Federal Motor Vehicle Safety Standards; Electronic Stability Control Systems; Controls and Displays

Federal RegisterApr 6, 2007

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DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

49 CFR Parts 571 and 585

[Docket No. NHTSA-2007-27662]

RIN 2127-AJ77

Federal Motor Vehicle Safety Standards; Electronic Stability Control Systems; Controls and Displays

AGENCY:

National Highway Traffic Safety Administration (NHTSA), DOT.

ACTION:

Final rule.

SUMMARY:

As part of a comprehensive plan for reducing the serious risk of rollover crashes and the risk of death and serious injury in those crashes, this document establishes a new Federal motor vehicle safety standard (FMVSS) No. 126 to require electronic stability control (ESC) systems on passenger cars, multipurpose passenger vehicles, trucks, and buses with a gross vehicle weight rating of 4,536 Kg (10,000 pounds) or less. ESC systems use automatic computer-controlled braking of individual wheels to assist the driver in maintaining control in critical driving situations in which the vehicle is beginning to lose directional stability at the rear wheels (spin out) or directional control at the front wheels (plow out).

Preventing single-vehicle loss-of-control crashes is the most effective way to reduce deaths resulting from rollover crashes. This is because most loss-of-control crashes culminate in the vehicle leaving the roadway, which dramatically increases the probability of a rollover. Based on the best available data, drawn from crash data studies, NHTSA estimates that the installation of ESC will reduce single-vehicle crashes of passenger cars by 34 percent and single vehicle crashes of sport utility vehicles (SUVs) by 59 percent, with a much greater reduction of rollover crashes. NHTSA estimates that ESC has the potential to prevent 71 percent of the passenger car rollovers and 84 percent of the SUV rollovers that would otherwise occur in single-vehicle crashes.

NHTSA estimates that ESC would save 5,300 to 9,600 lives and prevent 156,000 to 238,000 injuries in all types of crashes annually once all light vehicles on the road are equipped with ESC systems. The agency further anticipates that ESC systems would substantially reduce (by 4,200 to 5,500) the more than 10,000 deaths each year on American roads resulting from rollover crashes.

Manufacturers equipped about 29 percent of model year (MY) 2006 light vehicles sold in the U.S. with ESC, and intend to increase the percentage to 71 percent by MY 2011. This rule requires installation of ESC in 100 percent of light vehicles by MY 2012 (with exceptions for some vehicles manufactured in stages or by small volume manufacturers). Once all light vehicles in the fleet have ESC, of the overall projected annual 5,300 to 9,600 highway deaths and 156,000 to 238,000 injuries prevented by stability control systems installed either voluntarily or under this rulemaking, we would attribute 1,547 to 2,534 prevented fatalities (including 1,171 to 1,465 involving rollover) to this rulemaking, in addition to the prevention of 46,896 to 65,801 injuries by increasing the percentage of light vehicles with ESC from 71 percent to 100 percent.

DATES:

Effective Date:

This final rule is effective June 5, 2007. The incorporation by reference of certain publications listed in the rule is approved by the Director of the Federal Register as of June 5, 2007.

Compliance Date:

Consistent with the phase-in commencing September 1, 2008, all new light vehicles must be equipped with an ESC system that meets the requirements of the standard by September 1, 2011, with the following exceptions. Vehicle manufacturers need not meet the standard's requirements for control and display requirements for the ESC malfunction indicator telltale and “ESC Off” switch and telltale (if provided) until September 1, 2011 (

i.e.

, at the end of the phase-in), and vehicles produced by final-stage manufacturers and alterers must be equipped with a compliant ESC system (including the control and display requirements) by September 1, 2012. However, manufacturers may voluntarily certify vehicles to FMVSS No. 126 and earn carry-forward credits for compliant vehicles, produced in excess of the phase-in requirements, that are manufactured between June 5, 2007, and the conclusion of the phase-in.

Petitions for Reconsideration:

If you wish to submit a petition for reconsideration of this rule, your petition must be received by May 21, 2007.

ADDRESSES:

Petitions for reconsideration should refer to the docket number above and be submitted to: Administrator, Room 5220, National Highway Traffic Safety Administration, 400 Seventh Street, SW., Washington, DC 20590.

See the

SUPPLEMENTARY INFORMATION

portion of this document (Section VI; Rulemaking Analyses and Notice) for DOT's Privacy Act Statement regarding documents submitted to the agency's dockets.

FOR FURTHER INFORMATION CONTACT:

For non-legal issues, you may call Mr. Patrick Boyd, Office of Crash Avoidance Standards (Telephone: 202-366-6346) (Fax: 202-366-7002).

For legal issues, you may call Mr. Eric Stas, Office of the Chief Counsel (Telephone: 202-366-2992) (Fax: 202-366-3820).

You may send mail to both of these officials at National Highway Traffic Safety Administration, 400 Seventh Street, SW., Washington, DC 20590.

SUPPLEMENTARY INFORMATION:

Table of Contents

I. Executive Summary

A. Requirements of the Final Rule

B. Lead Time and Phase-in

C. Differences Between the Final Rule and the Notice of Proposed Rulemaking

D. Impacts of ESC and of the Final Rule

II. Background

A. Overview of the Safety Problem

B. The Agency's Comprehensive Response to Rollover

C. Congressional Mandate Under Section 10301 of the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users of 2005

D. Electronic Stability Control as a Countermeasure to Address Single-Vehicle Crashes and Rollovers

III. September 2006 Notice of Proposed Rulemaking (NPRM) and Public Comments

A. The NPRM

B. Summary of the Public Comments on the NPRM

IV. The Final Rule and Response to Public Comments

A. Summary of the Requirements

B. Lead Time and Phase-in

C. Response to Public Comments by Issue

Major Issues

1. Approach of the ESC NPRM

(a) ESC Mandate vs. ESC Standardization

(b) ESC as Part of a Comprehensive Rollover Safety Program

2. The Definition of “ESC System” as the Basis of the Standard

3. Stringency of the Standard

4. Understeer Requirements

5. Lateral Responsiveness Criteria

6. Definition of “ESC System” and Required Equipment

(a) Clarification of Performance Expectations

(b) Clarification of Threshold Speed

(d) Request for Alternate Transducers

(e) Interaction with Other Vehicle Systems

(f) ESC Operation in Reverse

7. ESC Performance Requirements

(a) Definition for “Lateral Acceleration”

(b) Lateral Displacement Calculation

(d) Temperature and Pavement Specifications

(e) Data Processing Issues

(i) Determination of Beginning of Steering

(ii) Determination of End of Steering

(iii) Removing Offsets

(iv) Use of Interpolation

(v) Method for Determining Peak Steering Wheel Angle

(vi) Need for a Common Data Processing Kernel

(f) ESC Initialization Period

(g) ESC Calibration

Other Issues

8. ESC Malfunction Detection Requirements

(a) Types of Malfunctions to be Detected

(b) Practicability Problems with Malfunction Detection

(d) Minimum Performance Level

9. ESC Telltale Requirements

(a) ESC Telltale

(i) Telltale Symbol Text Enhancements

(ii) Telltale Symbol Alternative: Substitute Text

(iii) Waiver of Yellow Color Requirement for ESC Telltale When Message/Information Center is Used

(iv) Telltale Illumination Strategy

(v) Telltale Extinguishment

(vi) Telltale Location

(vii) Use of ESC Malfunction Telltale to Indicate Malfunctions of Related Systems/Functions

(b) “ESC Off” Indication

(i) “ESC Off” Symbol Alternative: Use of Text

(ii) Waiver of Yellow Color Requirement When “ESC Off” is Indicated Via Message/Information Center Text

(iii) “ESC Off” Telltale Clarification

(iv) “ESC Off” Telltale Strategy

(v) Use of Two-Part Telltales

(vi) Conditions for Illumination of “ESC Off” Telltale: Speed

(vii) Conditions for Illumination of “ESC Off” Telltale: Direction

(i) Visual and Auditory Indications of ESC Activation

(ii) Flashing Telltales as Activation Indication of Intervention by Related Systems/Functions

(d) Bulb Check

(i) Waiver of Bulb Check for Message/Information Centers

(ii) Clarification Regarding Bulb Check

10. System Disablement and the “ESC Off” Control

(a) Provision of an “ESC Off” Control

(b) Switch for Complete ESC Deactivation

(d) Default to “ESC On” Status

(e) Operation of Vehicle in 4WD Low Modes

(f) “ESC Off” Control Requirements

(i) Labeling of the “ESC Off” Control

(ii) Location of the “ESC Off” Control

11. Test Procedures

(a) Accuracy Requirements

(b) Tolerances

(d) Calculation of Lateral Displacement

(e) Maximum Steering Angle

(f) Vehicle Test Weight

(g) Data Filtering

(h) Outriggers

(i) Ambient Temperature Range

(j) Brake Temperatures

(k) Wind Speed

(l) Rounding of Steering Wheel Angle at 0.3 g

(m) Vehicle Speed Specification for the Slowly Increasing Steer Test

(n) Alternative Test Procedures

(o) Representativeness of Real World Conditions

12. Lead Time and Phase-in

(a) Lead Time for ESC Telltale(s)

(b) Phase-in Schedule

13. Impacts on the Aftermarket

(a) System Adaptability and Sharing ESC Information

(b) “Make Inoperative” Prohibition

14. Compliance with Relevant Legal Requirements

(a) Regulatory Flexibility Act

(b) Executive Orders 12866 and 13258

15. ESC Outreach Efforts

(a) ESC Test Procedures Workshop

(b) Public Information Campaign

16. Miscellaneous Issues

(a) Linking Brake Light Illumination to ESC Activation

(b) Vehicles with Dual Wheels on the Rear Axle

(d) Wheelchair-Accessible Vehicles

V. Benefits and Costs

A. Summary

B. ESC Benefits

C. ESC Costs

VI. Regulatory Analyses and Notices

Appendix: Technical Explanation in Response to Comments on Understeer

I. Executive Summary

As part of a comprehensive plan

that seeks to reduce the serious risk of rollover crashes and the risk of death and serious injury in those crashes, and that includes a number of complementary rulemaking actions, this rule establishes Federal Motor Vehicle Safety Standard (FMVSS) No. 126,

Electronic Stability Control Systems

, which requires passenger cars, multipurpose passenger vehicles (MPVs), trucks, and buses that have a gross vehicle weight rating (GVWR) of 4,536 kg (10,000 pounds) or less to be equipped with an ESC system that meets the requirements of the standard. ESC systems use automatic, computer-controlled braking of individual wheels to assist the driver in maintaining control (and the vehicle's intended heading) in situations where the vehicle is beginning to lose directional stability (

e.g.

, where the driver misjudges the severity of a curve or over-corrects in an emergency situation). In such situations (which occur with considerable frequency), intervention by the ESC system can assist the driver in preventing the vehicle from leaving the roadway, thereby preventing fatalities and injuries associated with crashes involving vehicle rollover or collision with various objects (

e.g.

