Document ID: NHTSA-2012-0065-0001
Agency: nhtsa
Document Type: Proposed Rule
Title: Federal Motor Vehicle Safety Standards: Electronic Stability Control Systems for Heavy Vehicles
Posted Date: 2012-05-23T04:00Z

[Federal Register Volume 77, Number 100 (Wednesday, May 23, 2012)]
[Proposed Rules]
[Pages 30766-30818]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2012-12212]

[[Page 30765]]

Vol. 77

Wednesday,

No. 100

May 23, 2012

Part III

Department of Transportation

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

National Highway Traffic Safety Administration

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

49 CFR Part 571

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

  Federal Register / Vol. 77 , No. 100 / Wednesday, May 23, 2012 / 
Proposed Rules  

[[Page 30766]]

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

DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

49 CFR Part 571

[Docket No. NHTSA-2012-0065]
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: Notice of proposed rulemaking (NPRM).

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

SUMMARY: This document proposes to establish 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 2012, we expect that about 26 percent of new truck tractors and 
80 percent of new buses affected by this proposed rule will be equipped 
with ESC systems. We believe that ESC systems could prevent 40 to 56 
percent of untripped rollover crashes and 14 percent of loss-of-control 
crashes. By requiring that ESC systems be installed on truck tractors 
and large buses, this proposal would prevent 1,807 to 2,329 crashes, 
649 to 858 injuries, and 49 to 60 fatalities at less than $3 million 
per equivalent life saved, while generating positive net benefits.

DATES: Comments: Submit comments on or before August 21, 2012.
    Public Hearing: NHTSA will hold a public hearing in the summer of 
2012. NHTSA will announce the date for the hearing in a supplemental 
Federal Register document. The agency will accept comments to the 
rulemaking at this hearing.

ADDRESSES: You may submit comments electronically [identified by DOT 
Docket Number NHTSA-2012-0065] by visiting the following Web site
     Federal eRulemaking Portal: Go to http://www.regulations.gov. Follow the online instructions for submitting 
comments.
    Alternatively, you can file comments using the following methods:
     Mail: Docket Management Facility: U.S. Department of 
Transportation, 1200 New Jersey Avenue SE., West Building Ground Floor, 
Room W12-140, Washington, DC 20590-0001
     Hand Delivery or Courier: West Building Ground Floor, Room 
W12-140, 1200 New Jersey Avenue SE., between 9 a.m. and 5 p.m. ET, 
Monday through Friday, except Federal holidays.
     Fax: (202) 493-2251
    Instructions: For detailed instructions on submitting comments and 
additional information on the rulemaking process, see the Public 
Participation heading of the SUPPLEMENTARY INFORMATION section of this 
document. Note that all comments received will be posted without change 
to http://www.regulations.gov, including any personal information 
provided. Please see the Privacy Act heading below.
    Privacy Act: Anyone is able to search the electronic form of all 
comments received into any of our dockets by the name of the individual 
submitting the comment (or signing the comment, if submitted on behalf 
of an association, business, labor union, etc.). You may review DOT's 
complete Privacy Act Statement in the Federal Register published on 
April 11, 2000 (65 FR 19477-78).
    Docket: For access to the docket to read background documents or 
comments received, go to http://www.regulations.gov. Follow the online 
instructions for accessing the dockets.

FOR FURTHER INFORMATION CONTACT: For technical issues, you may contact 
George Soodoo, Office of Crash Avoidance Standards, by telephone at 
(202) 366-4931, and by fax at (202) 366-7002. For legal issues, you may 
contact David Jasinski, Office of the Chief Counsel, by telephone at 
(202) 366-2992, and by fax at (202) 366-3820. 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. Safety Problem
    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
III. Stability Control Technologies
    A. Dynamics of a Rollover
    B. Description of RSC System Functions
    C. Description of ESC System Functions
    D. How ESC Prevents Loss of Control
    E. Situations in Which Stability Control Systems May Not Be 
Effective
    F. Difference in Vehicle Dynamics Between Light Vehicles and 
Heavy Vehicles
IV. Research and Testing
    A. UMTRI Study
    B. Simulator Study
    C. NHTSA Track Testing
    1. Effects of Stability Control Systems--Phase I
    2. Developing a Dynamic Test Maneuver and Performance Measure To 
Evaluate Roll Stability--Phase II
    (a) Test Maneuver Development
    (b) Performance Measure Development
    3. Developing a Dynamic Test Maneuver and Performance Measure To 
Evaluate Yaw Stability--Phase III
    (a) Test Maneuver Development
    (b) Performance Measure Development
    4. Large Bus Testing
    D. Truck & Engine Manufacturers Association Testing
    1. Slowly Increasing Steer Maneuver
    2. Ramp Steer Maneuver
    3. Sine With Dwell Maneuver
    4. Ramp With Dwell Maneuver
    5. Vehicle J Testing
    (a) EMA Testing of Vehicle J
    (b) NHTSA Testing of EMA's Vehicle J
    E. Other Industry Research
    1. Decreasing Radius Test
    2. Lane Change on a Large Diameter Circle
    3. Yaw Control Tests
V. Agency Proposal
    A. NHTSA's Statutory Authority
    B. Applicability
    1. Vehicle Types
    2. Retrofitting In-Service Truck Tractors, Trailers, and Buses
    3. Exclusions From Stability Control Requirement
    C. ESC System Capabilities
    1. Choosing ESC vs. RSC
    2. Definition of ESC
    D. ESC Disablement
    E. ESC Malfunction Detection, Telltale, and Activation Indicator
    1. ESC Malfunction Detection
    2. ESC Malfunction Telltale
    3. ESC Activation Indicator
    F. Performance Requirements and Compliance Testing
    1. Characterization Test--SIS
    2. Roll and Yaw Stability Test--SWD
    (a) Roll Stability Performance
    (b) Yaw Stability Performance
    (c) Lateral Displacement
    3. Alternative Test Maneuvers Considered
    (a) Characterization Maneuver
    (b) Roll Stability Test Maneuvers
    (c) Yaw Stability Test Maneuvers
    (d) Lack of an Understeer Test
    4. ESC Malfunction Test
    5. Test Instrumentation and Equipment
    (a) Outriggers
    (b) Automated Steering Machine
    (c) Anti-Jackknife Cables
    (d) Control Trailer
    (e) Sensors
    6. Test Conditions
    (a) Ambient Conditions
    (b) Road Test Surface
    (c) Vehicle Test Weight
    (d) Tires
    (e) Mass Estimation Drive Cycle
    (f) Brake Conditioning
    7. Data Filtering and Post Processing
    G. Compliance Dates and Implementation Schedule
VI. Benefits and Costs

[[Page 30767]]

    A. System Effectiveness
    B. Target Crash Population
    C. Benefits Estimate
    D. Cost Estimate
    E. Cost Effectiveness
    F. Comparison of Regulatory Alternatives
VII. Public Participation
VIII. 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. Plain Language
    K. Regulatory Identifier Number (RIN)
    L. Privacy Act

I. Executive Summary

    The agency proposes to reduce rollover and loss of directional 
control of truck tractors and large buses by establishing a new 
standard, Federal Motor Vehicle Safety Standard (FMVSS) No. 136, 
Electronic Stability Control Systems for Heavy Vehicles. The standard 
would require truck tractors and certain buses \1\ 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. Based on the 
agency's estimates regarding the effectiveness of ESC systems, we 
believe that an ESC standard could annually prevent 1,807 to 2,329 
crashes, 649 to 858 injuries, and 49 to 60 fatalities, while providing 
net economic benefits.
---------------------------------------------------------------------------

    \1\ As explained later in this notice, the applicability of this 
proposed standard to buses would be similar to the applicability of 
NHTSA's proposal to require seat belts on certain buses. These buses 
would have 16 or more designated seating positions (including the 
driver), at least 2 rows of passenger seats that are rearward of the 
driver's seating position and forward-facing or can convert to 
forward-facing without the use of tools. As with the seat belt NPRM, 
this proposed rule would exclude school buses and urban transit 
buses sold for operation as a common carrier in urban transportation 
along a fixed route with frequent stops.
---------------------------------------------------------------------------

    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 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 this proposed 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 crashes. 
Based on information we have received to date, the agency has 
tentatively determined that ESC and RSC systems are not available for 
hydraulic-braked medium or heavy vehicles.
    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.
    As a result of the data analysis research, we have tentatively 
determined that ESC systems can be 28 to 36 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.\2\ 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.
---------------------------------------------------------------------------

    \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.
---------------------------------------------------------------------------

    In order to realize these benefits, the agency is proposing to 
require new truck tractors and certain buses with a GVWR of greater 
than 11,793 kilograms (26,000 pounds) to be equipped with an ESC 
system. This proposal 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 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. The responsibility for promulgation of Federal motor 
vehicle safety standards is delegated to NHTSA.
    This proposal requires ESC system must meet both definitional 
criteria and performance requirements. It is necessary to include 
definitional criteria in the proposal 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 would describe an ESC 
system as one that would enhance 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.
    The proposal requires that the system be able to detect a 
malfunction and provide a driver with notification of a malfunction by 
means of a telltale. This requirement would be similar to the 
malfunction detection and telltale requirements for light vehicles in 
FMVSS No. 126. An ESC system on/off switch is allowed for light 
vehicles; however, there is no provision in this proposal for allowing 
an ESC system to be deactivated. For truck tractors and large buses, we 
do not believe such controls are necessary.

[[Page 30768]]

    After considering and evaluating several test maneuvers, the agency 
is proposing to use 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 relationship between a vehicle's steering wheel angle and 
the lateral acceleration. This test serves both to normalize the 
severity of the SWD maneuver and to ensure that the system has the 
ability to reduce engine torque. The SIS maneuver is performed by 
driving at a constant speed of 48 km/h (30 mph), and then increasing 
the steering wheel angle at a constant rate of 13.5 degrees per second 
until ESC system activation occurs. Using linear regression followed by 
extrapolation, the steering wheel angle that would produce a lateral 
acceleration of 0.5g is determined.
    Using the steering wheel angle derived from the SIS maneuver, the 
agency would conduct the sine with dwell maneuver. The SWD test 
maneuver challenges both roll and yaw stability by subjecting the 
vehicle to a sinusoidal input. To conduct the SWD maneuver, the vehicle 
is accelerated to 72 km/h (45 mph) and then turned in a clockwise or 
counterclockwise direction to reach a set steering wheel angle in 0.5 
seconds. The steering wheel is then turned in the opposite direction 
until the same steering wheel angle is reached in the opposite 
direction in one second. The steering wheel is then held at that 
steering wheel angle for one second, and then the steering wheel angle 
returned to zero degrees within 0.5 seconds. 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.
    The lateral acceleration, yaw rate, and engine torque data from the 
test runs would be measured, recorded, and processed to determine the 
four performance metrics: Lateral acceleration ratio (LAR), yaw rate 
ratio (YRR), lateral displacement, and engine torque reduction. The LAR 
and YRR metrics would be used to ensure that the system reduces lateral 
acceleration and yaw rate, respectively, after an aggressive steering 
input, thereby preventing rollover and loss of control, respectively. 
These two metrics can effectively measure what NHTSA's testing has 
found to be the threshold of stability. The lateral displacement metric 
would be used to ensure that the stability control system is not set to 
intervene solely by making the vehicle nonresponsive to driver input. 
The engine torque reduction metric would be used to ensure that the 
system has the capability to automatically reduce engine torque in 
response to high lateral acceleration and yaw rate conditions. The 
manner in which the data would be filtered and processed is described 
in this proposal.
    The agency considered several test maneuvers based on its own work 
and that of industry. In particular, the agency's initial research 
focused on a ramp steer maneuver (RSM) for evaluating roll stability. 
In that 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 is input. The steering wheel angle is then held 
for a period of time before it is returned to zero. A stability control 
system would act to reduce lateral acceleration, and thereby wheel lift 
and roll instability, by applying selective braking. A vehicle without 
a stability control system would maintain high levels of lateral 
acceleration and potentially experience wheel lift or rollover.
    The proposed rule also sets forth the test conditions that the 
agency would use to ensure safety and demonstrate sufficient 
performance. All vehicles would be tested using outriggers for the 
safety of the test driver. The agency would use an automated steering 
controller to ensure reproducible and repeatable test execution 
performance. Truck tractors would be tested with an unbraked control 
trailer to eliminate the effect of the trailer's brakes on testing. 
Because the agency tests new vehicles, the brakes would be conditioned, 
as they are in determining compliance with the air brake standard. The 
agency would also test to ensure that system malfunction is detected.
    This proposed rule would take effect for most truck tractors and 
covered buses produced two years after publication of a final rule. We 
believe that this amount of lead time is 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 would provide two years 
additional lead time. We believe this additional time is 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 is not proposing 
to do so, given the integrated aspects of a stability control system.
    Based on the agency's effectiveness estimates, the adoption of this 
proposal would prevent 1,807 to 2,329 crashes per year resulting in 649 
to 858 injuries and 49 to 60 fatalities. The proposal also would result 
in significant monetary savings as a result of prevention of property 
damage and travel delays.
    Based on information obtained from manufacturers, the agency 
estimates that 26.2 percent of truck tractors manufactured in model 
year 2012 will be equipped with an ESC system and that 80 percent of 
covered buses manufactured in model year 2012 will be equipped with an 
ESC system. Information obtained from manufacturers indicates that the 
average unit cost of an ESC system is approximately $1,160. In 
addition, 16.5 percent of truck tractors manufactured in model year 
2012 will be equipped with an RSC system. The incremental cost of 
installing an ESC system in place of an RSC system is estimated to be 
$520 per vehicle. Based upon the agency's estimates that 150,000 truck 
tractors and 2,200 buses covered by this proposed rule will be 
manufactured in 2012, the agency estimates that the total cost of this 
proposal would be approximately $113.6 million.
    The agency believes that this proposal is cost effective. The net 
benefits of this proposal are estimated to range from $228 to $310 
million at a 3 percent discount rate and from $155 to $222 million at a 
7 percent discount rate. As a result, the net cost per equivalent live 
saved from this proposal ranges from $1.5 to $2.0 million at a 3 
percent discount rate and from $2.0 to $2.6 million at a 7 percent 
discount rate. The costs and benefits of this proposal are summarized 
in Table 1.

[[Page 30769]]

                   Table 1--Estimated Annual Cost, Benefits, and Net Benefits of the Proposal
                                          [In millions of 2010 dollars]
----------------------------------------------------------------------------------------------------------------
                                                                Property damage      Cost per
                                    Costs          Injury       and travel delay    equivalent     Net benefits
                                                  benefits          savings         live saved
----------------------------------------------------------------------------------------------------------------
At 3% Discount...............          $113.6        $328-405         $13.9-17.8        $1.5-2.0        $228-310
At 7% Discount...............           113.6         257-322          11.0-14.1         2.0-2.6         155-222
----------------------------------------------------------------------------------------------------------------

    The agency considered two regulatory alternatives. First, the 
agency considered requiring truck tractors and large buses to be 
equipped with RSC systems. When compared to this proposal, RSC systems 
would result in slightly lower cost per equivalent life saved, but 
would produce net benefits that are lower than the net benefits from 
this proposal. This is because RSC systems are less effective at 
preventing rollover crashes and much less effective at preventing loss-
of-control crashes. The second alterative considered was requiring 
trailers to be equipped with RSC systems. However, this alternative 
would save fewer than 10 lives at a very high cost per equivalent life 
saved and would provide negative net benefits.
    The remainder of this notice will describe in detail the following: 
(1) The size of the safety problem to be addressed by this proposed 
rule; (2) how stability control systems work to prevent rollover and 
loss of control; (3) the research and testing separately conducted by 
NHTSA and industry to evaluate the potential effectiveness of a 
stability control requirement and to develop dynamic test maneuvers to 
challenge system performance; (4) the specifics of the agency's 
proposal, including equipment and performance criteria, compliance 
testing, and the implementation schedule; and (5) the benefits and 
costs of this proposal.

II. Safety Problem

A. Heavy Vehicle Crash Problem

    The Traffic Safety Facts 2009 reports that tractor trailer 
combination vehicles are involved in about 72 percent of the fatal 
crashes involving large trucks, annually.\3\ According to FMCSA's Large 
Truck and Bus Crash Facts 2008, these vehicles had a fatal crash 
involvement rate of 1.92 crashes per 100 million vehicle miles traveled 
during 2007, whereas single unit trucks had a fatal crash involvement 
rate of 1.26 crashes per 100 million vehicle miles traveled.\4\ 
Combination vehicles represent about 25 percent of large trucks 
registered but travel 63 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.
---------------------------------------------------------------------------

    \3\ DOT HS 811 402, available at http://www-nrd.nhtsa.dot.gov/Pubs/811402.pdf (last accessed May 9, 2012).
    \4\ FMCSA-RRA-10-043 (Mar. 2010), available at http://www.fmcsa.dot.gov/facts-research/ltbcf2008/index-2008largetruckandbuscrashfacts.aspx (last accessed May 9, 2012).
---------------------------------------------------------------------------

    According to Traffic Safety Facts 2009, the overall crash problem 
for tractor trailer combination vehicles is approximately 150,000 
crashes, 29,000 of which involve injury. The overall crash problem for 
single-unit trucks is nearly as large--approximately 146,000 crashes, 
24,000 of which are injury crashes. However, the fatal crash 
involvement for truck tractors is much higher. In 2009, there were 
2,334 fatal combination truck crashes and 881 fatal single-unit truck 
crashes.
    The rollover crash problem for combination trucks is much greater 
than for single-unit trucks. In 2009, there were approximately 7,000 
crashes involving combination truck rollover and 3,000 crashes 
involving single-unit truck rollover. As a percentage of all crashes, 
combination trucks are involved in rollover crashes at twice the rate 
of single-unit trucks. Approximately 4.4 percent of all combination 
truck crashes were rollovers, but 2.2 percent of single-unit truck 
crashes were rollovers. Combination trucks were involved in 3,000 
injury crashes and 268 fatal crashes, and single-unit trucks were 
involved in 2,000 injury crashes and 154 fatal crashes.
    According to FMCSA's Large Truck and Bus Crash Facts 2008, cross-
country intercity buses were involved in 19 of the 247 fatal bus 
crashes in 2008, which represented about 0.5 percent of the fatal 
crashes involving large trucks and buses, annually. The bus types 
presented in the crash data include school buses, intercity buses, 
cross-country buses, transit buses, and other buses. These buses had a 
fatal crash involvement rate of 3.47 crashes per 100 million vehicle 
miles traveled during 2008. From 1998 to 2008, cross-country intercity 
buses, on average, accounted for 12 percent of all buses involved in 
fatal crashes, whereas transit buses and school buses accounted for 35 
percent and 40 percent, respectively, of all buses involved in fatal 
crashes. Most of the transit bus and school bus crashes are not 
rollover or loss-of-control crashes that ESC systems are capable of 
preventing. The remaining 13 percent of buses involved in fatal crashes 
were classified as other buses or unknown. 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).\5\ In the 10-year period 
between 1999 and 2008, there were 34 fatalities on buses with a GVWR 
between 4,536 kg and 11,793 kg (10,000 lb and 26,000 lb) compared to 
254 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.
---------------------------------------------------------------------------

    \5\ This data was taken from the FARS database and was presented 
in the NPRM that would require seat belts on certain buses. See 75 
FR 50,958, 50,917 (Aug. 18, 2010).
---------------------------------------------------------------------------

    Furthermore, the size of the rollover crash problem for cross-
country intercity buses is greater than in other buses. According to 
FARS data from 1999 to 2008, there were 97 occupant fatalities as a 
result of rollover events on cross-country intercity buses with a GVWR 
of greater than 11,793 kg (26,000 lb), which represents 52 percent of 
cross-country intercity bus fatalities.\6\ In comparison, rollover 
crashes were responsible for 21 occupant fatalities on other buses with 
a GVWR of greater than 11,793 kg (26,000 lb) and 9 occupant fatalities 
on all buses with a GVWR between 4,536 kg and 11,793 kg (10,000 lb and 
26,000 lb). That is, 95 percent of bus occupant rollover fatalities on 
buses over 4,536 kg (10,000 lb) were occupants on buses with a GVWR of 
over 11,793 kg (26,000 lb).
---------------------------------------------------------------------------

    \6\ See U.S. Department of Transportation Motorcoach Safety 
Action Plan, DOT HS 811 177, at 13 (Nov. 2009), available at http://www.fmcsa.dot.gov/documents/safety-security/MotorcoachSafetyActionPlan_finalreport-508.pdf (last accessed May 
9, 2012).

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

[[Page 30770]]

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).
     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--The vehicle yaw 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. 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 result is more 
likely to be vehicle yaw instability than vehicle roll instability.
     Road design configuration--Some drivers may misjudge the 
curvature of ramps and not brake sufficiently to negotiate the curve 
safely. This includes ramps with decreasing radius curves as well as 
curves and ramps with improper signage. 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.

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 all 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 \7\ 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.
---------------------------------------------------------------------------

    \7\ 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.\8\ 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.\9\ Consistent with 
that plan, NHTSA made a decision to pursue a stability control 
requirement for large buses.
---------------------------------------------------------------------------

    \8\ See supra, note 6.
    \9\ Id. at 28-29.
---------------------------------------------------------------------------

    In March 2011, NHTSA issued its latest Vehicle Safety and Fuel 
Economy Rulemaking and Research Priority Plan (Priority Plan).\10\ 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.
---------------------------------------------------------------------------

    \10\ 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

[[Page 30771]]

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 is 2012 for most vehicles, with a 
phase-in based on the vehicle type.

III. Stability Control Technologies

A. Dynamics of a Rollover

    Whenever a vehicle is steered, the lateral forces that result from 
the steering input lead to one of the following results: (1) Vehicle 
maintains directional control; (2) vehicle loses directional control 
due to severe understeer or plowing out; (3) vehicle loses directional 
control due to severe oversteer or spinning out; or (4) vehicle 
experiences roll instability and rolls over.
    A turning maneuver initiated by the driver's steering input results 
in a vehicle response that can be broken down into two phases. Phase 1 
is the yaw response that occurs when the front wheels are turned. 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.
    This rotation leads to Phase 2. In Phase 2, 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 leads to 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 semi-trailer, an additional phase is the turning response of 
the trailer. Once the tractor begins to achieve a yaw and lateral 
acceleration response, the trailer begins to yaw as well. This leads to 
the trailer's tires developing slip angles and producing lateral forces 
at the trailer tires. Thus, there is a slight delay in the turning 
response of the trailer 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. However, if the lateral 
forces generated at the tires result in a vehicle lateral acceleration 
that exceeds the rollover threshold of the vehicle, then rollover will 
result.
    Lateral acceleration is the primary cause of rollovers. Figure 1 
depicts a simplified rollover condition. As shown, when the lateral 
force (i.e., lateral acceleration) is sufficient 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 is more likely to roll than 
a vehicle entering the curve at a lower speed. Also, transporting a 
high center of gravity (CG) load would increase the rollover 
probability more than transporting a relatively lower CG load.
[GRAPHIC] [TIFF OMITTED] TP23MY12.002

    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, which is designed to help prevent on-
road, untripped rollovers by automatically decelerating the vehicle 
using brakes and engine control. The other technology is electronic 
stability control, or ESC,\11\ which is designed to

[[Page 30772]]

assist the driver in mitigating severe oversteer or understeer 
conditions by automatically applying selective brakes to help the 
driver maintain directional control of the vehicle. On heavy vehicles, 
ESC also includes the RSC function described above.
---------------------------------------------------------------------------

    \11\ In light vehicles, the term ESC generally describes a 
system that helps the driver maintain directional control and 
typically does not include the RSC function because these vehicles 
are much less prone to untripped rollover.
---------------------------------------------------------------------------

B. Description of RSC System Functions

    Currently, RSC systems are available for air-braked tractors with a 
GVWR of greater than 11,793 kilograms (26,000 pounds) 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.\12\ The ECU 
continuously estimates the roll stability threshold of the 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. Some 
RSC systems also use a steering wheel angle sensor, which allows the 
system to identify potential roll instability events earlier.
---------------------------------------------------------------------------

    \12\ 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. When a high lateral acceleration 
that is likely to cause the trailer to rollover is detected, the ECU 
commands application of the trailer brakes to slow the combination 
vehicle. In this case, the trailer brakes on the outside wheels can be 
applied with full pressure since the ECU can directly monitor the 
trailer wheels for braking-related lockup. The system modulates the 
brake pressure as needed to achieve maximum braking force without 
locking the wheels. 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.

C. Description of ESC System Functions

    Currently, ESC systems are available for heavy vehicles, including 
truck tractors and buses, equipped with air brakes. An ESC system 
incorporates all of the inputs of an RSC system. In addition, an ESC 
system monitors steering wheel angle and yaw rate of the vehicle.\13\ 
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.\14\
---------------------------------------------------------------------------

    \13\ Because ESC systems must monitor steering inputs from the 
tractor, ESC systems are not available for trailers.
    \14\ 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.
---------------------------------------------------------------------------

D. How ESC Prevents Loss of Control

    Like an RSC system, an ESC system has a lateral acceleration 
sensor. 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 intended direction of a vehicle. 
The other is a yaw rate sensor, which measures the actual turning 
movement of the vehicle. When a discrepancy between the intended and 
actual headings of the vehicle occurs, it is because the vehicle is in 
either an understeering (plowing out) or an oversteering (spinning out) 
condition. The ESC system responds to such a discrepancy by 
automatically intervening and applying brake torque selectively at 
individual wheel ends on the tractor, by reducing engine torque output 
to the drive axle wheels, or by both means. If only the wheel ends at 
one corner of the vehicle are braked, the uneven brake force will 
create a correcting yaw moment that causes the vehicle's heading to 
change. An ESC system also has the capability to reduce the engine 
torque output to the drive wheels, which effectively reduces the 
vehicle speed and helps the wheels to regain traction. This means of 
intervention by the ESC system may occur separate from or simultaneous 
with the automatic brake application at selective wheel ends. An ESC 
system is further differentiated from an RSC system in that it has the 
ability to selectively apply the front steer axle brakes while the RSC 
system does not incorporate this feature.
    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.

