Conversely, rollover
conditions occur on a vehicle when high lateral forces are generated at
the tires from steering or sliding and result in a vehicle lateral
acceleration that exceeds the rollover threshold of the vehicle.
    High lateral acceleration is one of the primary causes of
rollovers. Figure 1 depicts a simplified untripped rollover condition.
As shown, when the lateral force (i.e., lateral acceleration) is
sufficiently large and exceeds the roll stability threshold of the
tractor-trailer combination vehicle, the vehicle will roll over. Many
factors related to the drivers' maneuvers, heavy vehicle loading
conditions, vehicle handling characteristics, roadway design, and road
surface properties would result in various lateral accelerations and
influences on the rollover propensity of a vehicle. For example, given
other factors are equal, a vehicle entering a curve at a higher speed
has a higher lateral acceleration and, as a result, is more likely to
roll than a vehicle entering the curve at a lower speed. Also,
transporting a high-CG load would increase the rollover probability
more than transporting a relatively lower CG load.

[GRAPHIC] [TIFF OMITTED] TR23JN15.008

    Stability control technologies help a driver maintain directional
control and help to reduce roll instability. Two types of heavy vehicle
stability control technologies have been developed. One such technology
is roll stability control or RSC. RSC systems are available for truck
tractors and for trailers. A tractor-based RSC system consists of an
electronic control unit (ECU) that is mounted on a vehicle and
continually monitors the vehicle's speed and lateral acceleration based
on an accelerometer, and estimates vehicle mass based on engine torque
information.\9\ The ECU continuously estimates the roll stability
threshold of a vehicle, which is the lateral acceleration above which a
combination vehicle will roll over. When the vehicle's lateral
acceleration approaches the roll stability threshold, the RSC system
intervenes. Depending on how quickly the vehicle is approaching the
estimated rollover threshold, the RSC system intervenes by one or more
of the following actions: Decreasing engine power, using engine
braking, applying the tractor's drive-axle brakes, or applying the
trailer's brakes. When RSC systems apply the trailer's brakes, they use
a pulse modulation protocol to prevent wheel lockup because tractor
stability control systems cannot currently detect whether or not the
trailer is equipped with ABS.
---------------------------------------------------------------------------

    \9\ RSC systems are not presently available for large buses.
---------------------------------------------------------------------------

    An RSC system can reduce rollovers, but is not designed to help to
maintain directional control of a truck tractor. Nevertheless, RSC
systems may provide some additional ability to maintain directional
control in some scenarios, such as in a low-center-of-gravity scenario,
where an increase in a lateral acceleration may lead to yaw instability
rather than roll instability.
    In comparison, a trailer-based RSC system has an ECU mounted on the
trailer, which typically monitors the trailer's wheel speeds, the
trailer's suspension to estimate the trailer's loading condition, and
the trailer's lateral acceleration. A trailer-based RSC system works
similarly to a tractor-based system. However, a trailer-based RSC
system can only apply the trailer brakes to slow a combination vehicle,
whereas a tractor-based RSC system can apply brakes on both the tractor
and trailer.
    The other type of stability control systems available for truck
tractors and large buses is an ESC system. An ESC system incorporates
all of the inputs of an RSC system. However, it also has two additional
sensors to monitor a vehicle for loss of directional control, which may
result due to either understeer or oversteer. The first additional
sensor is a steering wheel angle sensor, which senses the driver's
steering input.10 11 The other is a yaw rate sensor, which
measures the actual turning movement of the vehicle. These system
inputs are monitored by the system's ECU, which estimates when the
vehicle's directional response begins to deviate from the driver's
steering command, either by oversteer or understeer. An ESC system
intervenes to restore directional control by taking one or more of the
following actions: Decreasing engine power, using engine braking,
selectively applying the brakes on the truck tractor to create a
counter-yaw moment to turn the vehicle back to its steered direction,
or applying the brakes on the trailer. An ESC system enhances the RSC
functions because it has the added information from the steering wheel
angle and yaw rate sensors, as well as more braking power because of
its additional capability to apply the tractor's steer axle brakes.\12\
---------------------------------------------------------------------------

    \10\ Because ESC systems must monitor steering inputs from the
tractor, ESC systems are not available for trailers.
    \11\ Some RSC systems also use a steering wheel angle sensor,
which allows the system to identify potential roll instability
events earlier.
    \12\ This is a design strategy to avoid the unintended
consequences of applying the brakes on the steering axle without
knowing where the driver is steering the vehicle.
---------------------------------------------------------------------------

    Figure 2 illustrates the oversteering and understeering conditions.
While Figure 2 may suggest that a particular vehicle loses control due
to either oversteer or understeer, it is quite possible that a vehicle
could require both understeering and oversteering interventions during
progressive phases of a complex crash avoidance maneuver such as a
double lane change.

[GRAPHIC] [TIFF OMITTED] TR23JN15.009

    Understeering. The left side of Figure 2 shows a truck tractor
whose driver has lost directional control during an attempt to drive
around a right curve. The ESC system momentarily applies the right rear
brake, creating a clockwise rotational force, to turn the heading of
the vehicle back to the correct path. It will also reduce engine power
to gently slow the vehicle and, if necessary, apply additional brakes
(while maintaining the uneven brake force to create the necessary yaw
moment).
    Oversteering. The right side of Figure 2 shows that the truck
tractor whose driver has lost directional control during an attempt to
drive around a right curve. In a vehicle equipped with ESC, the system
immediately detects that the vehicle's heading is changing more quickly
than appropriate for the driver's intended path (i.e., the yaw rate is
too high). To counter the clockwise rotation of the vehicle, it
momentarily applies the left front brake, thus creating a counter-
clockwise counter-rotational force and turning the heading of the
vehicle back to the correct path. It will also reduce engine power to
gently slow the vehicle and, if necessary, apply additional brakes
(while maintaining the uneven brake force to create the necessary yaw
moment). The ESC activation can be so subtle that the driver does not
perceive the need for steering corrections.
    A stability control system will not prevent all rollover and loss-
of-control crashes. A stability control system has the capability to
prevent many untripped on-road rollovers and first-event loss-of-
control events. Nevertheless, there are real-world situations in which
stability control systems may not be as effective in avoiding a
potential crash. Such situations include:
     Off-road maneuvers in which a vehicle departs the roadway
and encounters a steep incline or an unpaved surface that significantly
reduces the predictability of the vehicle's handling
     Entry speeds that are much too high for a curved roadway
or entrance/exit ramp
     Cargo load shifts or liquid sloshing within the trailer
during a steering maneuver
     Vehicle tripped by a curb or other roadside object or
barrier
     Truck rollovers that are the result of collisions with
other motor vehicles
     Inoperative antilock braking systems--the performance of
stability control systems depends on the proper functioning of ABS
     Brakes that are out-of-adjustment or other defects or
malfunctions in the ESC, RSC, or brake system.
     Maneuvers during tire tread separation or sudden tire
deflation events.
    On April 6, 2007, the agency published a final rule that
established FMVSS No. 126, Electronic Stability Control Systems, which
requires all passenger cars, multipurpose passenger vehicles, trucks
and buses with a GVWR of 4,536 kg (10,000 lb.) or less to be equipped
with an electronic stability control system beginning in model year
2012.\13\ The system must be capable of applying brake torques
individually at all four wheels, and must comply with the performance
criteria established for stability and responsiveness when subjected to
the sine with dwell steering maneuver test. For light vehicles, the
focus of the FMVSS No. 126 is on addressing yaw instability, which can
assist the driver in preventing the vehicle from leaving the roadway,
thereby preventing fatalities and injuries associated with crashes
involving tripped rollover, which often occur when light vehicles run
off the road. The standard does not include any equipment or
performance requirements for roll stability.
---------------------------------------------------------------------------

    \13\ 72 FR 17236.
---------------------------------------------------------------------------

    The dynamics of light vehicles and heavy vehicles differ in many
respects. First, on light vehicles, the yaw stability threshold is
typically lower than the roll stability threshold. This means that a
light vehicle making a crash avoidance maneuver, such as a lane change
on a dry road, is more likely to reach its yaw stability threshold and
lose directional control before it reaches its roll stability threshold
and rolls over. On a heavy vehicle, however, the roll stability
threshold is lower than the yaw stability threshold in most operating
conditions, primarily because of its higher center-of-gravity
height.\14\ As a result, there is a greater propensity for a heavy
vehicle, particularly in a loaded condition, to roll during a severe
crash avoidance maneuver or when negotiating a curve, than to become
yaw unstable, as compared with light vehicles.
---------------------------------------------------------------------------

    \14\ One instance where a heavy vehicle's yaw stability
threshold might be higher than its roll stability threshold is in an
unloaded condition on a low-friction road surface.
---------------------------------------------------------------------------

    Second, a tractor-trailer combination unit is comprised of a power
unit and one or more trailing units with one or more articulation
points. In contrast, although a light vehicle may occasionally tow a
trailer, a light vehicle is usually a single rigid unit. The tractor
and the trailer have different center-of-gravity heights and different
lateral acceleration threshold limits for rollover. A combination
vehicle rollover frequently begins with the trailer where the rollover
is initiated by trailer wheel lift.
    Third, due to greater length, mass, and mass moments of inertia of
heavy vehicles, they respond more slowly to steering inputs than do
light vehicles. The longer wheelbase of a heavy vehicle, compared with
a light vehicle, results in a slower response time, which gives the
stability control system the opportunity to intervene and prevent
rollovers.
    Finally, the larger number of wheels on a heavy vehicle, as
compared to a light vehicle, makes heavy vehicles less

likely to become yaw unstable on dry road surface conditions.