, trees, highway infrastructure, other vehicles).

70 FR 49223, at 49229 (August 23, 2005).

Based upon current estimates regarding the effectiveness of ESC systems, we believe that an ESC standard could save thousands of lives each year, providing potentially the greatest safety benefits produced by any safety device since the introduction of seat belts. The following discussion highlights the research and regulatory efforts that have culminated in this safety standard.

Since the early 1990's, NHTSA has been actively engaged in finding ways to address the problem of vehicle rollover, because crashes involving rollover are responsible for a disproportionate number of fatalities and serious injuries (over 10,000 of the 33,000 fatalities of vehicle occupants in 2004). Although various options were explored, the agency ultimately chose to add a rollover resistance component to its New Car Assessment Program (NCAP) consumer information program in 2001. In response to NCAP's market-based incentives, vehicle manufacturers made modifications to their product lines to increase their vehicles' geometric stability and rollover resistance by utilizing wider track widths (typically associated with passenger cars) on many of their newer sport utility vehicles (SUVs) and by making other improvements to truck-based SUVs during major redesigns (

e.g.

, introduction of roll stability control). This approach was successful in terms of reducing the much higher rollover rate of SUVs and other high-center-of-gravity vehicles, as compared to passenger cars. However, manipulating vehicle configuration alone cannot entirely resolve the rollover problem (particularly when consumers continue to demand vehicles with greater carrying capacity and higher ground clearance).

Accordingly, the agency began exploring technologies that could confront the issue of vehicle rollover from a different perspective or line of inquiry, which led to today's final rule. We believe that the ESC requirement offers a complementary approach that may provide substantial benefits to drivers of both passenger cars and LTVs (light trucks/vans). Undoubtedly, keeping vehicles from leaving the roadway is the best way to prevent deaths and injuries associated with rollover, as well as other types of

crashes. Based on its crash data studies, NHTSA estimates that the installation of ESC systems will reduce single vehicle crashes of passenger cars by 34 percent and single vehicle crashes of sport utility vehicles (SUVs) by 59 percent. Its effectiveness is especially great for single-vehicle crashes resulting in rollover, where ESC systems were estimated to prevent 71 percent of passenger car rollovers and 84 percent of SUV rollovers in single vehicle crashes (

see

Section V).

In short, we believe that preventing single-vehicle loss-of-control crashes is the most effective way to reduce rollover deaths, and we believe that ESC offers considerable promise in terms of meeting this important safety objective while maintaining a broad range of vehicle choice for consumers. In fact, among the agency's ongoing and planned rulemakings, it is the single most effective way of reducing the total number of traffic deaths. It is also the most cost-effective of those rulemakings.

We note that this final rule also satisfies the recent mandate in section 10301 of the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users of 2005 (SAFETEA-LU).

That provision requires the Secretary of Transportation to “establish performance criteria to reduce the occurrence of rollovers consistent with stability enhancing technologies” and to “issue a proposed rule * * * by October 1, 2006, and a final rule by April 1, 2009.” In light of the tremendous life-saving potential anticipated to be associated with a requirement for ESC to be standard equipment on all light vehicles, the agency determined that, consistent with its mission to save lives, prevent injuries and reduce economic costs due to road traffic crashes, it was important to issue a final rule as soon as possible and accelerate the rate of installation. Accordingly, today's final rule is being published well in advance of the statutory deadline under SAFETEA-LU.

Pub. L. 109-59, 119 Stat. 1144 (2005).

The balance of this notice discusses (1) The background regarding the size of the safety problem, the agency's comprehensive response to rollover-related safety problems, the agency's mandate under SAFETEA-LU, and ESC systems as a countermeasure to address single-vehicle crashes and rollovers (

see

Section II); (2) the agency's September 2006 NPRM for ESC and public comments on that proposal (

see

Section III); (3) the requirements and implementation of the final rule, including a detailed discussion regarding resolution of the issues raised in public comments (

see

Section IV); and (4) costs and benefits associated with the final rule (

see

Section V). However, before turning to this more detailed analysis, we summarize the key points of the final rule, including the requirements for ESC systems under FMVSS No. 126, lead time and phase-in, differences between the final rule and the NPRM, and the anticipated impacts of the final rule.

A. Requirements of the Final Rule

After careful consideration of all available information, including the public comments, the agency has decided to adopt in the ESC final rule most of the elements of the proposed rule. Consistent with SAFETEA-LU, NHTSA is requiring all light vehicles to be equipped with an ESC system with, at the minimum, the capabilities of current production systems. We believe that a requirement for such ESC systems is desirable in terms of both ensuring technological feasibility and providing the desired safety benefits in a cost-effective manner. Although vehicle manufacturers have been increasing the portion of the light vehicle fleet equipped with ESC, we believe that given the relatively high cost of this technology, a mandatory standard is necessary to maximize the safety benefits associated with electronic stability control, and is required by SAFETEA-LU.

In order to realize these benefits, we have decided to require vehicles to be equipped with an ESC system meeting definitional requirements and to pass a dynamic test. The definitional requirements specify the necessary elements of a stability control system that is capable of both effective oversteer and understeer intervention. These requirements are necessary due to the extreme difficulty in establishing tests adequate, by themselves, to ensure the desired level of ESC functionality in a variety of circumstances.

The test that we are adopting is necessary to ensure that the ESC system is robust and meets a level of performance at least comparable to that of current ESC systems. This approach is similar to the one we took, for similar reasons, in 1995 in mandating antilock brakes for medium and heavy vehicles pursuant to the Intermodal Surface Transportation Efficiency Act (ISTEA) of 1991.

An equipment requirement is necessary because it would be almost impossible to devise a single performance test that could not be met through some action by the manufacturer other than providing an ESC system. Establishing a battery of performance tests to achieve our intended results is not possible at this time because we have not been able to develop a practical, repeatable limit-understeer test, and there are no applicable tests in vehicle dynamics literature. Although the agency has undertaken its own preliminary research efforts related to understeer, the complexity of such research would require several years of additional work before any conclusions could be reached regarding an ESC understeer performance test.

Given this, the agency determined that it had three available options: (1) Delay the ESC final rule and conduct research and development; (2) drop the understeer requirement and amend the standard once an ESC performance test is developed; or (3) include a requirement for understeer as part of the definition of “ESC System,” along with requiring specific components that will permit the system to intervene in excessive understeer situations.

The agency eliminated the first and second options on the grounds of safety.

The agency believes that the third option, adopting an understeer requirement as part of the definition of “ESC System,” along with a requirement for specific equipment suitable for that purpose, will accomplish the purposes of the statutory mandate. Such requirement is objective in terms of explaining to manufacturers what type of performance is required and the minimal equipment necessary for that purpose. The agency can verify that the system has the necessary hardware and logic for understeer mitigation. Since the necessary components for effective understeer intervention are already present on all ESC systems, we believe that manufacturers are highly unlikely to decrease their ESC systems' understeer capabilities simply because the standard does not have a specific test for understeer. The agency believes that its chosen approach will ensure that vehicle manufacturers maintain understeer intervention as a feature of the ESC system, without delaying the life-saving benefits of the ESC rule. In the meantime, the agency will conduct additional research in the area of ESC understeer intervention and consider taking additional action, as appropriate.

Even with an understeer test, the ultimate practicability of a standard without an equipment requirement remains in doubt because of the possible large number of test conditions that would be required.

60 FR 13216 (March 10, 1995).

These requirements are summarized below:

• Consistent with the definition of ESC contained in a voluntary consensus standard, the Society of Automotive Engineers

(SAE) Surface Vehicle Information Report J2564 (rev. June 2004), we are requiring vehicles covered under the standard to be equipped with an ESC system that:

The Society of Automotive Engineers is an association of engineers, business executives, educators, and students who share information and exchange ideas for advancing the engineering of mobility systems. SAE currently has over 90,000 members in approximately 97 countries. The organization's activities include development of standards, events, and technical information and expertise used in designing, building, maintaining, and operating self-propelled vehicles for use on land or sea, in air or space.

See http://www.sae.org.

(1) Augments vehicle directional stability by applying and adjusting the vehicle brake torques individually to induce a correcting yaw moment to a vehicle;

(2) Is computer-controlled, with the computer using a closed-loop

algorithm

to limit vehicle oversteer and to limit vehicle understeer;

A “closed-loop algorithm” is a cycle of operations followed by a computer that includes automatic adjustments based on the result of previous operations or other changing conditions.

(3) Has a means to determine vehicle yaw rate

and to estimate its sideslip

or the time derivative of sideslip;

“Yaw rate” means the rate of change of the vehicle's heading angle measured in degrees/second of rotation about a vertical axis through the vehicle's center of gravity.

“Sideslip” 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.

(4) Has a means to monitor driver steering input;

(5) Has an algorithm to determine the need, and a means to modify engine torque, as necessary, to assist the driver in maintaining control of the vehicle, and

(6) Is operational over the full speed range of the vehicle (except at vehicle speeds less than 15 km/h (9.3 mph) or when being driven in reverse).

• The ESC system, as defined above, is also required to be capable of applying brake torques individually at all four wheels and to have an algorithm that utilizes this capability.

Except for the situations specifically set forth in part (6) of the definition of “ESC System” above, the system is also required to be operational during all phases of driving, including acceleration, coasting, and deceleration (including braking). It is also required to be capable of activation even if the anti-lock brake system or traction control system is also activated.

The standard was developed based on new vehicles produced in 2005 and 2006. The definition of ESC is limited to four-wheel ESC systems because existing two-wheel ESC systems are not capable of understeer invention or four-wheel automatic braking during an intervention, even though these systems also produced substantial (but lesser) benefits.

• In order to ensure that a vehicle is equipped with an ESC system that meets the definition of “ESC System” under S4, the final rule requires vehicle manufacturers to submit, upon the request of NHTSA's Office of Vehicle Safety Compliance, ESC system technical documentation as to when understeer intervention is appropriate for a given vehicle (

see

S5.6). Specifically, NHTSA may seek information such as a system diagram that identifies all ESC components, a written explanation describing the ESC system's basic operational characteristics, a logic diagram supporting the explanation of system operations, and a discussion of the pertinent inputs to the vehicle computer or calculations within the computer and how its algorithm uses that information and controls ESC system hardware to limit vehicle understeer.

• We are also requiring vehicles covered under the standard to meet a performance test. It must satisfy the standard's stability criteria and responsiveness criterion when subjected to the sine with dwell steering maneuver test. This test involves a vehicle's coasting at an initial speed of 50 mph while a steering machine steers the vehicle with a steering wheel pattern as shown in Figure 2 of the regulatory text. The test maneuver is then repeated over a series of increasing maximum steering angles. This test maneuver was selected over a number of other alternatives because we decided that it has the best set of characteristics, including severity of the test, repeatability and reproducibility of results, and the ability to address lateral stability and responsiveness.