[[Page 30773]]

[GRAPHIC] [TIFF OMITTED] TP23MY12.003

    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. The rear wheels of the tractor have 
exceeded the limits of road traction. As a result, the rear of the 
tractor is beginning to slide. This would lead a vehicle without an ESC 
system to spin out. If the tractor is towing a trailer, as the tractor 
in the figure is, this would result in a jackknife crash. In such a 
crash, the tractor spins and may make physical contact with the side of 
the trailer. The oversteering tractor in this figure is considered to 
be yaw-unstable because the tractor rotation occurs without a 
corresponding increase in steering wheel angle by the driver. 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 
leftward rotation of the vehicle, it momentarily applies the right 
front brake, thus creating a rightward (clockwise) counter-rotational 
force and turning the heading of the vehicle back to the correct path. 
It will also cut 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 action happens quickly 
so that the driver does not perceive the need for steering corrections.
    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, except that in this case, it is the front wheels 
that have exceeded the limits of road traction. As a result, the 
tractor is sliding at the front (``plowing out''). Such a vehicle is 
considered to be yaw-stable because no increase in tractor rotation 
occurs when the driver increases the steering wheel angle. However, the 
driver has lost directional control of the tractor. In this situation, 
the ESC system rapidly detects that the vehicle's heading is changing 
less quickly than appropriate for the driver's intended path (i.e., the 
yaw rate is too low). In other words, the vehicle is not turning right 
sufficiently to remain on the right curve and is instead heading off to 
the left. The ESC system momentarily applies the right rear brake, 
creating a rightward rotational force, to turn the heading of the 
vehicle back to the correct path. Again, it will also cut 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).

E. Situations in Which Stability Control Systems May Not Be Effective

    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 recovery maneuvers in which a vehicle departs the 
roadway and encounters an incline too steep to effectively maneuver the 
vehicle 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 on 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.

F. Difference in Vehicle Dynamics Between Light Vehicles and Heavy 
Vehicles

    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.\15\ The rule also requires a phase-in of 55 percent, 75 percent, 
and 95 percent of vehicles produced by each manufacturer during model 
years 2009, 2010, and 2011, respectively, to be equipped with a 
compliant ESC system. 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.
---------------------------------------------------------------------------

    \15\ 72 FR 17236.
---------------------------------------------------------------------------

    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.
    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

[[Page 30774]]

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.\16\ 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.
---------------------------------------------------------------------------

    \16\ 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. The trailer roll torque is 
transmitted to the tractor through the vehicles' articulation point, 
which subsequently leads to tractor rollover. In addition to the 
trailer's loading condition, the trailer rollover threshold is also 
related to the torsional stiffness of the trailer body. A trailer with 
a low torsional stiffness, such as a flatbed open trailer, would 
typically experience wheel lift earlier during a severe turning 
maneuver than a trailer with a high torsional stiffness, such as a van 
trailer. Hence, compared with a light vehicle, the roll dynamics of a 
tractor trailer combination vehicle is a more complex interaction of 
forces acting on the units in the combination, as influenced by the 
maneuver, the loading condition, and the roadway.
    Unlike with light vehicles, there is a large range of loading 
scenarios possible for a given heavy vehicle, particularly for truck 
tractors towing trailers. A tractor-trailer combination vehicle can be 
operated empty, loaded to its maximum weight rating, or loaded anywhere 
in between the two extremes. The weight of a fully loaded combination 
vehicle is generally more than double that of the vehicle with an empty 
trailer. Furthermore, the load's center of gravity height can vary over 
a large range, which can have substantial effects on the dynamics of a 
combination vehicle.
    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, results in making heavy vehicles less 
likely to yaw on dry road surface conditions.
    As a result of the differences in vehicle dynamics between light 
vehicles and heavy vehicles, the requirements in FMVSS No. 126 for 
light vehicle ESC systems cannot translate directly into requirements 
for heavy vehicles. Nevertheless, many requirements in FMVSS No. 126 
are pertinent to heavy vehicles because they do not relate to any 
difference in vehicle dynamics between light vehicles and heavy 
vehicles. For example, the ESC system malfunction detection and 
telltale requirements already developed for light vehicles can be 
translated to heavy vehicles.

IV. Research and Testing

    NHTSA has been studying ways to prevent untripped heavy vehicle 
rollovers for many years. In the mid-1990s, the agency sponsored the 
development of a prototype roll stability advisor (RSA) system that 
displayed information to the driver regarding the truck's roll 
stability threshold and the peak lateral acceleration achieved during 
cornering maneuvers. This was followed by a fleet operational test 
sponsored by the Federal Highway Administration, under the Department 
of Transportation's Intelligent Vehicle Initiative. The tractors were 
equipped with a RSA system using an engine retarder, which was an early 
configuration of an RSC system. As that test program was concluding, 
industry developers of stability control systems began to add tractor 
and trailer foundation braking capabilities to increase the 
effectiveness these systems.
    In 2006, the agency initiated a test program at the Vehicle 
Research and Test Center (VRTC) to conduct track testing on RSC- and 
ESC-equipped tractors and semitrailers. The initial testing focused 
only on roll stability testing and provided comparative data on the 
performance of the different stability control systems in several test 
maneuvers. Subsequent testing focused on refining test maneuvers and 
developing performance metrics suitable for a safety standard. The 
agency studied a slowly increasing steer maneuver that would 
characterize a tractor's steering system and verify the ability of a 
tractor-based system to control engine torque. The agency also 
developed a ramp steer maneuver to evaluate the roll stability 
performance of a stability control system, and investigated a sine with 
dwell maneuver to evaluate both yaw and roll stability performance. In 
addition to tests conducted on combination unit trucks, the VRTC 
research program included testing of three large buses equipped with 
ESC using these test maneuvers. As part of the research at VRTC, the 
agency also developed data collection and analysis methods to 
characterize the performance of stability control systems.
    NHTSA researchers began updating their vehicle dynamics simulation 
programs to include a stability control model, and coordinated with 
researchers at the National Advanced Driving Simulator (NADS) at the 
University of Iowa to add stability control modeling capability to 
their tractor trailer simulations. NHTSA sponsored a research program 
with the NADS to evaluate potential RSC and ESC effectiveness in 
several tractor-trailer driving scenarios involving potential rollover 
and loss of control, using sixty professional truck drivers who were 
recruited as test participants.
    NHTSA purchased three tractors equipped with ESC or RSC systems for 
testing: A Freightliner 6x4 \17\ tractor that had ESC as a production 
option, a Sterling 4x2 tractor that had RSC as a production option, and 
a Volvo 6x4 tractor that had ESC included as standard equipment. NHTSA 
also obtained a RSC control unit that could be retrofitted on the 
Freightliner 6x4 tractor so that it could be comparatively tested with 
both ESC and RSC. The agency also purchased a Heil 9,200-gallon tanker 
semitrailer that was equipped with a trailer-based RSC system, and 
retrofitted a Fruehauf 53-foot van semitrailer with a trailer-based RSC 
system. NHTSA also obtained three large buses equipped with stability 
control systems: A 2007 MCI D4500 (MCI 1), a 2009 Prevost H3, 
and a second 2007 MCI D4500 (MCI 2). The MCI buses were 
equipped with a Meritor WABCO ESC system and the Prevost was equipped 
with a Bendix ESC system.
---------------------------------------------------------------------------

    \17\ The 6x4 description for a tractor represents the total 
number of wheel positions (six) and the total number of wheel 
positions that are driven (four), which means that the vehicle has 
three axles with two of them being drive axles. Similarly, a 4x2 
tractor has four wheel positions, two of which are driven, meaning 
that the vehicle has two axles, one of which is a drive axle.
---------------------------------------------------------------------------

    Although the manufacturers of truck tractors and large buses and 
the suppliers of stability control systems have performed extensive 
development

[[Page 30775]]

work to bring these systems to the market, there are few sources of 
objective evaluations for testing on stability control systems in the 
public domain beyond the research programs described above. The agency 
coordinated with truck, bus, and stability control system manufacturers 
throughout the VRTC test program so that industry organizations had the 
opportunity to contribute additional test data and other relevant 
information on test maneuvers that the agency could consider for use 
during the research program. Potential maneuvers suggested by industry 
included a decreasing radius test from the Truck & Engine Manufacturers 
Association (EMA),\18\ a sinusoidal steering maneuver and a ramp with 
dwell maneuver from Bendix, and a lane change maneuver (on a large 
diameter circle) from Volvo.\19\ In late 2009, the EMA provided results 
from their tests of the ramp steer, sine with dwell, and ramp with 
dwell maneuvers to NHTSA. The agency evaluated these data from a 
measures-of-performance perspective. EMA provided data in December 2010 
discussing additional testing with the sine with dwell, J-turn, and a 
wet-Jennite drive through maneuver. Additional details on these 
research programs are included in the sections below.
---------------------------------------------------------------------------

    \18\ EMA was formerly known as the Truck Manufacturers 
Association (TMA). Many docket materials refer to EMA as TMA.
    \19\ Presentations from briefings NHTSA had with EMA have been 
included in the docket. See Docket Nos. NHTSA-2010-0034-0025 through 
NHTSA-2010-0034-0031; Docket Nos. NHTSA-2010-0034-0041 and NHTSA-
2010-0034-0042. Research notes provided by EMA, Bendix, and Volvo 
Trucks have also been included in the docket. See Docket Nos. NHTSA-
2010-0034-0032 through NHTSA-2010-0034-0040.
---------------------------------------------------------------------------

A. UMTRI Study

    NHTSA sponsored a research program with Meritor WABCO and the 
University of Michigan Transportation Research Institute (UMTRI) to 
examine the potential safety effectiveness of stability control systems 
for five-axle tractor-trailer combination vehicles. The systems 
investigated included both RSC and ESC.\20\ The research results are 
provided in the report ``Safety Benefits of Stability Control Systems 
for Tractor-Semitrailers.'' A copy of this report has been included in 
the docket.\21\
---------------------------------------------------------------------------

    \20\ A similar study has been initiated with respect to straight 
trucks over 10,000 pounds GVWR.
    \21\ DOT HS 811 205 (Oct. 2009), Docket No. NHTSA-2010-0034-0006
---------------------------------------------------------------------------

    The objectives of the study were: (1) To use the Large Truck Crash 
Causation Study (LTCCS) to define typical pre-crash scenarios and 
identify factors associated with loss-of-control and rollover crashes 
for tractor-trailers; (2) to study the effectiveness of RSC and ESC in 
a range of realistic scenarios through hardware-in-the-loop simulation 
testing, and through case reviews by a panel of experts; (3) to apply 
the results of this research to generate national estimates from the 
Trucks Involved in Fatal Accidents (TIFA) and General Estimates System 
(GES) crash databases of the safety benefits of RSC and ESC in 
preventing tractor-trailer crashes; and (4) to review crash data from 
2001 through 2007 from a large trucking fleet that had started 
purchasing RSC on all of its new tractors starting in 2004, to 
determine if there was an influence of this system on reducing crashes.
    The LTCCS was a joint study undertaken by the Federal Motor Carrier 
Safety Administration (FMCSA) and NHTSA, based on a sample of 963 
crashes between April 2001 and December 2003 with a reported injury or 
fatality involving 1,123 trucks with a GVWR over 10,000 pounds. The 
LTCCS crash data formed the backbone for this study because of the high 
quality and consistent detail contained in the case files. Included in 
the LTCCS are categorical data, comprehensive narrative descriptions of 
each crash, scene diagrams, and photographs of the vehicle and roadway 
from various angles. This information allowed the researchers to 
achieve a high level of understanding of the crash mechanics for 
particular cases. The LTCCS was used to help develop the crash 
scenarios for modeling (hardware-in-the-loop) performed as part of the 
engineering analyses for this stability control project. In addition, 
LTCCS cases of interest with respect to stability control systems were 
also reviewed by a panel of three experts (two from UMTRI and one from 
industry) to help estimate the safety benefits of RSC and ESC.
    One method for assessing the safety benefits of vehicle 
technologies is to analyze crash datasets containing data on the safety 
performance of vehicles equipped with the subject technology. However, 
because the deployment of the stability control technologies for large 
trucks is still in its early stages, national crash databases do not 
yet have sufficient cases that can be used to evaluate the safety 
performance of stability control technology. Given this limitation, 
this study used an indirect method to estimate the safety performance 
of stability control technologies based on probable outcome estimates 
derived from hardware-in-the-loop simulation, field test experience, 
expert panel assessment, and crash data from trucking fleets.
    UMTRI's study made several conclusions. First, identifying relevant 
loss-of-control and rollover crashes within the national databases 
proved a difficult task because the databases are developed for general 
use and this project required very precise definitions of loss-of-
control and rollover (e.g., tripped versus untripped). Relying on the 
general loss-of-control or rollover categories captures a wide range of 
crashes, many of which cannot be prevented by the stability control 
technology. Furthermore, many of the crashes involved vehicles that 
were not equipped with ABS. Because ABS is now mandatory for the target 
population of vehicles, the researchers had to factor in what effect 
the presence of ABS on the vehicle may have reduced the likelihood of 
or prevented the crash.
    Second, the LTCCS was highly valuable in providing a greater level 
of detail concerning rollover and loss-of-control crashes, which was 
used to construct a number of relevant crash scenarios so that the 
technical potential of the candidate RSC and ESC technologies could be 
estimated systematically. However, the inability to determine with 
confidence if a vehicle lost control and the lack of detailed 
information on driver input and vehicle state placed limitations on the 
ability to assess the potential for stability control technologies to 
alter the outcome of a particular crash scenario. In contrast, for 
rollover crashes, it was clear that rollover occurred. Tire marks and 
road alignment provide strong evidence of the vehicle path and the 
point of instability.
    Third, UMTRI concluded that ESC systems would provide more overall 
safety benefits than RSC systems. The difference between the estimated 
effectiveness of RSC and ESC varied among crash scenarios. ESC systems 
were slightly more effective at preventing rollovers than RSC systems 
and much more effective at preventing loss-of-control crashes.
    Finally, the safety benefits estimates derived from this study were 
limited to five-axle tractor-trailer combination vehicles, which 
constitute a majority of the national tractor fleet. However, the study 
did not include benefits estimates for multi-trailer combinations or 
for tractors not towing a trailer.

B. Simulator Study

    NHTSA sponsored a research study with the University of Iowa to 
study the effectiveness of heavy truck electronic stability control 
systems in reducing jackknife and rollover incidents using the NADS-1 
National Advanced Driving Simulator. The NADS-1 is a high-fidelity, 
full motion driving simulator with a 360-degree visual display system

[[Page 30776]]

that is typically used for the study of driver behavior. Sixty 
professional truck drivers were recruited to participate in the study. 
The participants drove a typical tractor-semitrailer in five scenarios 
designed to have a high potential for rollover or jackknife. The study 
used the NADS heavy truck cab and vehicle dynamics model to simulate a 
typical 6x4 tractor-trailer combination vehicle in a baseline (ABS-
only), RSC-equipped, and ESC-equipped configurations, using twenty 
truck drivers per configuration. The purpose of the study was to 
determine the effectiveness of both roll stability control and yaw 
stability control systems, to demonstrate driver behavior while using 
stability control systems, and to help NHTSA refine safety benefits 
estimates for heavy truck stability technologies.\22\
---------------------------------------------------------------------------

    \22\ The final report is available in the docket. ``Heavy Truck 
ESC Effectiveness Study Using NADS'' (DOT HS 811 233, November 
2009), Docket No. NHTSA-2010-0034-0007.
---------------------------------------------------------------------------

    The NADS truck model performance was compared with test track data 
from VRTC. The test maneuver used was a ramp steer maneuver with a 
steering wheel angle of 190 degrees and an angular steering rate of 175 
degrees per second. The steering angle was held constant for five 
seconds after reaching 190 degrees, and then returned to zero. Steering 
inputs on the NADS were performed manually rather than by using an 
automated steering machine. The RSM was performed in the NADS to both 
the right and left directions to check for any simulation 
abnormalities, and was performed for the baseline, RSC, and ESC test 
conditions. Exact matching of values to the test track data was not 
possible because the NADS model was developed by simulating the braking 
properties of a Freightliner tractor while using the inertial 
properties of a Volvo tractor. Also, the NADS was modeled with rigid 
body tractor and trailer vehicle models that did not include the 
torsional chassis compliance that is a variable in actual vehicles. The 
result of the testing was that the NADS model tractor-semitrailer 
experienced wheel lift at slightly lower speeds in the RSM in all three 
conditions (baseline, RSC, and ESC) than in the VRTC track tests. An 
additional comparison of VRTC track test data and the NADS ESC model 
was performed for lane change maneuvers at 45 and 50 mph and showed 
that the NADS ESC system responses closely matched the responses of the 
actual test vehicle.
    The maneuvering events used to assess the influence of ESC systems 
consisted of lane incursion from the left side on a snow-covered road 
and from the right side on a dry road surface, with each event 
necessitating a sudden lane change to avoid collision. These events 
provided a greater challenge for the stability control systems due to 
the aggressive steering and braking inputs by the drivers. Neither 
stability control system showed benefits in preventing rollover on the 
dry road surface. ESC systems did provide improved vehicle control on 
the snow-covered surface; however, two jackknife events still occurred 
with the ESC system. A large number of jackknife events occurred on the 
snow-covered surface with the RSC system (11 loss-of-control events in 
20 runs) which may have been a result of the aggressive RSC braking 
strategy found in the model interfering with the driver's ability to 
maintain steering control of the tractor.
    The NADS research study indicated that the RSC system showed a 
statistically significant benefit in preventing rollovers on both 
curves and exit ramps on dry, high-friction road surfaces. The tractors 
equipped with RSC and ESC systems showed a benefit over the baseline 
tractor in assisting drivers to avoid a jackknife on a low-friction 
road surface and a rollover on a high-friction road surface when 
encountering a directional change due roadway geometry. However, in 
several instances the ESC system was found to activate at abnormally 
high levels of lateral acceleration in a curve with a high-friction 
road surface. Although the reason for this was not determined, there 
may have been problems with the mass estimation algorithm or vehicle 
parameter inaccuracies in the model.

C. NHTSA Track Testing

    NHTSA researchers at VRTC in East Liberty, Ohio, initiated a test 
program in 2006 to evaluate the performance of stability control 
systems under controlled conditions on a test track, and to develop 
objective test procedures and measures of performance that could form 
the basis of a new FMVSS. Researchers tested three truck tractors, all 
of which were equipped with an RSC or ESC system (one vehicle was 
tested with both an RSC and ESC system), one trailer equipped with a 
trailer-based RSC system, and three large buses equipped with an ESC 
system. Additionally, the agency tested five baseline semi-trailers not 
equipped with a stability control system, including an unbraked control 
trailer that is used to conduct tractor braking tests as prescribed by 
FMVSS No. 121, Air brake systems.
    The testing was conducted in three phases. Phase I research focused 
on understanding how stability control systems performed. Phase II 
research focused on the development of a dynamic test maneuver to 
evaluate the roll stability of tractor semitrailers and large buses. 
Phase III research focused on the development of a dynamic test 
maneuver to evaluate the yaw stability of truck tractors and large 
buses.
    The Phase I and II research results are documented in the report 
``Tractor Semi-Trailer Stability Objective Performance Test Research--
Roll Stability.'' \23\ The Phase III research results for truck 
tractors are documented in the report ``Tractor Semitrailer Stability 
Objective Performance Test Research--Yaw Stability.'' \24\ The 
information provided in sections IV.C.1, IV.C.2, and IV.C.3 below is 
based on these two reports. The motorcoach research is documented in 
the report ``Test Track Lateral Stability Performance of Motorcoaches 
Equipped with Electronic Stability Control Systems.'' \25\ The 
information in section IV.C.4 is based on this report.
---------------------------------------------------------------------------

    \23\ DOT HS 811 467 (May 2011), Docket No. NHTSA-2010-0034-0009. 
Results from Phase I are also summarized in the paper ``NHTSA's 
Class 8 Truck-Tractor Stability Control Test Track Effectiveness'' 
(ESV 2009. Paper No. 09-0552). Docket No. NHTSA-2010-0034-0008.
    \24\ Docket No. NHTSA-2010-0034-0046.
    \25\ Docket No. NHTSA-2010-0034-0045.
---------------------------------------------------------------------------

1. Effects of Stability Control Systems--Phase I
    The test vehicles used in Phase I included a 2006 Freightliner 6x4 
tractor equipped with air disc brakes and a Meritor WABCO ESC system as 
factory-installed options, a 2006 Volvo 6x4 tractor with S-cam drum 
brakes and a Bendix ESC system included as standard equipment, and a 
2000 Fruehauf 53-foot van trailer that was retrofitted with a Meritor 
WABCO trailer-based RSC system. Tests were conducted by enabling and 
disabling the stability control systems on the tractor and the trailer 
to compare the individual performance of each system, evaluate the 
performance of the combined tractor and trailer stability control 
systems, establish the baseline performance of each tractor-trailer 
combination without any stability control system. All tests were 
conducted with the tractor connected to the trailer, in either the 
unloaded condition (lightly loaded vehicle weight (LLVW)) or loaded to 
a 80,000 pound combination weight with the ballast located to produce 
either a low or high center of gravity height (low CG or high CG) 
loading condition. During testing, all

[[Page 30777]]

combination vehicles were equipped with outriggers.
    The first test maneuver evaluated in Phase I was a constant radius 
circle test (either a 150 foot or a 200 foot radius) conducted on dry 
pavement. In this constant radius circle test, the driver maintained 
the vehicle on the curved path while slowly increasing the vehicle 
speed until the stability control system activated, wheel lift 
occurred, or the tractor experienced a severe understeer condition.
    With the stability control systems disabled, no cases of wheel lift 
were observed under the LLVW or low CG condition. Under these load 
conditions, both tractors went into a severe understeer condition. The 
LLVW tractor did not reach a velocity greater than 40 mph and the low 
CG tractor did not reach a velocity greater than 34 mph. However, in 
the high CG condition with the tractor ESC systems disabled, wheel lift 
occurred in every test that resulted in a lateral acceleration greater 
than 0.45g at 30 mph.
    With the tractor ESC systems enabled, the performance of the two 
ESC-equipped vehicles improved during the constant radius tests. Both 
ESC systems limited the maximum lateral acceleration of the tractor by 
reducing the engine output torque and prevented wheel lift and severe 
tractor understeer with the different loads tested. With ESC systems 
enabled, both tractors tested allowed higher maximum lateral 
accelerations for the LLVW condition compared to the low CG and high CG 
conditions. There was little difference in peak lateral acceleration 
for the low CG and high CG conditions.
    The trailer-based RSC system limited the maximum lateral 
acceleration by applying the trailer brakes, which mitigated wheel lift 
and understeer with the different loads tested. The maximum lateral 
acceleration of both tractors was limited by the trailer RSC system to 
below 0.50g for the LLVW condition, 0.40g to 0.50g for the low CG 
condition, and 0.35g to 0.40g for the high CG condition.
    When both tractor- and trailer-based stability control systems were 
enabled, results were similar to the results of the tractor-based 
stability control system for the low CG and high CG conditions. Under 
the LLVW condition, results were similar to the trailer-based RSC 
system values observed.
    The second maneuver evaluated in Phase I was a J-turn, also 
conducted on dry pavement, in which the test driver accelerated the 
vehicle to a constant speed in a straight lane and then negotiated 180 
degrees of arc along a 150-foot radius curve. The initial maneuver 
entrance speed was 20 mph and it was incrementally increased in 
subsequent runs, until a test termination condition was reached. The 
test terminated upon the occurrence of one of the following: The 
trailer outriggers making contact with the ground, indicating that 
wheel lift was occurring; the tractor experiencing a severe understeer 
condition; a stability control system brake activating; or the maneuver 
entry speed reaching 50 mph.
    For both tractors in the baseline configuration (stability control 
disabled), trailer wheel lift occurred in all load combinations except 
for the Freightliner in the LLVW condition, which went into a severe 
understeer condition at a maneuver entry speed of 50 mph. For the Volvo 
in the LLVW load condition, trailer wheel lift was observed when the 
tractor's maximum lateral acceleration exceeded 0.75g at 48 mph. With 
stability control disabled in the low CG load condition, trailer wheel 
lift was observed when the tractor's maximum lateral acceleration was 
greater than 0.67g at 40 mph for the Freightliner and 0.60g at 38 mph 
for the Volvo. For the high CG load condition, trailer wheel lift was 
observed when the tractor's maximum lateral acceleration was 
approximately 0.45g at 33 mph for the Freightliner and 0.42g at 31 mph 
for the Volvo.
    Tractor ESC systems limited the maximum lateral acceleration for 
both the tractor and the trailer. Wheel lift was not observed for the 
range of speeds evaluated. For both tractors tested in the low CG and 
high CG loading conditions, the tractor's ESC intervened at a speed 
that was well below the speed that would produce trailer wheel lift. 
With the trailer in the LLVW load condition, the tractor's maximum 
lateral acceleration was limited to approximately 0.60g for the 
Freightliner and the Volvo. With the trailer tested in either the low 
CG or high CG load conditions, the tractor's lateral acceleration was 
limited to 0.50g and 0.40g for the Freightliner and Volvo respectively.
    The trailer-based RSC system also improved the baseline vehicle's 
roll stability in the J-turn maneuver. For the LLVW load condition, the 
trailer-based RSC system activated at speeds similar to those of the 
tractor-based systems. For the low CG and high CG load conditions, the 
tractor-based systems activated at approximately a 3 mph lower speed 
than the trailer-based RSC system. With both systems enabled, the 
tractor-based system activated and mitigated the roll propensity before 
the trailer RSC system activated.
    The third maneuver evaluated in Phase I was a double-lane-change 
maneuver, in which the test driver accelerated the vehicle up to a 
constant speed on a dry road surface and then negotiated a lane change 
maneuver followed by a return to the original lane within physical 
boundaries (gates) marked by cones. The maneuver entry speed was 
incrementally increased in subsequent test runs. Although the top speed 
in this maneuver was intended to be limited to 50 mph for safety 
reasons, the test driver performed runs at speeds as high as 51 mph.
    In the baseline configuration, both tractors completed the maneuver 
at 50 mph without wheel lift or yaw instability in the LLVW and the low 
CG loading conditions. In the high CG loading condition, the 
Freightliner experienced trailer wheel lift at a maneuver entry speed 
of 41 mph and the Volvo experienced trailer wheel lift at a maneuver 
entry speed of 45 mph.
    With the ESC system, the Freightliner's stability control system 
was observed to limit peak lateral acceleration to approximately 0.50g, 
which prevented trailer wheel lift in the high CG load condition for 
tests performed up to 50 mph. Tests performed at 51 mph resulted in 
trailer wheel lift. The Volvo's stability control system limited the 
tractor's maximum lateral acceleration to approximately 0.40g and 
prevented trailer wheel lift for the high CG condition up to a maximum 
test speed of 51 mph.
    With only a trailer-based RSC system, trailer wheel lift was 
observed during the high CG load condition when the system was 
overdriven at 41mph when tested with the Freightliner, which 
represented no improvement over the baseline condition. Trailer wheel 
lift was observed at 50 mph when tested with the Volvo, which 
represented a 5 mph improvement over the baseline condition. When 
tested with this maneuver in the high CG load condition, the trailer-
based RSC system activated the trailer brakes at entrance speeds of 30 
and 33 mph for the Freightliner and Volvo, respectively.
    All stability control systems tested improved the roll stability of 
the vehicle over the baseline condition. For each maneuver, the 
tractor-based stability control systems were able to mitigate trailer 
wheel lift at the same or higher maneuver entrance speeds than trailer-
based systems. The trailer-based RSC system was typically able to 
mitigate trailer wheel lift at a higher maneuver entry speed than the 
baseline condition, with the exception of the double-lane-change 
maneuver with one of the tractors. In the tests with both tractor-