IV. Safety Need

A. Heavy Vehicle Crash Problem

    This section presents data on the safety problem associated with
rollover and loss of control of heavy vehicles. The information has
been updated from similar information contained in the NPRM. For the
specific target population used to support the agency's system
effectiveness and estimated benefits, see Section XIV.
    The Traffic Safety Facts 2012 reports that tractor trailer
combination vehicles are involved in about 72 percent of the fatal
crashes involving large trucks, annually.\15\ According to FMCSA's
Large Truck and Bus Crash Facts 2011, these vehicles had a fatal crash
involvement rate of 1.46 crashes per 100 million vehicle miles traveled
during 2011, whereas single-unit trucks had a fatal crash involvement
rate of 1.00 crashes per 100 million vehicle miles traveled.\16\
Combination vehicles represent about 24 percent of large trucks
registered but travel 61 percent of the large truck miles, annually.
Traffic tie-ups resulting from loss-of-control and rollover crashes
also contribute to in millions of dollars of lost productivity and
excess energy consumption each year.
---------------------------------------------------------------------------

    \15\ DOT HS 812 032, available at http://www-nrd.nhtsa.dot.gov/Pubs/812032.pdf.
    \16\ FMCSA-RRA-13-049 (Oct. 2013), available at http://www.fmcsa.dot.gov/sites/fmcsa.dot.gov/files/docs/LargeTruckandBusCrashFacts2011.pdf.
---------------------------------------------------------------------------

    According to Traffic Safety Facts 2012, the overall crash problem
for tractor trailer combination vehicles in that year was approximately
180,000 crashes, 42,000 of which involve injury. The overall crash
problem for single-unit trucks is nearly as large--in 2012, there were
approximately 154,000 crashes, 35,000 of which were injury crashes.
However, the fatal crash involvement for truck tractors is much higher.
In 2011, there were 2,736 fatal combination truck crashes and 1,066
fatal single-unit truck crashes.
    The rollover crash problem for combination trucks is much greater
than for single-unit trucks. In 2011, there were approximately 8,000
crashes involving combination truck rollover and 5,000 crashes
involving single-unit truck rollover. As a percentage of all crashes,
combination trucks are involved in rollover crashes at a higher rate
compared to single-unit trucks. Approximately 4.6 percent of all
combination truck crashes were rollovers, but 3.2 percent of single-
unit truck crashes were rollovers. Combination trucks were involved in
3,000 injury crashes and 373 fatal crashes, and single-unit trucks were
involved in 3,000 injury crashes and 194 fatal crashes.
    According to FMCSA's Large Truck and Bus Crash Facts 2011, cross-
country intercity buses were involved in 39 of the 242 fatal bus
crashes in 2011. The bus types presented in the crash data include
school buses, cross-country intercity buses, transit buses, van-based
buses, and other buses. From 2002 to 2011, cross-country intercity
buses, on average, accounted for approximately 12 percent of all buses
involved in fatal crashes, whereas transit buses and school buses
accounted for 34 percent and 40 percent, respectively, of all buses
involved in fatal crashes. However, most of the transit bus and school
bus crashes are not rollover or loss-of-control crashes that ESC
systems are capable of preventing. Fatal rollover and loss-of-control
crashes are a subset of these crashes.
    There are many more fatalities in buses with a GVWR greater than
11,793 kg (26,000 lb.) compared to buses with a GVWR between 4,536 kg
and 11,793 kg (10,000 lb. and 26,000 lb.).\17\ In the 10-year period
between 2000 and 2009, there were 42 fatalities on buses with a GVWR
between 4,536 kg and 11,793 kg (10,000 lb. and 26,000 lb.) compared to
209 fatalities on buses with a GVWR greater than 11,793 kg (26,000
lb.). Among buses with a GVWR of greater than 11,793 kg (26,000 lb.),
over 70 percent of the fatalities were cross-country intercity bus
occupants, ``other buses,'' and ``unknown buses.'' \18\ Thus, although
these buses are only involved in 12 percent of fatal crashes involving
buses, they represent the majority of fatalities from bus crashes.
---------------------------------------------------------------------------

    \17\ This data was taken from the FARS database and was
presented in the final rule requiring that seat belts be installed
on certain buses. See 78 FR 70415, 70423-26 (Nov. 25, 2013).
    \18\ The FARS database has five bus body type categories: (1)
Cross-country/intercity bus, (2) transit bus, (3) school bus, (4)
other bus, and (5) unknown bus. Transit bus and school bus body
types were excluded from the analysis because they are easily
recognized and categorized as such by crash investigators and those
coding the FARS data. Thus, those vehicles are unlikely to be
miscoded as other buses.
---------------------------------------------------------------------------

    Furthermore, the size of the rollover crash problem for cross-
country intercity buses is greater than in other buses. According to
FARS data from 2000 to 2009, there were 114 occupant fatalities as a
result of rollover events on cross-country intercity buses, ``other
buses,'' and ``unknown buses'' with a GVWR of greater than 11,793 kg
(26,000 lb.), which represents 55 percent of bus fatalities on those
bus types.

B. Contributing Factors in Rollover and Loss-of-Control Crashes

    Many factors related to heavy vehicle operation, as well as factors
related to roadway design and road surface properties, can cause heavy
vehicles to become yaw unstable or to roll. Listed below are several
real-world situations in which stability control systems may prevent or
lessen the severity of such crashes.
     Speed too high to negotiate a curve--The entry speed of
vehicle is too high to safely negotiate a curve. When the lateral
acceleration of a vehicle during a steering maneuver exceeds the
vehicle's roll or yaw stability threshold, a rollover or loss of
control is initiated. Curves can present both roll and yaw instability
issues to these types of vehicles due to varying heights of loads (low
versus high, empty versus full) and road surface friction levels (e.g.,
wet, dry, icy, snowy).
     Road design configuration--Some drivers may misjudge the
curvature of ramps and not brake sufficiently to negotiate the curve
safely. This includes driving on ramps with decreasing radius curves as
well as operating on curves and ramps with improper signage. A vehicle
traveling on a curve with a decrease in super-elevation (banking) at
the end of a ramp where it merges with the roadway causes an increase
in vehicle lateral acceleration, which may increase even more if the
driver accelerates the vehicle in preparation to merge.
     Sudden steering maneuvers to avoid a crash--The driver
makes an abrupt steering maneuver, such as a single- or double-lane-
change maneuver, or attempts to perform an off-road recovery maneuver,
generating a lateral acceleration that is sufficiently high to cause
roll or yaw instability. Maneuvering a vehicle on off-road, unpaved
surfaces such as grass or gravel may require a larger steering input
(larger wheel slip angle) to achieve a given vehicle response, and this
can lead to a large increase in lateral acceleration once the vehicle
returns to the paved surface. This increase in lateral acceleration can
cause the vehicle to exceed its roll or yaw stability threshold.
     Loading conditions--A loss of yaw stability due to severe
over-steering is more likely to occur when a vehicle is in a lightly
loaded condition and has a lower center-of-gravity height than it would
have when fully loaded. Heavy vehicle rollovers are much more likely to
occur when the vehicle is in a fully loaded condition, which results in
a high center of gravity for the vehicle.

Cargo placed off-center in the trailer may result in the vehicle being
less stable in one direction than in the other. It is also possible
that improperly secured cargo can shift while the vehicle is
negotiating a curve, thereby reducing roll or yaw stability. Sloshing
can occur in tankers transporting liquid bulk cargoes, which is of
particular concern when the tank is partially full because the vehicle
may experience significantly reduced roll stability during certain
maneuvers.
     Road surface conditions--The road surface condition can
also play a role in the loss of control a vehicle experiences. On a
dry, high-friction asphalt or concrete surface, a tractor trailer
combination vehicle executing a severe turning maneuver is likely to
experience a high lateral acceleration, which may lead to roll or yaw
instability. However, a similar maneuver performed on a wet or slippery
road surface is not as likely to experience the high lateral
acceleration because of less available tire traction. Hence, the
vehicle is more likely to be yaw unstable than roll unstable.

C. NTSB Safety Recommendations

    The National Transportation Safety Board (NTSB) has issued several
safety recommendations relevant to ESC systems on heavy and other
vehicles. One is H-08-15, which addresses ESC systems and collision
warning systems with active braking on commercial vehicles.
Recommendations H-11-07 and H-11-08 specifically address stability
control systems on commercial motor vehicles and buses with a GVWR
above 10,000 pounds. Two other safety recommendations, H-01-06 and H-
01-07, relate to adaptive cruise control and collision warning systems
on commercial vehicles and are indirectly related to ESC on heavy
vehicles because these technologies require the ability to apply brakes
without driver input.
     H-08-15: Determine whether equipping commercial vehicles
with collision warning systems with active braking \19\ and electronic
stability control systems will reduce commercial vehicle accidents. If
these technologies are determined to be effective in reducing
accidents, require their use on commercial vehicles.
---------------------------------------------------------------------------

    \19\ Active braking involves using the vehicle's brakes to
maintain a certain, preset distance between vehicles.
---------------------------------------------------------------------------

     H-11-07: Develop stability control system performance
standards for all commercial motor vehicles and buses with a gross
vehicle weight rating greater than 10,000 pounds, regardless of whether
the vehicles are equipped with a hydraulic or pneumatic brake system.
     H-11-08: Once the performance standards from Safety
Recommendation H-11-07 have been developed, require the installation of
stability control systems on all newly manufactured commercial vehicles
with a GVWR greater than 10,000 pounds.