The maneuver is severe enough to produce spinout for most vehicles without ESC. The stability criteria for the test measure how quickly the vehicle stops rotating after the steering wheel is returned to the straight-ahead position. A vehicle that continues to rotate for an extended period after the driver steers straight is out of control, which is what ESC is designed to prevent. The quantitative stability criteria are expressed in terms of the percent of the peak yaw rate after maximum steering that persists at a period of time after the steering wheel has been returned to straight ahead. They require that the vehicle yaw rate decrease to no more than 35 percent of the peak value after one second and that it continue to drop to no more than 20 percent after 1.75 seconds. Since a vehicle that simply responds very little to steering commands could meet the stability criteria, a minimum responsiveness criterion is applied to the same test.

• Because the benefits of the ESC system can only be realized if the system is functioning properly, we are requiring that a telltale be mounted inside the occupant compartment in front of and in clear view of the driver. The ESC malfunction telltale is required to illuminate after the occurrence of one or more malfunctions that affect the generation or transmission of control or response signals in the vehicle's ESC system. Such telltale must remain continuously illuminated for as long as the malfunction(s) exists, whenever the ignition locking system is in the “On” (“Run”) position.

• In certain circumstances, drivers may have legitimate reasons to disengage the ESC system or limit its ability to intervene, such as when the vehicle is stuck in sand/gravel, is being used while equipped with snow chains, or is being run on a track for maximum performance. Accordingly, under this final rule, vehicle manufacturers may include a driver-selectable switch that places the ESC system in a mode in which it does not satisfy the performance requirements of the standard (

e.g.

, “sport” mode or full-off mode). However, if the vehicle manufacturer chooses this option, it must ensure that the ESC system always returns to the fully-functional default mode at the initiation of each new ignition cycle, regardless of the mode the driver had previously selected (with certain exceptions for low speed off-road axle/transfer case selections that turn off ESC, but cannot be reset electronically). If the vehicle manufacturer chooses this option, it must also provide an “ESC Off” control and a telltale that is mounted inside the occupant compartment in front of and in clear view of the driver. Such telltale must remain continuously illuminated for as long as the ESC is in a mode that renders it unable to meet the performance requirements of the standard, whenever the ignition locking system is in the “On” (“Run”) position.

• We are not requiring the ESC system to be equipped with a roll stability control system. Roll stability control systems involve relatively new technology. There is currently an insufficient body of data to judge the efficacy of such systems. However, the agency will continue to monitor the development of these systems.

B. Lead Time and Phase-In

In order to provide the public with what are expected to be the significant safety benefits of ESC systems as rapidly as possible, compliance with this final rule is set to commence on September 1, 2008. That date marks the start of a three-year phase-in period. Subject to the special provisions discussed below, NHTSA has decided to require compliance in accordance with the following schedule: 55 percent of a vehicle manufacturer's light vehicles manufactured during the period from September 1, 2008 to August 31, 2009; 75 percent of those manufactured during the period from September 1, 2009 to August 31, 2010; 95 percent of those manufactured during the period from September 1, 2010 to August 31, 2011, and all light vehicles thereafter.

For the reasons discussed in detail in Section IV.B of this notice, we believe that it is practicable for vehicle manufacturers to meet the requirements of the phase-in discussed above, subject

to the exceptions below. Because ESC is so cost-effective and has such high benefits in terms of potential fatalities and injuries that may be prevented, the agency has decided that it is important to require ESC installation in light vehicles as quickly as possible. Given the product plans we have from six vehicle manufacturers, and the desire to provide manufacturers with flexibility by having a carry-forward provision, we have chosen the most aggressive phase-in alternative that we believe is reasonable (

i.e.

, 55/75/95%). In doing so, we have carefully considered the financial and technological practicability of the final rule (in keeping with our statutory mandate), while at the same time facilitating ESC installation in the light vehicle fleet as expeditiously as possible.

With the above said, the agency has decided that it is appropriate to provide the following exceptions to the phase-in. First, we have decided to defer the standard's requirements related to the ESC telltales and controls until the end of the phase-in (

i.e.

, September 1, 2011 for most manufacturers; September 1, 2012 for final-stage manufacturers and alterers). Although vehicle manufacturers generally commented that they could bring their ESC systems into full compliance (including the control and telltale requirements), they stated that additional lead time would be necessary to accomplish those changes, suggesting that they could do so by the end of the phase-in. As a complicating matter, vehicle manufacturers and their trade associations explained that even though most current ESC systems would largely meet the performance requirements of the proposed standard, manufacturers' inability to meet the proposed control and display requirements would prevent them from earning the carry-forward credits needed to comply with the ESC phase-in schedule. Our analysis demonstrates that the safety benefits associated with early introduction of ESC systems, even without standardized controls and displays, far outweigh the benefits of delaying the standard until all systems can fully meet the control and display requirements (

see

FRIA's lead time/phase-in discussion). Accordingly, we believe that it is preferable to move rapidly to implement the standard, but to delay the compliance date only for the ESC control and telltale requirements.

As proposed, vehicle manufacturers may earn carry-forward credits for compliant vehicles, produced in excess of the phase-in requirements, which are manufactured between the effective date of the final rule and the conclusion of the phase-in period.

We note that carry-forward credits may not be used to defer the mandatory compliance date of September 1, 2011 for all covered vehicles.

This final rule excludes small volume manufacturers (

i.e.

, manufacturers producing less than 5,000 vehicles for sale in the U.S. market in one year) from the phase-in, instead requiring those manufacturers to fully comply with the standard beginning on September 1, 2011.

In addition, consistent with the policy set forth in NHTSA's February 14, 2005 final rule on certification requirements for vehicles built in two or more stages and altered vehicles (70 FR 7414), final-stage manufacturers and alterers are excluded from the requirements of the phase-in and are permitted an additional one year for compliance (

i.e.

, until September 1, 2012). However, final-stage manufacturers and alterers may voluntarily certify compliance with the standard prior to this date.

C. Differences Between the Final Rule and the Notice of Proposed Rulemaking

As noted above, NHTSA has decided to adopt most of the provisions in the NPRM as part of this final rule. We made a number of changes in response to the public comments on the NPRM. The main differences between the NPRM and the final rule involve an increase in the percentages of FMVSS No. 126-compliant vehicles that must be produced during the phase-in period, a delay in the requirements for standardized symbols and acronyms for ESC controls and displays until the end of the phase-in, and the inclusion of engine control as part of the standard's definition of “ESC system.”

The following points briefly describe the main differences between the NPRM and this final rule.

• In order to increase fleet installation of life-saving ESC systems, the phase-in schedule for ESC is being accelerated to require 55 percent phase-in in the first year, 75 percent in the second year, and 95 percent in the third year, rather than the 30 percent, 60 percent, and 90 percent schedule that was proposed (

see

S8.1, S8.2, and S8.3 in the regulatory text of this final rule).

• The effective date for the requirement to use standardized symbols and acronyms as well as certain malfunction detection and “ESC Off” control functions has been moved to the end of the phase-in period. This was done in recognition of the fact that manufacturers will be relying on the carry-forward and compliance credits for vehicles in current production that pass all the ESC performance requirements, but currently lack the standardized controls and displays features proposed in the NPRM (

see

S5.3.1, S5.3.2; S5.3.4; S5.3.9; S5.4.2; S5.5.2; S5.5.3; S5.5.6).

• The definition of “ESC System” has been changed to require ESC systems with engine control, a feature that allows the ESC system to reduce vehicle speed during an intervention by cutting engine power as well as by brake application (

see

S4 ESC (5)). It was a feature on most vehicles in the crash data analysis and on all the vehicles in the ESC cost study.

• The definition of “ESC System” has been changed to delete the word “as appropriate” from the description of when the system must intervene to mitigate vehicle understeer (

see

S4 ESC (2)). Instead, in order to ensure that a vehicle is equipped with an ESC system that meets the definition of “ESC System” under S4, we have decided to require vehicle manufacturers to submit, upon the request of NHTSA's Office of Vehicle Safety Compliance, ESC system technical documentation as to when understeer intervention is appropriate for a given vehicle (

see

We note here that we anticipate that much of this information is proprietary and would be submitted under a request for confidential treatment pursuant to 49 CFR Part 512.

• The “ESC System” definition and performance requirements have been changed to refer to generating brake torques at all four wheels individually, rather than applying individual brakes, so that the action of regenerative braking by electric motors is included (

see

S4 ESC (1); S5.1.1).

• The definition of “ESC System” has been further changed to recognize that some systems operate by estimating the time derivative of side slip, rather than by measuring side slip directly. The final rule also defines the low speed threshold for ESC operation as 15 km/h (

see

S4 ESC (3), (6)).

• The responsiveness criterion has been changed to a two-stage criterion with a lower lateral displacement requirement for large vehicles (

i.e.

, ones

over 7,716 pounds GVWR). It is applied during tests with a peak commanded steering angle of five times or greater than the steering wheel angle necessary to produce 0.3g steady-state lateral acceleration. This is a change from applying it simply for tests with steering wheel angles greater than 180 degrees. It compensates for the slower steering gear ratios of large vehicles. (

see

S5.2; S5.2.3; S6.3.5).

• Low-speed four-wheel-drive (4WD) modes that have the side effect of turning off ESC and that are selected by mechanical controls that cannot be automatically reset electrically are excluded from the requirement for automatic ESC restoration at the next ignition cycle (

see

S5.4.1).

• Under the final rule, outriggers will be used for testing of trucks, MPVs, and buses, and the maximum weight and roll moment of inertia are also specified for outriggers (

see

S6.3.4).

• The ESC malfunction detection test procedure has been modified to include a short driving and turning procedure so that ESC systems with self-diagnostics requiring vehicle motion can accomplish their function (

see

S7.10.2).

D. Impacts of ESC and of the Final Rule

Based on its analysis of the best available data, NHTSA estimates that ESC—both installed voluntarily and under this regulatory mandate—will save 5,300 to 9,600 lives and prevent 156,000 to 238,000 injuries in all types of crashes annually once all light vehicles on the road are equipped with ESC systems. A large portion of these savings will come from preventing large numbers of rollover crashes. ESC systems will substantially reduce (by 4,200 to 5,500) the more than 10,000 deaths that occur on American roads each year as a result of rollover crashes.

Manufacturers installed ESC in about 29 percent of model year (MY) 2006 light vehicles sold in the U.S., and intend to increase the percentage of ESC installation in light vehicles to 71 percent by MY 2011. This rule accelerates that rate of installation by requiring a 100 percent installation rate by MY 2012 (with exceptions for some vehicles manufactured in stages or by small volume manufacturers). We took that step because, in response to public comments and our review of vehicle manufacturers' production plans, we determined that it is practicable to increase the percentage of new light vehicles that must comply with Standard No. 126 under the phase-in, thereby accelerating the benefits expected to be provided by ESC systems.