[[Page 30778]]

based ESC systems and trailer-based RSC systems enabled, the tractor-
based ESC system was often found to be the first system to intervene to 
reduce wheel lift or understeer.
    Based on the results of Phase I, the agency determined that a 
performance test based on the J-turn was suitable to evaluate tractor 
and trailer stability control systems. The J-turn maneuver generates a 
sufficient amount of lateral acceleration to provide a challenging test 
at reasonable test speeds. The J-turn maneuver is also more 
representative of the real-world conditions, such as curved off-ramp, 
that could generate untripped rollover. Because the results from Phase 
I showed that tractor-based stability control systems increased the 
roll stability by a larger margin than trailer-based RSC systems, NHTSA 
concluded that Phase II research should focus on tractor-based 
stability control systems.
2. Developing a Dynamic Test Maneuver and Performance Measure To 
Evaluate Roll Stability--Phase II
(a) Test Maneuver Development
    The researchers at VRTC conducted Phase II to develop test methods 
that could evaluate stability control system performance objectively 
and measures of performance that would ensure that a stability control 
system could prevent rollover effectively. After Phase I test results 
demonstrated that a test driver's steering input variation could affect 
test outcome, an automated steering machine was used for subsequent 
research. The testing focused on tractor-based stability control 
systems that were determined to be most effective in preventing 
rollovers from the Phase I research.
    Both the Freightliner and Volvo 6x4 tractors equipped with an ESC 
system from Phase I were tested, and an RSC electronic control unit was 
also obtained for the Freightliner. A Sterling 4x2 equipped with a 
Meritor WABCO RSC system was also tested in Phase II. In addition to 
the Fruehauf 53-foot van trailer used in Phase I (its trailer-based RSC 
system was disabled throughout the Phase II testing), five additional 
trailers were tested, including a second 53-foot van trailer, two 48-
foot flatbed trailers, a 9200-gallon tanker trailer, and a 28-foot 
flatbed trailer which is used as a control trailer in FMVSS No. 121 
brake system testing.
    The first maneuver evaluated in Phase II was a slowly increasing 
steer maneuver. The SIS maneuver has been used by the agency and the 
industry to determine the unique dynamic characteristics of each 
vehicle. This maneuver is included in the FMVSS No. 126 test procedure 
for ESC systems on light vehicles. The maneuver provides the steering 
wheel angle to lateral acceleration relationship for each vehicle, 
accounting for the differences in steering gear ratios, suspension 
systems and wheelbases among vehicles. It also normalizes test 
conditions to account for variations in test conditions, such as road 
surface friction. The steering wheel angle derived from the SIS test 
was used to program the automated steering machine for the ramp steer 
maneuver discussed below.
    To initiate the SIS maneuver, the test driver accelerated the 
vehicle to a constant speed of 30 mph on a dry road surface. The driver 
then activated the steering machine to input a steadily increasing 
steering wheel angle up to 270 degrees at a rate of 13.5 degrees per 
second. The test driver manually maintained constant speed using the 
accelerator pedal while the tractor's path radius steadily decreased 
and the tractor's lateral acceleration steadily increased. The SIS 
maneuvers were conducted with the tractor in the bobtail condition (no 
trailer attached). The SIS maneuver also demonstrated that tractor-
based stability control systems are capable of detecting a high lateral 
acceleration condition and intervening by reducing the engine output 
torque.
    The SIS maneuver was used to determine the steering wheel angle 
projected to generate 0.5g of lateral acceleration when traveling at 30 
mph. This value varied depending on characteristics of the tractor such 
as its wheelbase and steering ratio. For tractors, that steering wheel 
angle and lateral acceleration data was found to have a linear 
relationship at the lateral acceleration values between 0.05 and 0.3g. 
Over this range of data a linear regression method followed by linear 
extrapolation was used to estimate the steering wheel angle at 0.5g 
lateral acceleration for each SIS maneuver. The final steering wheel 
angle was then calculated by averaging the values from tests conducted 
while turning to the left and while turning to the right. The resulting 
calculated steering wheel angles were 193 degrees for the Freightliner, 
199 degrees for the Volvo, and 162 degrees for the Sterling. This 
indicates that the Sterling, which was a 4x2 configuration, had a 
higher steering wheel gain than the other tractors which were 6x4 
configurations.
    The SIS testing was repeated for the three tractors throughout the 
test program to determine the consistency of the steering wheel angle 
calculations and the test speeds. The resulting standard deviations in 
steering wheel angle were 2.5 degrees for the Sterling, 7.4 degrees for 
the Freightliner, and 10.2 degrees for the Volvo, although the 
replacement of the tires on the Volvo may have contributed to an 
increase in steering wheel angle during one of the repeat tests. The 
tractor speed at the beginning of the SIS steering input ranged from 
29.6 to 32.2 mph for all of the tests.
    After the SIS testing, tests were conducted using a ramp steer 
maneuver to assess the roll stability of tractor-trailer combinations 
and the effectiveness of both types of tractor-based stability control 
systems. The RSM was derived from and is similar to the J-turn 
maneuver, but instead of the driver controlling the steering wheel to 
follow a fixed path, the steering controller turns the steering wheel 
to an angle determined from the results of the SIS test. One advantage 
of the RSM over the J-turn maneuver is that the RSM uses a steering 
machine, which allows for a more consistent and repeatable steering 
input.
    To conduct the RSM, the test driver accelerated the vehicle to a 
constant speed of one to two mph above the target maneuver entry speed 
on a dry surface and then released the throttle and de-clutched the 
engine. Once the vehicle coasted down to the desired maneuver entry 
speed, the automated steering controller initiated a steering input, at 
a constant rate of 175 degrees per second, up to the steering wheel 
angle that was derived for the tractor in the SIS test. Once the 
steering wheel angle was reached (the end of ramp input), it was held 
constant for five seconds, and then the controller returned the 
steering wheel angle back to zero at a steering rate of 175 degrees per 
second. The initial maneuver entry speed was 20 mph and it was 
incrementally increased in subsequent runs until a test termination 
condition was met. The termination conditions were as follows: Two 
inches of wheel lift occurring at either the tractor drive wheels or 
the trailer wheels; the tractor reaching a severe oversteer condition 
(safety cables were installed to limit the tractor-trailer articulation 
angle for testing safety); or the maneuver entry speed reached 50 mph 
without a roll or yaw instability condition. Although the intent of the 
RSM was to evaluate combination vehicle roll stability, testing with 
the trailers in the unloaded condition resulted in several occurrences 
of tractor yaw instability.
    For all of the RSM tests, each tractor was tested with all six 
trailers and the trailers were either unloaded, or loaded to a high CG, 
on-highway combination

[[Page 30779]]

weight appropriate for the number of axles on the combination vehicle. 
For the flatbed and van trailers, the load ballast was placed on 24-
inch high tables to produce a high CG height, and the tanker trailer 
was loaded with water.
    The purpose of the RSM test is not to cause a rollover, but to 
create a high lateral acceleration condition to demonstrate that a 
stability control system has the capability to reduce the likelihood of 
a rollover. Typically, wheel lift occurred first at the trailer wheels 
although the flatbed trailer combinations had tractor drive wheel lift 
occurring first or in unison with the trailer wheels. In the RSM tests 
with the stability control system disabled and the trailer in the high 
CG condition, wheel lift occurred at entry speeds between 25 and 31 mph 
for all combinations of tractors and trailers. The peak tractor lateral 
acceleration at wheel lift was in the range of 0.45 to 0.50g, showing 
that the high CG loading condition was representative of fully loaded 
tractor-trailers with a medium density cargo.
    Tractor-based stability control systems applied the foundation 
brakes on the tractor and trailer, which reduced the vehicle speed and 
lateral acceleration during the RSM. The entry speed at which wheel 
lift was first visible improved to between 31 and 42 mph for three of 
the four tractors tested (Freightliner RSC, Freightliner ESC, and Volvo 
ESC).
    In tests with the trailer brakes disabled, the entry speed at which 
wheel lift was detected was between 29 and 41 mph, which showed that 
the contribution of trailer braking to prevent wheel lift was evident, 
but that it was relatively small in comparison to the deceleration 
resulting from tractor braking. The Sterling tractor equipped with an 
RSC system had wheel lift with three of the trailers at the same speed 
as with the stability control system disabled, and with the other three 
trailers at speeds between two and four mph over the disabled test 
condition. In all of the RSM tests, the Sterling tractor's RSC system 
was not as effective at mitigating wheel lift for this maneuver.
    The results indicated that, in general, the ESC systems provided a 
higher level of deceleration compared to the RSC systems and typically 
had the higher maneuver entry speeds prior to wheel lift. However, 
there were individual trailer combinations in which the RSC system 
performed as well or slightly better than the ESC system on the 
Freightliner. We believe the better performance by the RSC system in 
some tests is attributable to the RSC system having a more aggressive 
braking strategy than the ESC system tested.
    The RSM was then performed with each of the six trailers in the 
unloaded condition, with the tractor stability control system enabled 
with the trailer brakes disabled. Tests were not conducted with the 
systems disabled. The initial maneuver entry speed was 20 mph and was 
incrementally increased in subsequent runs until the speed reached 50 
mph, severe oversteer occurred, or wheel lift occurred. The tractors 
with ESC systems enabled were able to complete all but one of the RSM 
tests up to 50 mph without any tractor instability or wheel lift. The 
Volvo tractor towing the empty tanker trailer resulted in wheel lift of 
the tractor drive wheels and the trailer wheels at a speed of 47 mph.
    In comparison, most of the tests with the tractors equipped with 
RSC systems towing unloaded trailers resulted in severe tractor 
oversteer, with the tractor-trailer articulation angle typically 
reaching the limits allowed by the safety cables. This occurred at 
speeds between 35 and 39 mph for the Freightliner 6x4 tractor and 
between 34 and 42 mph for the Sterling 4x2 tractor. However, both of 
these tractors were able to complete the RSM up to 50 mph when coupled 
to the unloaded 28-foot control trailer, and the Freightliner reached 
50 mph without wheel lift or severe understeer when coupled to the 
unloaded tanker trailer.
    In summary, the goal of the Phase II research was to develop a test 
maneuver to challenge the roll propensity of a truck tractor. The RSM 
is similar in test severity to the J-turn and demonstrates that the 
stability control systems are able to mitigate wheel lift in most cases 
that occurred when the stability control systems were disabled. In the 
high CG load condition, the ESC systems were observed to mitigate wheel 
lift at or above the speed observed with RSC-equipped vehicles, with 
the exception of a few instances with the Freightliner's ESC system. 
When tested with the unloaded test trailer, substantial improvements in 
tractor yaw stability were evident in the tractors equipped with ESC 
systems during RSM tests.
(b) Performance Measure Development
    NHTSA's Phase II testing also examined possible performance 
measures to evaluate roll stability. In situations where the vehicle's 
stability limits are approached in a gradual manner, engine/power unit 
control can improve stability in these situations. However, in 
situations where stability limits of the vehicle are approached 
rapidly, application of the vehicle's foundation brakes may be a more 
appropriate means of improving stability.
    The agency investigated four measures for development as metrics 
for engine/power unit control. They were truck tractor speed, truck 
tractor lateral acceleration, truck tractor longitudinal acceleration, 
and actual engine torque and driver requested engine torque.
    The forward speed of a truck tractor appears to be directly related 
to the lateral forces generated during an untripped rollover. Test data 
from four different vehicles with stability control enabled indicated 
that forward speed was reduced from the target maneuver entrance speed 
of 30 mph. However, due to the nature of the roll maneuver, it is 
possible for the vehicle to lose traction on the inside wheels, which 
results in a reduction in vehicle speed but does not necessarily 
enhance vehicle stability.
    Lateral acceleration was a possible measure of performance because 
of its direct relationship in producing the forces associated with 
untripped rollover. Data from four different tractors with the 
stability control system enabled indicate that each combination of 
tractor and stability control system had a different lateral limit that 
the system has allowed. This shows that the control strategy used by 
the manufacturer is different depending on the vehicle and system used. 
One strategy allows the vehicle to build lateral acceleration to a set 
threshold level and then allows that level to be maintained throughout 
the maneuver. The other strategy allows lateral acceleration to build 
and then the stability control system reduces the lateral acceleration. 
Both of these strategies were observed to increase lateral stability. 
Because the lateral acceleration limits were different for vehicles 
using these control strategies, lateral acceleration alone was not 
found to be a good measure for stability control performance.
    Longitudinal acceleration of a vehicle is reduced when a vehicle's 
stability control system is enabled and is directly related to a 
reduction in forward speed. On the four vehicles tested, the stability 
control activation had measurable differences in longitudinal 
acceleration, but had similar disadvantages to forward speed in being 
used as a performance metric.
    Engine torque measures were observed to be a direct way to 
determine ESC activation during the SIS tests. Engine torque refers to 
two different measures. The first relates to the torque output from the 
engine and is expressed

[[Page 30780]]

as a percentage of maximum engine output. The second relates to the 
throttle pedal used by the driver to control engine torque output. This 
value is also expressed as a percentage of maximum engine output and is 
referred to as the ``driver requested torque.'' During normal operation 
the ``driver requested torque'' and ``engine torque'' measures were 
observed to be equal to each other. However, during ESC activation when 
engine control intervened, the two measures were observed to be 
separate. In every case, the ``engine torque'' was much less than the 
``driver requested torque'' and continued to reduce until vehicle 
stability was regained. After careful review of the data the torque 
separation activity was confirmed for all the SIS test series in which 
stability control was enabled for each vehicle. This led the agency to 
conclude that this measure was a good candidate for further analysis 
and development as a measure of performance for truck tractors equipped 
with a stability control system.
    The engine torque data analysis was based on the test driver 
attempting to maintain a constant vehicle speed at the point of 
stability control engine torque intervention by making a substantial 
increase in driver-requested engine torque. For the four vehicles 
tested, the driver requested engine torque after stability control 
intervention was between 60 percent and 100 percent of engine output 
whereas the engine torque output after stability control intervention 
ranged from zero to 60 percent. The analysis of engine torque 
differentials was limited to the first four seconds after stability 
control engine torque intervention since none of the SC systems were 
observed to make substantial reapplications of engine torque output 
during this initial time- frame. On two vehicles engine torque 
interventions reduced engine output torque to zero during the first 
four seconds, and both systems allowed engine torque to be momentarily 
reapplied to over 50 percent of engine torque output. The Volvo had the 
highest engine torque output during the first four seconds after 
intervention, which ranged from 23 percent to 18 percent of maximum 
engine torque.
    The agency also investigated several other measures for development 
for foundation braking in rollover tests because stability control 
systems were observed to improve the vehicle's roll stability by 
applying the foundation brakes. The measures investigated were wheel 
lift, lateral acceleration, lateral acceleration ratio, trailer lateral 
acceleration ratio, and trailer roll angle ratio.
    Wheel lift is a direct measure of performance with minimal 
calculations needed to determine its value. The measure is simple and 
directly represents the pre-crash condition that immediately precedes a 
rollover. If wheel lift can be prevented, a rollover cannot occur. For 
our research, wheel lift was considered to occur upon two inches of 
lift for the tractor drive axle wheels or the trailer wheels. Wheel 
lift does not always indicate that rollover is imminent, particularly 
because certain suspension designs will lift a wheel during hard 
cornering. We estimated the vehicle speed that produced wheel lift 
during the ramp steer maneuver and found that between 29 mph and 32 
mph, there is a high probability of wheel lift occurring on the 
combination vehicles tested. Given that only four different truck 
tractors and six different test trailers were used, we believed that 
the data may not be sufficient to assess the real world service of 
tractors with ESC expected to function with different trailers having 
different torsional stiffness and loads.
    Using lateral acceleration as a performance metric is based on the 
principle that a tractor-trailer combination vehicle with a high center 
of gravity that achieves a certain level of lateral acceleration would 
roll over. Tests performed on the Freightliner in combination with all 
trailers configured with a high-CG load, at a mean entrance speed of 28 
mph generated a lateral acceleration. The data showed that using 
tractor maximum lateral acceleration as a performance criteria would 
not discriminate between vehicles equipped with stability control and 
those without it. However, it did show that a ratio-based metric could 
be more appropriate for such a performance metric.
    Lateral acceleration ratio is calculated by dividing the tractor's 
lateral acceleration at a given time interval by the measured lateral 
acceleration at the end of ramp input, which is the end of the steering 
maneuver and the point near which the vehicle experiences its peak 
lateral acceleration. The LAR was plotted at five equal one-second 
intervals for several truck tractors and test trailers. The plots 
indicated sharp decreases in LAR caused by activation of the stability 
control system.
    A similar ratio metric for trailers, trailer lateral acceleration 
ratio, also showed the ability to discriminate between vehicles with 
stability control systems and those without. A third ratio metric was 
considered, trailer roll angle ratio based on a test trailer roll 
angle, but it did not clearly discriminate between vehicles with 
stability control systems and those without.
3. Developing a Dynamic Test Maneuver and Performance Measure To 
Evaluate Yaw Stability--Phase III
(a) Test Maneuver Development
    The purpose of the Phase III research was to develop maneuvers to 
evaluate the yaw stability performance of stability control systems on 
tractors. Although we have examined several maneuvers to evaluate yaw 
stability, two maneuvers were fully investigated because other 
maneuvers were not able to provide a consistent, repeatable performance 
test. We fully considered a sine with dwell test maneuver that is 
similar to the test maneuver used in FMVSS No. 126 for light vehicles; 
and a half-sine with dwell (HSWD) test maneuver. The steering inputs 
for the SWD and HSWD maneuvers are depicted in the figures below, and 
as discussed in additional detail, variations on the steering wheel 
angle, the frequency of the sine wave (cycles per second, Hz), and the 
dwell time were evaluated for both maneuvers. A steering machine was 
used to achieve consistent steering wheel inputs for these maneuvers.

[[Page 30781]]

[GRAPHIC] [TIFF OMITTED] TP23MY12.004

    The test vehicles used in Phase III included: A 2006 Freightliner 
6x4, which was tested with both ESC and RSC systems; a 2006 Volvo 6x4 
tractor with an ESC system; and a Sterling 4x2 tractor equipped with an 
RSC system. Although most of the testing was performed using the 28-
foot flatbed control trailer, each tractor was also tested with a 53-
foot Strick van trailer, a 48-foot Fontaine spread axle flatbed 
trailer, and a 9600-gallon Heil tanker trailer. Tests were conducted 
with the trailer brakes both enabled and disabled.
    Two tractor loading conditions were used for both the SWD and HSWD 
testing. Each tractor was tested in the bobtail condition (no trailer 
attached) and using a trailer loaded over the fifth wheel so that the 
tractor drive axle(s) was loaded to 60 percent of its gross axle weight 
rating (GAWR). The yaw instability that occurred in the RSM testing 
showed that the unloaded 28-foot control trailer was too light to 
produce yaw instability. Therefore, additional weight was added for 
these tests. Testing was conducted on two test surfaces: A high-
friction dry road surface and a slippery wet Jennite road surface.
    Additional SIS tests were performed, similar to the bobtail SIS 
tests described in Phase II, conducted with each tractor coupled to the 
28-foot control trailer and loaded to the 60 percent GAWR condition. 
The steering wheel angles from these tests were 197 degrees for the 
Freightliner with ESC, 200 degrees for the Freightliner with RSC, 200 
degrees for the Volvo, and 153 degrees for the Sterling. The average 
tractor lateral acceleration at engine torque intervention in the SIS 
tests was 0.40g for the Freightliner with ESC, 0.34g for the 
Freightliner with RSC, 0.35g for the Volvo, and 0.4g for the Sterling.
    For the SWD and the HSWD test maneuvers, the maneuver entrance 
speed for the bobtail tractor tests was 50 mph, and for the tests at 60 
percent GAWR the entry speed was 45 mph. The driver accelerated the 
test vehicle up to a speed slightly over the desired speed in a 
straight lane, then released the throttle and de-clutched the engine. 
Once the vehicle coasted down to the desired speed, the automated 
steering machine initiated either the sinusoidal or half-sine steering 
input, at a specified test frequency as described below (e.g., 0.3 Hz, 
0.5 Hz, etc.), with the steering wheel angle held constant during the 
dwell, as depicted in the figures. Two dwell times were evaluated as 
described below, 0.5 and 1.0 second. The initial test run began with a 
steering wheel angle equal to 30 percent of the angle determined from 
an SIS test. The test severity was increased in subsequent runs by 
increasing the steering wheel angle in 10 percentage point increments 
until reaching 130 percent of the SIS steering wheel angle. Thus, 11 
test runs were needed to complete a test series. If severe oversteer or 
wheel lift greater than two inches was detected, then the test was 
repeated using the previous steering wheel angle in which the systems 
was observed to be stable. If the tractor-trailer was stable during the 
repeated run, additional tests were performed by increasing the 
steering wheel angle in 5 percent increments until instability was 
observed.
    Tests were conducted on baseline tractors in the 60 percent GAWR 
condition on dry pavement to evaluate frequency and dwell time for the 
SWD and HSWD test maneuvers. Frequencies between 0.3 and 0.7 Hz were 
evaluated. A frequency of 0.5 Hz was found to require the lowest 
steering scalar to produce severe oversteer in the Sterling and Volvo 
tractors in the SWD maneuver, and 0.4 Hz was found to require the 
lowest steering scalar to produce severe oversteer in the Freightliner 
tractor (and 0.5 Hz was the second-most severe frequency for this 
tractor). A dwell time of 1.0 second was found to result in severe 
tractor oversteer at lower steering scalars. Thus the researchers 
selected a 0.5 Hz frequency and 1.0 second dwell time as the parameters 
for the SWD and HSWD maneuvers. However, the researchers also found 
that the SWD maneuver was less sensitive to differences in steering 
frequency compared to the HSWD maneuver.
    In tests conducted with baseline tractors in the bobtail condition, 
no yaw instability occurred; however, in both the SWD and HSWD tests 
the Sterling tractor experienced wheel lift at the tractor drive 
wheels. Seventy test series were conducted on the baseline tractors in 
the 60 percent GAWR load condition, with fifteen of the series 
terminated due to roll instability and 28 due to severe tractor 
oversteer.
    In tests conducted with the tractor stability control system 
enabled and in the 60 percent GAWR load condition, all of the tractors 
with an ESC system were able to complete the SWD maneuver at test 
scalars up to 130 percent. However, the tractors equipped with RSC 
systems experienced severe oversteer in 12 of 15 test series at the 
steering scalars of 120 and 130 percent. In tests conducted using the 
HSWD maneuver, the ESC-equipped tractors completed seven of eight test 
series without tractor yaw instability, and the RSC-equipped tractors 
experienced

[[Page 30782]]

severe oversteer at steering scalars ranging from 80 to 125 percent. In 
both test maneuvers, the RSC systems improved tractor yaw stability 
compared to the baseline tractor, but they could not maintain yaw 
stability at the higher steering scalars.
    Additional SWD tests were conducted with the 53-foot van trailer 
and the 48-foot flatbed trailer using the 60 percent GAWR loading 
condition. In eight test series conducted with the tractor stability 
control systems enabled, seven were completed without wheel lift or 
tractor yaw instability, but the Sterling tractor equipped with an RSC 
system tested with the 48-foot flatbed reached a termination condition 
at a steering scalar of 105 percent. In tests with stability control 
enabled, all of the tractors coupled to the tanker trailer experienced 
wheel lift in the SWD maneuver at scalars between 60 and 95 percent.
    SWD tests were also conducted on a low-friction wet Jennite surface 
using a lower maneuver entry speed of 30 mph. In the baseline condition 
with the tractor stability control systems disabled, 43 test series 
were conducted and a termination condition was reached in only four 
test series. Testing on the dry, high-friction surface was found to 
result in more yaw instabilities than the testing conducted on the low-
friction, wet Jennite surface.
    In summary, the purpose of Phase III research was to develop a 
maneuver to evaluate the yaw stability of a tractor trailer combination 
vehicle. VRTC researchers found that the SWD maneuver with a one-second 
dwell time based on a single cycle of steering input with a frequency 
of 0.5 Hz conducted on a high friction surface appropriately assessed 
the ability of an ESC system to improve yaw stability. From this 
maneuver, performance measure were investigated for lateral stability 
and responsiveness: the lateral acceleration ratio, which is directly 
correlated to roll stability and the yaw rate ratio, which the 
performance metric used in FMVSS No. 126 for light vehicle ESC systems 
and was found to be a direct performance measure of yaw stability. A 
responsiveness measure was also studied to evaluate the lateral 
displacement of a vehicle during SWD maneuvers.
(b) Performance Measure Development
    Phase III of NHTSA's research also examined potential measures of 
yaw instability prevention performance. In light of the conclusion in 
Phase II that lateral acceleration ratio was a suitable metric to 
measure a stability control system's ability to prevent lateral 
acceleration, the agency examined a yaw rate ratio metric. The YRR 
expresses the lateral stability criteria for the sine with dwell test 
to measure how quickly the vehicle stops turning, or rotating about its 
vertical axis, after the steering wheel is returned to the straight-
ahead position. Similar to the LAR, the YRR metric is the percent of 
peak yaw rate that is present at a designated time after completion of 
steer. This performance metric is identical to the metric used in the 
light vehicle ESC system performance requirement in FMVSS No. 126. 
Phase III research found that both LAR and YRR were capable of 
measuring stability during the SWD maneuver. However, while LAR was 
better at predicting roll instability, YRR was better at predicting yaw 
instability.
4. Large Bus Testing
    Researchers at VRTC tested three large buses equipped with 
stability control systems: A 2007 MCI D4500 (MCI 1), a 2009 
Prevost H3, and a second 2007 MCI D4500 (MCI 2). The MCI buses 
were equipped with a Meritor WABCO ESC system and the Prevost was 
equipped with a Bendix ESC system. RSC systems were not offered on 
large buses and, consequently, were not evaluated. All of the buses 
were equipped with air disc brakes. Both the MCI 1 and the MCI 
2 had a GVWR of 48,000 lb and a wheelbase of 317 in., and the 
Prevost had a GVWR of 53,000 lb and a wheelbase of 317 in. Each of the 
buses had three axles: A steer axle, a drive axle, and a non-driven tag 
axle.
    The MCI 1 was equipped with outriggers supplied by MCI and 
Meritor WABCO. The outriggers limited the use of higher maneuver entry 
speeds for tests without the ESC system enabled. At higher speeds, the 
lower support portion of the outrigger would dig into the test surface 
and influence the dynamics of the vehicle. Therefore, tests of the MCI 
1 at higher speeds had no baseline performance to compare to.
    The Prevost and MCI 2 buses were tested using NHTSA-
designed outriggers. The outriggers designed for combination vehicles 
were adapted for installation on the mid-section of each bus, just in 
front of its drive axle and slightly behind its longitudinal center of 
gravity. Using these outriggers, the vehicles were able to complete 
testing for all speeds, with or without ESC enabled.
    Each bus was tested using two primary simulated load conditions. 
The first condition was a lightly loaded vehicle weight (LLVW) that 
included the weight of the test instrumentation, outriggers, and 
driver. The second load condition, gross person occupancy weight 
(GPOW), included the LLVW weight plus the addition of 175-lb water 
dummies in each available passenger seat without exceeding the GVWR of 
the vehicle. This condition was used to represent a high CG load that a 
bus may experience while in service. A third loading condition was 
conducted with the Prevost, which added ballast to the cargo holds 
under the mid-section of the bus. This condition loaded the vehicle to 
its GVWR.
    Test maneuvers that were conducted included the 150 ft. constant 
radius increasing velocity test, SIS, RSM, HSWD, and SWD. Tests were 
conducted using an automated steering machine, except for the constant 
radius maneuvers. The severity for each test maneuver was increased 
either by increasing vehicle speed or steering angle.
    SIS maneuvers were conducted under both loading conditions, with 
ESC systems enabled and disabled, and in both left and right directions 
in order to characterize each vehicle. Initially, the maneuver was 
executed exactly as it was for the tractor testing. However it was 
observed that steering to a maximum steering wheel angle of 270 degrees 
generated barely over 0.3g of lateral acceleration. From this, it was 
clear that large buses have a larger steering ratio, and it would take 
a larger steering input to achieve the appropriate lateral acceleration 
levels. The steering wheel angle necessary to achieve 0.5g in the LLVW 
loading condition was 405 degrees for the MCI 1, 352 degrees 
for the Prevost, and 407 degrees for the MCI 2. In the GPOW 
loading condition, steering wheel angles were found to be 405 degrees 
for the MCI 1, 383 degrees for the Prevost, and 461 degrees 
for the MCI 2.
    SIS tests were conducted at GPOW to evaluate the ability of the ESC 
system to reduce speed by limiting engine torque. For the three buses 
tested the average speed at activation for each SIS maneuver ranged 
between 29.8 and 30.6 mph. At four seconds following SC activation the 
average speed for each SIS had been reduced to 27.9 mph for the MCI 
1, 26.5 mph for the Prevost, and 26.6 mph for the MCI 
2. Without stability control enabled, speeds did not decrease. 
The average lateral acceleration for a test series observed at 
activation was 0.32g for MCI 1, 0.27g for the Prevost, 0.31g 
for MCI 2.
    RSM testing was completed for each bus to evaluate their roll 
propensity while loaded in the LLVW and GPOW conditions. Tests were 
conducted using the same RSM protocol as the one developed for 
tractors. Using an