D. Motorcoach Safety Plan

    In November 2009, the U.S. Department of Transportation Motorcoach
Safety Action Plan was issued.\20\ Among other things, the Motorcoach
Safety Action Plan includes an action item for NHTSA to assess the
safety benefits for stability control on large buses and develop
objective performance standards for these systems.\21\ Consistent with
that plan, NHTSA made a decision to pursue a stability control
requirement for large buses.
---------------------------------------------------------------------------

    \20\ See supra, note 6.
    \21\ Id. at 28-29.
---------------------------------------------------------------------------

    In March 2011, NHTSA issued its latest Vehicle Safety and Fuel
Economy Rulemaking and Research Priority Plan (Priority Plan).\22\ The
Priority Plan describes the agency plans for rulemaking and research
for calendar years 2011 to 2013. The Priority Plan includes stability
control on truck tractors and large buses, and states that the agency
plans to develop test procedures for a Federal motor vehicle safety
standard on stability control for truck tractors, with the
countermeasures of roll stability control and electronic stability
control, which are aimed at addressing rollover and loss-of-control
crashes.
---------------------------------------------------------------------------

    \22\ See Docket No. NHTSA-2009-0108-0032.
---------------------------------------------------------------------------

E. International Regulation

    The United Nations (UN) Economic Commission for Europe (ECE)
Regulation 13, Uniform Provisions Concerning the Approval of Vehicles
of Categories M, N and O with Regard to Braking, has been amended to
include Annex 21, Special Requirements for Vehicles Equipped with a
Vehicle Stability Function. Annex 21's requirements apply to trucks
with a GVWR greater than 3,500 kg (7,716 lb.), buses with a seating
capacity of 10 or more (including the driver), and trailers with a GVWR
greater than 3,500 kg (7,716 lb.). Trucks and buses are required to be
equipped with a stability system that includes rollover control and
directional control, while trailers are required to have a stability
system that includes only rollover control. The directional control
function must be demonstrated in one of eight tests, and the rollover
control function must be demonstrated in one of two tests. For
compliance purposes, the ECE regulation requires a road test to be
performed with the function enabled and disabled, or as an alternative,
accepts results from a computer simulation. No test procedure or pass/
fail criterion is included in the regulation, but it is left to the
discretion of the Type Approval Testing Authority in agreement with the
vehicle manufacturer to show that the system is functional. The
implementation date of Annex 21 was 2012 for most vehicles, with a
phase-in based on the vehicle type.

V. Summary of the May 2012 NPRM

    Since 2006, the agency has been involved in testing truck tractors
and large buses with stability control systems. To evaluate these
systems, NHTSA sponsored studies of crash data in order to examine the
potential safety benefits of stability control systems. NHTSA and
industry representatives separately evaluated data on dynamic test
maneuvers. At the same time, the agency launched a three-phase testing
program to improve its understanding of how stability control systems
in truck tractors and buses work and to develop dynamic test maneuvers
to challenge roll propensity and yaw stability. By combining the
studies of the crash data with the testing data, the agency is able to
evaluate the potential effectiveness of stability control systems for
truck tractors and large buses.
    The agency conducted a three-phase testing program for truck
tractors and large buses that was described at length in the NPRM and
in published reports in order to develop one or more test maneuvers to
ensure that ESC systems can reduce vehicle instability. As a result of
the agency's testing program and the test data received from industry,
the agency was able to develop reliable and repeatable test maneuvers
that could demonstrate a stability control system's ability to prevent
rollover and loss of directional control among the varied
configurations of truck tractors and buses in the fleet.
    After considering and evaluating several test maneuvers, the agency
proposed using two test maneuvers for performance testing: The slowly
increasing steer (SIS) maneuver and the sine with dwell (SWD) maneuver.
The SIS maneuver is a characterization maneuver used to determine the
amount of steering input required by the SWD maneuver. By determining
the relationship between a vehicle's steering wheel angle and the
lateral acceleration,

the SIS maneuver normalizes the severity of the SWD maneuver. The SIS
maneuver was also proposed to be used to ensure that the system has the
ability to reduce engine torque.
    Using a steering wheel angle derived from the SIS maneuver, the
agency proposed conducting the sine with dwell maneuver. The SWD test
maneuver challenges both roll and yaw stability by subjecting the
vehicle to a sinusoidal input. This maneuver would be repeated for two
series of test runs (first in the counterclockwise direction and then
in the clockwise direction) at several target steering wheel angles
from 30 to 130 percent of the angle derived in the SIS maneuver.
    We proposed measuring, recording, and processing lateral
acceleration, yaw rate, and engine torque data derived from the SIS and
SWD maneuvers to determine four performance metrics: Lateral
acceleration ratio (LAR), yaw rate ratio (YRR), lateral displacement,
and engine torque reduction. The LAR and YRR metrics ensure that the
system reduces lateral acceleration and yaw rate, respectively, after
an aggressive steering input, thereby preventing rollover and loss of
control, respectively. The lateral displacement metric ensures that the
stability control system is not set to intervene solely by making the
vehicle nonresponsive to driver input. The engine torque reduction
metric ensures that the system has the capability to automatically
reduce engine torque in response to high lateral acceleration and yaw
rate conditions.
    The agency also considered several test maneuvers based on its own
work and that of industry. In particular, the agency's research
included both a J-turn maneuver and a ramp steer maneuver (RSM) for
evaluating roll stability. The J-turn maneuver is a path-following
maneuver where a vehicle is driven on a test course consisting of a
straight lane followed by a fixed radius curve. The steering wheel
angle is determined by the driver making adjustments and corrections to
maintain the fixed path. In the RSM maneuver, a vehicle is driven at a
constant speed and a steering wheel input that is based on the steering
wheel angle derived from the SIS maneuver. The steering wheel angle is
then held for a period of time before it is returned to zero. In both
the J-turn and RSM maneuvers, a stability control system acts to reduce
lateral acceleration, and thereby wheel lift and roll instability, by
applying selective braking. A vehicle without a stability control
system being tested with these maneuvers would exhibit high levels of
lateral acceleration and potentially experience wheel lift or rollover.
    The NPRM also set forth the test conditions that the agency would
use to ensure safety and demonstrate sufficient performance. All
vehicles were proposed to be tested using outriggers for the safety of
the test driver. The agency proposed using an automated steering
controller for the RSM, SIS, and SWD maneuvers to ensure reproducible
and repeatable test execution performance. The agency proposed testing
truck tractors with an unbraked control trailer to eliminate the effect
of the trailer's brakes on testing. The agency also proposed a test to
ensure that system malfunction is detected.
    The NPRM proposed that a final rule would take effect for most
truck tractors and applicable buses produced two years after
publication of a final rule. We stated that two years of lead time
would be necessary to ensure sufficient availability of stability
control systems from suppliers of these systems and to complete
necessary engineering on all vehicles. For three-axle tractors with one
drive axle, tractors with four or more axles, and severe service
tractors, we proposed allowing two years of additional lead time. We
stated this additional time would be necessary to develop, test, and
equip these vehicles with ESC systems. Although the agency has
statutory authority to require retrofitting of in-service truck
tractors, trailers, and large buses, the agency did not propose to
require retrofitting, but sought comment on its feasibility, given the
integrated aspects of a stability control system.

VI. Overview of the Comments

    This section presents a brief overview of the comments received in
response to the NPRM. The comments are addressed in detail in the
section related to the subject of the comment. However, those comments
that merely advocated the adoption or rejection of the proposal or some
aspect thereof without any underlying explanation are not addressed
further.
    We also conducted a public hearing on July 24, 2012 in Washington,
D.C.\23\ Summaries of the oral testimony and a transcript of the
hearing are both available in the docket.\24\ Although we have
considered the public hearing testimony as if it was a written comment
received in the docket, much of the testimony was duplicated in the
written comments. We have discussed public hearing testimony below only
where that testimony was not reflected in written comments received by
the agency.
---------------------------------------------------------------------------

    \23\ Notice of the hearing was published in the Federal Register
on July 2, 2012. 77 FR 39206.
    \24\ Summaries of the oral testimony provided by the presenters
are contained in Docket No. NHTSA-2012-0065-0049. A transcript of
the public hearing is contained in Docket No. NHTSA-2012-0065-0056.
---------------------------------------------------------------------------

    In addition to the comments received at the public hearing, we
received written comments from 43 individuals or entities. The
commenters represented wide-ranging interests, including individuals,
truck drivers, truck fleet operators, vehicle component manufacturers,
truck and bus manufacturers, and safety advocacy organizations. The
identity of the 46 commenters, their self-identified interest or
affiliation, if given, where the comments can be located in the docket
are cited in Table 2.\25\
---------------------------------------------------------------------------

    \25\ Three commenters presented comments only at the public
hearing.