As the discussion below demonstrates, ESC not only has a very significant life-saving and injury-preventing potential in absolute terms, but it also achieves these benefits in a very cost-effective manner vis-à-vis other agency rulemakings. ESC offers consistently strong benefits and cost-effectiveness across all types of light vehicles, including passenger cars, SUVs, vans, and pick-up trucks. Of the 5,300 to 9,600 highway deaths and 156,000 to 238,000 MAIS 1-5 injuries that we project will be prevented annually for all types of crashes once all light vehicles on the road are equipped with ESC, we attribute 1,547 to 2,534 prevented fatalities (including 1,171 to 1,465 involving rollover) to this rulemaking, in addition to the prevention of 46,896 to 65,801 injuries.

The agency estimates that the production-weighted, average cost per vehicle to meet the proposed standard's requirements will be $58 ($90.3 per passenger car and $29.2 per light truck).

These are incremental costs over the manufacturers' MY 2011 plans for installation of ABS, which is expected to be installed in almost 93 percent of the light vehicle fleet, and ESC, which is expected to be installed in 71 percent of the light vehicle fleet. Vehicle costs are estimated to be $368 (in 2005$) for anti-lock brakes (ABS) and an additional $111 for ESC, for a total system cost of $479 per vehicle. The total annual vehicle cost of this regulation, based on ESC installation beyond manufacturers' planned percentages, is expected to be approximately $985 million.

We note that the costs for passenger cars are higher because a greater portion of those vehicles require installation of ABS in addition to ESC.

In terms of cost-effectiveness, this final rule is expected to save 1,547 to 2,534 lives and prevent 46,896 to 65,801 injuries at a cost of $0.18 to $0.33 million per equivalent life saved at a 3 percent discount rate and $0.26 to $0.45 million at a 7 percent discount rate.

The final rule is highly cost-effective even when passenger cars are considered alone. The passenger car portion of the final rule will save 945 lives and prevent 32,196 injuries at a cost of $0.38 million per equivalent life saved at a 3 percent discount rate and $0.50 at a 7 percent discount rate.

II. Background

A. Overview of the Safety Problem

The following discussion explains the nature and scope of the safety problem which the agency seeks to address through this rulemaking for ESC, based upon our analysis of recent single-vehicle crash and rollover statistics. About one in seven light vehicles involved in police-reported crashes collides with something other than another vehicle. However, the proportion of these single-vehicle crashes increases steadily with increasing crash severity, and almost half of serious and fatal injuries occur in single-vehicle crashes. We can describe the relationship between crash severity and the number of vehicles involved in the crash using information from the agency's crash data programs. We limit our discussion here to “light vehicles,” which consist of passenger cars, multipurpose passenger vehicles (MPVs), trucks, and buses with a gross vehicle weight rating (GVWR) of 4,536 kilograms (10,000 pounds) or less.

For brevity, we use the term “light trucks” in this document to refer to multipurpose passenger vehicles (

e.g.

, vans, minivans, and SUVs), trucks, and buses with a GVWR of 4,536 kilograms (10,000 pounds) or less.

The 2000-2005 data from the National Automotive Sampling System (NASS) Crashworthiness Data System (CDS) and 2005 data from the Fatality Analysis Reporting System (FARS) were combined to estimate the current target population for this rulemaking. It includes 27,680 people who were killed as occupants of light vehicles (both single-vehicle and multi-vehicle crashes). Over half of these (15,191) occurred in single-vehicle crashes. Of these, 8,596 occurred in rollovers. About 1.0 million injuries (AIS 1-5) occurred in crashes that could be affected by ESC, almost 458,000 in single vehicle crashes (of which almost half were in rollovers). Multi-vehicle crashes that could be affected by ESC accounted for 12,485 fatalities and almost 547,000 injuries.

Rollover crashes are complex events that reflect the interaction of driver, road, vehicle, and environmental factors. We can describe the relationship between these factors and the risk of rollover using information from the agency's crash data programs.

According to 2005 data from FARS, 10,836 people were killed as occupants in light vehicle rollover crashes, which represents 34 percent of all occupants killed that year in crashes. Of those, 8,769 were killed in single-vehicle rollover crashes. Seventy-four percent of the people who died in single-vehicle rollover crashes were not using a seat belt, and 61 percent were partially or completely ejected from the vehicle (including 50 percent who were completely ejected). FARS shows that 55 percent of light vehicle occupant fatalities in single-vehicle crashes involved a rollover event.

Using data from the 2000-2004 NASS CDS files, we estimate that 266,000 light vehicles were towed from a police-reported rollover crash each year (on average), and that 29,000 occupants of these vehicles were seriously injured. Of these 266,000 light vehicle rollover crashes, 219,000 were single-vehicle crashes. Sixty-one percent of those people who suffered a serious injury in a single-vehicle tow-away rollover crash were not using a seat belt, and 52 percent were partially or completely ejected (including 41 percent who were completely ejected). Estimates from NASS CDS indicate that 82 percent of tow-away rollovers were single-vehicle crashes, and that 88 percent (197,000) of the single-vehicle rollover crashes occurred after the vehicle left the roadway. An audit of 1992-96 NASS CDS data showed that about 95 percent of rollovers in single-vehicle crashes were tripped by mechanisms such as curbs, soft soil, pot holes, guard rails, and wheel rims digging into the pavement, rather than by tire/road interface friction as in the case of untripped rollover events.

B. The Agency's Comprehensive Response to Rollover

As mentioned above, this final rule for ESC is but one part of the agency's comprehensive plan to address the issue of vehicle rollover. The following discussion provides background on NHTSA's comprehensive plan to reduce rollover crashes. In 2002, the agency formed an Integrated Project Team (IPT) to examine the rollover problem and to make recommendations on how to reduce rollovers and to improve safety when rollovers nevertheless occur. In June 2003, based on the work of that team, the agency published a report titled, “Initiatives to Address the Mitigation of Vehicle Rollover.”

The report recommended improving vehicle stability, ejection mitigation, roof crush resistance, as well as road improvements and behavioral strategies aimed at consumer education.

See

Docket Number NHTSA 2003-14622-1.

Since then, the agency has been working to implement these recommendations as part of its comprehensive agency plan for reducing the serious risk of rollover crashes and the risk of death and serious injury when rollover crashes do occur. It is evident that the most effective way to reduce deaths and injuries in rollover crashes is to prevent the rollover crash from occurring. This final rule adopting a new Federal motor vehicle safety standard for electronic stability control systems is one key part of that comprehensive agency plan.

Moreover, we note that the agency also published a notice of proposed rulemaking in the

Federal Register

in August 2005, seeking to upgrade our safety standard on roof crush resistance (FMVSS No. 216); that notice, like the present one, contains an in-depth discussion of the rollover problem and the countermeasures which the agency intends to pursue as part of its comprehensive response to the rollover problem (

see

70 FR 49223 (August 23, 2005)).

C. Congressional Mandate Under Section 10301 of the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users of 2005

During the course of the ongoing agency's research into ESC systems, Congress passed the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users of 2005 (SAFETEA-LU).

Section 10301 of that Act contains legislative mandates for the agency to initiate a number of rulemakings, including ones for rollover prevention and occupant ejection prevention. In relevant part, that provision states:

Pub. L. 109-59, 119 Stat. 1144 (2005).

(a) In General.—The Secretary [of Transportation] shall initiate rulemaking proceedings, for the purpose of establishing rules or standards that will reduce vehicle rollover crashes and mitigate deaths and injuries associated with such crashes for motor vehicles with a gross vehicle weight rating of not more than 10,000 pounds.

(b) Rollover Prevention.—One of the rulemaking proceedings initiated under subsection (a) shall be to establish performance criteria to reduce the occurrence of rollovers consistent with stability enhancing technologies. The Secretary shall issue a proposed rule in this proceeding by rule by October 1, 2006, and a final rule by April 1, 2009.

This SAFETEA-LU mandate is consistent with the agency's efforts under its Comprehensive Rollover Safety Program (discussed above). The agency's research efforts had already identified electronic stability control systems as a mature and effective technology which has had adequate time to be analyzed in both the scientific literature, as well as by NHTSA researchers. These research results strongly suggest that fleet-wide installation of ESC systems should yield tremendous benefits in terms of the prevention of fatalities and injuries. Although the agency considered other potential “stability enhancing technologies,” there was no evidence to demonstrate that they would meet the need for motor vehicle safety (

see

Section IV.C.3 below). Accordingly, the agency has determined that adopting a requirement for installation of ESC systems in light vehicles would be consistent with the statutory mandate under section 10301 of SAFETEA-LU. Under our interpretation of that statutory provision, Congress provided the agency discretion to evaluate various stability enhancing technologies and to adopt a requirement for a system that the agency determines would best reduce the occurrence of rollovers. The agency agrees with Congress regarding the tremendous life-saving potential associated with ESC as a proven stability enhancing technology, and because of the agency's prior efforts, it was possible to publish today's final rule well in advance of the statutory deadline under SAFETEA-LU.

As this final rule makes clear, the agency has decided to implement the statutory mandate contained in section 10301 of SAFETEA-LU through promulgation of a Federal motor vehicle safety standard for ESC pursuant to 49 U.S.C. Chapter 301,

Motor Vehicle Safety

. Adoption of an FMVSS for ESC meets the statutory directive to “establish performance criteria” consistent with stability enhancing technologies. Furthermore, this approach is consistent with the agency's implementation of the statutory mandate for tire pressure monitoring systems contained in section 13

of the Transportation Recall Enhancement, Accountability, and Documentation (TREAD) Act.

See

49 U.S.C. 30123 note (2003).

Pub. L. 106-414, 114 Stat. 1800 (2000).

D. Electronic Stability Control as a Countermeasure to Address Single-Vehicle Crashes and Rollovers

General Principles of ESC System Operation

Although Electronic Stability Control (ESC) systems have been known by a number of different trade names such as Vehicle Stability Control (VSC), Electronic Stability Program (ESP), StabiliTrak and Vehicle Stability Enhancement (VSE), their function and performance are similar. They are systems that use computer control of individual wheel brakes to help the driver maintain control of the vehicle during extreme maneuvers by keeping the vehicle headed in the direction the driver is steering even when the vehicle nears or reaches the limits of road traction.

When a driver attempts an “extreme maneuver” (

e.g.

, one initiated to avoid

a crash or due to misjudgment of the severity of a curve), the driver may lose control if the vehicle responds differently as it nears the limits of road traction than it does during ordinary driving. The driver's loss of control can result in either the rear of the vehicle “spinning out” or the front of the vehicle “plowing out.” As long as there is sufficient road traction, a highly skilled driver may be able to maintain control in many extreme maneuvers using countersteering (

i.e.

, momentarily turning away from the intended direction) and other techniques. However, average drivers in a panic situation in which the vehicle is beginning to spin out would be unlikely to countersteer to regain control.

ESC uses automatic braking of individual wheels to adjust the vehicle's heading if it departs from the direction the driver is steering. Thus, it prevents the heading from changing too quickly (spinning out) or not quickly enough (plowing out). Although it cannot increase the available traction, ESC affords the driver the maximum possibility of keeping the vehicle under control and on the road in an emergency maneuver using just the natural reaction of steering in the intended direction.