[[Page 30783]]

automated steering machine programmed with the steering wheel angle 
calculated from the SIS maneuver, tests were conducted with ESC systems 
enabled and disabled. The initial maneuver entry speed was 20 mph and 
was incrementally increased in subsequent runs until two inches of 
wheel lift occurred at any of the wheels, the vehicle went into a 
severe oversteer condition, or the entry speed reached 50 mph without a 
roll or yaw instability condition.
    For RSM tests with ESC systems disabled and the buses loaded in the 
LLVW condition, wheel lift was observed in both MCI test vehicles at 
speeds of 41 to 45 mph, and no wheel lift was observed for tests with 
the Prevost for the speeds tested. When tested in the GPOW condition, 
wheel lift was observed at 35 to 39 mph for all vehicles tested.
    For RSM tests with ESC systems enabled and the buses loaded in the 
LLVW condition, no instances of wheel lift were observed over the range 
of speeds tested. During tests in the GPOW condition wheel lift was not 
observed in either MCI over the range of speeds tested, but was 
observed in some of the Prevost tests at speeds between 42 and 48 
mph.\26\
---------------------------------------------------------------------------

    \26\ Initial tests conducted with the Prevost demonstrated that 
the vehicle was able to complete the RSM at up to 48 mph without 
wheel lift for the GPOW condition. The Prevost was not tested to 50 
mph because there was not enough test area to bring the vehicle up 
to this speed and allow the driver to recover safely if the test 
needed to be aborted. RSM tests under the same conditions were 
repeated less than a week later. During these tests, wheel lift 
greater than 2 inches was observed at speeds of 42 to 44 mph with 
ESC enabled. Upon further investigation when preparing to de-
instrument the vehicle, a broken roll stabilizer bar was discovered. 
Researchers attributed the change in performance observed to the 
broken stabilizer bar.
---------------------------------------------------------------------------

    SWD testing was completed for each bus to evaluate its yaw 
propensity while loaded in the LLVW and GPOW conditions. All tests were 
conducted with the ESC systems enabled and disabled. Using an automated 
steering machine, the SWD tests were run using steering frequencies of 
0.3, 0.4, 0.5, and 0.6 Hz, dwell times of 0.5 and 1.0 seconds, and a 
maneuver entry speed of 45 mph. Test severity was increased by 
increasing the steering wheel angle by a scalar from 30 to 130 percent 
in 10 percent increments. A test series was terminated if the vehicle 
experienced wheel lift greater than 2 inches, the vehicle spun out, or 
the steering input reached a terminating scalar of 130 percent.
    No instances of spinout were observed during this testing, but 
tests at higher steering wheel angles produced drift. Although the 
buses were yaw stable in the maneuvers, the test results demonstrated 
that the SWD maneuver was challenging the buses' roll propensity. 
Several SWD test series with the GPOW condition produced wheel lift 
when the ESC system was disabled. When the ESC systems were enabled, 
all vehicles were able to complete their series without exceeding 
either roll or yaw stability thresholds.
    The SWD test data from the GPOW load condition were analyzed to 
determine a frequency and dwell time for a candidate performance 
maneuver. For all tests with ESC disabled, maneuvers with a 1.0-second 
dwell time required an equal or lower steering scalar (0 to 50 percent 
lower) to exceed a threshold of 6 degrees of yaw angle. As with the 
tractor testing, this suggested that the 1.0-second dwell time was more 
challenging to large buses because it required less steering to exceed 
the threshold.
    Using only the 1.0-second dwell time tests, analysis to determine 
the optimum frequency for the SWD test was completed by evaluating the 
roll and yaw angles. Review of the test data indicated that the largest 
roll and yaw angles were produced in the maneuvers using 0.4 and 0.5 Hz 
frequencies.
    The large buses were also tested using the HSWD maneuver. Like the 
SWD, the test results for the HSWD indicated that the longer dwell time 
was more challenging to stability. Unlike the SWD, the lower 
frequencies were observed to produce wheel lift at lower steering wheel 
angle scalars. Tests results from both the SWD and HSWD maneuvers 
indicated that both maneuvers generated dynamic responses from the 
vehicles. There were clear differences in lateral acceleration and yaw 
rate between test series conducted with ESC systems enabled compared to 
test series with ESC systems disabled. The data showed that ESC systems 
were reducing both rollover and spinout propensities. However, the SWD 
maneuver was favored over the HSWD maneuver because the SWD maneuver 
could be conducted in a smaller area, would be representative of a 
crash avoidance or lane change maneuver, and its use in FMVSS No. 126 
accelerated performance measure research.
    This research indicates that large buses equipped with ESC systems 
can use the same objective performance maneuver as was developed for 
tractors. Testing also indicates that the same performance measures can 
be used to assess lateral stability and responsiveness, but the 
performance measures must be tailored for the vehicle differences.

D. Truck & Engine Manufacturers Association Testing

    The Truck & Engine Manufacturers Association (EMA) performed tests 
on ten tractors listed in the following table equipped with stability 
control systems using the three test maneuvers developed at VRTC.

                         Table 2--EMA Test Tractors Including Type, GVWR, and Wheelbase
----------------------------------------------------------------------------------------------------------------
                                                                                                     Wheelbase
   Tractor configuration (EMA Vehicle I.D.)          Stability control type          GVWR (lb)       (inches)
----------------------------------------------------------------------------------------------------------------
6x4 Typical Tractor (Vehicle A)...............  ESC.............................          52,000             228
4x2 (Vehicle B)...............................  ESC.............................          32,000             140
4x2 (Vehicle C)...............................  RSC with steering wheel angle             34,700             152
                                                 sensor.
6x4 Severe Service (Vehicle D)................  ESC.............................          66,000             220
6x4 w/Pusher Axle (Vehicle E).................  ESC.............................          86,000             270
8x6 Tridem Drive Axle (Vehicle F).............  ESC.............................          89,000             263
6x4 w/Pusher Axle (Vehicle G).................  ESC.............................          92,000             243
6x4 Severe Service (Vehicle H)................  RSC.............................          60,600             246
6x4 (Vehicle I)...............................  ESC.............................          52,000             232
6x4 (Vehicle J)...............................  ESC.............................          52,350             245
----------------------------------------------------------------------------------------------------------------

[[Page 30784]]

    EMA provided its test data to the agency.\27\ Although the tractors 
were not identified by make or model, EMA provided the configuration 
and weight ratings for each tractor. Eight tractors were subjected to 
the SIS and RSM to evaluate rollover prevention, and three tractors 
were subjected to the SWD maneuver, and the ramp with dwell (RWD) 
maneuver on a low-friction surface to evaluate yaw stability. Two of 
the tractors were equipped with RSC systems and seven tractors were 
equipped with ESC systems. EMA also submitted test data for several 
maneuvers in which the test parameters were varied. With the exception 
of Vehicle J, EMA did not submit baseline test data--that is, EMA 
submitted data only for maneuvers with ESC or RSC systems enabled.
---------------------------------------------------------------------------

    \27\ Data from Vehicles A through I are included have been 
placed in the docket. Docket Nos. NHTSA-2010-0034-0011 through 
NHTSA-2010-0034-0021 and Docket No. NHTSA-2010-0034-0024. Vehicle J 
testing is discussed in detail in a later section.
---------------------------------------------------------------------------

1. Slowly Increasing Steer Maneuver
    For all tractors, test data were provided for the SIS tests used to 
derive the steering wheel angle with each tractor in the bobtail 
condition. In the first SIS series conducted on eight of the tractors, 
three SIS tests were conducted in each direction on a dry road surface, 
and a best fit linear regression was used to project the steering wheel 
angle for a lateral acceleration of 0.5g. The average of the absolute 
value of each of the six runs was calculated for the final angle.
    Compared to the steering wheel angles that were derived for the 
three VRTC tractors, a much wider range in SWA was seen among EMA's 
results. The steering wheel angles generally increased with the 
tractor's wheelbase from an angle of 126 degrees for the 140-inch 
wheelbase 4x2 to an angle of 291 degrees for the 270-inch wheelbase 6x4 
with a pusher axle. For Vehicle H, EMA also provided data from direct 
measurement of the steering wheel angle from driving the tractor at 
0.5g of lateral acceleration. This angle was 290 degrees, which is 
slightly larger than the calculated value of 281 degrees extrapolated 
from the SIS test data in the 0.05 to 0.30g operating region. The EMA 
data provided for these SIS tests did not include information on 
stability control engine torque reduction.
    Additional SIS tests were conducted on three tractors that were to 
be subsequently tested using the SWD maneuver to evaluate tractor yaw 
stability. The SIS test conditions were identical to the prior SIS 
tests. A best fit linear regression was used to project the steering 
wheel angle for a lateral acceleration of 0.5g, and the average of the 
absolute value of each of the six runs was calculated for the final 
angle as in the prior SIS tests. Comparing these data to the prior SIS 
test results, Vehicle B, which had the smallest angle of 126 degrees in 
the prior SIS tests, showed a ten degree reduction of its angle in this 
test series. Vehicle G's angle was nearly identical (203 degrees in the 
first series vs. 205 degrees in the second series).
2. Ramp Steer Maneuver
    For the RSM tests on eight tractors, the tractors were attached to 
a FMVSS No. 121 control trailer and were loaded to their GVWR by 
placing the ballast over the fifth wheel, with the ballast placed 
directly on the trailer deck resulting in a low center of gravity 
height. The weight on the FMVSS No. 121 control trailer's single axle 
ranged between 5,720 and 5,930 lb for all eight tractor tests, and the 
trailer brakes were not enabled. While the weight on the trailer axle 
is nominally 4,500 lb when the trailer is used for FMVSS No. 121 
stopping distance tests, the increased weight in these RSM tests 
reflects the added weight of the outriggers installed on the trailer. 
In general, each of the tractors was loaded to its GVWR with the steer, 
drive, and auxiliary axles loaded to, or very close to, their 
respective GAWRs. The only exception was the 140-inch wheelbase 4x2 
which only had 9,950 lb on the steer axle, although it was rated for 
12,000 lb.
    In the tests, the stability control systems automatically applied 
the tractor's foundation brakes to reduce speed and lateral 
acceleration. The initial vehicle deceleration generally coincided with 
the end of ramp steer input, indicating that the stability control 
systems were effective at reducing the lateral acceleration. The speed 
at wheel lift for EMA's tests ranged from 33 to 38 mph, as compared to 
31 to 39 mph for the VRTC tests that used a similar unbraked trailer, 
but with a higher center of gravity loading condition and a higher 
overall vehicle test weight. Both 4x2 tractors tested by EMA 
experienced oversteer in addition to the wheel lift.
3. Sine With Dwell Maneuver
    EMA provided test results for the SWD maneuver for four tractors 
equipped with ESC systems. The sinusoidal steering frequency used for 
testing was 0.5 Hz and the dwell time was one second. The amplitude of 
the steering wheel inputs started at 30 percent of the steering wheel 
angle derived from SIS testing, and in subsequent test runs was 
increased by 10 percent increments up to 130 percent of the steering 
angle. The SWD tests were conducted with two tractor loading 
conditions: Loaded to 60 percent of the drive axle(s) GAWR with the 
FMVSS No. 121 unbraked control trailer attached (loaded tests), and in 
the unloaded condition with no trailer attached (bobtail tests). The 
maneuver entrance speed was 45 mph and the test was conducted on dry 
pavement.
    The results of the loaded tests for Vehicles G and I indicated that 
both tractors remained roll and yaw stable through the full range of 
testing, and there were no indications of tractor wheel lift in the 
test comments or the unprocessed data. The largest steering wheel angle 
produced the highest peak lateral acceleration, which occurred during 
the dwell portion of the maneuver for both tractors. Vehicle I reached 
approximately 0.75g and Vehicle G reached just under 0.6g. Although 
both tractors were close in wheelbase and tested with similar steering 
wheel angles, Vehicle G, tested with its liftable axle in the lowered 
position, was either less responsive in the SWD maneuver or its ESC 
performed slightly better than the ESC on Vehicle I. Both tractors had 
similar overall vehicle decelerations; however, the ESC on Vehicle G 
commanded higher steer axle braking pressures than the ESC on Vehicle 
I. Vehicle I appeared to have more lateral sliding in the maneuver, as 
its yaw rate decay was slower at the end of steering input.
    Vehicle B (140-inch wheelbase 4x2) exhibited yaw instability in the 
SWD maneuver. This tractor had high lateral acceleration that was 
attained at lower steering wheel angles than for the 6x4 tractors. For 
example, the peak tractor lateral acceleration was already reaching 
0.70g at 80 percent of the SIS-derived steering wheel angle, compared 
to Vehicle I which reached 0.60g and Vehicle G which reached 0.45g at 
this steering wheel angle scalar. The yaw rate decay after completion 
of steer was also much slower than for the 6x4 tractors, which appears 
to indicate that the vehicle was sliding much more and taking longer to 
return to the straight-ahead position. This is most evident in the 
testing at 130 percent of the SIS-derived steering wheel angle, in 
which the decay yaw rate decay was about 3.5 seconds.
    The maneuver entrance speed was reduced to 30 mph in the bobtail 
SWD tests, which were conducted on a low-friction wet Jennite surface. 
The short wheelbase 4x2 tractor, Vehicle B, appeared to complete all of 
the test series without any observed instability

[[Page 30785]]

or control issues, and the peak tractor lateral acceleration was 
limited to approximately 0.3g in all tests. However, both 6x4 tractors 
(Vehicles G and I) appeared to have steering responsiveness issues that 
were particularly noticeable at higher steering wheel angles. At the 
reversal in steering wheel angle direction, the yaw rate and lateral 
acceleration response was delayed, indicating severe understeer. During 
the dwell portion of the maneuver at higher steering wheel angles, 
Vehicle I slowly built lateral acceleration up to 0.3g, while Vehicle G 
achieved similar but slightly lower acceleration levels. Vehicle G's 
yaw rate also was slower to respond at the completion of steer, taking 
as long as 2.5 seconds to decay to zero for the test conducted at the 
highest steering wheel angle tested.
4. Ramp With Dwell Maneuver
    The three tractors equipped with ESC systems tested in the SWD 
maneuvers were also tested to the RWD maneuver. Once the initial 
steering wheel angle and test speed were attained, the steering machine 
increased the steering wheel angle to 180 degrees in one second, held 
that steering wheel angle constant for three seconds (the dwell portion 
of the maneuver), and then reduced the steering wheel angle to zero in 
one second. In subsequent RWD test runs, the steering wheel angle was 
increased in 90 degree increments up to 540 degrees.
    The test results show that for Vehicles B and I, the steady-state 
lateral acceleration (prior to the ramp steer) was approximately 0.2g, 
and for Vehicle G the steady-state tractor lateral acceleration was 
approximately 0.1g. When the steering wheel angle was increased during 
the initial steering ramp input, the lateral acceleration and yaw rate 
increased slightly and in many of the test runs was then observed to 
drop off, indicating that the tractor was not responsive to the 
steering input. During the first two seconds of the steering dwell 
portion of the maneuver, the tractor lateral acceleration typically 
remained at 0.25g or less for all tests. During the last one second of 
the steering dwell, all of the test runs for Vehicles G and I showed 
steadily increasing lateral acceleration, as high as 0.5g, even as the 
steering wheel angle was reduced to zero. This indicates that the 
tractors were in a severe oversteer condition, and the agency 
speculates that the relatively high lateral acceleration may have been 
a result of the tractor running off of the low friction wet Jennite 
surface and onto a higher friction road surface. The test data show 
that this was always accompanied by braking on the steer axle, which is 
indicative of oversteer corrections being commanded by the ESC. Vehicle 
B had much less increase in lateral acceleration at the end of the 
maneuver and appeared to be under control. Late in the maneuver the 
commanded brake pressures for Vehicle B showed that both front and rear 
brake applications were made on the right side of the tractor, and the 
application pressures were nearly identical. Whether this is a data 
collection anomaly or stability control braking strategy is not 
certain, but Vehicle B was the vehicle that exhibited the least amount 
of oversteer.
    The RWD test results demonstrated that the stability control 
systems on these tractors correctly identified the vehicle loss of 
control problems (severe oversteer and understeer) and took corrective 
action, including engine output torque intervention and commanding 
individual applications of the tractor's foundation brakes. However, 
the severity of the RWD test maneuver was sufficiently high to 
overdrive the capability of the stability control systems to mitigate 
severe understeer.
    In summary, EMA provided test data for nine tractors each tested 
for the three maneuvers developed by NHTSA researchers. The nine 
tractors included a wider variety of tractor configurations than those 
tested by the agency, and included severe service tractors, tractors 
with auxiliary lift axles, a tridem drive axle tractor, and a very 
short wheelbase two-axle tractor. Slowly increasing steer vehicle 
characterization tests were conducted on all nine tractors (two with 
RSC and seven with ESC) in the bobtail condition and the test data were 
used to extrapolate the steering wheel angle that would provide 0.5g of 
lateral acceleration at 30 mph. These data produced a wider range of 
steering wheel angles than had been seen from the agency's tests on its 
three tractors, with the short wheelbase 4x2 having an angle of only 
116 degrees, and a 6x4 tractor with a liftable pusher axle having the 
highest angle at 291 degrees.
    EMA provided ramp steer maneuver test results for eight tractors 
that were loaded to their GVWRs using an unbraked 28-foot control 
trailer. Data were only provided for tests with the stability control 
system enabled, and the RSM was conducted up to speeds at which the 
system could successfully intervene. The range of speeds achieved at 
the point of overdriving the stability control systems was similar to 
the range of speeds from the VRTC RSM tests, although the loading 
conditions were slightly different. The two 4x2 tractors (one with RSC, 
and one with ESC) tested by EMA experienced oversteer and wheel lift, 
while the other tractors all experienced wheel lift.
    SWD test results were provided for three tractors, each equipped 
with ESC, using a 0.5 Hz sinusoidal steering input frequency and a 1.0 
second dwell time, and the tractors were tested in the bobtail 
condition and loaded to 60 percent of drive axle(s) GAWR. In the tests 
on dry pavement at a maneuver entrance speed of 45 mph, the typical 6x4 
completed all tests, while the 6x4 equipped with a lift axle (tested in 
the lowered position) also completed all tests but appeared to be 
slower to respond to the steering inputs. The short wheelbase 4x2 
tractor appeared to exhibit control problems and at the highest 
steering wheel angle tested. The sine with dwell tests on the three 
tractors in the bobtail condition were conducted on a low-friction wet 
Jennite test surface with a lower maneuver entrance speed of 30 mph. In 
these tests, the short wheelbase 4x2 tractor completed all tests, while 
the two 6x4 tractors appeared to experience severe understeer at the 
higher steering wheel angles tested.
5. Vehicle J Testing
(a) EMA Testing of Vehicle J
    In December 2010, EMA provided testing data on a tenth vehicle they 
tested.\28\ Vehicle J was intended to be representative of a typical 
6x4 tractor, with a 245 inch wheelbase and a GVWR of 52,350 pounds. EMA 
subjected Vehicle J to four different test maneuvers: The slowly 
increasing steer test; the sine with dwell test; a J-turn maneuver, and 
a wet Jennite drive through test.
---------------------------------------------------------------------------

    \28\ Vehicle J data provided to the agency has been placed in 
Docket No. NHTSA-2010-0034-0022 and Docket No. NHTSA-2010-0034-0023.
---------------------------------------------------------------------------

    EMA first conducted the slowly increasing steer test maneuver with 
a steering controller on Vehicle J to determine the steering wheel 
angle that would produce a lateral acceleration of 0.5g. EMA conducted 
two series of test runs, one in each direction. A best fit linear 
regression was used to determine that the average steering angle on the 
six runs that would produce a lateral acceleration of 0.5g was 197 
degrees. This value was used for subsequent testing.
    EMA next conducted sine with dwell testing. EMA conducted two 
series of SWD tests--one with the ESC system on and one with the ESC 
system off. EMA equipped the vehicle with an FMVSS No. 121 control 
trailer and loaded the

[[Page 30786]]

vehicle so that the drive axles were loaded to 60 percent of the GAWR, 
which resulted in the vehicle being loaded to approximately 78.6 
percent of its GVWR.
    EMA provided data on six runs of the SWD maneuver. EMA conducted 
the test at scalars from 0.8 to 1.3 of the SIS-derived steering wheel 
angle. EMA also provided data on three runs of the SWD maneuver with 
the system deactivated. Those tests were conducted at scalars of 1.0 
and 1.3, and 1.5.
    Each test run with the system enabled showed a 20- to 25-mph 
reduction of speed during the test maneuver. In contrast, tests 
conducted with the system off indicated only limited speed reduction of 
less than five mph. This indicated that the ESC system acted to reduce 
vehicle speed.
    Each test run with the system enabled conducted at scalars between 
0.8 and 1.2 resulted in a peak lateral acceleration between 0.6g and 
0.7g. The lateral acceleration then quickly dropped to zero within 0.3 
to 0.4 seconds after the completion of the steer. Yaw rate during the 
dwell portion of the maneuver peaked at approximately 18 to 22 degrees 
per second, except at a scalar of 1.2 where yaw rate peaked at 
approximately 24 degrees per second) and showed a downward trend during 
the dwell, dropping by approximately five degrees per second. The yaw 
rate dropped to zero within 0.2 seconds after completion of steer. The 
vehicle's ESC system used selective braking to reduce the speed, 
lateral acceleration, and yaw rate responses.
    With the system disabled, the test run at a scalar of 1.0 resulted 
in a peak lateral acceleration of approximately 0.8g. A 0.2g drop in 
lateral acceleration was observed at the beginning of the dwell portion 
of the maneuver followed by a sudden rise of the same amount, 
indicating possible oversteer. The lateral acceleration dropped to zero 
less quickly than in tests with the system on (approximately 0.5 
seconds) after completion of steer. This was largely due to the drop in 
lateral acceleration starting later with the system off than with the 
system on. The yaw rate peaked at approximately 21 degrees per second. 
Unlike with the system on, there was not a clear drop in yaw rate 
during the dwell portion of the maneuver. The yaw rate also dropped to 
zero slower than in tests with the system off (approximately 0.25 
seconds after completion of steer).
    For test runs at steering wheel angle scalars of 1.3, the peak 
lateral acceleration was slightly lower with the system on 
(approximately 0.75g) in comparison to the test run with the system off 
(over 0.8g). Momentary variability in lateral acceleration was observed 
in both tests, indicating possible tractor instability. Again, with the 
system on, the lateral acceleration decayed faster at the completion of 
steer (approximately 0.4 seconds) than it did with the system off (over 
0.6 seconds). This was largely due to the reduction in lateral 
acceleration starting later with the system off than with the system 
on. The yaw rate peaked for both tests at approximately 25 degrees per 
second. Again, however, the yaw rate decreased by approximately five 
degrees during the dwell portion of the maneuver with the system on 
while no clear decay was observed with the system off. Also, the yaw 
rate decreased to zero slower after completion of steer with the system 
off (0.25 seconds) than it did with the system on (less than 0.2 
seconds).
    EMA also submitted data on one SWD test run with the system off at 
a steering wheel angle scalar of 1.5. Peak lateral acceleration 
observed during this test run was nearly 0.9g. The lateral acceleration 
rate dropped to zero in slightly over 0.5 seconds after completion of 
steer. The yaw rate peaked at approximately 24 degrees per second. 
Unlike in runs with lower steering wheel angles, a reduction in yaw 
rate was observable during the dwell portion. However, that reduction 
was much sharper, occurring entirely within a 0.5 second period rather 
than throughout the entire 1.0 second dwell period. Like in prior 
tests, the yaw rate dropped to zero within approximately 0.25 seconds.
    EMA's SWD maneuver test data from Vehicle J demonstrated that the 
ESC system activated to lower lateral acceleration and yaw rate during 
the SWD maneuver. However, even with the ESC system turned off, the 
lateral acceleration and yaw rates dropped relatively quickly at the 
end of the test maneuver, indicating that the vehicle did not become 
unstable during testing. Although EMA only provided test data from 
three runs with the system off compared to six runs with the system 
enabled, the runs with the system off did include a run with a steering 
wheel angle scalar of 1.5, which was higher than any run in NHTSA's 
testing, and no severe incidents of instability were observed.
    EMA next conducted J-turn testing both with the system enabled and 
disabled. The test was conducted on a 150-foot fixed radius curve. The 
vehicle was tested with an FMVSS No. 121 control trailer and was loaded 
to the FMVSS No. 121 loading conditions. The tests were conducted at 
initial entry speeds of 30 to 36 mph, in increments of two mph.
    In tests conducted with the ESC system enabled, system activation 
occurred at each test speed. The system commanded brake activations to 
reduce vehicle speed to 18 mph from initial speeds of 30 mph and 32 
mph, down to 10 mph from an initial speed of 34 mph, and down to 6 mph 
at an initial speed of 36 mph. The vehicle was able to maintain the 
lane at all speeds tested. Lateral acceleration peaked at 0.4 to 0.5g 
at 30 and 32 mph and peaked at 0.6g at 34 mph and 36 mph. Yaw rate 
peaked at approximately 15 degrees per second at 30 and 32 mph and 
peaked at approximately 20 degrees per second at 34 mph and 36 mph. At 
the higher speeds tested, lateral acceleration and yaw rate were 
observed to drop coincident with speed.
    With the system disabled, no reduction in speed during the maneuver 
was observed. Thus, lateral acceleration and yaw rates remained 
relatively constant throughout the maneuver. At test speeds of 30 and 
32 mph, lateral acceleration peaked at approximately 0.55 to 0.65g and 
yaw rate peaked at approximately 20 degrees per second. At 34 mph, the 
lateral acceleration peaked at approximately 0.9g and the steering 
wheel angle necessary to maintain the lane decreased substantially. Yaw 
rate peaked at approximately 22 degrees per second and dropped to 
approximately 15 degrees per second, indicating the vehicle was 
starting to plow out. At 36 mph, the vehicle plowed out of the lane.
    The fourth maneuver EMA performed on Vehicle J was a wet Jennite 
drive-through (WJDT) maneuver. This maneuver was intended to test yaw 
stability. The WJDT maneuver is identical to method for determining the 
maximum drive-through speed when testing vehicles for compliance with 
S5.3.6.1 of FMVSS No. 121. The vehicle is driven through a 500-foot 
radius curve with a wet surface having a peak coefficient of friction 
of approximately 0.5 at successively increasing speeds (up to 40 mph) 
to determine the maximum speed at which the vehicle can maintain the 
curve.\29\
---------------------------------------------------------------------------

    \29\ To conduct the FMVSS No. 121 stability and control during 
braking compliance test, the vehicle is driven at the lesser of 30 
mph or 75 percent of the maximum drive-through speed. A full brake 
application is made and a vehicle must stop at least three times out 
of four within the 12-foot lane.
---------------------------------------------------------------------------

    EMA performed this test with both the stability control system 
enabled and disabled in two load configurations. First, the vehicle was 
tested in the bobtail (unloaded) configuration.