   Table 2--List of Commenters and Location of Comments in the Docket
------------------------------------------------------------------------
            Commenter                          Docket Number
------------------------------------------------------------------------
Vehicle Manufacturers:
Blue Bird Body Company (Blue       NHTSA-2012-0065-0034
 Bird).
Daimler Trucks North America LLC   NHTSA-2012-0065-0028
 (Daimler).
EvoBus GmbH......................  NHTSA-2012-0065-0027
Fire Apparatus Manufacturer's      NHTSA-2012-0065-0014
 Association.
Navistar, Inc....................  NHTSA-2012-0065-0039
Schneider National Inc.            NHTSA-2012-0065-0033
 (Schneider).
Temsa Global (Temsa).............  NHTSA-2012-0065-0019
Truck & Engine Manufacturers       NHTSA-2012-0065-0044
 Association (EMA).
Volvo Group......................  NHTSA-2012-0065-0031

Component Manufacturers:
Bendix Commercial Vehicle Systems  NHTSA-2012-0065-0046
                                   NHTSA-2012-0065-0048
                                   NHTSA-2012-0065-0055
Heavy Duty Brake Manufacturers     NHTSA-2012-0065-0041
 Council (HDBMC).
Meritor WABCO....................  NHTSA-2012-0065-0035
Robert Bosch LLC (Bosch).........  NHTSA-2012-0065-0036
Drivers and Fleet Operators:
American Trucking Associations,    NHTSA-2012-0065-0016
 Inc. (ATA), including report of   NHTSA-2012-0065-0030
 the American Transportation       NHTSA-2012-0065-0057
 Research Institute (ATRI).
Associated Logging Contractors--   NHTSA-2012-0065-0042
 Idaho.
John Boyle.......................  NHTSA-2012-0065-0017
Jim Burg, James Burg Trucking      NHTSA-2012-0065-0056 (public hearing)
 Company.
John H. Hill, The Hill Group.....  NHTSA-2012-0065-0056 (public hearing)
Alexander J. MacDonald...........  NHTSA-2012-0065-0005
National Ready Mixed Concrete      NHTSA-2012-0065-0038
 Association.
National School Transportation     NHTSA-2012-0065-0037
 Association.
Owner-Operator Independent         NHTSA-2012-0065-0024
 Drivers Association (OOIDA).
Skagit Transportation Inc........  NHTSA-2012-0065-0006
Bob Waterman.....................  NHTSA-2012-0065-0052
Safety Organizations:
AAA Public Affairs (AAA).........  NHTSA-2012-0065-0043
Advocates for Highway and Auto     NHTSA-2012-0065-0047
 Safety (Advocates).
American Highway Users Alliance..  NHTSA-2012-0065-0040
Commercial Vehicle Safety          NHTSA-2012-0065-0050
 Alliance (CVSA).
Consumers Union..................  NHTSA-2012-0065-0053
Insurance Institute for Highway    NHTSA-2012-0065-0021
 Safety (IIHS).
Kentucky Injury Prevention and     NHTSA-2012-0065-0007
 Research Center.
National Association for Pupil     NHTSA-2012-0065-0023
 Transport (NAPT).
National Transportation Safety     NHTSA-2012-0065-0015
 Board (NTSB).
Road Safe America................  NHTSA-2012-0065-0004
Other Organizations and Private
 Individuals:
American Association for Justice   NHTSA-2012-0065-0020
 (AAJ).
American Trauma Society..........  NHTSA-2012-0065-0009
Justin C. Barriault..............  NHTSA-2012-0065-0010
Robert M. Chin...................  NHTSA-2012-0065-0011
Jerry R. Curry...................  NHTSA-2012-0065-0018
Jerry J. Evans...................  NHTSA-2012-0065-0003
Fried Rogers Goldberg, LLC.......  NHTSA-2012-0065-0025
Nadya V. Gerber..................  NHTSA-2012-0065-0012
The Martec Group, Inc. (Martec)..  NHTSA-2012-0065-0051
Mercatus Center at George Mason    NHTSA-2012-0065-0022
 University (Mercatus).
Josh A. Sullivan.................  NHTSA-2012-0065-0013
Hon. Betty Sutton................  NHTSA-2012-0065-0056
                                   (public hearing)
------------------------------------------------------------------------

VII. Key Differences Between the Final Rule and the NRPM

    This section summarizes the significant differences between the
NPRM and this final rule. Less significant changes are noted in the
appropriate sections of the preamble.
    The most significant change between the NPRM and the final rule is
that the agency has chosen an alternative performance test maneuver to
demonstrate an ESC system's ability to maintain vehicle stability.
After considering public comments and conducting additional track
testing, we have adopted a 150-foot J-turn maneuver as the performance
test maneuver in this final rule. In the NPRM, we proposed using a
slowly increasing steer (SIS) maneuver as a characterization maneuver
and a sine with dwell (SWD) maneuver as a roll and yaw performance
maneuver. The 150-foot J-turn test maneuver is discussed in the NPRM
and is a variation of an alternative test maneuver proposed in the
NPRM.
    Because the 150-foot J-turn test maneuver only tests an ESC
system's ability to mitigate roll instability and the agency lacks any
alternative test maneuver to test an ESC system's ability to mitigate
yaw instability, this final rule does not include a performance test to
evaluate yaw instability. However, this final rule carries forward the
requirement that an ESC system be capable of mitigating yaw
instability.
    The 150-foot J-turn maneuver also uses a different performance
metric than the SWD maneuver. The SWD maneuver's performance criteria
were the change in lateral acceleration and yaw rate through the
maneuver. In this final rule, we are using a simpler metric--reduction
in forward speed.
    The change in performance test maneuver has also led to changes in
the test conditions and equipment. Because the test maneuver in this
final rule is conducted over a fixed path, rather than fixed steering
used for the SWD maneuver, an automated steering wheel controller will
not be used for the J-turn maneuver. We have also modified the

loading condition for vehicles to test them at GVWR. We have also
reduced the instrumentation requirements in light of the simpler
performance metric.

VIII. ESC Requirement

A. Whether to Require Stability Control

    In the May 2012 NPRM, the agency proposed to require that all truck
tractors and certain buses with a GVWR of more than 11,793 kg (26,000
lb.) to be equipped with ESC. The agency preliminarily found that the
proposed standard met the need for motor vehicle safety.\26\ That
finding was based upon the safety problem discussed in the NPRM and
summarized in section IV above.\27\ Moreover, the agency found that
requiring ESC systems on truck tractors and certain large buses would
be cost-effective.\28\
---------------------------------------------------------------------------

    \26\ 77 FR 30788.
    \27\ 77 FR 30769-71.
    \28\ 77 FR 30791.
---------------------------------------------------------------------------