Keeping the vehicle on the road prevents single-vehicle crashes, which are the circumstances that lead to most rollovers. However, if the speed is simply too great for the available road traction, even a vehicle with ESC will unavoidably drift off the road (but not spin out). Furthermore, ESC cannot prevent road departures due to driver inattention or drowsiness rather than loss of control.

How ESC Prevents Loss of Vehicle Control

The following explanation of ESC operation illustrates the basic principle of yaw stability control, but it does not attempt to explain advanced refinements of the yaw control strategy described below that use vehicle sideslip (lateral sliding that may not alter yaw rate) to optimize performance on slippery pavements.

An ESC system maintains what is known as “yaw” (or heading) control by determining the driver's intended heading, measuring the vehicle's actual response, and automatically turning the vehicle if its response does not match the driver's intention. However, with ESC, turning is accomplished by applying a brake force at a single wheel rather than by steering input. (The uneven brake force from braking only one wheel creates a yaw torque or moment that rotates the vehicle around a vertical axis.)

Speed and steering angle measurements are used to determine the driver's intended heading. The vehicle response is measured in terms of lateral acceleration and yaw rate by onboard sensors. If the vehicle is responding in a manner corresponding to driver input, the yaw rate will be in balance with the speed and lateral acceleration.

The concept of “yaw rate” can be illustrated by imaging the view from above of a car following a large circle painted on a parking lot. One is looking at the top of the roof of the vehicle and seeing the circle. If the car starts in a heading pointed north and drives half way around circle, its new heading is south. Its yaw angle has changed 180 degrees. If it takes 10 seconds to go half way around the circle, the “yaw rate” is 180 degrees per 10 seconds or 18 deg/sec. If the speed stays the same, the car is constantly rotating at a rate of 18 deg/sec around a vertical axis that can be imagined as piercing its roof. If the speed is doubled, the yaw rate increases to 36 deg/sec.

While driving in a circle, the driver notices that he must hold the steering wheel tightly to avoid sliding toward the passenger seat. The bracing force is necessary to overcome the lateral acceleration that is caused by the car following the curve. The lateral acceleration is also measured by the ESC system. When the speed is doubled the lateral acceleration increases by a factor of four if the vehicle follows the same circle. There is a fixed physical relationship between the car's speed, the radius of its circular path, and its lateral acceleration.

The ESC system uses this information as follows: Since the ESC system measures the car's speed and its lateral acceleration, it can compute the radius of the circle. Since it then has the radius of the circle and the car's speed, the ESC system can compute the correct yaw rate for a car following the path. Of course, the system includes a yaw rate sensor, and it compares the actual measured yaw rate of the car to that computed for the path the car is following. If the computed and measured yaw rates begin to diverge as the car that is trying to follow the circle speeds up, it means the driver is beginning to lose control, even if the driver cannot yet sense it. Soon, an unassisted vehicle would have a heading significantly different from the desired path and would be out of control either by oversteering (spinning out) or understeering.

When the ESC system detects an imbalance between the measured yaw rate of a vehicle and the path defined by the vehicle's steering wheel angle, speed, and lateral acceleration, the ESC system automatically intervenes to turn the vehicle. The automatic turning of the vehicle is accomplished by uneven brake application rather than by steering wheel movement. If only one wheel is braked, the uneven brake force will cause the vehicle's heading to change. Figure 1 shows the action of ESC using single wheel braking to correct the onset of oversteering or understeering. (Please note that all Figures discussed in this preamble may be found at the end of the preamble, immediately preceding the proposed regulatory text.)

•

Oversteering.

In Figure 1 (bottom panel), the vehicle has entered a left curve that is extreme for the speed it is traveling. The rear of the vehicle begins to slide which would lead to a vehicle without ESC turning sideways (or “spinning out”) unless the driver expertly countersteers. 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). It momentarily applies the right front brake to turn 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. Even if the driver brakes because the curve is sharper than anticipated, the system is still capable of generating uneven braking if necessary to correct the heading.

•

Understeering.

Figure 1 (top panel) shows a similar situation faced by a vehicle whose response as it nears the limits of road traction is to slide at the front (“plowing out” or understeering) rather than oversteering. 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). It momentarily applies the left rear brake 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).

While Figure 1 may suggest that particular vehicles go out of control as either vehicles prone to oversteer or vehicles prone to understeer, it is just as likely that a given vehicle could require both understeer and oversteer interventions during progressive phases

of a complex avoidance maneuver such as a double lane change.

Although ESC cannot change the tire/road friction conditions the driver is confronted with in a critical situation, there are clear reasons to expect it to reduce loss-of-control crashes, as discussed below.

In vehicles without ESC, the response of the vehicle to steering inputs changes as the vehicle nears the limits of road traction. All of the experience of the average driver is in operating the vehicle in its “linear range”,

i.e.

, the range of lateral acceleration in which a given steering wheel movement produces a proportional change in the vehicle's heading. The driver merely turns the wheel the expected amount to produce the desired heading. Adjustments in heading are easy to achieve because the vehicle's response is proportional to the driver's steering input, and there is very little lag time between input and response. The car is traveling in the direction it is pointed, and the driver feels in control. However, at lateral accelerations above about one-half “g” on dry pavement for ordinary vehicles, the relationship between the driver's steering input and the vehicle's response changes (toward oversteer or understeer), and the lag time of the vehicle response can lengthen. When a driver encounters these changes during a panic situation, it adds to the likelihood that the driver will lose control and crash because the familiar actions learned by driving in the linear range would not be the correct steering actions.

However, ordinary linear range driving skills are much more likely to be adequate for a driver of a vehicle with ESC to avoid loss of control in a panic situation. By monitoring yaw rate and sideslip, ESC can intervene early in the impending loss-of-control situation with the appropriate brake forces necessary to restore yaw stability before the driver would attempt an over correction or other error. The net effect of ESC is that the driver's ordinary driving actions learned in linear range driving are the correct actions to control the vehicle in an emergency. Also, the vehicle will not change its heading from the desired path in a way that would induce further panic in a driver facing a critical situation.

Besides allowing drivers to cope with emergency maneuvers and slippery pavement using only “linear range” skills, ESC provides more powerful control interventions than those available to even expert drivers of non-ESC vehicles. For all practical purposes, the yaw control actions with non-ESC vehicles are limited to steering. However, as the tires approach the maximum lateral force sustainable under the available pavement friction, the yaw moment generated by a given increment of steering angle is much less than at the low lateral forces occurring in regular driving

. This means that as the vehicle approaches its maximum cornering capability, the ability of the steering system to turn the vehicle is greatly diminished, even in the hands of an expert driver. ESC creates the yaw moment to turn the vehicle using braking at an individual wheel rather than the steering system. This intervention remains powerful even at limits of tire traction because both the braking force of the individual tire and the reduction of lateral force that accompanies the braking force act to create the desired yaw moment. Therefore, ESC can be especially beneficial on slippery surfaces. While a vehicle's possibility of staying on the road in a critical maneuver ultimately is limited by the tire/pavement friction, ESC maximizes an ordinary driver's ability to use the available friction.

Liebemann

et al.

, (2005) Safety and Performance Enhancement: The Bosch Electronic Stability Control (ESP), 19th International Technical Conference on the Enhanced Safety of Vehicles (ESV), Washington, DC.

Overview of ESC Effectiveness in Preventing Single-Vehicle and Rollover Crashes

Crash data studies conducted in the U.S., Europe, and Japan indicate that ESC is very effective in reducing single-vehicle crashes. Studies of the behavior of ordinary drivers in critical situations using the National Advanced Driving Simulator also show a very large reduction in instances of loss of control when the vehicle is equipped with ESC. Based on its crash data studies, NHTSA estimates that ESC will reduce single vehicle crashes of passenger cars by 34 percent and single vehicle crashes of SUVs by 59 percent. NHTSA's latest crash data study also shows that ESC is most effective in reducing single-vehicle crashes that result in rollover. ESC is estimated to prevent 71 percent of passenger car rollovers and 84 percent of SUV rollovers in single vehicle crashes. It is also estimated to reduce some multi-vehicle crashes but at a much lower rate than its effect on single vehicle crashes. The following discussion explains in detail the research finding upon which the agency has relied in determining the anticipated effectiveness of ESC systems.

Electronic stability control can directly reduce a vehicle's susceptibility to on-road untripped rollovers as measured by the “fishhook” test that is part of NHTSA's NCAP rollover rating program. The direct effect is mostly limited to untripped rollovers on paved surfaces. However, untripped on-road rollovers are a relatively infrequent type of rollover crash. In contrast, the vast majority of rollover crashes occur when a vehicle runs off the road and strikes a tripping mechanism such as soft soil, a ditch, a curb or a guardrail.

We expect that requiring ESC to be installed on light trucks and passenger cars would result in a large reduction in the number of rollover crashes by greatly reducing the number of single-vehicle crashes. As noted previously, over 80 percent of rollovers are the result of a single-vehicle crash. The purpose of ESC is to assist the driver in keeping the vehicle on the road during impending loss-of-control situations. In this way, it can prevent the exposure of vehicles to off-road tripping mechanisms. We note, however, that this yaw stability function of ESC is not direct “rollover resistance” and cannot be measured by the NCAP rollover resistance rating.

Although ESC is an indirect countermeasure to prevent rollover crashes, we believe it is the most powerful countermeasure available to address this serious risk. Effectiveness studies by NHTSA and others worldwide

estimate that ESC reduces single vehicle crashes by at least a third in passenger cars and perhaps reduces loss-of-control crashes (

e.g.

, road departures leading to rollovers) by an even greater amount. In fact, NHTSA's latest data study that is discussed in this section found a reduction in single-vehicle crashes leading to rollover of 71 percent for passenger cars and 84 percent for SUVs. Thus, ESC can reduce the numbers of rollovers of all vehicles, including lower center of gravity vehicles (

e.g.

, passenger cars, minivans and two-wheel drive pickup trucks), as

well as of the higher center of gravity vehicle types (

e.g.

, SUVs and four-wheel drive pickup trucks). ESC can affect both crashes that would have resulted in rollover as well as other types of crashes (

e.g.

, road departures resulting in impacts) that result in deaths and injuries.

Aga M, Okada A. (2003) Analysis of Vehicle Stability Control (VSC)'s Effectiveness from Accident Data, 18th International Technical Conference on the Enhanced Safety of Vehicles (ESV), Nagoya.

Dang, J. (2004) Preliminary Results Analyzing Effectiveness of Electronic Stability Control (ESC) Systems, Report No. DOT HS 809 790. U.S. Dept. of Transportation, Washington, DC.

Farmer, C. (2004) Effect of Electronic Stability Control on Automobile Crash Risk, Traffic Injury Prevention Vol. 5:317-325.

Kreiss J-P,

et al.

(2005) The Effectiveness of Primary Safety Features in Passenger Cars in Germany. 19th International Technical Conference on the Enhanced Safety of Vehicles (ESV), Washington, DC.