[[Page 30787]]

Second, the vehicle was loaded to the FMVSS No. 121 test loading 
condition.
    In the bobtail configuration with the ESC system enabled, test runs 
at 30 and 32 mph yielded no system activation. At 33 mph, system 
activation occurred as both engine torque reduction and selective 
braking to improve yaw stability occurred. As a result, the vehicle 
speed decreased to approximately 29 mph during the maneuver and the 
driver responded by rapidly straightening the steering wheel. Vehicle 
yaw rate peaked at approximately 10 degrees per second. A second run at 
33 mph showed only brief system activation and a minimal reduction in 
speed. During two runs at 34 mph, ESC system intervention was again 
observed as torque reduction and selective braking reduced vehicle 
speed to 28 to 29 mph and the driver again responded by rapidly 
straightening the steering wheel. Yaw rate peaked at near 10 degrees 
per second and again, as the driver responded, decreased. During two 
runs at 35 mph, the vehicle was unable to maintain the lane due to 
understeer, despite system intervention.
    In the bobtail configuration with the system disabled, at 32 mph, 
the driver had to adjust steering by adding steering input during both 
runs attempted at this speed, indicating substantial understeer. During 
two runs at 33 mph, the vehicle was unable to maintain the lane, 
despite large steering inputs from the driver.
    In the loaded configuration with the ESC system enabled, system 
activation occurred at a speed of 30 mph, though only slight (1 to 2 
mph) reduction in speed was observed. The driver had to increase his 
steering input, but there was no corresponding increase in yaw rate, 
indicating understeer. At 32 mph, both engine torque reduction and 
selective braking occurred to improve yaw stability occurred. As a 
result, the vehicle speed decreased to approximately 27 to 28 mph 
during the maneuver. At 34 mph, the ESC system intervened more 
substantially, resulting in a reduction of speed to approximately 26 
mph. Nevertheless, the vehicle was able to maintain the lane. At 35 
mph, the vehicle was unable to maintain the lane due to understeer, 
despite system intervention.
    In the loaded configuration with the system disabled, understeer 
was observed at 32 mph, as evident by substantial increase in steering 
input by the driver; however, the vehicle was able to maintain the 
lane. At 33 mph, the vehicle was unable to maintain the lane.
    The maximum drive through speed in both vehicle configurations was 
only 32 mph with the system off, compared to 34 mph with the system on. 
This demonstrates that an ESC system has some ability to mitigate 
understeer when navigating a curve on a low-friction surface, and allow 
the driver to maintain control at higher curve entrance speeds.
(b) NHTSA Testing of EMA's Vehicle J
    At NHTSA's request, EMA provided Vehicle J to NHTSA for NHTSA to 
duplicate EMA's testing.\30\ In particular, the agency was interested 
in the performance of Vehicle J during the sine with dwell maneuver. 
NHTSA's two 6x4 tractors that were tested in with the SWD represented 
the upper and lower size bounds of what would be considered a typical 
6x4 tractor and both tractors could not maintain stability during a SWD 
maneuver with the ESC system disabled. Vehicle J's size is within the 
bounds of the two typical 6x4 tractors tested by NHTSA.
---------------------------------------------------------------------------

    \30\ A copy of NHTSA's Vehicle J test data has been placed in 
the docket. Docket No. NHTSA-2010-0034-0044.
---------------------------------------------------------------------------

    NHTSA conducted 20 test runs of Vehicle J in the SWD maneuver at 
steering wheel angle scalars of 0.4 to 1.3 of the SIS-derived steering 
wheel angle attached to VRTC's FMVSS No. 121-style control trailer. 
When tested with the ESC system disabled at a steering wheel angle 
scalar of 1.2, NHTSA was able to detect lateral instability that 
continued for almost two seconds after completion of the SWD 
maneuver.\31\
---------------------------------------------------------------------------

    \31\ NHTSA was able to conduct 19 test maneuvers with Vehicle J 
that did not result in substantial roll instability. NHTSA did not 
find any yaw instability in any of the 20 test maneuvers.
---------------------------------------------------------------------------

    It was discovered that EMA conducted its testing of Vehicle J with 
a control trailer with different specifications than NHTSA used. NHTSA 
then attempted to duplicate EMA's Vehicle J's testing using the control 
trailer used by EMA.\32\ The results of NHTSA's tests with EMA's 
control trailer were not meaningfully different than the results of 
EMA's testing. That is, there were no instances of substantial roll or 
yaw instability in 20 test runs conducted by NHTSA.
---------------------------------------------------------------------------

    \32\ NHTSA's test data identifies the trailer used by EMA as a 
``Link'' trailer and the trailer used by NHTSA as the ``NHTSA'' or 
``VRTC'' trailer.
---------------------------------------------------------------------------

    As a result of NHTSA's testing of Vehicle J, the agency discovered 
that there exist three areas of variability in FMVSS No. 121-style 
control trailers and loading which, while not necessarily relevant to 
FMVSS No. 121 testing, could affect the results of stability control 
system testing if the specifications for an FMVSS No. 121-style control 
trailer were simply carried over to a stability control standard. 
First, EMA's control trailer had a wider track width \33\ than NHTSA's 
trailer, which made EMA's trailer, and thereby the combination vehicle, 
more stable during SWD testing. Second, EMA's control trailer had a 
lower deck height than NHTSA's trailer, which contributed to a lower 
center of gravity on EMA's trailer. Third, EMA loaded its trailer with 
steel for ballast, whereas NHTSA loaded its trailer with concrete for 
ballast, which also contributed to the lower center of gravity on EMA's 
trailer because steel would not have to be stacked as high to achieve a 
full load.
---------------------------------------------------------------------------

    \33\ The track width is the distance between the centerlines of 
a vehicle's left and right tires. In vehicles with dual tires, the 
track width would be measured from between the dual tires on each 
side of the vehicle.
---------------------------------------------------------------------------

E. Other Industry Research

    The SAE Truck and Bus Control Systems Task Force (renamed as the 
Truck and Bus Stability Control Committee) was formed in 2007 to 
facilitate information sharing among the industry and government 
regarding heavy vehicle stability control systems.\34\ The information 
shared included proposed test maneuvers that could potentially be used 
to evaluate the performance of stability control systems. Although the 
Task Force has not published any formal documents describing these test 
maneuvers, the following provides an overview of the maneuvers that 
have been discussed.
---------------------------------------------------------------------------

    \34\ See http://www.sae.org/events/cve/presentations/2007truckbus.pdf for an overview of the SAE Truck and Bus Council 
organizational chart.
---------------------------------------------------------------------------

1. Decreasing Radius Test
    A decreasing radius test (DRT) was developed to evaluate the roll 
stability performance of a heavy vehicle stability control system.\35\ 
With the DRT, the test conditions could also be adjusted to evaluate 
yaw stability as well. In the DRT, the vehicle is accelerated to a 
constant speed of 29 mph on a dry road surface, and an initial steering 
input is made to follow a curve with a 150-foot radius. Once the 
initial curve radius is achieved, the radius is linearly reduced to a 
radius of 90 feet as the vehicle negotiates 120 degrees of arc. Thus, 
it is similar to the J-turn maneuver. The speed of 29 mph was derived 
based on a vehicle dynamics simulation, which estimated that the 
maneuver would produce 0.3g of lateral acceleration during the initial 
steering input and this would steadily increase to 0.6g at the 90-foot 
radius curve.
---------------------------------------------------------------------------

    \35\ See Docket No. NHTSA-2010-0034-0036.
---------------------------------------------------------------------------

    Tests would be conducted in a loaded condition with the tractor 
coupled to a trailer and an unloaded condition in a

[[Page 30788]]

bobtail configuration. Because actual vehicle testing had not been 
conducted using this maneuver, pass/fail criteria have not yet been 
developed. Simulations of this test have been run using driver-
controlled steering inputs; however, parameters could also be developed 
to conduct this maneuver using an automated steering controller.
2. Lane Change on a Large Diameter Circle
    Volvo provided information on the Lane Change on a Large Diameter 
Circle (LC-LDC) maneuver that they have used to evaluate stability 
control system performance.\36\ In this maneuver the vehicle is driven 
at a constant speed, just below the threshold speed for rollover or 
loss of control, around the inside lane of an 800-foot radius curve 
that has two lanes. The driver then drifts to the outside lane, and 
steers back into the inside lane. For rollover testing the asphalt road 
surface is dry and for yaw testing the surface is wet. The test can be 
conducted using a bobtail tractor, a tractor towing an FMVSS No. 121 
control trailer, or a tractor towing any other type of trailer in a 
fully loaded condition. Volvo evaluated the roll stability performance 
during this maneuver based on whether the trailer outrigger made 
contact with the ground. Volvo considers this maneuver to be 
representative of certain highway segments that are encountered, and 
that the maneuver is severe enough to fully challenge a stability 
control system.
---------------------------------------------------------------------------

    \36\ See Docket No. NHTSA-2010-0034-0042.
---------------------------------------------------------------------------

3. Yaw Control Tests
    Bendix developed two yaw stability test maneuvers to evaluate the 
ability of stability control systems to prevent severe oversteer and 
understeer conditions. The first test maneuver is a Sinusoidal Steering 
Maneuver (SSM) to evaluate oversteer prevention.\37\ The first step in 
this test is to identify the steering wheel angle that produces a 
tractor lateral acceleration of 0.5g at 30 mph on dry pavement with the 
tractor in the bobtail condition. Bendix recommended that this angle be 
derived by either a slowly increasing steer test (SIS test described in 
section IV.D.2 above) or an equation developed by Bendix for estimating 
the angle based on the tractor's wheelbase:

    \37\ See Docket No. NHTSA-2010-0034-0037.
---------------------------------------------------------------------------

Steering Wheel Angle ([delta]) = (35.5 x (tractor wheelbase in meters)) 
+ 30.94

    The Sinusoidal Steering Maneuver test is then conducted with the 
tractor in the bobtail condition using a low-friction wet Jennite road 
surface (nominal peak friction coefficient of 0.5). The vehicle is 
driven at a constant speed of approximately 30 mph and, as a sinusoidal 
steering input is initiated (continuous left and right steering inputs 
using the steering wheel angle determined above), the driver increases 
the throttle position to request 100 percent of engine torque.
    The second test maneuver developed by Bendix was the ramp with a 
dwell maneuver discussed in section IV.D.4 above.\38\ The RWD maneuver 
is intended to evaluate understeer prevention, though oversteer can 
also occur during the maneuver. The RWD test is conducted with the 
tractor in the bobtail condition and using a wet Jennite road surface. 
The first step in this test is to characterize the vehicle's steering 
by conducting a series of drive-through speed evaluations at a constant 
speed on a 500-foot radius curve. Once the maximum constant travel 
speed is determined (typically between 28 and 32 mph, but not to exceed 
35 mph), the steering wheel angle is measured for negotiating the curve 
at that speed. The RWD test maneuver speed is then conducted at the 
maximum drive-through speed. Bendix suggested that manual steering by a 
test driver or an automated steering machine could be used. Once the 
vehicle has been accelerated to the test maneuver speed, the speed is 
held constant by the driver and he inputs the drive-through steering 
wheel angle. After the vehicle reaches a constant lateral acceleration 
condition, the steering wheel angle is increased to 180 degrees in a 
period of one second. That increased angle is held constant for three 
seconds, and then the angle is reduced to zero in a period of one 
second. Subsequent test runs are conducted by increasing the steering 
wheel angle in increments of 90 degrees up to 540 degrees.
---------------------------------------------------------------------------

    \38\ See Docket No. NHTSA-2010-0034-0038.
---------------------------------------------------------------------------

    The RWD test performance measures would be based upon test data 
showing that the vehicle's stability control system successfully 
identified a vehicle control problem (understeer or oversteer) and 
intervened by reducing the engine torque output and commanding the 
application of individual foundation brakes in a manner that is 
suitable to mitigate the control problem. Bendix did not believe that 
vehicle yaw or path-following pass/fail criteria would be appropriate 
for this test maneuver.
    Two maneuvers that the industry has developed to evaluate the 
performance of stability control systems, lane change on a large 
diameter circle and sinusoidal steering, can be used to demonstrate 
that a stability control system is capable of preventing a rollover or 
a yaw instability condition. The RWD maneuver may exceed the 
capabilities of stability control systems but provides brake 
application data that can be reviewed to determine if a stability 
control system provides the correct control responses to address a 
severe oversteer or understeer condition.

V. Agency Proposal

    Based upon the foregoing research, the agency is proposing a new 
FMVSS to require ESC systems be installed on truck tractors and buses 
with a GVWR of greater than 11,793 kilograms (26,000 pounds).\39\ There 
are several issues raised by this proposed rule on which the agency 
seeks public comment, each of which is discussed in detail in the 
following sections.
---------------------------------------------------------------------------

    \39\ To distinguish this new FMVSS from the light vehicle ESC 
requirement in FMVSS No. 126, we are proposing to revise the title 
FMVSS No. 126 to reflect that it is applicable only to light 
vehicles.
---------------------------------------------------------------------------

A. NHTSA's Statutory Authority

    NHTSA is proposing today's NPRM 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 proposed 
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

[[Page 30789]]

responsibility for promulgation of Federal motor vehicle safety 
standards is delegated to NHTSA. In making the proposals in today's 
NPRM, the agency carefully considered all the aforementioned statutory 
requirements.

B. Applicability

1. Vehicle types
    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).
    The vast majority of vehicles with a GVWR of greater than 4,536 
kilograms (10,000 pounds) for which stability control systems are 
currently available are truck tractors. Approximately 150,000 truck 
tractors with a GVWR of greater than 11,793 kilograms (26,000 pounds) 
are manufactured each year. In 2009, about 20 percent of Class 7 and 8 
truck tractors were equipped with a stability control system.
    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.'' Two-axle (4x2) tractors and severe service 
tractors (those with three axles that are not ``typical 6x4 tractors'' 
or those with four or more axles) represent about 15 percent of the 
truck-tractor market in the U.S.
    The majority of the research on the effectiveness of stability 
control systems to date has been performed on typical 6x4 tractors. As 
a result, the agency's research included two typical 6x4 tractors. The 
agency also included one 4x2 tractor in its testing because two-axle 
tractors represent the next largest segment of the truck-tractor 
market. No severe service tractors were tested. EMA performed tests on 
nine tractors equipped with stability control systems. The tractors 
included two 4x2 tractors, two typical 6x4 tractors, two severe service 
6x4 tractors, two 6x4 tractors with a liftable auxiliary axle in front 
of the drive axles, and one 8x6 tractor.
    This proposal would also require certain buses to be equipped with 
an ESC system. We intend the applicability of this proposed requirement 
to be similar to the applicability of the agency's proposal that 
certain buses be equipped with seat belts.\40\ That proposal 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 is proposing a very similar applicability in 
this NPRM. We have not made this proposal applicable to buses with a 
GVWR of exactly 11,793 kilograms (26,000 pounds) in order to exclude 
Class 6 vehicles from this proposal. We believe that this proposal 
encompasses 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.
---------------------------------------------------------------------------

    \40\ 75 FR 50,958 (Aug. 18, 2010).
---------------------------------------------------------------------------

    The agency tested three buses, all of which had a GVWR over 14,969 
kg (33,000 pounds). There are seven manufacturers or distributors of 
Class 8 buses covered by this proposal for the U.S. market: Prevost, 
MCI, VanHool, Daimler/Setra, CAIO, BlueBird, and BCI. Three of them 
(Prevost, MCI, and VanHool), have stated that an ESC system is a 
standard feature on their buses sold in the U.S. Daimler/Setra 
indicated that an ESC system will be available as an option on its 
buses beginning in model year 2011 and that no decision has been made 
to make it a standard feature. No official information is available 
from CAIO, Bluebird, and BCI regarding ESC system availability.
    There are also at least nine manufacturers of Class 7 buses covered 
by this proposal for the U.S. market: Champion, ElDorado National, 
Federal Coach, Glaval, IC Bus, MCI, Rexhall, Stallion, and VanHool. 
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 is not aware of any Class 7 bus currently available 
with ESC, we are aware that stability control systems are available on 
a limited number of Class 8 single unit trucks, such as ready mix 
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 believe are also air-braked vehicles.
    Although this proposal would not apply to all buses with a GVWR of 
greater than 11,793 kilograms (26,000 pounds), we seek comment on 
whether this proposal should be applied to the types of buses that are 
excluded from the proposed rule such as school buses and transit buses. 
We also seek comment on the feasibility of including the Class 7 buses 
described in the prior paragraph that are built on chassis similar to 
those of single unit trucks within two years. In particular, we believe 
that ESC systems are readily available for air-braked buses; however, 
system availability for any hydraulically braked buses that may be 
covered by this proposed rule may be more limited. If hydraulically 
braked buses are covered by this proposal, we request comment on 
manners in which hydraulically braked buses may be differentiated for 
exclusion or a different phase-in period.
    The agency is not proposing to include single unit trucks with a 
GVWR over 4,536 kg (10,000 pounds) at this time. There are substantial 
differences in the complexity of the single unit truck population 
compared to the truck-tractor population. The single unit truck 
population has wide variations in vehicle weight, wheelbase, number of 
axles, center of gravity height, and cargo type, among other things 
that affect the calibration and performance of stability control 
systems. While some variation exists in the truck tractor market, the 
degree of complexity and diversity is substantially less.
    Further, the single unit truck market is structurally different 
than the truck tractor market in that the chassis supplier, who is 
generally responsible for the brake systems and therefore would likely 
provide stability control systems, is often different than the final 
body builder. Hence, the chassis supplier may not have knowledge of 
critical vehicle design parameters that would affect stability control 
system calibration. In contrast, manufacturers of truck tractors have 
more complete control of the final, delivered vehicle.
    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. We believe that 
approximately 1 percent of newly manufactured single-unit trucks are 
equipped with stability control systems, and that few, if any, of those 
are for

[[Page 30790]]

vehicles with hydraulic brakes. The development of stability control 
system for vehicles over 10,000 pounds GVWR has been focused on air-
braked vehicles, which include the truck tractors and buses addressed 
in this proposal. Because we are concerned about the availability of 
production-ready systems on these vehicles, they are not included in 
the proposal. However, we seek comment on these observations.
    The agency has initiated a safety benefit study to determine the 
safety need for stability control on single-unit trucks, and has also 
initiated vehicle research, similar to the research conducted on truck 
tractors and large buses described in part IV.C above, which is 
expected to be completed in 2012. However, the agency proposes to 
require stability control systems on truck tractors without waiting for 
the study on the effectiveness of stability control systems on single-
unit trucks to be completed. Waiting for that study to be completed 
would unnecessarily delay the benefits of having stability control 
systems on truck tractors and large buses, for which testing has been 
completed the benefits of stability control systems identified.
    The agency is not proposing to include a requirement for stability 
control systems on trailers, primarily because trailer-based RSC 
systems were judged 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. The trailer-
based RSC systems provide some improvement in roll stability compared 
to a base trailer without an RSC system, but a vehicle could still be 
overdriven at a lower speed with trailer-based RSC systems than with a 
tractor-based system. This means that the maneuver entrance speed 
beyond which the stability control system is unable to reduce the 
vehicle speed to prevent a rollover was lower for the trailer-based 
system than for the tractor-based system. 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.
    Therefore, the agency proposes to require stability control systems 
on truck tractors and buses with a GVWR of greater than 11,793 
kilograms (26,000 pounds).
2. Retrofitting In-Service Truck Tractors, Trailers, and Buses
    NHTSA has considered proposing to require retrofitting of in-
service truck tractors, trailers, and large buses with stability 
control systems proposed to be required by this NPRM. The Secretary has 
the statutory authority to promulgate safety standards for ``commercial 
motor vehicles and equipment subsequent to initial manufacture.'' \41\ 
The Secretary has delegated authority to NHTSA to ``promulgate safety 
standards for commercial motor vehicles and equipment subsequent to 
initial manufacture when the standards are based upon and similar to 
[an FMVSS] promulgated, either simultaneously or previously, under 
chapter 301 of title 49, U.S.C.'' \42\ Additionally, the Federal Motor 
Carrier Safety Administration (FMCSA) is authorized to promulgate and 
enforce vehicle safety regulations, including those aimed at 
maintaining commercial motor vehicles so they continue to comply with 
the safety standards applicable to commercial motor vehicles at the 
time they were manufactured. Although this NPRM does not propose 
requiring truck tractors, trailers, or large buses to be equipped with 
stability control systems ``subsequent to initial manufacture,'' we are 
requesting public comment on several issues related to retrofitting in-
service truck tractors, trailers, and buses:
---------------------------------------------------------------------------

    \41\ See Motor Carrier Safety Improvement Act of 1999, sec. 
101(f), Pub. L. 106-159 (Dec. 9, 1999).
    \42\ See 49 CFR 1.50(n).
---------------------------------------------------------------------------

     The extent to which a proposal to retrofit in-service 
vehicles with stability control systems would be complex and costly 
because of the integration between a stability control system and the 
vehicle's chassis, engine, and braking systems.
     The changes necessary to an originally manufactured 
vehicle's systems that interface with a stability control system, such 
as plumbing for new air brake valves and lines and a new electronic 
control unit for a revised antilock brake system.
     The additional requirements that would have to be 
established to ensure that stability control components are at an 
acceptable level of performance for a compliance test, given the 
uniqueness of the maintenance condition for vehicles in service, 
particularly for items such as tires and brake components that are 
important for ESC performance.
     The original manufacture date of vehicles that should be 
subject to any retrofitting requirements.
     Whether the performance requirements for retrofitted 
vehicles should be less stringent or equally stringent as for new 
vehicles, and, if less stringent, the appropriate level of stringency.
     The cost of retrofitting a stability control system on a 
vehicle, which we believe would exceed the cost of including stability 
control on a new vehicle.
    In light of these questions, the agency is not proposing that in-
service vehicles be required to be retrofitted with stability control 
systems. Instead, this proposed requirement would be applicable only to 
newly manufactured vehicles. However, the comments we receive on the 
issue of retrofitting will help us determine whether we should issue a 
separate supplemental NPRM to require a retrofit.
3. Exclusions From Stability Control Requirement
    Our proposed rule excludes 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.
    Specifically, FMVSS No. 121, Air brake systems, excludes certain 
heavy air-braked heavy vehicles from that standard. For truck tractors 
and buses, these exclusions include:
     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.
     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.
    We believe that the vehicles that are excluded from the 
requirements of FMVSS No. 121 should also be excluded from the proposed 
stability control requirements because the speed at which these 
vehicles operate would make it unlikely that roll or yaw instability 
would occur. Accordingly, the proposed stability control requirement 
excludes these vehicles.