    We received many comments addressing the general question of
whether stability control systems should be required on truck tractors
and large buses. Several commenters questioned the need for a stability
control mandate on truck tractors and certain large buses and
recommended against adopting a final rule requiring any type of
stability control system. A consistent theme in many of the comments
received from private individuals was also expressed in the comment
from Yankee Trucks. These commenters argued that the decision to
include ESC should be decided by the vehicle's end user.
    Other commenters such as Mercatus and OOIDA were concerned that
NHTSA failed to look at alternative methods to improve motor vehicle
safety problems caused by rollover and loss-of-control crashes.
Mercatus suggested that NHTSA failed to look at driver fatigue
detection, road condition sensors, improved safety procedures, or
driver training, which might be less costly. OOIDA highlighted driver
training, enforcement of traffic laws, driver incentives, improved
crashworthiness, and road signage as alternative ways to deal with the
rollover problem. Several other commenters highlighted driver training
and accountability related to both driving and vehicle loading as
alternative methods that could prevent rollover and loss-of-control
crashes. The Boyle Brothers, OOIDA, and several individual commenters
both noted that stability control systems would not prevent crashes
caused by driving too fast for conditions. Both Mercatus and OOIDA
believe that alternative measures are less costly than a stability
control mandate at preventing rollover and loss-of-control crashes.
    Individual commenters, many of whom identified themselves as truck
drivers, also questioned the safety of stability control systems and
their ability to prevent crashes. One commenter believes that stability
control systems are unsafe based on personal experience because it
often engaged the service brakes in curves. Another commenter was
concerned that drivers would become too dependent on stability control
systems and cause them to drive through curves faster with the system
than without.
    OOIDA and many individual commenters were concerned about the total
cost of the rule and whether the benefits justified the costs.
Relatedly, several commenters raised concerns that stability control
systems would add complexity to the brake system by requiring
additional parts, and thus, higher repair costs. Yankee Trucks also
raised concerns that if a stability control system malfunctions, ABS
would also not function. OOIDA claimed that a stability control
requirement would cause drivers and truck companies to keep existing
vehicles in service longer or even go out of business due to the added
costs of stability control and other regulatory mandates.
    Some commenters also expressed concerns that stability control
technologies could have negative effects on safety. For example,
individual commenters questioned whether it was safe to have stability
control systems braking the vehicle automatically in wet conditions or
on curves. Associated Logging Contractors opposed a mandate because it
believes that a stability control requirement may cause safety issues
on forest roads, which are different from highways.
    Commenters from a wide variety of backgrounds supported a stability
control mandate. These organizations include organizations such as Road
Safe America, the Kentucky Injury Prevention and Research Center, the
American Trauma Society, the American Association for Justice,
Advocates, the American Highway Users Alliance, AAA, the Commercial
Vehicle Safety Alliance, and Consumers Union. Business associations
representing brake suppliers (HDBMC), truck manufacturers (EMA), and
truck fleet operators (ATA) all supported a stability control mandate.
Brake suppliers such as Bosch, Bendix, and Meritor WABCO also supported
a stability control mandate. Individual truck and bus manufacturers who
commented also such as Daimler, Volvo, and Navistar supported a
stability control mandate. Some motor carriers who commented also
supported a stability control mandate. The NTSB and a former Member of
Congress, Betty Sutton, both supported a stability control mandate.
Many individual commenters also supported a stability control mandate.
    Although these commenters come from varied backgrounds, their
reasons for supporting a stability control mandate were generally
consistent. Commenters supporting a mandate generally cited research
from NHTSA, the manufacturing industry, and others regarding the
effectiveness of stability control systems, and their ability to
prevent rollover and loss-of-control crashes and save lives. IIHS, for
example, cited its own research suggesting that having ESC systems on
all truck tractors could prevent as many as 295 fatal crashes each
year. Some individual commenters also cited personal experience with
stability control systems. John Hill observed that the cost of a
stability control system on a vehicle is comparable to the cost to the
government of a single compliance review of a motor carrier's safety
practices. These commenters generally agreed that the benefits of a
stability control mandate far exceed its costs.
    After considering all public comments, the agency is proceeding
with adopting FMVSS No. 136 to require all truck tractors and certain
large buses with a GVWR of more than 11,793 kg (26,000 lb.) to have
stability control systems. This decision is largely driven by the data
before the agency. In developing the proposal, the agency analyzed
crash data to identify risks not addressed in existing FMVSSs. These
safety risks include rollover and loss-of-control crashes that are
caused by many factors including traveling at a speed too high to
negotiate a curve, sudden steering maneuvers to avoid a crash, loading
conditions, road surface conditions, and road design configuration. The
agency's research, described at length in the NPRM, shows that
stability control technologies could prevent crashes in these
situations.
    With respect to the comments suggesting that vehicles braking
during a curve or on wet conditions could have adverse safety
consequences, we observe that an ESC system is designed to slow the
vehicle in a curve in order to reduce the lateral acceleration and
allow the operator to maintain roll and yaw control of the vehicle only
in situations where instability is imminent. After careful qualitative
and quantitative assessment, we have concluded that requiring stability

control systems will improve the overall safety of the vehicle.
    Regarding other possible improvements to reduce crashes, we do not
disagree that many of the suggestions regarding driver training,
enforcements, and crashworthiness of trucks and buses could improve
motor vehicle safety and (except for the latter) reduce vehicle
rollover and loss-of-control crashes. However, driver training and
enforcement of traffic safety laws are outside of NHTSA's regulatory
authority under the Safety Act. Moreover, the commenters advocating
these alterative means to address the safety problem did not provide
data to support their conclusions that their alternatives would be less
costly or more cost-effective than a stability control mandate.
Although the issues related to costs and benefits will be addressed
more specifically in section XIV below, the agency has concluded that
requiring ESC systems on truck tractors and certain large buses is
cost-effective and the most effective means to address the safety
problem identified in this rulemaking.

B. Whether to Require ESC or RSC

    The agency proposed to require that truck tractors and large buses
be equipped with ESC systems rather than RSC systems. An ESC system is
capable of all of the functions of an RSC system. In addition, an ESC
system has the additional ability to detect yaw instability, provide
braking at front wheels, and detect the steering wheel angle. These
additions, as demonstrated by NHTSA's testing, allow an ESC system to
have better rollover prevention performance than an RSC system in
addition to the yaw instability prevention component. This is because
the steering wheel angle sensor allows the ESC system to anticipate
changes in lateral acceleration based upon driver input and to
intervene with engine torque reduction or selective braking sooner,
rather than waiting for the lateral acceleration sensors to detect
potential instability.
    The NPRM stated that mandating ESC systems rather than RSC systems
will prevent more crashes, injuries, and fatalities. The additional
benefits from ESC systems can be attributed to both the ESC's system's
ability to intervene sooner and its ability to prevent yaw instability
that would lead to loss-of-control crashes.
    The NPRM stated that mandating ESC systems rather than RSC systems
will result in higher initial costs to manufacturers. Moreover, while
our benefit and cost estimates led to the preliminary conclusion that
mandating RSC systems would be more cost-effective than mandating ESC
systems, mandating ESC systems would result in higher net benefits.
    Several commenters agreed with NHTSA's proposal to require ESC
systems rather than RSC systems. Jerry Curry and Bendix specifically
mentioned that ESC systems should be required instead of RSC systems.
Mr. Curry and IIHS also commented that RSC systems would not be the
best platform to use when considering future technological advances.
John Hill similarly observed that ESC systems have the potential to
support future collision avoidance and crash mitigation technologies.
Mr. Hill also observed that loss-of-control crashes can be difficult to
identify and classify. Road Safe America, Mr. MacDonald, and AAA said
the agency should require ESC equipment on truck tractors and buses.
IIHS and Jim Burg recommended requiring ESC systems over RSC systems
because loss-of-control collisions can be reduced using ESC systems.
Volvo, while not expressly advocating for an ESC mandate, stated that
it had investigated the use of RSC systems, but found they were unable
to provide stability control in a wide range of driving conditions and
environments that its customers operate.
    In its comment, Bendix stated that an ESC system has an
effectiveness that is 31% greater than a RSC system. Bendix also
commented that ESC systems provide ``more information about what the
vehicle is doing'' because these systems include two additional
sensors. Bendix also said that ESC systems provide more effective
interventions through selective application of all available vehicle
brakes.
    Other commenters supported RSC as a minimum requirement rather than
ESC. Schneider, for example, asserted that it considered purchasing
vehicles with ESC system, but determined that ESC systems would provide
a negligible benefit at substantially higher costs when compared to
RSC. ATA also asserted that marginal benefit of ESC over RSC is not
justified by the added cost based on current information. ATA cited the
variability of the truck-tractor industry in four areas: (1) Private
trucking vs. for-hire companies; (2) the size of loads; (3) the type of
truck and trailer being used (e.g., box, van, refrigerated, liquid and
bulk tankers); and by operation (e.g., agricultural, long haul, short
haul, over size, overweight, etc.). ATA believes this diversity may
warrant choosing ESC or RSC depending on the individual vehicle.
    Both Schneider and ATA cited a study by the American Transportation
Research Institute (ATRI) that surveyed stability control technology
used in the trucking industry. This study collected crash and financial
data from the trucking industry, including information regarding
whether the vehicle was equipped with an ESC system, an RSC system, or
no stability control system at all. The sample included 135,712 trucks,
of which 68,647 had RSC systems, 39,529 had ESC systems, and 27,536 had
no stability control systems. The study included unit costs of
stability systems, average annual miles per tractor, the total number
of safety incidents (including rollover crashes), and the average cost
of each incident. The crash analysis concluded that industry-wide
installation of RSC systems would result in fewer rollover, jackknife,
and tow/stuck crashes compared to industry-wide installation of ESC
systems.
    NHTSA agrees with those commenters recommending ESC systems instead
of RSC systems. However, we are not relying on the assertions of Mr.
Curry, Mr. Hill and IIHS that ESC systems provide a better platform for
future technological advances. We believe the justification for ESC
systems is satisfied using benefits estimates for today's ESC systems,
without having to consider possible future advances such as forward
collision mitigation systems. Similarly, we are not relying on Bendix's
assessment of ESC system effectiveness. While Bendix's analysis of the
effectiveness of ESC and RSC systems is addressed in more detail in
section XIV below, we believe that our own analysis based on an
effectiveness study conducted by University of Michigan Transportation
Research Institute (UMTRI) and Meritor WABCO is a more accurate
assessment of the effectiveness of ESC and RSC systems. Although both
NHTSA and Bendix reached the conclusion that ESC systems will be more
effective than RSC systems at preventing rollover crashes, we believe
that Bendix's method of determining system effectiveness is arbitrarily
biased in favor of ESC systems.
    Regarding ATA's assertion of the variability of trucks, we agree
that truck tractors are varied and that some of those variations affect
vehicle stability. However, we believe that variability justifies
choosing to require ESC systems rather than RSC systems. In particular,
ATA observed that trucks carry various loads, implying that certain
kinds of loads may be more suited to ESC systems whereas other

loads may only require RSC systems to achieve equal effectiveness.
However, the nature of the trucking industry is such that a truck
tractor may end up towing many different types of trailers in its
lifetime, including flatbed trailers, box trailers, and tanker
trailers. A vehicle manufacturer is unlikely to know at the time of a
vehicle's production whether a specific truck tractor is going to be
carrying loads that are more likely to cause a rollover or loss-of-
control crash because the load has a high center of gravity or has the
potential to slosh. The only way to ensure that the vehicles that ATA
believes would perform better with ESC systems is to require all truck
tractors to be equipped with ESC systems.
    The ATRI study will be addressed more specifically in the benefits
and costs discussion in section XIV below and in the FRIA accompanying
this final rule. However, for the purpose of determining whether to
require ESC systems or RSC systems, the ATRI study's suggestion that
RSC systems would be more beneficial than ESC systems reflects the
specific truck carriers they studied, but does not necessarily
constitute a representative sample of the truck fleet. ATRI's
conclusion is contrary to NHTSA's own findings that ESC systems are
more effective and have greater net benefits than RSC systems. First,
as explained above, ESC systems contain all of the functions of RSC
systems, plus have additional sensors such as a steering wheel angle
sensor, to allow a system to intervene based on a predicted rise in
lateral acceleration rather than waiting for the lateral acceleration
to rise. Second, ESC systems have the capability to braking all of the
vehicle's axles, whereas an RSC system is generally unable to brake the
steering axle of the vehicle. Third, although NHTSA's own research
found that one RSC system performed as well or slightly better than an
ESC system under certain conditions, we attributed the performance
difference to that particular RSC system being programmed to brake more
aggressively than the ESC system on the same vehicle.\29\ For these
reasons, we conclude that the ATRI study is not representative of the
entire trucking industry or the performance of ESC systems compared to
RSC systems.
---------------------------------------------------------------------------