Lie A.,

et al.

(2005) The Effectiveness of ESC (Electronic Stability Control) in Reducing Real Life Crashes and Injuries. 19th International Technical Conference on the Enhanced Safety of Vehicles (ESV), Washington, DC.

Human Factors Study on the Effectiveness of ESC

A study by the University of Iowa using the National Advanced Driving Simulator demonstrated the effect of ESC on the ability of ordinary drivers to maintain control in critical situations.

A sample of 120 drivers equally divided between men and women and between three age groups (18-25, 30-40, and 55-65) was subjected to the following three critical driving scenarios. The “Incursion Scenario” forced drivers to attempt a double lane change at high speed (65 mph speed limit signs) by presenting them first with a vehicle that suddenly backs into their lane from a driveway and then with another vehicle driving toward them in the left lane. The “Curve Departure Scenario” presented drivers with a constant radius curve that was uneventful at the posted speed limit of 65 mph followed by another curve that appeared to be similar but that had a decreasing radius that was not evident upon entry. The “Wind Gust Scenario” presented drivers with a sudden lateral wind gust of short duration that pushed the drivers toward a lane of oncoming traffic. The 120 drivers were further divided evenly between two vehicles, an SUV and a midsize sedan. Half the drivers of each vehicle drove with ESC enabled, and half drove with ESC disabled.

Papelis

et al.

(2004) Study of ESC Assisted Driver Performance Using a Driving Simulator, Report No. N04-003-PR, University of Iowa.

In 50 of the 179 test runs performed in a vehicle without ESC, the driver lost control. In contrast, in only six of the 179 test runs performed in a vehicle with ESC, did the driver lose control. One test run in each ESC status had to be aborted. These results demonstrate an 88 percent reduction in loss-of-control crashes when ESC was engaged. The study also concluded that the presence of an ESC system helped reduce loss of control regardless of age or gender, and that the benefit was substantially the same for the different driver subgroups in the study. Because of the obvious danger to participants, an experiment like this cannot be performed safely with real vehicles on real roads. However, the National Advanced Driver Simulator provides extraordinary verisimilitude with the driver sitting in a real vehicle, seeing a 360-degree scene and experiencing the linear and angular accelerations and sounds that would occur in actual driving of the specific vehicle.

Crash Data Studies of ESC Effectiveness

There have been a number of studies of ESC effectiveness in Europe and Japan beginning in 2003.

All of them have shown large potential reductions in single-vehicle crashes as a result of ESC. However, the sample sizes of crashes of vehicles new enough to have ESC tended to be small in these studies. A preliminary NHTSA study published in September 2004

of crash data from 1997-2003 found ESC to be effective in reducing single-vehicle crashes, including rollover. Among vehicles in the study, the results suggested that ESC reduced single vehicle crashes in passenger cars by 35 percent and in SUVs by 67 percent. In October 2004, the Insurance Institute for Highway Safety (IIHS) released the results of a study of the effectiveness of ESC in preventing crashes of cars and SUVs. The IIHS found that ESC is most effective in reducing fatal single-vehicle crashes, reducing such crashes by 56 percent. NHTSA's later peer-reviewed study

of ESC effectiveness found that ESC reduced single vehicle crashes in passenger cars by 34 percent and in SUVs by 59 percent, and that its effectiveness was greatest in reducing single vehicle crashes resulting in rollover (71 percent reduction for passenger cars and an 84 percent reduction for SUVs). It also found reductions in fatal single-vehicle crashes and fatal single-vehicle rollover crashes that were commensurate with the overall crash reductions cited. ESC reduced fatal single-vehicle crashes in passenger cars by 35 percent and in SUVs by 67 percent and reduced fatal single-vehicle crashes involving rollover by 69 percent in passenger cars and 88 percent in SUVs.

See Footnote 10.

Dang, J. (2004) Preliminary Results Analyzing Effectiveness of Electronic Stability Control (ESC) Systems, Report No. DOT HS 809 790. U.S. Dept. of Transportation, Washington, DC.

Dang, J. (2006) Statistical Analysis of The Effectiveness of Electronic Stability Control (ESC) Systems, U.S. Dept. of Transportation, Washington, DC (publication pending peer review). A draft version of this report, as supplied to peer reviewers, has been placed in the docket for this rulemaking.

(a) NHTSA's preliminary study

In September, 2004, NHTSA issued an evaluation note on the

Preliminary Results Analyzing the Effectiveness of Electronic Stability Control (ESC) Systems

. The study evaluated the effectiveness of ESC in reducing single vehicle crashes in various domestic and imported cars and SUVs. It was based on Fatality Analysis Reporting System (FARS) data from calendar years 1997-2003 and crash data from five States that reported partial Vehicle Identification Number (VIN) information in their data files (Florida, Illinois, Maryland, Missouri, and Utah) from calendar years 1997-2002. The data were limited to mostly luxury vehicles because ESC first became available in 1997 in luxury vehicles such as Mercedes-Benz and BMW. The analysis compared specific make/models of passenger cars and SUVs with ESC versus earlier versions of the same make/models, using multi-vehicle crash involvements as a control group.

The passenger car sample consisted of mainly Mercedes-Benz and BMW models (61 percent). Mercedes-Benz installed ESC in certain luxury models in 1997 and had made it standard equipment in all their models (except one) by 2000. BMW also installed ESC in certain 5, 7, and 8 series models as early as 1997 and had made it standard equipment in all their models by 2001. The passenger car sample also included some luxury GM cars, which constituted 23 percent of the sample, and a few cars from other manufacturers. GM cars where ESC was offered as standard equipment are the Buick Park Avenue Ultra, the Cadillac DeVille, Seville STS and SLS, the Oldsmobile Aurora, the Pontiac Bonneville SSE and SSEi, and the Chevrolet Corvette. The SUV make/models in the study with ESC include Mercedes-Benz (ML320, ML350, ML430, ML500, G500, G55 AMG), Toyota (4Runner, Landcruiser), and Lexus (RX300, LX470).

The first set of analyses used multi-vehicle crash involvements as a control group, essentially assuming that ESC has no effect on multi-vehicle crashes. Specific make/models with ESC were compared with earlier versions of similar make/models using multi-vehicle crash involvements as a control group, creating 2x2 contingency tables as shown in Tables 1 and 2. The study found that single vehicle crashes were reduced by

1 − {(699/1483)/(14090/19444)} = 35 percent

for passenger cars and by 67 percent for SUVs (Table 1). Similarly, fatal single vehicle crashes were reduced by 30 percent in cars and by 63 percent in SUVs (Table 2). Reductions of single vehicle crashes in passenger cars and SUVs were statistically significant at the .01 level, as evidenced by chi-square statistics exceeding 6.64 in each 2x2 contingency table (Table 1). Reductions of fatal single vehicle crashes are

statistically significant at the .01 level in SUVs and at the .05 level in passenger cars with chi-square statistic greater than 3.84 (Table 2).

Table 1.—Effectiveness of ESC in Reducing Single Vehicle Crashes in Passenger Cars and SUVs

[Preliminary study with 1997-2002 crash data from five States]

Single vehicle crashes

Multi-vehicle crashes

(control group)

Passenger Cars

No ESC

1483

19444

ESC

699

14090

Percent reduction in single vehicle crashes in passenger cars with ESC

35%

Approximate 95 percent confidence bounds

29% to 41%

Chi-square value

84.1

SUVs

No ESC

512

6510

ESC

3661

Percent reduction in single vehicle crashes in SUVs with ESC

67%

Approximate 95 percent confidence bounds

60% to 74%

Chi-square value

104.4

Table 2.—Effectiveness of ESC in Reducing Fatal Single Vehicle Crashes in Passenger Cars and SUVs

[Preliminary study with 1997-2003 FARS data]

Fatal single vehicle crashes

Fatal multi-vehicle crashes

(control group)

Passenger Cars

No ESC

186

330

ESC

110

278

Percent reduction in fatal single vehicle crashes in passenger cars with ESC

30%

Approximate 95 percent confidence bounds

10% to 50%

Chi-square value

6.0

SUVs

No ESC

129

199

ESC

103

Percent reduction in fatal single vehicle crashes in SUVs with ESC

63%

Approximate 95 percent confidence bounds

44% to 81%

Chi-square value

16.1

NHTSA has now updated and modified last year's report, extending it to model year 1997-2004 vehicles—and to calendar year 2004 for the FARS analysis and calendar year 2003 for the State data analysis. Nevertheless, even as of 2004, a large proportion of the vehicles equipped with ESC were still luxury vehicles. Moreover, only passenger cars and SUVs had been equipped with ESC—no pickup trucks or minivans.

The State databases included crash cases from California (2001-2003), Florida (1997-2003), Illinois (1997-2002), Kentucky (1997-2002), Missouri (1997-2003), Pennsylvania (1997-2001, 2003), and Wisconsin (1997-2003). The FARS database included fatal crash involvements from calendar years 1997 to 2004. The extra year of exposure and the availability of data from more states significantly increased the sample size of crashes of vehicles with ESC. In the preliminary study, the state crash database contained 699 single-vehicle crashes of cars with ESC and 95 single-vehicle crashes of SUVs with ESC. The FARS database contained 110 single-vehicle crashes of cars with ESC and 25 single-vehicle crashes of SUVs with ESC. For the updated study, the state crash database contains 2,251 single-vehicle crashes of cars with ESC and 553 single-vehicle crashes of SUVs with ESC, and the FARS database of fatal single-vehicle crashes contains 157 and 47 crashes respectively, for passenger cars and SUVs with ESC.

The larger sample of crashes in the updated study facilitated a new analysis of the effectiveness of ESC on specific subsets of single-vehicle crashes (SV run-off-road crashes and SV crashes resulting in rollover). It also facilitated the use of a more focused control group of crashes that were unlikely to be affected by ESC so that a new analysis of the effect of ESC on multi-vehicle crashes could be undertaken.

The basic analytical approach was to estimate the reduction of crash involvements of the types that are most likely to have benefited from ESC—relative to a control group of other types of crashes where ESC is unlikely to have made a difference in the vehicle's involvement. Crash types taken as the new control group (non-relevant involvements because ESC would in almost all cases not have prevented the crash) were crash involvements in which a vehicle:

(1) Was stopped, parked, backing up, or entering/leaving a parking space prior to the crash,

(2) Traveled at a speed less than 10 mph,

(3) Was struck in the rear by another vehicle, or

(4) Was a non-culpable party in a multi-vehicle crash on a dry road.

The types of crash involvements where ESC would likely or at least possibly have an effect are:

(1) All single vehicle crashes, except those with pedestrians, bicycles, or animals (SV crashes).

(2) Single vehicles crashes in which a vehicle ran off the road (SV ROR) and hit a fixed object and/or rolled over.

(3) Single vehicles crashes in which a vehicle rolled over (SV Rollover), mostly a subset of SV ROR.