C. ESC System Capabilities

1. Choosing ESC vs. RSC
    We are proposing to require that truck tractors and large buses be 
equipped

[[Page 30791]]

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.
    As discussed in greater length in Section VI, 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.
    Mandating ESC systems rather than RSC systems will result in higher 
costs to manufacturers. Moreover, our benefit and cost estimates lead 
to the preliminary conclusion that mandating RSC systems would be more 
cost-effective than mandating ESC systems. However, these extra costs 
are more than offset by higher net benefits that would accrue by 
mandating ESC systems rather than RSC systems.
2. Definition of ESC
    Definitional requirements in an FMVSS define and describe the type 
of system that can be used to meet the performance requirements of a 
particular FMVSS. However, the inclusion of a definitional requirement 
in an FMVSS may be design restrictive because it would be based on 
currently available technology. Limiting the equipment that can be used 
to satisfy an FMVSS may limit future technological advancements and 
innovation. As stability control technologies are developed even 
further, a definitional requirement could be a hindrance to safety 
improvements if it limits the use of a newly developed equipment or 
technology that is not addressed by the specified definitional 
requirement. On the other hand, 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 does not believe it is practical to develop 
performance tests that would address the full range of possibilities 
and remain cost-effective. Accordingly, the agency is proposing to 
include a definitional requirement in this proposed rule that includes 
equipment that would be required as part of a compliant ESC system. We 
note that, when developing the ESC requirement for light vehicles, the 
agency chose to include such a requirement in FMVSS No. 126.
    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 has reviewed the 
functional attributes contained in the SAE and the ECE definitions, and 
has incorporated portions of both of these definitions in this NPRM. We 
have developed a definition that is 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, this NRPM proposes to require a stability control system 
that also helps to mitigate roll instability conditions. As a result, 
we have expanded the definition from the one in FMVSS No. 126 to 
include a requirement that the system be capable of sensing impending 
rollover and reducing the vehicle's lateral acceleration to prevent 
rollover.
    Furthermore, we believe 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 has obtained from vehicle manufacturers and ESC 
suppliers, this 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 a proposed regulation, we 
believe that setting a single low speed threshold would be preferable 
since the yaw and roll stability functions during a test maneuver are 
closely intertwined, which could make it difficult to differentiate 
when the roll or yaw function ends. Therefore, we propose a single 
threshold of 20 km/h (12.4 mph) as the speed below which ESC is not 
required to be operational.
    Therefore, the agency proposes to require the installation of an 
ESC system on truck tractors and large buses, which has all of the 
following attributes:
    1. Augments vehicle directional stability by applying and adjusting 
vehicle brake torques individually at each wheel position on at least 
one front and at least one rear axle of the vehicle to induce 
correcting yaw moment to limit vehicle oversteer and to limit vehicle 
understeer;
    2. Enhances rollover stability by applying and adjusting the 
vehicle brake torques individually at each wheel position on at least 
one front and at least one rear axle of the vehicle to reduce lateral 
acceleration of a vehicle;
    3. Computer-controlled with the computer using a closed-loop 
algorithm to induce correcting yaw moment and enhance rollover 
stability;
    4. Has a means to determine the vehicle's lateral acceleration;
    5. Has a means to determine the vehicle's yaw rate and to estimate 
its side slip or side slip derivative with respect to time;
    6. Has a means to estimate vehicle mass or, if applicable, 
combination vehicle mass;
    7. Has a means to monitor driver steering input;
    8. Has a means to modify engine torque, as necessary, to assist the 
driver in maintaining control of the vehicle; and
    9. When installed on a truck tractor, has the means to provide 
brake pressure to automatically apply and modulate the brake torques of 
a towed semi-trailer.
    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

[[Page 30792]]

tests proposed in this NPRM would only evaluate ESC system performance 
under very specific environmental conditions. To ensure that a vehicle 
is equipped with an ESC system that meets the proposed definition, we 
are proposing that vehicle manufacturers make available to the agency 
documentation that would enable us to ascertain that the system 
includes the components and performs the functions of an ESC system.
    We are proposing 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 includes the capability to 
provide brake pressure to a towed vehicle, the agency is proposing to 
require 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.
    It is common practice for the NHTSA's Office of Vehicle Safety 
Compliance to request relevant technical information from a 
manufacturer prior to conducting many of its compliance test programs. 
The agency included such a requirement in the light vehicle ESC 
standard. Prior to conducting any of the FMVSS No. 126 compliance 
tests, NHTSA requires manufacturers to provide the documentation 
required by that standard, including identification of all ESC system 
hardware and an explanation of the system operational characteristics. 
We also request additional information about the ESC system including 
manufacturer make and model, telltale(s), pertinent owner's manual 
excerpts and suggested malfunction scenarios. All of the requested 
information allows NHTSA to verify that the ESC system meets the 
definitional and operational requirements that cannot necessarily be 
verified during the performance test. Furthermore, this information 
aids the test engineers with execution and completion of the compliance 
test.

D. ESC Disablement

    The agency has also considered whether to allow a control for the 
ESC to be disabled by the driver; however, heavy vehicles currently 
equipped with ESC systems do not include on/off controls for ESC that 
would allow a driver to deactivate or adjust the ESC system. Given the 
lack of on/off switches on heavy vehicles equipped with ESC, we do not 
propose to allow an on/off switch for ESC systems in this NPRM. 
Nevertheless, we seek comment on the need to allow an on/off switch. 
Such comments should address why manufacturers might need this 
flexibility and how manufacturers would implement a switch in light of 
the ABS requirements for truck tractors and large buses.

E. ESC Malfunction Detection, Telltale, and Activation Indicator

1. ESC Malfunction Detection
    This proposed rule would require that vehicles be equipped with an 
indicator lamp, mounted in front of and in clear view of the driver, 
which is activated whenever there is a malfunction that affects the 
generation or transmission of control or response signals in the 
vehicle's ESC system. Heavy vehicles presently equipped with ESC 
generally do not have a dedicated ESC malfunction lamp. Instead, they 
share that function with the mandatory ABS malfunction indicator lamp 
or the traction control activation lamp. The agency proposes requiring 
a separate ESC malfunction lamp because it would alert the driver to 
the malfunction condition of the ESC and would help to ensure that the 
malfunction is corrected at the earliest opportunity.
    We believe that there are safety benefits associated with such a 
warning. An ESC malfunction indicator warns the driver in the event of 
an ESC system malfunction so that the system can be repaired. ESC 
system activations on a heavy vehicle will be infrequent events in 
panic situations, and drivers should not experience the activation of a 
stability control system during the normal operation of the vehicle. 
Because most steering maneuvers performed during the normal operation 
of a heavy vehicle are not severe enough to activate the ESC system, a 
vehicle may be operated for long periods without an ESC activation 
event. Without such a malfunction indicator, a driver might have no way 
of knowing that an ESC system is malfunctioning until a loss of control 
or rollover event occurs. For example, the agency received a complaint 
recently in which a heavy truck had an inoperative ESC system, but the 
driver was unaware of the malfunction, primarily due to the lack of a 
malfunction indicator lamp. The agency believes that such a warning is 
important to ensure that the driver could have the malfunction 
corrected at the earliest opportunity in order to continue to realize 
the system's safety benefits.
    The ESC malfunction telltale would be required to remain 
illuminated continuously as long as the malfunction exists whenever the 
ignition locking system is in the ``On'' (``Run'') position. The ESC 
malfunction telltale must extinguish after the malfunction has been 
corrected. These proposed requirements are identical to the 
requirements established in the light vehicle ESC standard, FMVSS No. 
126, and help to ensure that the system provides a warning indication 
in the event of a malfunction.
    Because many malfunctions cannot be detected when the vehicle is 
stationary, this NPRM includes a test that would allow the engine to be 
running and the vehicle to be in motion as part of the diagnostic 
evaluation. We are aware that some malfunctions are not time-based, but 
instead require comparisons of sensor outputs generated when the 
vehicle is driven. Hence, some malfunctions would require certain 
driving motions to make the ESC system's malfunction detection 
possible. We believe that an ESC malfunction should be detected within 
a reasonable time of starting to drive. As a result, we propose that 
the malfunction telltale illuminate within two minutes after attaining 
a test speed of 48 km/h (30 mph) so that the parts of a system's 
malfunction detection capability that depend on vehicle motion can 
operate. This two-minute period is identical to the period included in 
the test procedure in FMVSS No. 126 for ESC malfunction detection.
    We anticipate that FMCSA will issue a companion proposal to NHTSA's 
proposal to require ESC on truck tractors and large buses, which would 
require that the ESC system on a commercial vehicle be maintained in a 
fully operating condition. In addition, we expect that the roadside 
inspection procedures developed for commercial vehicle ESC systems 
would be facilitated by the ESC malfunction telltale and the format 
that is required to indicate whether or not the system is operational.
2. ESC Malfunction Telltale
    The ESC malfunction lamp requirement in this NPRM states that each 
truck tractor and large bus must be equipped with a telltale that 
provides a warning to the driver when one or more malfunctions that 
affect the generation of control or response signals in the vehicle's 
electronic stability control system is detected. Specifically, the ESC 
malfunction telltale will be required to

[[Page 30793]]

be mounted in the driver's compartment in front of and in clear view of 
the driver and be identified by the symbol shown for ``ESC Malfunction 
Telltale'' or the specified words or abbreviations listed in Table 1 of 
FMVSS No. 101, Controls and displays. FMVSS No. 101 includes a 
requirement for the telltale symbol, or abbreviation, and the color 
required for the indicator lamp to show a malfunction in the ESC 
system.
    The agency believes that the symbol used to identify ESC 
malfunction should be standardized with the symbol used on light 
vehicles. The symbol established in FMVSS No. 126 is the International 
Organization for Standardization (ISO) ESC symbol, designated J.14 in 
ISO Standard 2575. The symbol shows the rear of a vehicle trailed by a 
pair of ``S'' shaped skid marks, shown below in Figure 5. The agency 
found that the ISO J.14 symbol and close variations were the symbols 
used by the greatest number of vehicle manufacturers that used an ESC 
symbol before the requirement was established. Furthermore, FMVSS No. 
126 allows, as an option, the use of the text ``ESC'' in place of the 
telltale symbol. This same option is being proposed.
[GRAPHIC] [TIFF OMITTED] TP23MY12.005

    The color of the ESC malfunction telltale specified in Table 1 of 
FMVSS No. 101 for light vehicles equipped with ESC is yellow, which is 
the color used to communicate to the driver the condition of a 
malfunctioning vehicle system that does not require immediate 
correction. The agency chose to associate indication of an ESC system 
malfunction with a yellow telltale color as a warning to the driver 
because we believe that it communicates the level of urgency with which 
the driver must seek to remedy the malfunction of the ESC system.
    For this proposed rule, we believe that the ESC malfunction 
telltale and color designation developed for light vehicles would be 
appropriate for use on heavy vehicles. Accordingly, the agency proposes 
that the ESC malfunction telltale symbol and color requirements of 
FMVSS No. 101 be proposed for use on truck tractors and buses, and that 
the abbreviation ``ESC'' should be allowed as an option instead of the 
symbol.
    In addition to the ESC malfunction telltale being used to warn the 
driver of a malfunction in the ESC, the telltale is also used as a 
check of lamp function during vehicle start-up. We believe that the ESC 
malfunction telltale should be activated as a check of lamp function 
either when the ignition locking system is turned to the ``On'' 
(``Run'') position whether or not the engine is running. This function 
provides drivers with the information needed to ensure that the ESC 
system is operational before the vehicle is driven. It also provides 
Federal and State inspectors with the means to determine the 
operational status of the ESC system during a roadside safety 
inspection.
    Accordingly, this NPRM proposes that the ESC malfunction telltale 
must be activated as a check of lamp function either when the ignition 
locking system is turned to the ``On'' (``Run'') position when the 
engine is not running or when the ignition locking system is in a 
position between the ``On'' (``Run'') and ``Start,'' which is 
designated by the manufacturer as a check position.
3. ESC Activation Indicator
    The agency is requesting comment on whether there is a safety need 
for an ESC activation indicator. In the light vehicle ESC rulemaking, 
the agency considered the safety need for an ESC activation indicator 
to alert the driver during an emergency situation that the ESC is 
activating. NHTSA conducted a study using the National Advanced Driving 
Simulator (NADS), which included experiments to gain insight into the 
various possibilities regarding ESC activation indicators. The study 
compared the performance of 200 participants in driving maneuvers on a 
wet pavement, and used road departures and eye glances to the 
instrument panel as measures of driver performance. The significant 
finding was that the drivers who received various ESC activation 
indicators did not perform better than drivers who were given no 
indicator. That finding formed the basis for the agency's decision not 
to require an ESC activation indicator for light vehicles.

F. Performance Requirements and Compliance Testing

    The agency's research initially focused on a variety of maneuvers 
which we could use to evaluate the roll stability performance and the 
yaw stability performance of truck tractors and large buses. Several of 
these maneuvers were also tested by industry and some of them are 
allowed for use in testing for compliance to the UN ECE stability 
control regulation. The agency's goal was to develop one or more 
maneuvers that showed the most promise as repeatable and reproducible 
roll and yaw performance tests for which objective pass/fail criteria 
could be developed.
    As the research program progressed, the data indicated that the 
ramp steer maneuver to evaluate roll stability performance and the sine 
with dwell maneuver to evaluate yaw stability performance were the most 
promising. The slowly increasing steer maneuver was developed to 
normalize testing conditions for each vehicle so that the level of 
stringency for each test vehicle would be similar. The agency also 
found that the SIS maneuver could also be used to evaluate the engine 
torque reduction capability of a vehicle's ESC system, which is 
important because engine torque reduction may bring a vehicle under 
control before brakes are applied. After further testing, the agency 
was able to develop test parameters for the SWD maneuver so that both 
roll stability and the yaw stability could be evaluated using a single 
maneuver and loading condition. This development eliminated the need 
for the ramp steer maneuver to evaluate roll stability performance.
    Therefore, based on testing at VRTC and the results from industry-
provided test data, two stability proposed performance tests have been 
chosen to

[[Page 30794]]

evaluate ESC systems on truck tractors and large buses--the SIS test 
and the SWD test.
    The agency also considered the ECE performance tests for heavy 
vehicle stability control systems, which are included in the brake 
systems regulation, ECE Regulation 13. The performance test for a heavy 
vehicle with a directional control function includes meeting the 
requirements in one of eight tests allowed for compliance. The eight 
tests are as follows: Reducing radius test (which is identical to the 
decreasing radius test discussed above), step steer input test, sine 
with dwell, J-turn, mu-split lane change, double lane change, reversed 
steering test or ``fish hook'' test, and asymmetrical one period sine 
steer or pulse steer input test. No test procedure or pass/fail 
criteria are included in ECE Regulation 13, 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 issue of whether the U.S. should adopt the stability control 
requirements similar to those in ECE Regulation 13 is addressed in the 
context of whether a definitional requirement specifying required 
equipment along with a performance test that does not include a test 
procedure or pass/fail criteria would be considered sufficiently 
objective for a safety standard. The agency considered several of the 
eight ECE tests that we believed showed the most promise for 
repeatability and reproducibility, and decided to focus on the SWD 
test, which is one of the eight tests allowed for compliance testing to 
ECE Regulation 13. However, in light of the requirement in the Motor 
Vehicle Safety Act that FMVSSs be stated in objective terms, NHTSA is 
required to develop objective performance criteria for the SWD test to 
be set forth in the regulatory text.
1. Characterization Test--SIS
    The agency is proposing to conduct compliance testing 
characterization using a slowly increasing steer to determine the 
steering wheel angle needed to achieve 0.5g of lateral acceleration at 
30 mph and also to evaluate the capability of the ESC system to reduce 
engine torque. The SIS maneuver has been used for many years by the 
agency and the industry to determine the unique dynamic characteristics 
of a vehicle. This maneuver allows the agency to determine the 
relationship between the steering wheel angle and lateral acceleration 
for a vehicle, which varies due to different steering gear ratios, 
different suspension systems, and wheelbase and other dimensions, among 
other things. To normalize the severity of the SWD maneuver that 
follows, each vehicle is tested based on its steering wheel angle 
determined in the SIS maneuver. The agency is proposing a 0.5g lateral 
acceleration target because our test results indicated that a truck 
tractor or large bus is highly likely to experience instability at that 
level of lateral acceleration. Even though the vast majority of truck 
tractors are typical 6x4 tractors, there are other configurations, such 
as those with 2-axle or 4-axle configurations and buses, which would 
require a different steering wheel angle to normalize the test 
conditions for each different vehicle.
    To perform the SIS maneuver, the tractor or bus is driven at a 
constant speed of 30 mph, and then the steering controller increases 
the steering wheel angle at a slow, continuous rate of 13.5 degrees per 
second. The steering wheel angle is increased linearly from zero to 270 
degrees and then held constant for one second, after which the maneuver 
concludes. The vehicle is subjected to two series of runs, one using 
clockwise steering and the other using counterclockwise steering, with 
three tests performed for each test series. During each test run, ESC 
system activation must be confirmed. If ESC system activation does not 
occur during the maneuver, then the commanded steering wheel angle is 
increased by 270-degree increments up to the vehicle's maximum 
allowable steering angle until ESC activation is confirmed.
    From the SIS tests, the value ``A'' is determined. ``A'' is the 
steering wheel angle, in degrees, that is estimated to produce a 
lateral acceleration of 0.5g for that vehicle. Using linear regression 
on the lateral acceleration data recorded between 0.05g and 0.3g for 
each of the six valid SIS tests, a linear extrapolation is used to 
calculate a steering wheel angle where the lateral acceleration would 
be 0.5g. If ESC system activation occurs prior to the vehicle 
experiencing lateral acceleration of 0.3g, then the data used during 
the linear regression will be that data recorded between 0.05g and the 
lateral acceleration measured at the time of ESC system activation. The 
six values derived from the linear regression are then averaged and 
rounded to the nearest 0.1 degree to produce the final quantity, ``A,'' 
used during the SWD maneuver.
    As part of the SIS characterization test, the engine torque 
reduction test is also conducted. As mentioned above, during each of 
the six completed SIS maneuvers, ESC activation is confirmed by 
verifying that the system automatically attempts to reduce engine 
torque. To confirm ESC activation, engine torque output and driver 
requested torque data are collected from the vehicle's J1939 
communication data link and compared. During the initial stages of each 
maneuver, the rate of change over time of engine torque output and 
driver requested torque will be consistent. Upon ESC activation, the 
ESC system activation causes a commanded engine torque reduction, even 
though the driver requests increased torque by attempting to accelerate 
the vehicle to maintain the required constant speed. Therefore, the 
rate of change over time of engine torque output and driver requested 
torque will diverge.
    For each of the six SIS test runs, the commanded engine torque and 
the driver requested torque signals must diverge at least 10 percent 
1.5 seconds after the beginning of ESC system activation. This test 
demonstrates that the ESC system has the capability to reduce engine 
torque, as required in the functional definition.
    The metric used to measure the engine torque reduction performance 
is stated in terms of the difference in percent between the actual 
engine torque output and driver requested torque input just after ESC 
activation. The pass-fail criterion that the agency proposes for this 
test is that the stability control system must be able to reduce engine 
torque output by a minimum of 10 percent from the torque output 
requested by the driver, which will be measured 1.5 seconds after the 
time when the ESC activated. The vehicles that the agency tested were 
all able to meet this proposed performance level.
2. Roll and Yaw Stability Test--SWD
    The objective of the sine with dwell test is to subject a vehicle 
to a maneuver that will cause both roll and yaw instabilities and to 
verify that the ESC system activates to mitigate those instabilities. 
The SWD test is based on a single cycle of a sinusoidal steering input. 
For testing, we are proposing to use a frequency of 0.5 Hz (\1/2\ cycle 
per second or 1 cycle in 2 seconds) was used with a pause or dwell of 
1.0 second after completion of the third quarter-cycle of the sinusoid. 
We chose a 0.5 Hz frequency because it produces the most consistently 
high severity on the majority of the vehicles tested by the agency. 
Hence, the total time for the steering maneuver is three seconds.
    Conceptually, the steering profile of this maneuver is similar to 
that expected to be used by real drivers during some crash avoidance 
maneuvers. As the agency found in the

[[Page 30795]]

light vehicle ESC research program, the severity of the SWD maneuver 
makes it a rigorous test while maintaining steering rates within the 
capabilities of human drivers. We believe that the maneuver is severe 
enough to produce rollover or vehicle loss-of-control without a 
functioning ESC system on the vehicle.
    For a truck tractor, the SWD test would be conducted with the truck 
tractor coupled to an unbraked control trailer and loaded with ballast 
directly over the kingpin. The combination vehicle would be loaded to 
80 percent of the tractor's GVWR. Testing indicates that this is 
sufficient load on the tractor to enable the tractor's stability 
control mass estimation program to provide full tractor braking 
intervention during the SWD maneuver. The ballast is placed low on the 
trailer to minimize the likelihood of actual trailer rollover, and the 
trailer is equipped with outriggers in case the ESC system does not 
function properly to prevent the trailer from rolling over.
    For a bus, the vehicle is loaded with a 68-kilogram (150-pound) 
water dummy in each of the vehicle's designated seating positions, 
which would bring the vehicle's weight to less than its GVWR. No 
ballast is placed in the cargo hold beneath the passenger compartment 
so that the desired CG height of the test load can be attained.
    The SWD test would be conducted at a speed of 72 km/h (45 mph). An 
automated steering machine would be used to initiate the steering 
maneuver. Each vehicle is subjected to two series of test runs. One 
series uses counterclockwise steering for the first half-cycle, and the 
other series uses clockwise steering for the first half-cycle. The 
steering amplitude for the initial run of each series is 0.3A, where A 
is the steering wheel angle determined from the SIS maneuvers discussed 
in section V.F.1 above. In each of the successive test runs, the 
steering amplitude would be increased by increments of 0.1A until a 
steering amplitude of 1.3A or 400 degrees, whichever is less, is 
achieved. Upon completion of the two series of test runs, post-
processing of the yaw rate and lateral acceleration data to determine 
the lateral acceleration ratio, yaw rate ratio, and lateral 
displacement, as discussed below.
(a) Roll Stability Performance
    The LAR is a performance metric developed to evaluate the ability 
of a vehicle's ESC system to prevent rollovers. Lateral acceleration is 
measured on a bus or a tractor and corrected for the vehicle's roll 
angle. As a performance metric, the corrected lateral acceleration 
value is normalized by dividing it by the maximum lateral acceleration 
that was determined at any time between 1.0 seconds after the beginning 
of steering and the completion of steering.
    Conceptually, stability control system intervention will reduce 
lateral acceleration of the vehicle during a crash avoidance steering 
maneuver. This intervention increases the roll stability of the vehicle 
by reducing the vehicle speed, which results in a reduction in the 
lateral acceleration, Ay, because Ay = V\2\/R, 
where V is the vehicle speed, and R is the radius of curvature of 
vehicle path. However, lateral acceleration was found to be less 
favorable than a ``normalized'' calculation, lateral acceleration 
ratio, developed from the vehicle's lateral acceleration measured 
during the maneuver because the lateral acceleration alone does not 
account for different stability thresholds among different vehicles. 
The agency believes that LAR has the most potential for an accurate 
measure of an ESC system to prevent rollovers. From the agency's 
testing, we have noted that LAR differentiates vehicles equipped with 
stability control systems as well as the potential determine and 
quantify roll instability. Lateral acceleration ratio is calculated by 
dividing the vehicle's lateral acceleration, corrected for roll angle, 
at a specified time after the completion of steer (COS) by the peak 
corrected lateral acceleration experienced during the second half of 
the sine maneuver (including the dwell period). The LAR at two time 
intervals after completion of steer is calculated to determine the 
change in lateral acceleration from the peak lateral acceleration. A 
reduction or decay in the lateral acceleration ratio at specified 
intervals after completion of steer is an indication that the stability 
control system has intervened to reduce the likelihood of vehicle 
rollover. The lateral acceleration ratio, LAR, is determined as 
follows:
[GRAPHIC] [TIFF OMITTED] TP23MY12.006

    Where A--y Veh (COS + 0.75 sec, + 1.5 sec,) is the 
corrected for roll lateral acceleration value at the specified time 
after the completion of steer, and Max Ay is the peak 
corrected lateral acceleration measured during the second half of the 
sine maneuver (including the dwell period), i.e., from time 1.0 second 
after the beginning of steer to the completion of steer.
    In developing the performance requirements for light vehicle ESC 
systems, several commenters requested that the agency include a 
definition for the term ``lateral acceleration'' and define a method 
for determining the lateral acceleration at the vehicle's center of 
gravity. In FMVSS No. 126, the agency uses the definition from SAE 
J670e, Vehicle Dynamics Terminology, which states, ``Lateral 
Acceleration means the component of the vector acceleration of a point 
in the vehicle perpendicular to the vehicle x axis (longitudinal) and 
parallel to the road plane.'' This definition was carried over, 
effectively unchanged, to the more recent revision of SAE's Vehicle 
Dynamics Terminology, SAE J670--200801. The agency is proposing to use 
the same definition of lateral acceleration for this standard as was 
used in FMVSS No. 126.
    The agency's research also looked at wheel lift measurement as a 
possible performance measure. Wheel lift is the most intuitive 
performance measure we considered because wheel lift precedes all 
rollovers. Wheel lift is considered to be lift that is two inches or 
greater, which occurs for any wheel of the vehicle, including the 
control trailer for the tractor during a test. One challenge with using 
wheel lift is that it does not necessarily indicate that rollover is 
imminent. For example, certain vehicle suspension designs are likely to 
cause wheel lift during severe cornering maneuvers, and also non-
uniform test surfaces can cause brief instances of wheel lift.
    Therefore, the agency proposes evaluating vehicle roll stability 
performance by calculating the LAR at 0.75 seconds and at 1.5 seconds 
after the completion of steer. The two performance criteria are 
described below:
     From data collected from each SWD maneuver executed, a 
vehicle equipped with a stability control system must have a LAR of 30 
percent or less 0.75 seconds after completion of steer. This

[[Page 30796]]

LAR will be calculated from the vehicle's lateral acceleration, 
corrected for roll angle, at its center of gravity position.
     From data collected from each SWD maneuver executed, a 
vehicle equipped with stability control must have a LAR of 10 percent 
or less at 1.5 seconds after completion of steer. This LAR will be 
calculated from the vehicle's lateral acceleration, corrected for roll 
angle, at its center of gravity position.
    The performance criteria mean that 0.75 seconds after the 
completion of the steering input, the corrected lateral acceleration 
must not exceed 30 percent of the maximum lateral acceleration recorded 
during the steering maneuver, and at 1.5 seconds after the completion 
of the steering input, the lateral acceleration must not exceed 10 
percent of the maximum lateral acceleration recorded during the 
steering maneuver. The agency believes that these criteria represent an 
appropriate stability threshold. NHTSA's research indicates that an ESC 
system's ability to maintain an LAR above these criteria would provide 
an acceptable probability that the vehicle would remain stable and that 
a level of LAR above these criteria would result in a high probability 
of the vehicle becoming unstable.
(b) Yaw Stability Performance
    The yaw rate ratio is a performance metric used to evaluate the 
ability of a vehicle's ESC system to prevent yaw instability. The YRR 
expresses the lateral stability criteria for the sine with dwell test 
to measure how quickly the vehicle stops turning, or rotating about its 
vertical axis, after the steering wheel is returned to the straight-
ahead position. A vehicle that continues to turn or rotate about its 
vertical axis for an extended period after the steering wheel has been 
returned to a straight-ahead position is most likely experiencing 
oversteer, which is what ESC is designed to prevent. The lateral 
stability criterion, expressed in terms of YRR, is the percent of peak 
yaw rate that is present at designated times after completion of steer.
    The yaw rate ratio, YRR, is determined as follows:
    [GRAPHIC] [TIFF OMITTED] TP23MY12.007
    