    \29\ 77 FR 30779.
---------------------------------------------------------------------------

    Based on the foregoing, this final rule will require that truck
tractors and certain buses be equipped with ESC systems rather than RSC
systems. As discussed in section XIV below, RSC systems are less
beneficial than ESC systems in reducing rollover crashes and much less
beneficial in addressing loss-of-control crashes. Although RSC systems
are slightly more cost beneficial than ESC systems, ESC systems provide
substantially higher net benefits because ESC systems will prevent many
more crashes.\30\ NHTSA has concluded that the additional safety
benefits of ESC systems in both rollover and loss-of-control crashes
justify the additional cost of ESC systems compared to RSC systems.
---------------------------------------------------------------------------

    \30\ Cost-effectiveness is measured in terms of lower cost per
equivalent life saved. For more discussion of the costs and benefits
of this rule see Section XIV, below, and the Final Regulatory Impact
Analysis accompanying this final rule, which has been placed in the
docket.
---------------------------------------------------------------------------

C. Definition of ESC

    The NPRM included definitional criteria in the proposed regulatory
text. We reasoned that, relying solely on performance-based tests
without mandating any specific equipment may require a battery of tests
to cover the complete operating range of the vehicle. Given the wide
array of possible configurations and operating ranges for heavy
vehicles, the agency did not believe it was practical to develop
performance tests that address the full range of possibilities and
remain cost-effective. Accordingly, the agency proposed to include
definitional criteria in the NPRM, which included equipment that would
be required as part of a compliant ESC system.\31\ We note that, when
developing the ESC requirement for light vehicles, the agency chose to
include such a requirement in FMVSS No. 126.
---------------------------------------------------------------------------

    \31\ Similar requirements exist in the light vehicle ESC
requirements. See 49 CFR 571.126, S4.
---------------------------------------------------------------------------

    SAE International has a Recommended Practice on Brake Systems
Definitions-Truck and Bus, J2627 (Aug. 2009), which includes a
definition of Electronic Stability Control and Roll Stability Control.
SAE International's definition of an ESC system requires that a system
have an electronic control unit that considers wheel speed, yaw rate,
lateral acceleration, and steering angle and that the system must
intervene and control engine torque and auxiliary brake systems to
correct the vehicle's path.
    The UN ECE Regulation 13 definition for the electronic stability
control system, promulgated in Annex 21, includes the following
functional attributes for directional control: Sensing yaw rate,
lateral acceleration, wheel speeds, braking input and steering input;
and the ability to control engine power output. For vehicles with
rollover control, the functions required by the stability control
include: Sensing lateral acceleration and wheel speeds; and the ability
to control engine power output.
    In developing a definition for ESC, the agency reviewed the
functional attributes contained in SAE J2627 and the requirements of
Annex 21 of UN ECE Regulation 13, and incorporated parts of both of
definitions the NPRM. The proposed definition was similar in wording to
the definition from FMVSS No. 126, which specifies certain features
that must be present, that ESC be capable of applying all the brakes
individually on the vehicle, and that it have a computer using a
closed-loop algorithm to limit vehicle oversteer and understeer when
appropriate. Unlike the light vehicle standard, which focuses on yaw
stability, the NPRM proposed to require a stability control system that
also helps to mitigate roll instability conditions.
    Furthermore, the proposed definition required that the ESC system
must be operational during all phases of driving, including
acceleration, coasting, deceleration, and braking, except when the
vehicle is below a low-speed threshold where loss of control or
rollover is unlikely. According to information the agency obtained from
vehicle manufacturers and ESC system suppliers, the low speed threshold
for a stability control system is 10 km/h (6.2 mph) for yaw stability
control and 20 km/h (12.4 mph) for roll stability control. For the
purposes of the NPRM, the agency set a single threshold of 20 km/h
(12.4 mph) as the speed below which ESC is not required to be
operational.
    The benefit of an ESC system is that it will reduce vehicle
rollovers and loss of control under a wide variety of vehicle
operational and environmental conditions. However, the performance
tests in the NPRM would only evaluate ESC system performance under very
specific conditions. To ensure that a vehicle is equipped with an ESC
system that met the proposed definition, we proposed that vehicle
manufacturers make available to the agency documentation that would
enable NHTSA to ascertain that the system includes the components and
performs the functions of an ESC system.
    Meritor WABCO, HDBMC, and Bendix recommended a change to the
definition of an ESC system. Where the definition required that the
system both augment vehicle directional stability and enhance rollover
stability by applying and adjusting brake torques, the commenters
recommended that the words ``having the capability of'' be added to
each instance. Bendix also recommended that each instance of

``brake torque'' should be changed to ``deceleration torque.''
    We agree with the commenters' recommendation to change the
requirement that ESC systems augment vehicle directional stability and
enhance rollover stability by ``applying and adjusting vehicle brake
torques'' to ``having the capability of applying and adjusting vehicle
brake torques.'' The wording in the NPRM could be construed to require
brake torques to be applied simultaneously at each wheel position for
correcting yaw moment or reduce lateral acceleration. This was not our
intention. Rather, we intended to require that brake torque at each
wheel position be capable of being applied and adjusted individually.
In analogous portions of the ESC system definition, we use the words
``has a means,'' which is similar in meaning to ``capable.''
    However, we are not making Bendix's suggested change of the term
``brake torque'' to ``deceleration torque.'' We are not sure that
Bendix's suggested language would be functionally different than the
proposal and cannot see how it adds clarity. We are specifically
interested in requiring that systems be capable of controlling the
brakes independently at each wheel end on at least one front and at
least one rear axle of the vehicle.
    Bendix also recommended a change to the requirement that the system
enhance vehicle directional stability by applying and adjusting the
vehicle brake torques. Bendix requested that NHTSA clarify that the
``vehicle'' referred to in this requirement is the truck tractor or bus
and not the trailer. That is, Bendix wanted to ensure that the trailer
is omitted from the vehicle directional stability requirements. Bendix
noted that the requirements regarding the system's ability to control
trailer brakes is addressed elsewhere.
    We agree with Bendix's recommendation. It was not our intention to
include trailers in the requirement that vehicles be capable of
maintaining directional stability. Bendix is correct that there could
to be some confusion with the proposed requirement because a trailer is
also a motor vehicle and consequently, the proposed requirement that
vehicles have the capability to maintain directional stability and the
roll stability may be misinterpreted to apply to a trailer. Therefore,
we have revised the ESC definition to specify that truck tractors and
buses must have the means to apply and adjust vehicle brake torques on
at least one front and at least one rear axle.
    Regarding the definitional criteria for mass estimation, Meritor
WABCO, HDBMC, and Bendix suggested an addition to the requirement that
a system have a means to estimate the vehicle (or combination vehicle)
mass. The commenters request that NHTSA include language allowing a
system to automatically obtain the vehicle's mass.
    NHTSA is not making the suggested change. The suggested change
would require a system to have a means to estimate or automatically
obtain vehicle mass. We do not believe there is a manner in which to
automatically obtain the vehicle's mass short of weighing it on a
scale. Any other calculation of the vehicle's mass is an estimate. We
note that the means for obtaining the vehicle's mass is not prescribed.
The requirement is necessary to ensure that the ESC system is capable
of using the vehicle mass data in the closed-loop algorithm of its
computer to apply and adjust the vehicle brake torques for enhancing
rollover stability and inducing correcting yaw moment. Adding
``automatically obtain'' to the definition does not improve or clarify
the requirement to have a means of estimating vehicle mass.
    In summary, NHTSA continues to believe that the definitional
criteria, including required equipment and system capabilities, are
necessary to ensure that ESC systems perform as they are intended and
as they currently perform. These criteria are objective in terms of
explaining to manufacturers what type of performance is required and
the minimal equipment necessary for that purpose.