(4) Involvements as a culpable party in a multi-vehicle crash on a dry or wet road (MV Culpable).

(5) Collisions with pedestrians, bicycles, or animals (Ped, Bike, Animal).

In the updated study we performed the state data analysis separately for each state. Then we used the median of the estimates from the seven states as the best indicator of the central tendency of the data, and the variation of the seven states as a basis for judging statistical significance and estimating confidence bounds. The results of this analysis are presented in Table 3.

Table 3.—Updated Study—Mean Effectiveness of ESC in Reducing Crashes in Passenger Cars and SUVs Based on Separate Analyses of 1997-2003 Crash Data From Seven States

SV Crashes

SV ROR

SV Rollover

MV Culpable

Ped, bike,

animal

Passenger Cars

Mean percent reduction of listed crash type in passenger cars with ESC

34%

46%

71%

11%

34%.

Approximate 90 percent confidence bounds

20% to 46%

35% to 55%

60% to 78%

4% to 18%

5% to 55%.

SUVs

Mean percent reduction of listed crash type in SUVs with ESC

59%

75%

84%

16%

−4% not statistically significant.

Approximate 90 percent confidence bounds

47% to 68%

68% to 80%

75% to 90%

7% to 24%

−28% to 15%.

Fatal crashes were analyzed separately using the FARS database as was done in the preliminary study, but larger sample sizes were possible because of an additional year of data. The results are given in Table 4.

Table 4.—Updated Study—Effectiveness of ESC in Reducing Fatal Crashes of Passenger Cars and SUVs Based on 1997-2004 FARS Data

SV Crashes

SV ROR

SV Rollover

MV Culpable

Ped, bike,

animal

Control group

Passenger Cars

No ESC

223

217

176

166

ESC

157

154

156

181

Percent reduction of listed crash type in passenger cars with ESC

35%

36%

69%

19% not statistically significant

38% not statistically significant

Approximate 90 percent confidence bounds

20% to 51%

19% to 51%

52% to 87%

−2% to 39%

−87% to 12%

Chi-square value

8.58

8.17

12.45

1.82

2.14

SUVs

No ESC

197

191

106

108

153

ESC

109

Percent reduction of listed crash type in SUVs with ESC

67%

72%

88%

38%

0% not statistically significant

Approximate 90 percent confidence bounds

55% to 78%

62% to 82%

81% to 95%

16% to 60%

−40% to 40%

Chi-square value

29.57

36.44

42.4

4.89

0.00

The effectiveness of ESC in reducing fatal single-vehicle crashes is similar to the effectiveness in reducing single-vehicle crashes from state data that included mostly non-fatal crashes. In the case of fatal crashes as well, the effectiveness of ESC in reducing single-vehicle rollover crashes was particularly high. The effectiveness of ESC in reducing fatal culpable multi-vehicle crashes of SUVs was also higher than in the analysis of state data, while the parallel analysis of multi-vehicle crashes of passenger cars did not achieve statistical significance.

The updated study of ESC effectiveness yielded robust results. The analysis of state data and a separate analysis of fatal crashes both reached similar conclusions on ESC effectiveness. ESC reduced single vehicle crashes of passenger cars by 34 percent and single vehicle crashes of

SUVs by 59 percent. The separate analysis of only fatal crashes supported the analysis of state data that included mostly non-fatal crashes. Therefore, the overall crash reductions demonstrated a significant life-saving potential for this technology. The effectiveness of ESC in reducing SV crashes shown in the latest data (Tables 3-4) is similar to the results of the preliminary analysis.

The effectiveness of ESC tended to be at least as great and possibly even greater for more severe crashes. Furthermore, the effectiveness of ESC in reducing the most severe type of crash in the study, the single-vehicle rollover crash, was remarkable. ESC reduced single-vehicle rollover crashes of passenger cars by 71 percent and of SUVs by 84 percent. This high level of effectiveness also carried over to fatal single-vehicle rollover crashes.

The benefits presented in Section V were calculated on the basis of the single-vehicle crash and single-vehicle rollover crash effectiveness results of Table 3 for reductions in non-fatal crashes and of Table 4 for reductions in fatal crashes. The single-vehicle rollover crash effectiveness results were applied only to first harmful event rollovers with the lower single-vehicle crash effectiveness results applied to all other rollover crashes for a more conservative benefit estimate.

III. September 2006 Notice of Proposed Rulemaking (NPRM) and Public Comments

A. The NPRM

As noted above, NHTSA published an NPRM on September 18, 2006 that proposed to establish FMVSS No. 126,

Electronic Stability Control Systems

(71 FR 54712). Specifically, it proposed to require passenger cars, multipurpose passenger vehicles, trucks, and buses with a GVWR of 4,536 kg (10,000 pounds) or less to be equipped with an ESC system that meets the requirements of the standard. As proposed, the vehicle would be required to meet a definitional requirement (

i.e.

, specifying the necessary elements of a stability control system that would be capable of both effective oversteer and understeer intervention) and to pass a dynamic performance test. These requirements are necessary due to the extreme difficulty in establishing a test adequate to ensure the desired level of ESC functionality.

The test is necessary to ensure that the ESC system is robust and meets a level of performance at least comparable to that of current ESC systems.

Without an equipment requirement, it would be almost impossible to devise a single performance test that could not be met through some action by the manufacturer other than providing an ESC system. Even a battery of performance tests still might not achieve our intended results, because although it might necessitate installation of an ESC system, we expect that it would be unduly cumbersome for both the agency and the regulated community.

The NPRM included the following points, which highlighted the key provisions of the proposed requirements. However, for a more complete discussion—including detailed information on the proposal, as well as various potential performance tests (for both lateral stability and vehicle responsiveness) and regulatory alternatives considered by the agency—interested persons are encouraged to consult the NPRM.

• Consistent with the industry consensus definition of ESC contained in the Society of Automotive Engineers (SAE) Surface Vehicle Information Report J2564 (rev. June 2004), we proposed to require vehicles covered under the standard to be equipped with an ESC system that:

(1) Augments vehicle directional stability by applying and adjusting the vehicle's brakes individually to induce correcting yaw torques to a vehicle;

(2) Is computer-controlled, with the computer using a closed-loop algorithm

to limit vehicle oversteer and to limit vehicle understeer when appropriate;

A “closed-loop algorithm” is a cycle of operations followed by a computer that includes automatic adjustments based on the result of previous operations or other changing conditions.

(3) Has a means to determine vehicle yaw rate

and to estimate its sideslip

;

“Yaw rate” means the rate of change of the vehicle's heading angle measured in degrees/second of rotation about a vertical axis through the vehicle's center of gravity.

“Sideslip” 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.

(4) Has a means to monitor driver steering input, and

(5) Is operational over the full speed range of the vehicle (except below a low-speed threshold where loss of control of the vehicle is unlikely).

• The proposed ESC system, as defined above, would also be required to be capable of applying all four brakes individually and to have an algorithm that utilizes this capability. The system would also be required to be operational during all phases of driving, including acceleration, coasting, and deceleration (including braking), and it would be required to remain operational when the antilock brake system or traction control system is activated.

• We also proposed to require vehicles covered under the standard to satisfy the standard's stability criteria and responsiveness criterion when subjected to the Sine with Dwell steering maneuver test. This test involves a vehicle coasting at an initial speed of 50 mph while a steering machine steers the vehicle with a steering wheel pattern as shown in Figure 2 of the NPRM. The test maneuver is then repeated over a series of increasing maximum steering angles. This test maneuver was selected over a number of other alternatives, because we tentatively decided that it has the most optimal set of characteristics, including severity of the test, repeatability and reproducibility of results, and the ability to address lateral stability and responsiveness.

The maneuver is severe enough to produce spinout for most vehicles without ESC. The stability criteria for the test measure how quickly the vehicle stops turning after the steering wheel is returned to the straight-ahead position. A vehicle that continues to turn for an extended period after the driver steers straight is out of control, which is what ESC is designed to prevent. The stability criteria are expressed in terms of the percent of the peak yaw rate after maximum steering that persists at a period of time after the steering wheel has been returned to straight ahead. The criteria require that the vehicle yaw rate decrease to no more than 35 percent of the peak value after one second and that it continues to drop to no more than 20 percent after 1.75 seconds. Since a vehicle that simply responds very little to steering commands could meet the stability criteria, a minimum responsiveness criterion is applied to the same test. It requires that the ESC-equipped vehicle must move laterally at least 1.83 meters (half a 12 foot lane width) during the first 1.07 seconds after the initiation of steering (a discontinuity in the steering pattern that is convenient for timing a measurement).

• Because the benefits of the ESC system can only be realized if the system is functioning properly, we proposed to require a telltale be mounted inside the occupant compartment in front of and in clear view of the driver and be identified by the symbol shown for “ESC Malfunction Telltale” in Table 1 of FMVSS No. 101,

Controls and Displays.

The ESC malfunction telltale would be required to illuminate not more than two minutes after the occurrence of one or more malfunctions that affect the generation or transmission of control or response signals in the vehicle's ESC system.

Such telltale would be required to remain continuously illuminated for as long as the malfunction(s) exists, whenever the ignition locking system is in the “On” (“Run”) position. (Vehicle manufacturers would be permitted to use the ESC malfunction telltale in a flashing mode to indicate ESC operation.)

• In certain circumstances, drivers may have legitimate reasons to disengage the ESC system or limit its ability to intervene, such as when the vehicle is stuck in sand/gravel or when the vehicle is being run on a track for maximum performance. Accordingly, under this proposal, vehicle manufacturers would be permitted to include a driver-selectable switch that places the ESC system in a mode in which it would not satisfy the performance requirements of the standard (

e.g.

, “sport” mode or full-off mode). However, if the vehicle manufacturer chooses this option, it would be required to ensure that the ESC system always returns to a mode that satisfies the requirements of the standard at the initiation of each new ignition cycle, regardless of the mode the driver had previously selected. Furthermore, the manufacturer would be required to provide an “ESC Off” switch and a telltale that are mounted inside the occupant compartment in front of and in clear view of the driver and which are identified by the symbol or text shown for “ESC Off” in Table 1 of FMVSS No. 101. Such telltale would be required to remain continuously illuminated for as long as the ESC is in a mode that renders it unable to meet the performance requirements of the standard, whenever the ignition locking system is in the On (“Run”) position.

• We did not propose to require the ESC system to be equipped with a roll stability control function (or a separate system to that effect). Roll stability control systems involve relatively new technology, and we decided that there is currently insufficient data to judge the efficacy of such systems. However, the agency stated that it will continue to monitor the development of roll stability control systems. The NPRM also stated that vehicle manufacturers may supplement the ESC system we are proposing to require with a roll stability control system/feature.