    Where [Psi]Vehicle (COS + 0.75 sec, + 1.5 sec) is yaw 
rate value at a specified time after the completion of steer, and Max 
[Psi]Vehicle is the maximum yaw rate measured during the 
second half of the sine maneuver including the dwell period from time 
1.0 second after the beginning of steer until the completion of steer 
during each maneuver.
    This performance metric is identical to the metric used in the 
light vehicle ESC system performance requirement in FMVSS No. 126. We 
believe that this metric is equally applicable to truck tractors and 
large buses, though it is calculated at different time intervals after 
the completion of steer.
    Therefore, the agency proposes to evaluate yaw stability 
performance by calculating the YRR at 0.75 seconds and at 1.5 seconds 
after the completion of steer. The two performance criteria are 
described below:
     From data collected from each 45-mph SWD maneuver 
executed, a vehicle equipped with a stability control system must have 
a YRR of 40 percent or less 0.75 seconds after completion of steer.
     From data collected from each 45-mph SWD maneuver 
executed, a vehicle equipped with stability control must have a YRR of 
15 percent or less at 1.5 seconds after completion of steer.
    The performance criteria mean that 0.75 seconds after the 
completion of the steering, the yaw rate must not exceed 40 percent of 
the peak yaw rate recorded during the second half of the sine maneuver 
including the dwell period, and at 1.5 seconds after the completion of 
the steering input, the yaw rate must not exceed 15 percent of the peak 
yaw rate recorded. The agency believes that these criteria represent an 
appropriate stability threshold. NHTSA's research indicates that an ESC 
system's ability to maintain an YRR above these criteria would provide 
an acceptable probability that the vehicle would remain stable and that 
a level of YRR above these criteria would result in a high probability 
of the vehicle becoming unstable.
(c) Lateral Displacement
    Lateral displacement is a performance metric used to evaluate the 
responsiveness of a vehicle, which relates to its ability to steer 
around objects. Stability control intervention has the potential to 
significantly increase the stability of the vehicle in which it is 
installed. However, we believe that these improvements in vehicle 
stability should not come at the expense of poor lateral displacement 
in response to the driver's steering input.
    A hypothetical way to pass a stability control performance test 
would be to make either the vehicle or its stability control system 
intervene simply by making the vehicle poorly responsive to the speed 
and steering inputs required by the test. An extreme example of this 
potential lack of responsiveness would occur if an ESC system locked 
both front wheels as the driver begins a severe avoidance maneuver that 
might lead to vehicle rollover. Front wheel lockup would create an 
understeer condition in the vehicle, which would result in the vehicle 
plowing straight ahead and colliding with an object the driver was 
trying to avoid. It is very likely that front wheel lockup would reduce 
the roll instability of the vehicle since the lateral acceleration 
would be reduced. This is clearly, however, not a desirable compromise.
    Because a vehicle that simply responds poorly to steering commands 
may be able to meet the proposed stability criteria, a minimum 
responsiveness criterion is also proposed for the SWD test. Using a 
lateral displacement metric to measure responsiveness ensures that the 
vehicle responds to an initial steering input to avoid an obstacle. 
This metric was chosen because it is objective, easy to measure, has 
good discriminatory capability, and has a direct relation to obstacle 
avoidance.
    The proposed lateral displacement criterion is that a truck tractor 
equipped with stability control must have a lateral displacement of 7 
feet or more at 1.5 seconds from the beginning of steer, measured 
during the sine with dwell maneuver. For a bus, the proposed 
performance criterion is a lateral displacement of 5 feet or more at 
1.5 seconds after the beginning of steer. The lateral displacement 
criteria is less for a bus because a large bus has a longer wheelbase 
than a truck tractor and higher steering ratio, which makes it less 
responsive than a truck tractor. The value will be calculated from the 
double integral with respect to time of the measurement of the 
corrected for roll lateral acceleration at the vehicle center of 
gravity, as expressed by the formula:
Lateral Displacement = [int][int]AyCG dt

    Where: AyCG is the corrected for roll lateral 
acceleration at the center of gravity height of the vehicle

[[Page 30797]]

    This is the same performance metric used in FMVSS No. 126. 
Furthermore, the vehicle would be required pass this requirement during 
the every execution the SWD maneuver where the steering wheel angle is 
0.7A or greater.
3. Alternative Test Maneuvers Considered
    We have considered other test maneuvers besides the sine with dwell 
test. The SWD maneuver was tentatively selected over the other 
maneuvers discussed above and below because our research demonstrates 
that it has the most optimal set of characteristics, including the 
severity of the test, repeatability and reproducibility of results, and 
the ability to address rollover, lateral stability, and responsiveness.
    The agency's research initially focused on developing the ramp 
steer maneuver to evaluate the roll stability performance and the sine 
with dwell maneuver to evaluate the yaw stability performance. However, 
after additional testing, we were able to develop test parameters for 
the sine with dwell maneuver so that both roll stability and yaw 
stability could be evaluated using a single loading condition and test 
maneuver. The sine with dwell maneuver has typically been used to 
evaluate only the yaw instability of a vehicle. The agency has 
previously used a lightly loaded vehicle weight condition for such 
evaluations where the lightly loaded condition and the resulting lower 
CG height were much more likely to cause vehicle directional loss-of-
control as opposed to rollover. In the light vehicle ESC standard, the 
sine with dwell maneuver is used to evaluate only yaw instability, not 
roll instability, with the vehicle loaded to LLVW only but not to GVWR. 
Given the different dynamics of heavy vehicles when compared to light 
vehicles, NHTSA evaluated several loading conditions and found that a 
loading condition which equals 80 percent of the tractor's GVWR enables 
us to evaluate roll instability as well as yaw instability.
    The number of tests that would be needed to cover all likely 
vehicle operational conditions for varying vehicle designs is 
potentially large, and many tests (particularly those using low 
friction surfaces) may not be sufficiently repeatable for an objective 
performance requirement. Our testing indicates that the SWD maneuver is 
sufficiently severe to ensure that nearly all vehicles without ESC 
would not be able to comply with the proposed performance requirements. 
For example, the vehicles we tested without ESC either had wheel lift 
or spun out during the SWD maneuver. Hence, a vehicle that avoids loss 
of control according to our objective lateral acceleration and yaw rate 
decay definitions demonstrates that it has an ESC system typical of 
today's technology and would have safety benefits.
    In addition to our test results, the agency thoroughly evaluated 
the test vehicles and test data submitted by EMA and others to the 
agency. EMA provided information on one tractor that appeared to 
satisfy the agency's proposed SWD performance criteria without a 
stability control system. After careful review of this data, we do not 
believe this fact means the test has no value.\43\ It is possible that 
there are currently truck tractors or large buses sold today that are 
exceptionally yaw stable, even in a severe maneuver such as a double 
lane change, which the SWD maneuver is designed to simulate. When 
evaluating light vehicles, the agency noted that there was a very small 
number of vehicles that were stable enough without a stability control 
system to pass our performance criteria without an ESC system. 
Therefore, the existence of vehicles that could pass the proposed SWD 
test without a stability control system simply indicates that it would 
take many tests to cover all potential instability scenarios across 
varying vehicle designs in order to design a perfect test regime, as 
discussed earlier. Such a complex test regime would require excessive 
costs to manufacturers to ensure compliance and excessive costs to the 
agency to determine and enforce compliance.
---------------------------------------------------------------------------

    \43\ As discussed earlier, EMA's testing of Vehicle J used a 
control trailer with a wider track width and a lower deck and used 
ballast that resulted in a lower vehicle center of gravity than used 
by NHTSA's researchers. Each of these differences caused EMA's 
combination vehicle to be more stable than NHTSA's during testing.
---------------------------------------------------------------------------

    We recognize that manufacturers may wish to base their 
certification of compliance with this proposed standard on their 
vehicles' performance in NHTSA's proposed test maneuvers. If 
manufacturers intend to conduct the maneuvers proposed by the agency, 
they may need to make additional investments in their facilities or 
have their certification testing performed at a contractor's facility. 
However, we believe some manufacturers may have already made these 
investments, and others would make similar investments as they develop 
and validate ESC systems for their vehicles. This is based on our 
understanding of the maneuvers used by the heavy-vehicle industry for 
ESC system development and validation, some of which include variations 
of the agency's proposed maneuver.
    We also recognize that, over time, manufacturers will be able to 
develop other methods for certifying compliance with the proposed 
standard. For example, manufacturers can develop computer models or 
simulations to demonstrate ESC system performance. However, we 
recognize that these alternative methods may not be suitable for 
atypical vehicles that are custom-built for customers. We seek comment 
on the issues surrounding manufacturers' certification of compliance 
including the assumptions made regarding manufacturers' current and 
future test facilities, the methods used by manufacturers to validate 
ESC system performance, the ability of manufacturers to use other 
methods (such as computer modeling, simulation, or alternative test 
maneuvers) to certify compliance, the cost of certification, and the 
issues surrounding certification of atypical truck tractors.
    Below, we discuss the alternative test maneuvers that were 
considered and what we considered to be acceptable performance criteria 
for each test. We also discuss why we are choosing the SWD maneuver for 
compliance testing in lieu of each of these maneuvers. We invite 
comment on each of these test maneuvers, including whether they should 
be used instead of, or along with, the proposed compliance test 
maneuvers.
(a) Characterization Maneuver
    While NHTSA has conducted extensive testing using the SIS maneuver, 
we believe that alternative methods may be used to determine the 
steering wheel angle needed to achieve 0.5g of lateral acceleration at 
30 mph. For example, a test based on the SAE J266 circle test may yield 
a similar steering wheel angle without requiring the track space 
necessary to conduct the SIS maneuver. The steering wheel angle that 
produces 0.5g of lateral acceleration at 30 mph may be above the ESC 
system's activation threshold for some vehicles, making it impractical 
to conduct a direct measurement of the steering wheel angle. The agency 
seeks comment on the feasibility of an alternative characterization 
test based upon the SAE J266 circle test.
(b) Roll Stability Test Maneuvers
    To evaluate roll instability, we have considered two alternative 
roll stability test maneuvers--the J-turn and the ramp steer maneuver. 
The two tests are similar in that both maneuvers require the tested 
vehicle to be driven at a

[[Page 30798]]

constant speed and then the vehicle is turned in one direction for a 
certain period of time. The test speed and the severity of the turn are 
designed to cause a test vehicle to approach or exceed its roll 
stability threshold such that, without a stability control system, the 
vehicle would exhibit signs of roll instability. Both tests would be 
performed with the tractor loaded to its GVWR. Furthermore, we would 
not expect a vehicle that could pass one test to fail the other.
    The most notable difference between the J-turn and the RSM 
maneuvers is that the J-turn is a path-following maneuver. That is, it 
is performed on a fixed path curve. In contrast, the RSM maneuver is a 
non-path-following maneuver that is performed with a fixed steering 
wheel input. For example, during the agency's and EMA's testing, the J-
turn maneuver was performed on a 150-foot radius curve. In contrast, 
the RSM is performed based on a steering wheel angle derived from the 
SIS test. We would expect that, with the RSM, the radius of the curve 
would be close to the fixed radius used in the J-turn maneuver. 
However, in the RSM, the driver would not have to make adjustments and 
corrections to steering to maintain the fixed path.
    When comparing the J-turn to the RSM, the agency considers the RSM 
to be a preferable test maneuver because the RSM maneuver can be 
performed with an automated steering wheel controller. Because the J-
turn is a path-following maneuver, a test driver must constantly make 
adjustments to the steering input for the vehicle to remain in the lane 
throughout the test maneuver. Moreover, driver variability could be 
introduced from test to test based upon minor variations in the timing 
of the initial steering input and the position of the test vehicle in 
the lane.
    In addition, the RSM appears to be more consistent because it 
involves a fixed steering wheel angle rather than a fixed path. There 
is negligible variability based on the timing of the initial steering 
input because the test is designed to begin at the initiation of 
steering input, rather than the vehicle's position on a track. 
Moreover, an automated steering wheel controller can more precisely 
maintain the required steering wheel input than a driver can. 
Therefore, we tentatively conclude that the RSM is more consistent and 
more repeatable than the J-turn, which is critical for agency 
compliance testing purposes.
    Notwithstanding the above observations, we recognize that many 
manufacturers perform NHTSA's compliance tests in order to certify that 
their vehicles comply with NHTSA's safety standards. We also recognize 
that, over time, manufacturers are likely to use other methods such as 
simulation, modeling, etc., to determine compliance with Federal Motor 
Vehicle Safety Standards. In this regard, we observe that, because the 
J-turn and the ramp steer maneuvers are so similar, manufacturers may 
be able to determine compliance with a stability control standard by 
using the J-turn maneuver even if the agency ultimately decides to use 
the RSM for compliance testing. Thus, if a manufacturer sought to 
certify compliance based upon performance testing, a manufacturer would 
not necessarily need to perform compliance testing with an automated 
steering controller.
    In considering the RSM test conditions, the agency looked to its 
test data and the data submitted by EMA. Data analysis indicated that 
the RSM test performed from at an initial speed of 30 mph is sufficient 
to demonstrate effective stability control performance for truck 
tractors. At GVWR, the tested buses were observed to have different 
speed thresholds at which wheel lift occurred and stability control 
initially activated. Without stability control, buses were observed to 
produce wheel lift between 35 and 39 mph in the RSM, compared to 
tractors, which ranged from 28 to 30 mph. Large bus stability control 
systems initially activated at speeds greater than 30 mph in the RSM, 
which was higher than the 26 mph observed with tractors. In light of 
these differences, an initial speed of 36 mph was selected for buses to 
ensure an appropriate level of test severity and that stability control 
would intervene.
    Another issue in conducting the RSM is whether to use fixed rate 
steering or to steer at a rate such that the full steering input is 
reached in a fixed time. Using fixed rate steering, the steering wheel 
is turned a 175 degrees per second until the desired steering wheel 
angle is reached. If a vehicle with a lower steering wheel angle input, 
such as a short wheelbase 4x2 tractor, is tested using this steering 
method, the desired steering wheel angle would be reached relatively 
quickly after the initial steering input. In contrast, for a longer 
wheelbase truck or a large bus, the desired steering wheel angle would 
be reached relatively slowly after the initial steering input. This 
results in a more severe test for vehicles with a lower steering wheel 
angle because the predicted lateral acceleration of 0.5g would be 
reached more quickly than for vehicles with a higher steering wheel 
angle. In an extreme case with an exceptionally large steering wheel 
angle, such as a bus with a long wheelbase the system may activate 
before the full steering wheel is input.
    Using a fixed-time steering input, we would program the steering 
wheel controller to reach the desired steering wheel angle in exactly 
1.5 seconds using a constant steering rate, which was derived from the 
manually steered 150-foot J-turn maneuver. Using this steering method 
would prevent the RSM results from varying with steering wheel angle 
input. We are requesting comment as to whether fixed-rate steering or 
fixed-time steering is a preferable manner for conducting the RSM.
    The RSM would use a similar, but not identical lateral acceleration 
ratio performance metric to evaluate roll stability. As with the SWD 
maneuver, the LAR used in the RSM would indicate that the stability 
control system is applying selective braking to lower lateral 
acceleration experienced during the steering maneuver. In the SWD 
maneuver, the LAR is the ratio of the lateral acceleration at a fixed 
point in time to the peak lateral acceleration during the period from 
one second after the beginning of steer to the completion of steer. In 
contrast, the LAR metric we would use for the RSM would be the ratio of 
the lateral acceleration at a fixed point in time to the lateral 
acceleration at the end of ramp input, which is the moment at which the 
steering wheel angle reaches the target steering wheel angle for the 
test. Also, in contrast to the SWD maneuver, the LAR measurements for 
the RSM would be taken at a time when the steering wheel is still 
turned. This means that, although the SWD maneuver is a more dynamic 
steering maneuver, the LAR criteria for the RSM would be greater than 
the LAR criteria for the SWD maneuver.
    The performance criteria for the RSM would depend on whether fixed-
rate steering or fixed-time steering input is used. For truck tractors 
and large buses using fixed-time steering input, we would expect that 
the LAR would be less than 1.05 two seconds after the end of ramp input 
and less than 0.8 three seconds after the end of ramp input. For truck 
tractors tested using fixed-rate steering inputs, we would expect that 
the LAR would be less than 1.1 two seconds after the end of ramp input 
(the point in time at which the target steering wheel angle is reached) 
and less than 0.9 three seconds after the end of ramp input. For buses 
using fixed-rate steering, we would expect that the LAR would be less 
than 1.0 two seconds after the end of ramp input and less than 0.7 
three seconds after the end of ramp input. The performance criteria for 
large

[[Page 30799]]

buses would be lower because, as we stated above, when using fixed-rate 
steering input, the longer wheelbases of buses cause the maneuver to be 
less dynamic.
    In a March 2012 submission, which was revised with additional 
details in April 2012, EMA suggested that NHTSA use different test 
speeds and performance criteria for the J-turn maneuver.\44\ EMA 
suggested that a test speed that is 30 percent greater than the minimum 
speed at which the ESC system intervenes with engine, engine brake, or 
service brake control. Instead of measuring LAR, EMA suggested that, 
during three out of four runs, the vehicle would be required to 
decelerate at a minimum deceleration rate. NHTSA has conducted testing 
on variations of this EMA maneuver, and we plan to conduct further 
testing. We request comments on EMA's suggested test procedure and 
performance criteria for the J-turn maneuver.
---------------------------------------------------------------------------

    \44\ Docket No. NHTSA-2010-0034-0032; Docket No. NHTSA-2010-
0034-0040.
---------------------------------------------------------------------------

    Based on our testing to date, the agency tentatively concludes that 
the RSM is a preferable test to the J-run to demonstrate a stability 
control system's ability to prevent roll instability. However, as 
discussed in greater detail below, in order to reduce the number of 
compliance tests that the agency and those manufacturers who choose to 
demonstrate compliance by conducting the agency's performance tests 
must perform, the agency proposes using on test maneuver, the SWD, to 
demonstrate both roll and yaw stability performance. Although we are 
proposing to use the SWD maneuver for evaluating roll stability, we 
request comment on issues related to the RSM and J-turn tests, 
including test conditions, steering input method, and performance 
criteria.
(c) Yaw Stability Test Maneuvers
    After evaluating several maneuvers on different surfaces, the 
agency was unable to develop any alterative performance-based dynamic 
yaw test maneuvers that were repeatable enough for compliance testing 
purposes. Bendix described two maneuvers intended to evaluate the yaw 
stability of tractors.\45\ However, neither of these test maneuvers was 
developed to a level that would make them suitable for the agency to 
consider using as yaw performance tests.
---------------------------------------------------------------------------

    \45\ These tests are discussed in section IV.E.3. See Docket No. 
NHTSA-2010-0034-0037 and Docket No. NHTSA-2010-0034-0038.
---------------------------------------------------------------------------

    In July 2009, EMA provided research information on several yaw 
stability test maneuvers.\46\ One of these maneuvers was the SWD on dry 
pavement that is similar to what is proposed in this notice. The second 
maneuver was an SWD maneuver conducted on wet Jennite. The third 
maneuver was a ramp with dwell maneuver on wet Jennite.\47\ EMA did not 
provide any test data on the last two maneuvers. Thus, we considered 
them to be concepts rather than fully developed maneuvers that we could 
consider using for yaw stability testing.
---------------------------------------------------------------------------

    \46\ Docket No. NHTSA-2010-0034-0035.
    \47\ This ramp with dwell maneuver is the same one identified by 
Bendix referenced in the prior paragraph and in section IV.E.3.
---------------------------------------------------------------------------

    We received no other alternative yaw performance tests from 
industry until EMA's submission of Vehicle J data in late 2010.\48\ EMA 
suggested using a wet Jennite drive through test maneuver demonstrated 
yaw performance in a curve on a low friction surface. The maneuver is 
based upon a maneuver the agency currently conducts on heavy vehicles 
to verify stability and control of antilock braking systems while 
braking in a curve. As part of the test, a vehicle is driven into a 
500-foot radius curve with a low-friction wet Jennite surface at 
increasing speeds to determine the maximum drive-through speed at which 
the driver can keep the vehicle within a 12-foot lane. As with the J-
turn, we are concerned about the repeatability of this test maneuver 
because of variability in the wet Jennite test surface and the driver's 
difficulty in maintaining a constant speed and steering input in the 
curve.
---------------------------------------------------------------------------

    \48\ Docket No. NHTSA-2010-0034-0022; Docket No. NHTSA-2010-
0034-0023.
---------------------------------------------------------------------------

    In a March 2012 submission, which was revised with additional 
details in April 2012, EMA provided information about another yaw 
stability test along with additional information on the J-turn 
maneuver.\49\ This maneuver would simulate a single lane change on a 
wet roadway surface. It would be conducted within a 4 meter (12 foot) 
wide path. The roadway condition would be a wet, low friction surface 
such as wet Jennite with a peak coefficient of friction of 0.5. The 
other test conditions (i.e., road conditions, burnish procedure, 
liftable axle position, and initial brake temperatures) would be 
similar to those proposed in this NPRM. In this maneuver, the truck 
would enter the path at progressively higher speeds to establish the 
minimum speed at which the ESC system intervenes and applies the 
tractor's brakes. The maneuver would then be repeated four times at 
that speed with the vehicle remaining within the lane at all times 
during the maneuver. EMA suggests, as a performance criterion, that 
during at least three of the four runs, the ESC system must provide a 
minimum level (presently unspecified) of differential braking. The 
agency has not had an opportunity to conduct testing of this maneuver, 
but we intend to do so to determine whether this is a viable 
alternative yaw stability test.
---------------------------------------------------------------------------

    \49\ Docket No. NHTSA-2010-0034-0032; Docket No. NHTSA-2010-
0034-0040.
---------------------------------------------------------------------------

    In light of the inability to develop a different performance-based 
yaw stability test, the agency is proposing to use the SWD test 
maneuver to evaluate yaw stability performance. Although we are 
proposing to use the SWD maneuver for evaluating yaw stability, we 
request comment on other yaw stability tests that could be suitable for 
performance testing and possible performance criteria for any such 
test. Furthermore, we specifically request comment on all aspects of 
EMA's yaw stability test discussed in its March and April 2012 
submissions, including the test conditions, test procedure, and 
possible performance criteria that would allow the agency to test both 
trucks and buses with this maneuver.
(d) Lack of an Understeer Test
    The SWD maneuver is designed to induce both roll and yaw responses 
from the vehicle being evaluated. However, the agency has no test to 
evaluate how the ESC responds when understeer is induced. The technique 
used by a stability control system for mitigating wheel lift, excessive 
oversteer or understeer conditions is to apply unbalanced wheel braking 
so as to generate moments (torques) to reduce lateral acceleration and 
to correct excessive oversteer or understeer. However, for a vehicle 
experiencing excessive understeer, if too much oversteering moment is 
generated, the vehicle may oversteer and spin out with obvious negative 
safety consequences. In addition, excessive understeer mitigation acts 
like an anti-roll stability control where it momentarily increases the 
lateral acceleration the vehicle can attain. Hence, too much understeer 
mitigation can create safety problems in the form of vehicle spin out 
or rollover.\50\
---------------------------------------------------------------------------

    \50\ EMA's testing of Vehicle J on the 500-foot wet Jennite 
curve shows understeer mitigation at maneuver entry speeds up to 34 
mph, but at 35 mph, the vehicle could not overcome understeer. See 
Docket No. NHTSA-2010-0034-0022; Docket No. NHTSA-2010-0034-0023. At 
these low levels of lateral acceleration, no adverse effects 
appeared to occur as a result of the understeer mitigation.
---------------------------------------------------------------------------

    During the testing to develop FMVSS No. 126, the agency concluded 
that understanding both what understeer mitigation can and cannot do is 
complicated, and that there are certain

[[Page 30800]]

situations where understeer mitigation could potentially produce safety 
disbenefits if not properly tuned. Therefore, the agency decided to 
enforce the requirements to meet the understeer criterion included in 
the ESC definition using a two-part process. First, the requirement to 
meet definitional criteria ensured that all had the hardware needed to 
limit vehicle understeer. Second, the agency required manufacturers to 
submit engineering documentation at the request of NHTSA's Office of 
Vehicle Safety Compliance to show that the system is capable of 
addressing vehicle understeer.
    Based on the agency's experience from the light vehicle ESC 
rulemaking and the lack of a suitable test to evaluate understeer 
performance, the agency is not proposing a test for understeer to 
evaluate ESC system performance for truck tractors and large buses. The 
agency requests comment on this NPRM's lack of a proposed understeer 
test.
4. ESC Malfunction Test
    During execution of a compliance test the agency proposes 
simulating several malfunctions to ensure the system and corresponding 
malfunction telltale provides the required warning to the vehicle 
operator. Malfunctions are generally simulated by disconnecting the 
power source to an ESC system component or disconnecting an electrical 
connection to or between ESC system components. Examples of simulated 
malfunctions might include the electrical disconnection of the sensor 
measuring yaw rate, lateral acceleration, steering wheel angle sensor, 
or wheel speed. When simulating an ESC system malfunction, the 
electrical connections for the telltale lamp would not be disconnected. 
Also, because a vehicle may require a driving phase to identify a 
malfunction, the vehicle would be driven for at least two minutes 
including at least one left and one right turning maneuver. A similar 
drive time exists in the FMVSS No. 126 test procedure.
    After a malfunction has been simulated and identified by the 
system, the system is restored to normal operation. The engine is 
started and the malfunction telltale is checked to ensure it has 
cleared.
5. Test Instrumentation and Equipment
    For the truck tractor and large bus stability control system 
research program, each test vehicle was fitted with specific 
instrumentation and equipment necessary to execute each test safely and 
to collect necessary performance data. The compliance test program 
proposed in this NPRM would use essentially the same equipment and a 
subset of the instrumentation. As was done for FMVSS No. 126, the 
agency proposes including in the regulatory text the basic design 
parameters for the automated steering machine, outriggers, and the 
control trailer because this test equipment and instrumentation can 
influence test vehicle performance. However, the proposed regulatory 
text does not include a list of the less critical test instrumentation 
used during the compliance test. The agency's common practice has been 
to provide instrumentation details, test instrumentation range, 
resolution, and accuracy for all the required instrumentation in the 
separate NHTSA Laboratory Test Procedure. Furthermore, the agency is 
aware that manufacturers and test facilities will be interested in 
knowing what instruments will be used for a compliance test program. 
The following table and corresponding discussions identify the critical 
equipment and instrumentation used by NHTSA's researchers and for the 
most part, the same or similar is proposed for use by NHTSA's Office of 
Vehicle Safety Compliance.