D. Technical Documentation

    The NPRM proposed requiring that the vehicle manufacturer provide a
system diagram that identifies all ESC system hardware; a written
explanation, with logic diagrams included, describing the ESC system's
basic operational characteristics; and a discussion of the pertinent
inputs to the computer and how its algorithm uses that information to
prevent rollover and limit oversteer and understeer. Because the
proposed definition for ESC systems on truck tractors included the
capability to provide brake pressure to a towed vehicle, the agency
proposed requiring that, as part of the system documentation, the
manufacturer include the information that shows how the tractor
provides brake pressure to a towed trailer under the appropriate
conditions.
    Volvo questioned the need for manufacturers to submit technical
documentation to NHTSA, stating that NHTSA has relied on the
manufacturer's certification that the system meets the FMVSSs. HDBMC
and Bendix requested confirmation that this technical documentation
would be considered proprietary information and would not be released
to the public. Finally, Bendix was concerned about the acceptance
criteria for the evaluation of the submitted technical documentation.
Bendix stated that there was no objective acceptance criteria in the
proposed standard and recommended that the agency add acceptance
criteria.
    Upon consideration of the comments, we have decided to remove from
the regulatory text references to specific documentation that NHTSA
would request from manufacturers. However, NHTSA's Office of Vehicle of
Safety Compliance often requests, as part of its testing to verify
compliance with the FMVSSs, certain information from manufacturers. For
example, NHTSA may ask how a manufacturer's system meets the definition
of an ``ESC System'' set forth in this final rule. Information such as
the technical documentation that was listed in the regulatory text of
the NPRM may be included in or responsive to such a request. Of course,
a manufacturer's inability to demonstrate that its system meets the
definition of an ``ESC System'' could lead to a finding of
noncompliance with S5.1 of FMVSS No. 136.

IX. Vehicle Applicability and Phase-In

A. Trucks

1. Summary of the NPRM
    Vehicles with a GVWR greater than 10,000 pounds include a large
variety of vehicles ranging from medium duty pickup trucks to different
types of single-unit trucks, buses, trailers and truck tractors.
Vehicles with a GVWR of greater than 10,000 pounds are divided into
Classes 3 through 8. Class 7 vehicles are those with a GVWR greater
than 11,793 kilograms (26,000 pounds) and up to 14,969 kilograms
(33,000 pounds), and Class 8 vehicles are those with a GVWR greater
than 14,969 kilograms (33,000 pounds).
    About 85 percent of truck tractors sold annually in the U.S. are
air-braked three-axle (6x4) tractors with a front axle that has a GAWR
of 14,600 pounds or less and with two rear drive axles that have a
combined GAWR of 45,000 pounds or less, which we will refer to as
``typical 6x4 tractors.'' Other truck tractors, including two-axle
(4x2) tractors, tractors with four or more axles, and severe service
tractors, represent about 15 percent of the truck-tractor market in the
U.S.
    In the NPRM, the agency proposed that truck tractors with a GVWR
greater

than 11,793 kilograms (26,000 pounds) would be required to have ESC
systems. The agency did not propose requiring stability control systems
on trailers, primarily because trailer-based RSC systems were
determined by the agency research to be much less effective than
tractor-based RSC or ESC systems in preventing rollover. Trailer-based
RSC systems are capable of applying braking only on the trailer's
brakes. Tractor-based systems can command more braking authority by
using both the tractor and trailer brakes. As a result, trailer-based
RSC systems do not appear to provide additional safety benefits when
used in combination with tractor-based RSC or ESC systems. In addition,
the typical service life of a trailer is 20 to 25 years compared with
about 8 to 10 years for a truck tractor. Because new tractors are added
to the U.S. fleet at a faster rate than new trailers, the safety
benefits from stability control systems would be achieved at a faster
rate by requiring stability control systems to be installed on a
tractor.
    Our proposed rule also excluded certain types of low-volume, highly
specialized vehicle types. In these cases, the vehicle's speed
capability does not allow it to operate at speeds where roll or yaw
instability is likely to occur. These exclusions were drawn from FMVSS
No. 121, Air brake systems, which exclude any vehicle equipped with an
axle that has a gross axle weight rating of 29,000 pounds or more; any
truck or bus that has a speed attainable in two miles of not more than
33 mph; and any truck that has a speed attainable in two miles of not
more than 45 mph, an unloaded vehicle weight that is not less than 95
percent of its GVWR, and no capacity to carry occupants other than the
driver and operating crew.
2. Exclusions From ESC Requirement
    The Fire Apparatus Manufacturers' Association (FAMA) was generally
supportive of the rule. However, they stated that the rule would not be
feasible if it is interpreted to apply to a Tractor Drawn Aerial
Apparatus. As FAMA explained, this apparatus is a combination vehicle
used for firefighting, which are used in many large urban fire
departments. The distinguishing feature of this vehicle is that it has
two drivers, one in the truck tractor and one in the trailer. FAMA
believes that an ESC algorithm on such a vehicle would be very complex
because it would need to consider two steering wheels rather than one.
FAMA suggested that NHTSA exclude from a final rule any combination
vehicle that requires more than one operator to steer it.
    The agency is not adding the exclusion suggested by FAMA. Although
FAMA stated that its vehicles would not be subject to the exclusion of
vehicles with an axle having a gross axle weight rating of 29,000
pounds or more, it is not clear that this or other exclusions do not
apply. Moreover, absent specific information that more fully explains
why an exclusion is necessary and not overly broad, NHTSA cannot agree
that an exclusion for all combination vehicles that require more than
one operator to steer it is necessary.
    Furthermore, the scope of the exclusion suggested by FAMA is not
consistent with the scope of the rule. Specifically, this final rule,
like the NPRM, applies to truck tractors, not trailers. However, the
suggested exclusion would apply to combination vehicles, which include
both a truck tractor and a trailer. That is, the presence of a trailer
would form the basis for the exclusion. If this exclusion was added to
the final rule, then the basis for the exclusion would be dependent on
the trailer that is attached to the vehicle. This would be confusing
and unnecessarily complicate enforcement.
    Finally, FAMA has not articulated why its vehicles cannot be
equipped with ESC systems. Because the ESC requirement applies only to
the truck tractor, the system would only need to take account of one
steering wheel input. There would be no requirement that the vehicle
respond to any inputs from the trailer. Moreover, NHTSA would conduct
compliance testing of the truck tractor using the control trailer
specified in the test procedure, not a trailer with a steering wheel.
    Several commenters suggested that the agency reduce the scope of
the ESC requirement. EMA requested that NHTSA exclude all severe duty
trucks from the scope of a final rule. It reasoned that manufacturers
offer multiple configurations of truck tractors with different
wheelbases, axle, and suspension combinations. Furthermore, it claimed
that manufacturers often build only a few vehicles in each
configuration and in some cases of severe duty trucks, may only build a
single vehicle in a particular configuration.
    The agency is not excluding severe duty trucks as EMA suggests.
Currently, manufacturers are able to produce products in small volumes
that meet all the requirements of the Federal Motor Vehicle Safety
Standards (FMVSS). The addition of the ESC rule will not unduly burden
the manufacturers with regard to their small volume products. EMA's
actions related to this rulemaking support this conclusion. For
example, EMA provided test data to the agency after performing multiple
test maneuvers with severe duty trucks equipped with ESC systems. EMA
also included the test results from the severe duty trucks to form its
recommended test criteria for an alternate roll stability test.
    Meritor WABCO requested NHTSA to add the words ``pneumatically
braked'' to the definitions of truck tractors and buses in the ESC
rule. Similarly, EMA recommended that NHTSA include the ESC
requirements within FMVSS No. 121 rather than in a separate standard.
    We are not expressly limiting the scope of the final rule to air
braked vehicles. Although Class 8 vehicles typically use pneumatic or
air brakes, Class 7 vehicles vary between either air or hydraulic
brakes. The scope of the NPRM includes all truck tractors and Class 7
and 8 buses, which showed the greatest rollover problem of all the
buses according to our research. In order to address the safety problem
with these classes of buses, the ESC rule must include both air and
hydraulic brakes. Limiting the scope of this rulemaking to air braked
vehicles could provide an incentive for some manufacturers to equip
vehicles with hydraulic brakes rather than air brakes to circumvent an
ESC system requirement.
3. Single-Unit Trucks
    The agency did not propose to include single-unit trucks with a
GVWR over 4,536 kg (10,000 pounds). Several commenters recommended
expanding the scope of the rule to include straight trucks. Skagit,
NTSB, IIHS, and NAPT all suggested that ESC should be mandated on all
commercial vehicles greater than 10,000 pounds GVWR, including straight
trucks. Advocates recommended that NHTSA should consider the FMCSA
study stating the number of fatalities by single-unit trucks, based on
data from 2008, are 1,147 each year. Bosch stated that the rule should
be expanded to cover all vehicles over 10,000 pounds GVWR vehicles,
including hydraulic-braked vehicles, because this segment accounts for
a large number of commercial and load bearing vehicles on the U.S.
roads. Bosch claims that a mandate with a phase-in period is needed to
facilitate industry development of ESC systems on these vehicles. On
the other hand, Bendix recommended that ``[t]he decision by the agency
regarding if and when to consider rulemaking on single-unit trucks
should be based on the same