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

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

[[Page 30801]]

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

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

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

[[Page 30802]]

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

    \52\ The FMVSS No. 121 control trailer specifications, set forth 
in S6.1.10.2 and S6.1.10.3 of FMVSS No. 121 provide that the center 
of gravity of the ballast on the loaded control trailer be less than 
24 inches above the top of the tractor's fifth wheel and that the 
trailer have a single axle with a GAWR of 18,000 pounds and a 
length, measured from the transverse centerline of the axle to the 
centerline of the kingpin, of 258  6 inches.
---------------------------------------------------------------------------

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

[[Page 30803]]

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

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

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

[[Page 30804]]

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

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

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

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

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

[[Page 30805]]

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

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

Where:

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

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

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

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

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

G. Compliance Dates and Implementation Schedule

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

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

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

VI. Benefits and Costs

A. System Effectiveness

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

[[Page 30806]]

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

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

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

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

B. Target Crash Population

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

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

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

[[Page 30807]]

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

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

C. Benefits Estimate

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

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

[[Page 30808]]

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

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

D. Cost Estimate

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

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

[[Page 30809]]

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

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

E. Cost Effectiveness

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

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

F. Comparison of Regulatory Alternatives

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

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

[[Page 30810]]

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

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

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

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

VII. Public Participation

How do I prepare and submit comments?

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

How can I be sure that my comments were received?

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

How do I submit confidential business information?

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

[[Page 30811]]

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

Will the Agency consider late comments?

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

How can I read the comments submitted by other people?

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

VIII. Regulatory Analyses and Notices

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

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

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

B. Regulatory Flexibility Act

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

[[Page 30812]]

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

C. Executive Order 13132 (Federalism)

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

D. Executive Order 12988 (Civil Justice Reform)

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

E. Protection of Children From Environmental Health and Safety Risks

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

F. Paperwork Reduction Act

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

[[Page 30813]]

G. National Technology Transfer and Advancement Act

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

H. Unfunded Mandates Reform Act

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

I. National Environmental Policy Act

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

J. Plain Language

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

K. Regulatory Identifier Number (RIN)

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

L. Privacy Act

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

List of Subjects in 49 CFR Part 571

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

Proposed Regulatory Text

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

PART 571--FEDERAL MOTOR VEHICLE SAFETY STANDARDS

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

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

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

Sec.  571.5  Matter incorporated by reference.

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

[[Page 30814]]

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

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

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

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

    S1. Scope. This standard establishes performance and equipment 
requirements for electronic stability control (ESC) systems on heavy 
vehicles.
    S2. Purpose. The purpose of this standard is to reduce crashes 
caused by rollover or by directional loss-of-control.
    S3. Application. This standard applies to truck tractors and buses 
with a gross vehicle weight rating of greater than 11,793 kilograms 
(26,000 pounds). However, it does not apply to:
    (a) Any truck tractor or bus equipped with an axle that has a gross 
axle weight rating (GAWR) of 29,000 pounds or more;
    (b) Any truck tractor or bus that has a speed attainable in 2 miles 
of not more than 33 mph;
    (c) Any truck tractor that has a speed attainable in 2 miles of not 
more than 45 mph, an unloaded vehicle weight that is not less than 95 
percent of its gross vehicle weight rating (GVWR), and no capacity to 
carry occupants other than the driver and operating crew;
    (d) Any bus with fewer than 16 designated seating positions 
(including the driver);
    (e) Any bus with fewer than 2 rows of passenger seats that are 
rearward of the driver's seating position and are forward-facing or can 
convert to forward-facing without the use of tools;
    (f) School buses; and
    (g) Any urban transit buses sold for operation as a common carrier 
in urban transportation along a fixed route with frequent stops.
    S4. Definitions.
    Ackerman Steer Angle means the angle whose tangent is the wheelbase 
divided by the radius of the turn at a very low speed.
    Electronic stability control system or ESC system means a system 
that has all of the following attributes:
    (1) That augments vehicle directional stability by applying and 
adjusting the vehicle brake torques individually at each wheel position 
on at least one front and at least one rear axle of the vehicle to 
induce correcting yaw moment to limit vehicle oversteer and to limit 
vehicle understeer;
    (2) That enhances rollover stability by applying and adjusting the 
vehicle brake torques individually at each wheel position on at least 
one front and at least one rear axle of the vehicle to reduce lateral 
acceleration of a vehicle;
    (3) That is computer-controlled with the computer using a closed-
loop algorithm to induce correcting yaw moment and enhance rollover 
stability;
    (4) That has a means to determine the vehicle's lateral 
acceleration;
    (5) That has a means to determine the vehicle's yaw rate and to 
estimate its side slip or side slip derivative with respect to time;
    (6) That has a means to estimate vehicle mass or, if applicable, 
combination vehicle mass;
    (7) That has a means to monitor driver steering inputs;
    (8) That has a means to modify engine torque, as necessary, to 
assist the driver in maintaining control of the vehicle and/or 
combination vehicle; and
    (9) That, when installed on a truck tractor, has the means to 
provide brake pressure to automatically apply and modulate the brake 
torques of a towed semi-trailer.
    Initial brake temperature means the average temperature of the 
service brakes on the hottest axle of the vehicle immediately before 
any stability control system test maneuver is executed.
    Lateral acceleration means the component of the vector acceleration 
of a point in the vehicle perpendicular to the vehicle x axis 
(longitudinal) and parallel to the road plane.
    Oversteer means a condition in which the vehicle's yaw rate is 
greater than the yaw rate that would occur at the vehicle's speed as 
result of the Ackerman Steer Angle.
    Peak friction coefficient or PFC means the ratio of the maximum 
value of braking test wheel longitudinal force to the simultaneous 
vertical force occurring prior to wheel lockup, as the braking torque 
is progressively increased.
    Sideslip or side slip angle means the arctangent of the lateral 
velocity of the center of gravity of the vehicle divided by the 
longitudinal velocity of the center of gravity.
    Understeer means a condition in which the vehicle's yaw rate is 
less than the yaw rate that would occur at the vehicle's speed as 
result of the Ackerman Steer Angle.
    Yaw Rate means the rate of change of the vehicle's heading angle 
measure in degrees per second of rotation about a vertical axis through 
the vehicle's center of gravity.
    S5. Requirements. Each vehicle must be equipped with an ESC system 
that meets the requirements specified in S5 under the test conditions 
specified in S6 and the test procedures specified in S7 of this 
standard.
    S5.1 Required Equipment. Each vehicle to which this standard 
applies must be equipped with an electronic stability control system, 
as defined in S4.
    S5.2 System Operational Capabilities.
    S5.2.1 An electronic stability control system must be operational 
over the full speed range of the vehicle except at vehicle speeds less 
than 20 km/h (12.4 mph), when being driven in reverse, or during system 
initialization.
    S5.2.2 An electronic stability control system must remain capable 
of activation even if the antilock brake system or traction control is 
also activated.
    S5.3 Performance Requirements.
    S5.3.1 Slowly Increasing Steer Maneuver. During the slowly 
increasing steer test maneuver performed under the test conditions of 
S6 and the test procedure of S7.6, the vehicle with the ESC system 
enabled must satisfy the engine torque reduction criteria of S5.3.1.1.
    S5.3.1.1 The engine torque reduction when measured 1.5 seconds 
after the activation of the electronic stability control system must be 
at least 10 percent less than the engine torque requested by the 
driver.
    S5.3.2 Sine With Dwell Maneuver. During each sine with dwell 
maneuver performed under the test conditions of S6 and the test 
procedure of S7.10, the vehicle with the ESC system enabled must 
satisfy the roll stability criteria of S5.3.2.1 and S5.3.2.2, the yaw 
stability criteria of S5.3.2.3 and S5.3.2.4, and the responsiveness 
criterion of S5.3.2.5 during each of those tests conducted with a 
commanded steering wheel angle of 0.7A or greater, where A is the 
steering wheel angle computed in S7.6.2.
    S5.3.2.1 The lateral acceleration measured at 0.75 seconds after 
completion of steer of the sine with dwell steering input must not 
exceed 30 percent of the peak value of the lateral acceleration 
recorded during the 2nd half of the sine maneuver (including the dwell 
period), i.e., from time 1 second after the beginning of steer to the 
completion of steer during the same test run.
    S5.3.2.2 The lateral acceleration measured at 1.5 seconds after 
completion of steer of the Sine With

[[Page 30815]]

Dwell steering input must not exceed 10 percent of the peak value of 
the lateral acceleration recorded during the 2nd half of the sine 
maneuver (including the dwell period), i.e., from time 1 second after 
the BOS to the COS during the same test run.
    S5.3.2.3 The yaw rate measured at 0.75 seconds after completion of 
steer of the Sine With Dwell steering input must not exceed 40 percent 
of the peak value of the yaw rate recorded during the 2nd half of the 
sine maneuver (including the dwell period), i.e., from time 1 second 
after the BOS to the COS during the same test run.
    S5.3.2.4 The yaw rate measured at 1.5 seconds after completion of 
steer of the Sine With Dwell steering input must not exceed 15 percent 
of the peak value of the yaw rate recorded during the 2nd half of the 
sine maneuver (including the dwell period), i.e., from time 1 second 
after the BOS to the COS during the same test run.
    S5.3.2.5 The lateral displacement of the vehicle center of gravity 
with respect to its initial straight path must be at least 2.13 meters 
(7 feet) for each truck tractor and at least 1.52 meters (5 feet) for 
each bus when computed 1.5 seconds after the BOS.
    S5.3.2.5.1 The computation of lateral displacement is performed 
using double integration with respect to time of the measurement of 
lateral acceleration at the vehicle center of gravity, as expressed by 
the formula:

Lateral Displacement = [int][int] AyCG dt

    S5.3.2.5.2 Time t = 0 for the integration operation is the instant 
of steering initiation, known as the BOS.
    S5.4 ESC System Malfunction Detection. Each vehicle shall be 
equipped with an indicator lamp, mounted in front of and in clear view 
of the driver, which is activated whenever there is a malfunction that 
affects the generation or transmission of control or response signals 
in the vehicle's electronic stability control system.
    S5.4.1 The ESC malfunction telltale must illuminate only when a 
malfunction exists and must remain continuously illuminated for as long 
as the malfunction exists, whenever the ignition locking system is in 
the ``On'' (``Run'') position.
    S5.4.2 The ESC Malfunction telltale must be identified by the 
symbol shown for ``Electronic Stability Control System Malfunction'' or 
the specified words or abbreviations listed in Table 1 of Standard No. 
101 (49 CFR 571.101).
    S5.4.3 The ESC malfunction telltale must be activated as a check of 
lamp function either when the ignition locking system is turned to the 
``On'' (``Run'') position when the engine is not running, or when the 
ignition locking system is in a position between the ``On'' (``Run'') 
and ``Start'' that is designated by the manufacturer as a check 
position.
    S5.4.4 The ESC malfunction telltale need not be activated when a 
starter interlock is in operation.
    S5.4.5 The ESC malfunction telltale lamp must extinguish at the 
next ignition cycle after the malfunction has been corrected.
    S5.5 ESC System Technical Documentation. To ensure that a vehicle 
is equipped with an ESC system that meets the definition of ``ESC 
System'' in S4, the vehicle manufacturer must make available to the 
agency, upon request, the following documentation:
    S5.5.1 A system diagram that identifies all ESC system hardware. 
The diagram must identify what components are used to generate brake 
torques at each controlled wheel, determine vehicle lateral 
acceleration and yaw rate, estimate side slip or the side slip 
derivative, monitor driver steering inputs, and for a tractor, generate 
the towed vehicle brake torques.
    S5.5.2 A written explanation describing the ESC system basic 
operational characteristics. This explanation must include a discussion 
of the system's capability to apply brake torques at each wheel, how 
the system estimates vehicle mass, and how the system modifies engine 
torque during ESC system activation. The explanation must also identify 
the vehicle speed range and the driving phases (acceleration, 
deceleration, coasting, during activation of ABS or traction control) 
under which the ESC system can activate.
    S5.5.3 A logic diagram that supports the explanation provided in 
S5.5.2.
    S5.5.4 Specifically for mitigating, avoiding, and preventing 
vehicle rollover, oversteer, and understeer conditions, a discussion of 
the pertinent inputs to the computer or calculations within the 
computer and how its algorithm uses that information and controls ESC 
system hardware to limit these loss of control conditions.
    S6. Test Conditions. The requirements of S5 shall be met by a 
vehicle when it is tested according to the conditions set forth in the 
S6. On vehicles equipped with automatic brake adjusters, the automatic 
brake adjusters must remain activated at all times.
    S6.1 Ambient conditions.
    S6.1.1 The ambient temperature is between 7 [deg]C (45[emsp14] 
[deg]F) and 40 [deg]C (104[emsp14] [deg]F).
    S6.1.2 The maximum wind speed is no greater than 5 m/s (11mph).
    S6.2 Road test surface.
    S6.2.1 The tests are conducted on a dry, uniform, solid-paved 
surface. Surfaces with irregularities and undulations, such as dips and 
large cracks, are unsuitable.
    S6.2.2 The road test surface produces a peak friction coefficient 
(PFC) of 0.9 when measured using an American Society for Testing and 
Materials (ASTM) E1136-93 (Reapproved 2003) standard reference test 
tire (incorporated by reference,, in accordance with ASTM Method E 
1337-90 (Reapproved 2002), at a speed of 64.4 km/h (40 mph), without 
water delivery (both documents incorporated by reference, see Sec.  
571.5).
    S6.2.3 The test surface has a consistent slope between 0% and 1%.
    S6.3 Vehicle conditions.
    S6.3.1 The ESC system is enabled for all testing, except for the 
ESC Malfunction test in S7.11.
    S6.3.2 Test Weight.
    S6.3.2.1 Truck tractors. The combined total weight of the truck 
tractor and control trailer (specified in S6.3.4) is 80 percent of the 
tractor GVWR. The tractor is loaded with the fuel tanks filled to at 
least 75 percent capacity, test driver, test instrumentation, and a 
ballasted control trailer with outriggers. Center of gravity of all 
ballast on the control trailer is located directly above the kingpin. 
The load distribution on non-steer axles is adjusted so that it is 
proportional to the tractor's respective rear axles GAWRs by adjusting 
the fifth wheel position, if adjustable. If the fifth wheel of the 
truck tractor cannot be adjusted without exceeding a GAWR, ballast is 
reduced so that axle load is equal to or less than the GAWR, 
maintaining load proportioning as close as possible to specified 
proportioning.
    S6.3.2.2 Buses. A bus is loaded to a simulated multi-passenger 
configuration. For this configuration the bus is loaded with the fuel 
tanks filled to at least 75 percent capacity, test driver, test 
instrumentation and simulated occupants in each of the vehicle's 
designated seating positions. The simulated occupant loads are attained 
by securing a 68-kg (150-lb) water dummy in each of the test vehicle's 
designated seating positions without exceeding the vehicle's GVWR and 
each axle's GAWR. If any rating is exceeded the ballast load is reduced 
until the respective rating or ratings are no longer exceeded.
    S6.3.3 Transmission selector position. The transmission selector

[[Page 30816]]

control is in a forward gear during all maneuvers.
    S6.3.4 Control Trailer.
    S6.3.4.1 The control trailer is an unbraked flatbed semi-trailer 
that has a single axle with a GAWR of 8,165 kilograms (18,000 pounds) 
and a length of 655 + 15 cm (258 + 6 inches) when measured from the 
transverse centerline of the axle to the centerline of the kingpin.
    S6.3.4.2 The center of gravity height of the ballast on the loaded 
control trailer is less than 61 cm (24 inches) above the top of the 
tractor's fifth wheel.
    S6.3.5 Tires. The vehicle is tested with the tires installed on the 
vehicle at time of initial vehicle sale. The tires are inflated to the 
vehicle manufacturer's recommended cold tire inflation pressure(s) 
specified on the vehicle's certification label or the tire inflation 
pressure label.
    S6.3.6 Outrigger. An outrigger is used for testing each vehicle. 
The outrigger is designed with a maximum weight of 726 kg (1,600 lb), 
excluding mounting fixtures.
    S6.3.7 Automated steering machine. A steering machine programmed to 
execute the required steering pattern is used during the slowly 
increasing steer and sine with dwell maneuvers. The steering machine is 
capable of supplying steering torques between 40 to 60 Nm (29.5 to 44.3 
lb-ft). The steering machine is able to apply these torques when 
operating with steering wheel velocities up to 1200 degrees per second.
    S6.3.8 Truck Tractor Anti-jackknife System. The truck tractor is 
equipped with anti-jackknife cables that allow a minimum articulation 
angle of 45 degrees between the tractor and the control trailer.
    S6.3.9 Special drive conditions. A vehicle equipped with an 
interlocking axle system or a front wheel drive system that is engaged 
and disengaged by the driver is tested with the system disengaged.
    S6.3.10 Liftable axles. A vehicle with a liftable axle is tested 
with the liftable axle down.
    S6.3.11 Initial brake temperature. The initial brake temperature is 
not less than 65 [deg]C (150 [deg]F) and not more than 204 [deg]C (400 
[deg]F).
    S6.3.12 Thermocouples. The brake temperature is measured by plug-
type thermocouples installed in the approximate center of the facing 
length and width of the most heavily loaded shoe or disc pad, one per 
brake. A second thermocouple may be installed at the beginning of the 
test sequence if the lining wear is expected to reach a point causing 
the first thermocouple to contact the rubbing surface of a drum or 
rotor. The second thermocouple is installed at a depth of 0.080 inch 
and located within 1.0 inch circumferentially of the thermocouple 
installed at 0.040 inch depth. For center-grooved shoes or pads, 
thermocouples are installed within 0.125 inch to 0.250 inch of the 
groove and as close to the center as possible.
    S6.4 Selection of compliance options. Where manufacturer options 
are specified, the manufacturer shall select the option by the time it 
certifies the vehicle and may not thereafter select a different option 
for the vehicle. Each manufacturer shall, upon request from the 
National Highway Traffic Safety Administration, provide information 
regarding which of the compliance options it has selected for a 
particular vehicle or make/model.
    S7. Test Procedure.
    S7.1 Tire inflation. Inflate the vehicle's tires to the cold tire 
inflation pressure(s) provided on the vehicle's certification label or 
tire information label.
    S7.2 Telltale lamp check. With the vehicle stationary and the 
ignition locking system in the ``Lock'' or ``Off'' position, activate 
the ignition locking system to the ``On'' (``Run'') position or, where 
applicable, the appropriate position for the lamp check. The ESC system 
must perform a check of lamp function for the ESC malfunction telltale, 
as specified in S5.3.3.
    S7.3 Mass Estimation Cycle. While driving in a straight line, one 
stop is performed from a speed of 65 km/h (40 mph), with a target 
longitudinal deceleration between 0.3-0.4g.
    S7.4 Tire Conditioning. Condition the tires using the following 
procedure to wear away mold sheen and achieve operating temperature 
immediately before beginning the Brake Conditioning, SIS and SWD 
maneuver test runs.
    S7.4.1 The test vehicle is driven around a circle 46 meters (150 
feet) in radius at a speed that produces a lateral acceleration of 
approximately 0.1g for two clockwise laps followed by two 
counterclockwise laps.
    S7.5 Brake Conditioning. Conditioning and warm-up the vehicle 
brakes must be completed before and during execution of the SIS and SWD 
maneuver test runs.
    S7.5.1 Prior to executing the first series of SIS maneuvers for a 
test vehicle, the brakes are burnished according to the procedure in 
S6.1.8 of Standard No. 121, Air brake systems.
    S7.5.2 After the brakes are burnished in accordance with S7.5.1, 
initiate the vehicle compliance test according to S7.6. For a vehicle 
on which a full FMVSS No. 121 compliance test was performed, 
immediately prior to executing any slowly increasing steer or sine with 
dwell maneuvers, the brakes are burnished using 40 brake application 
snubs from a speed of 64 km/h (40 mph) to a speed of 32 km/h (20 mph), 
with a target deceleration of approximately 0.3g. After each brake 
application, accelerate to 64 km/h (40 mph) and maintain that speed 
until making the next brake application at a point 1 mile from the 
initial point of the previous brake application. At end of the 40 
snubs, the hottest brake temperature is confirmed to be within the 
temperature range of 65 [deg]C-204 [deg]C (150 [deg]F-400 [deg]F). If 
the hottest brake temperature is above 204 [deg]C (400 [deg]F) a cool 
down period is performed until the hottest brake temperature is 
measured within that range. If the hottest brake temperature is below 
65 [deg]C (150 [deg]F) individual brake stops shall be repeated to 
increase any one brake temperature to within the target temperature 
range of 65 [deg]C-204[deg]C (150 [deg]F-400 [deg]F) before the subject 
maneuver can be performed.
    S7.6 Slowly Increasing Steer Test. The vehicle is subjected to two 
series of runs of the slowly increasing steer test using a constant 
vehicle speed of 48.3  1.6 km/h (30.0  1.0 mph) 
and a steering pattern that increases by 13.5 degrees per second until 
ESC system activation is confirmed. Three repetitions are performed for 
each test series. One series uses counterclockwise steering, and the 
other series uses clockwise steering. During each run ESC activation is 
required for the Engine Torque Reduction test and is confirmed as 
specified in S7.7.
    S7.6.1 The slowly increasing steer maneuver sequence is started 
using a commanded steering wheel angle of 270 degrees. If ESC 
activation did not occur during the maneuver then the commanded 
steering wheel angle is increased by 270 degree increments up to the 
vehicle's maximum allowable steering angle or until ESC activation is 
confirmed.
    S7.6.2 From the slowly increasing steer tests, the quantity ``A'' 
is determined. ``A'' is the steering wheel angle in degrees that is 
estimated to produce a lateral acceleration of 0.5g for the test 
vehicle. Utilizing linear regression on the lateral acceleration data 
recorded between 0.05g and 0.3g, and then linear extrapolation out to a 
lateral acceleration value of 0.5g, A is calculated, to the nearest 0.1 
degrees, from each of the six satisfactory slowly increasing steer 
tests. If ESC activation occurs prior to the vehicle experiencing

[[Page 30817]]

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

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

[[Page 30818]]

normal operation, activate the ignition system to the ``Start'' 
position and start the engine. Verify that the telltale has 
extinguished.
    S7.12 Post Data Processing--Calculations for Performance Metrics. 
Engine torque reduction, lateral acceleration and yaw rate decay 
calculations, and lateral responsiveness checks must be processed 
utilizing the following techniques:
    S7.12.1 Raw steering wheel angle data is filtered with a 12-pole 
phaseless Butterworth filter and a cutoff frequency of 10Hz. The 
filtered data is then zeroed to remove sensor offset utilizing static 
pretest data.
    S7.12.2 Raw yaw, pitch and roll rate data is filtered with a 12-
pole phaseless Butterworth filter and a cutoff frequency of 3 Hz. The 
filtered data is then zeroed to remove sensor offset utilizing static 
pretest data.
    S7.12.3 Raw lateral acceleration data is filtered with a 12-pole 
phaseless Butterworth filter and a cutoff frequency of 6Hz. The 
filtered data is then zeroed to remove sensor offset utilizing static 
pretest data. The lateral acceleration data at the vehicle center of 
gravity is determined by removing the effects caused by vehicle body 
roll and by correcting for sensor placement via use of coordinate 
transformation. For data collection, the lateral accelerometer shall be 
located as close as possible to the position of the vehicle's 
longitudinal and lateral centers of gravity.
    S7.12.4 Raw vehicle speed data is filtered with a 12-pole phaseless 
Butterworth filter and a cutoff frequency of 2 Hz.
    S7.12.5 Left and right side ride height data is filtered with a 
0.1-second running average filter.
    S7.12.6 The J1939 torque data collected as a digital signal does 
not get filtered. J1939 torque collected as an analog signal is 
filtered with a 0.1-second running average filter.
    S7.12.7 Steering wheel velocity is determined by differentiating 
the filtered steering wheel angle data. The steering wheel velocity 
data is then filtered with a moving 0.1-second running average filter.
    S7.12.8 Lateral acceleration, yaw rate and steering wheel angle 
data channels are zeroed utilizing a defined ``zeroing range.'' The 
``zeroing range'' is the 1.0-second time period prior to the instant 
the steering wheel velocity exceeds 40 deg/sec. The instant the 
steering wheel velocity exceeds 40 deg/sec is the instant defining the 
end of the ``zeroing range.''
    S7.12.9 The beginning of steer (BOS) is the first instance filtered 
and zeroed steering wheel angle data reaches -5 degrees (when the 
initial steering input is counterclockwise) or +5 degrees (when the 
initial steering input is clockwise). The value for time at the BOS is 
interpolated.
    S7.12.10 The Completion of Steer for the sine with dwell maneuver 
(COS) is the time the steering wheel angle returns to zero. The value 
for time at the COS is interpolated.
    S7.12.11 The peak lateral acceleration is the maximum lateral 
acceleration measured during the second half of the sine maneuver, 
including the dwell period from 1.0 second after the BOS to the COS. 
The lateral accelerations at 0.75 and 1.0 seconds after COS are 
determined by interpolation.
    S7.12.12 The peak yaw rate is the maximum yaw rate measured during 
the second half of the sine maneuver, including the dwell period from 
1.0 second after the BOS to the COS. The yaw rates at 0.75 and 1.0 
seconds after COS are determined by interpolation.
    S7.12.13 Determine lateral velocity by integrating corrected, 
filtered and zeroed lateral acceleration data. Zero lateral velocity at 
BOS event. Determine lateral displacement by integrating zeroed later 
velocity. Zero lateral displacement at BOS event. Lateral displacement 
at 1.50 seconds from BOS event is determined by interpolation.
    S7.12.14 The ESC activation point is the point where the measured 
driver demanded torque and the engine torque first begin to deviate 
from one another (engine torque decreases while driver requested torque 
increases) during the slowly increasing steer maneuver. The torque 
values are obtained directly from each vehicle's SAE J1939 
communication data bus. Torque values used to determine the ESC 
activation point are interpolated.
    S8. Compliance Date.
    S8.1 Buses. All buses manufactured on or after [date that is two 
years after publication of a final rule implementing this proposal] 
must comply with this standard
    S8.2 Truck tractors.
    S8.2.1 All two-axle and three-axle truck 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 manufactured 
on or after [date that is two years after publication of a final rule 
implementing this proposal] must comply with this standard.
    S8.2.2 All truck tractors manufactured on or after [date that is 
four years after publication of a final rule implementing this 
proposal] must comply with this standard.

    Issued: May 15, 2012.
Christopher J. Bonanti,
Associate Administrator for Rulemaking.
[FR Doc. 2012-12212 Filed 5-16-12; 4:15 pm]
BILLING CODE 4910-59-P