level of research undertaken for tractor and coach.''
    We are not expanding the scope of this rulemaking to include
single-unit trucks. We believe that a level of research closer to what
we had to support the NPRM for truck tractors and large buses is
necessary before NHTSA would propose to mandate ESC on all single-unit
trucks. After publishing the NPRM, we began a research and testing
program to study the safety benefits and performance criteria of ESC
systems on single-unit trucks. The research is not yet complete.
Furthermore, as we stated in the NPRM, the complexity of the single-
unit truck population and the limited crash data available present a
significant challenge to determining the effectiveness of stability
control on these vehicles. At this time, we will not include single-
unit trucks in the ESC rule. However, we believe including buses with
hydraulic brakes in this final rule will spur development of ESC
systems for other hydraulic-braked vehicles, including trucks with a
GVWR of greater than 4,536 kilograms (10,000 pounds) but not more than
11,793 kilograms (26,000 pounds).
4. Compliance Dates
    The agency proposed that all new typical 6x4 truck tractors would
be required to meet the proposed standard beginning two years after a
final rule is published. Because there are currently only two suppliers
of truck tractor and large bus stability control systems, Bendix and
Meritor WABCO, we reasoned that the industry would require lead time to
ensure that the necessary production stability control systems are
available to manufacturers. NHTSA also proposed a two-year lead time
for two-axle tractors.
    For severe service tractors and tractors with four axles or more,
which represent about 5 percent of annual truck tractor sales, the
agency believed additional lead time was necessary to develop, test,
and equip these vehicles with a stability control system. Therefore, we
proposed to require that severe service tractors and other atypical
tractors be equipped with ESC systems beginning four years after the
final rule is published.
    Four commenters addressed the compliance dates for trucks proposed
by the NPRM. Daimler requested an additional lead time for ESC
implementation because it said that it only has RSC systems developed
on some models and needs more time to design and validate ESC on all of
its models.
    In its comment, EMA mentioned that this ESC rule should align with
the implementation dates of the new FMVSS No. 121 stopping distance
requirements to give manufacturers the opportunity to refine the
braking systems prior to the implementation of this ESC rule. EMA said
it is impractical for manufacturers to certify compliance tests using
the tests in the NPRM for all typical 6x4 tractors within 2 years of
the final rule. Moreover, EMA said that tractors with four or more
axles and severe service tractors have not been evaluated using the
tests in the NPRM and likely would need additional lead time. However,
EMA did not specify how much additional lead time was necessary.
Finally, EMA and Bendix recommended including two-axle tractors in the
longer lead time period because it appears to be an error.
    In contrast, HDBMC stated its belief that the suppliers of ESC
systems are prepared to meet the anticipated deployment demands by the
implementation dates proposed.
    We recognize the recent changes to the stopping distance
requirements in FMVSS No. 121 affected truck tractors. Truck tractors,
other than three-axle truck tractors, were recently subjected to the
reduced stopping distance changes that went into effect on August 1,
2013. Manufacturers of these truck tractors were given two additional
years beyond the timeframe for three-axle truck tractors to comply with
the amendments to FMVSS No. 121. We agree with Daimler and EMA that at
least four years of lead time is warranted for all truck tractors other
than typical 6x4 tractors (three-axle truck tractors with a front axle
that has a GAWR of 6,622 kg (14,600 pounds) or less and with two rear
drive axles that have a combined GAWR of 20,412 kg (45,000 pounds) or
less). Although HDMA said that its member companies are ready to supply
brake components by the implementation dates proposed, we realize that
truck tractor manufacturers need extra time to integrate the ESC
systems into their products and to perform the necessary testing to
ensure compliance. In addition, manufacturers recently made brake
system changes to these models of truck tractors in order to comply
with the new requirements in the FMVSS No. 121 amendments. We recognize
that ESC systems must be integrated into the brake systems, and we
expect that manufacturers may need to modify the brake systems for a
second time.

B. Buses

1. Summary of the NPRM
    The NPRM proposed that certain buses would be required to be
equipped with ESC systems. The applicability of the proposal to buses
mirrored the applicability of the agency's proposal that certain large
buses be equipped with seat belts.\32\ The proposal for seat belts was
applicable to buses with a gross vehicle weight rating (GVWR) of 11,793
kilograms (26,000 pounds) or greater, 16 or more designated seating
positions (including the driver), and at least 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.'' That proposal excluded school buses and urban transit buses
sold for operation in urban transportation along a fixed route with
frequent stops. The agency proposed a very similar applicability in the
NPRM for this rulemaking.\33\ We believed that the proposal encompassed
the category of ``cross-country intercity buses'' represented in the
FARS and FMCSA data (identified in section II.A above) that had a
higher involvement of crashes that ESC systems are capable of
preventing.
---------------------------------------------------------------------------

    \32\ 75 FR 50958 (Aug. 18, 2010).
    \33\ The primary difference is that the ESC proposal was not
made applicable to buses with a GVWR of exactly 11,793 kilograms
(26,000 pounds) in order to exclude Class 6 vehicles from the
proposal.
---------------------------------------------------------------------------

2. Buses Built on Truck Chassis
(a) Summary of NPRM
    The agency tested three air-braked buses, all of which had a GVWR
over 14,969 kg (33,000 lb.) (Class 8). Nevertheless, the agency
included Class 7 buses (buses with a GVWR of more than 11,793 kg
(26,000 lb.) but not greater than 14,969 kg (33,000 lb.). We reasoned
that, although many Class 7 buses are built on chassis similar to those
of single-unit trucks for which ESC has not been widely developed, and
we are not aware of any Class 7 bus that is equipped or currently
available with ESC. Class 7 buses represent less than 20 percent of the
market. Although the agency was not aware of any Class 7 bus currently
available with ESC, we were aware that stability control systems are
available on a limited number of Class 8 single-unit trucks, such as
concrete trucks, refuse trucks, and other air-braked trucks, and that
the same technology could be developed for use on Class 7 buses, which
we believed were also air-braked vehicles. We also believed that the
manufacturers of Class 7 buses would need additional lead time to have
the ESC systems developed, tested and installed on their vehicles.
Hence, for large buses, the agency proposed an effective date of two
years after the final rule is published,

primarily to accommodate manufacturers of Class 7 buses.
    However, we sought comment on the feasibility of including Class 7
buses that are built on chassis similar to those of single-unit trucks
within two years. We noted that, although we believed that Class 7
buses were primarily air braked and that ESC systems were readily
available for air-braked buses, system availability for any hydraulic-
braked buses that may be covered may be more limited. We requested
that, if hydraulic-braked buses were covered by the proposal,
commenters address manners in which hydraulic-braked buses may be
differentiated for exclusion or a different phase-in period.
(b) Summary of Comments
    Several commenters raised issues related to the NPRM's definition
for large buses. EMA and Navistar commented that the ``large bus''
definition should not include commercial buses, which are buses greater
than 11,793 kg (26,000 lb.), but are not traditional intercity buses.
They claimed that many of these buses are built on truck chassis and
are different than the Class 8 buses tested by NHTSA. They stated that
these buses are built in multiple stages by multiple manufacturers,
which would make compliance certification difficult.
    According to Navistar, NHTSA did not ``reach out'' to Navistar
regarding its commercial buses because it claimed NHTSA was not aware
of its Class 8 commercial buses from the sole fact that they were not
specifically mentioned in list of bus manufacturers included in the
NPRM.
    In its comments, EMA opined that non-motorcoach buses with a GVWR
over 11,793 kg (26,000 lb.) are more closely related to single-unit
trucks. It also commented that some of the same issues related to
requiring ESC systems on single-unit trucks are also present for large
buses.
    EMA stated that consistent with the Motorcoach Enhanced Safety Act
(part of MAP-21), it considered the term ``motorcoach'' to have the
same meaning as ``over-the-road-bus,'' which ``means a bus
characterized by an elevated passenger deck located over a baggage
compartment.'' \34\ EMA and Daimler also commented that a
``motorcoach'' has some, if not all, of the following attributes: a
GVWR greater than 33,000 pounds (Class 8); air disc brakes; passenger
deck floor more than 45 inches above the ground; rear engine
configuration; monocoque \35\ construction; 40 or more passenger seats;
no provisions for standee passengers; and one passenger entrance and
exit door. EMA asserted that NHTSA did not study ESC on other non-
motorcoach buses, and therefore, the rule should not apply to those
buses.
---------------------------------------------------------------------------

    \34\ The rulemaking requirements of the Motorcoach Enhanced
Safety Act are addressed in section II above.
    \35\ Monocoque means a type of vehicular construction in which
the body is combined with the chassis as a single unit.
---------------------------------------------------------------------------

(c) NHTSA's Response to Comments
    NHTSA is not changing the general applicability of the ESC
requirement to buses. As we stated in the NPRM, we intended the
applicability of the ESC requirement to buses to be similar to the
applicability of the agency's requirement that buses have seat belts at
each passenger seating position. In both rulemakings, the target
vehicles were high occupancy buses associated with a known fatality and
injury risk. The buses typically carried a large number of passengers
and were operated at highway speeds. We examined the involvement of
high occupancy buses in fatal crashes over a 10-year period (FARS data
files, for the NPRM, 1999-2008). In this examination of high occupancy
bus data, we inspected crash data for buses with a GVWR greater than
4,536 kg (10,000 lb.). We analyzed the construction type and various
attributes of the vehicles. The 2000-2009 FARS data show that for buses
over 4,536 kg (10,000 lb.), there were 49 passenger fatalities in buses