In order to provide the public with the expected significant safety benefits of ESC systems as rapidly as possible, the NPRM proposed to require all light vehicles covered by this standard to be equipped with a FMVSS No. 126-compliant ESC system by September 1, 2011 (subject to the exception below). The agency proposed that compliance would commence on September 1, 2008, subject to the following phase-in schedule: 30 percent of a vehicle manufacturer's light vehicles manufactured during the period from September 1, 2008 to August 31, 2009 would be required to comply with the standard; 60 percent of those manufactured during the period from September 1, 2009 to August 31, 2010; 90 percent of those manufactured during the period from September 1, 2010 to August 31, 2011, and all light vehicles thereafter.

The NPRM stated that in order to encourage early compliance, the agency proposed that vehicle manufacturers would be permitted to earn carry-forward credits for compliant vehicles, produced in excess of the phase-in requirements, which are manufactured between the effective date of the final rule and the conclusion of the phase-in period. However, under the proposal, beginning September 1, 2011, all covered vehicles would be required to comply with the standard, without regard to any earlier carry-forward credits.

We proposed to exclude multi-stage manufacturers and alterers from the requirements of the phase-in and to extend by one year the time for compliance by those manufacturers (

i.e.

, until September 1, 2012). This NPRM also proposed to exclude small volume manufacturers (

i.e.

International Discussions of a Potential Global Technical Regulation on ESC

Based upon the agency's analysis of available research, we believe that the benefits of ESC are more broadly applicable than to just the U.S. driving environment. Instead, we believe that ESC has the potential to greatly benefit road users in all parts of the world. Therefore, throughout the development of its ESC proposal, NHTSA made particular efforts to keep other governments informed on the progress of its rulemaking. The agency accomplished this through several bilateral exchanges, as well as through its role in the United National World Forum for the Harmonization of Vehicle Regulations (WP.29) in Geneva, Switzerland.

Specifically, the United States negotiated the placement of electronic stability control systems on the Program of Work of WP.29 under the 1998 Global Agreement,

in order to formalize and facilitate information exchange on this topic. Since early 2005, agency officials have provided formal presentations on the ESC rulemaking to WP.29 and its specialized subsidiary body for stability control systems four times during formal session meetings. More recently, in November 2006, the NHTSA Administrator delivered remarks at the 140th session of WP.29, in which she outlined the benefits of this new technology and encouraged the Forum to pursue the development of a Global Technical Regulation (GTR) for ESC. The proposal

was met with great interest and was accepted by several of the government representatives in attendance. The representatives were especially impressed that the benefits of ESC technology are well-corroborated through several studies conducted independently around the world. Formal work to develop a GTR on electronic stability control is expected to begin in 2007.

Although commonly referred to as the 1998 Global Agreement, this provision is more formally titled the “1998 Agreement Concerning the Establishing of Global Technical Regulations for Wheeled Vehicles, Equipment and Parts which can be Fitted and/or be Used on Wheeled Vehicles.”

See http://www.unece.org/trans/doc/2007/wp29/ECE-TRANS-WP29-2007-17e.doc.

B. Summary of the Public Comments on the NPRM

NHTSA received comments on the September 18, 2006 NPRM from a variety of interested parties, including seven automobile manufacturers and their trade associations,

nine suppliers of automobile equipment and their trade association,

four safety advocacy organizations,

and two other interested organizations.

Comments

were also received from eight individuals. All of these comments may be found in Docket No. NHTSA-2006-25801.

Comments were received from the following automobile manufacturers and related trade associations: (1 and 2) Alliance of Automobile Manufacturers and Association of International Automobile Manufacturers (joint comments); (3) Honda Motor Co. Ltd. and American Honda Motor Co., Inc.; (4) Nissan North America, Inc.; (5) Porsche Cars North America, Inc.; (6) Toyota Motor North America, Inc., and (7) Verband der Automobilindustrie.

Comments were received from the following automobile equipment suppliers and their trade associations: (1) BorgWarner Torq Transfer Systems, Inc.; (2) Continental Automotive Systems; (3) Delphi Corporation; (4) Motor & Equipment Manufacturers Association; (5) Oxford Technical Solutions, Ltd.; (6) RLP Engineering; (7) Robert Bosch Corporation; (8) Specialty Equipment Market Association, and (9) TRW Automotive.

Comments were received from the following safety advocacy organizations: (1) Advocates for Highway and Auto Safety; (2) Consumers Union; (3) Insurance Institute for Highway Safety, and (4) Public Citizen.

Comments were received from the following other interested organizations: (1) National Mobility Equipment Dealers Association, and (2) SUVOA.

Although certain of the comments from individuals objected to the ESC proposal (on the grounds of cost, newness of the technology, and concerns that it inappropriately may wrest vehicle control from the driver during critical situations), the overwhelming majority of the commenters supported establishing a safety standard for ESC systems as required equipment on new light vehicles. Instead, the difference of opinion among the commenters involved the stringency of the standard (including a requirement for advanced features), the test procedures (including need for understeer performance requirements), and the proposed lead time and phase-in for implementing the new standard. Other topics included making the “ESC System” definition more performance-based, lateral responsiveness criteria, ESC performance requirements, ESC malfunction detection requirements, ESC telltale requirements, system disablement and the “ESC Off” switch, test procedures, impacts on the aftermarket, comments on the preliminary regulatory impact analysis (PRIA), ESC outreach efforts, and other topics. The following discussion summarizes the main issues raised by these public comments and the positions expressed on these topics. A more complete discussion of the public comments is provided under Section IV.C, which provides an explanation of the agency rationale for the requirements of the final rule and addresses related public comments by issue.

IV. The Final Rule and Response to Public Comments

A. Summary of the Requirements

After careful consideration of the public comments on the NPRM, this final rule establishes FMVSS No. 126,

Electronic Stability Control Systems.

Specifically, it requires passenger cars, multipurpose passenger vehicles, trucks, and buses with a gross vehicle weight rating of 4,536 Kg (10,000 pounds) or less to be equipped with an ESC system that meets the requirements of the standard, in order to assist the driver in maintaining control in critical driving situations in which the vehicle is beginning to lose directional stability at the rear wheels (spin out) or directional control at the front wheels (plow out). Subject to the phase-in schedule and the exceptions below, compliance with the requirements of the final rule commences for covered vehicles manufactured on or after September 1, 2008 (

i.e.

, MY 2009).

The following points highlight the key provisions of the final rule.

• Consistent with the industry consensus definition of ESC contained in the Society of Automotive Engineers (SAE) Surface Vehicle Information Report J2564 (rev. June 2004), we are requiring vehicles covered under the standard to be equipped with an ESC system that:

(1) Augments vehicle directional stability by applying and adjusting the vehicle brake torques individually to induce a correcting yaw moment to a vehicle;

(2) Is computer-controlled, with the computer using a closed-loop algorithm

to limit vehicle oversteer and to limit vehicle understeer;

A “closed-loop algorithm” is a cycle of operations followed by a computer that includes automatic adjustments based on the result of previous operations or other changing conditions.

(3) Has a means to determine vehicle yaw rate

and to estimate its sideslip

or the time derivative of sideslip;

“Yaw rate” means the rate of change of the vehicle's heading angle measured in degrees/second of rotation about a vertical axis through the vehicle's center of gravity.

“Sideslip” 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.

(4) Has a means to monitor driver steering input;

(5) Has an algorithm to determine the need, and a means to modify engine torque, as necessary, to assist the driver in maintaining control of the vehicle, and

(6) Is operational over the full speed range of the vehicle (except at vehicle speeds less than 15 km/h (9.3 mph) or when being driven in reverse).

• The ESC system as defined above is also required to be capable of applying brake torques individually at all four wheels and to have an algorithm that utilizes this capability. Except for the situations specifically set forth in part (6) of the definition of “ESC System” above, the system is also required to be operational during all phases of driving, including acceleration, coasting, and deceleration (including braking), and it is required to be capable of activation even if the anti-lock brake system or traction control system is also activated.

• In order to ensure that a vehicle is equipped with an ESC system that meets the definition of “ESC System” under S4, the final rule requires vehicle manufacturers to submit, upon the request of NHTSA s Office of Vehicle Safety Compliance, ESC system technical documentation as to when understeer intervention is appropriate for a given vehicle (

see

• We are also requiring vehicles covered under the standard to meet performance tests. It must satisfy the standard s stability criteria and responsiveness criterion when subjected to the Sine with Dwell steering maneuver test. This test involves a vehicle coasting at an initial speed of 50 mph while a steering machine steers the vehicle with a steering wheel pattern as shown in Figure 2 of the regulatory text. The test maneuver is then repeated over a series of increasing maximum steering angles. This test maneuver was selected over a number of other alternatives, because we decided that it has the most optimal set of characteristics, including severity of the test, repeatability and reproducibility of results, and the ability to address lateral stability and responsiveness.

The maneuver is severe enough to produce spinout for most vehicles without ESC. The stability criteria for the test measure is how quickly the vehicle stops turning after the steering wheel is returned to the straight-ahead position. A vehicle that continues to turn for an extended period after the driver steers straight is out of control, which is what ESC is designed to prevent. The quantitative stability criteria are expressed in terms of the percent of the peak yaw rate after maximum steering that persists at a period of time after the steering wheel has been returned to straight ahead. The criteria require that the vehicle yaw rate decrease to no more than 35 percent of the peak value after one second and that it continues to drop to no more than 20 percent after 1.75 seconds. Since a vehicle that simply responds very little to steering commands could meet the stability criteria, a minimum responsiveness criterion is applied to the same test. It requires that an ESC-equipped vehicle with a GVWR of 7,716 pounds or less must move laterally at least 6 feet during the first 1.07 seconds after the initiation of steering (a discontinuity in the steering pattern that is a convenient point for timing a

measurement). It also requires that a heavier vehicle with a GVWR up to 10,000 pounds must move at least 5 feet laterally in the same maneuver for specified steering angles.

• Because the benefits of the ESC system can only be realized if the system is functioning properly, we are requiring a telltale be mounted inside the occupant compartment in front of and in clear view of the driver and be identified by the symbol or text shown for “ESC Malfunction Telltale” in Table 1 of FMVSS No. 101,

Controls and Displays.

The ESC malfunction telltale is required to illuminate after the occurrence of one or more malfunctions that affect the generation or transmission of control or response signals in the vehicle's ESC system. Such telltale must remain continuously illuminated for as long as the malfunction(s) exists, whenever the ignition locking system is in the “On” (“Run”) position. (Vehicle manufacturers are permitted to use the ESC malfunction telltale in a flashing mode to indicate ESC operation.)

• In certain circumstances, drivers may have legitimate reasons to disengage the ESC system or limit its ability to intervene, such as when the vehicle is stuck in sand/gravel, using snow chains, or when the vehicle is being run on a track for maximum performance. Accordingly, under this final rule, vehicle manufacturers may include a driver-selectable control that places the ESC system in a mode in which it would not satisfy the performance requirements of the standard (

e.g.

, “sport” mode or full-off mode). However, if the vehicle manufacturer chooses this option, it must ensure that the ESC system always returns to the fully-functional default mode at the initiation of each new ignition cycle, regardless of the mode the driver had previously selected (with certain exceptions for low speed off-road axle/transfer case selections that turn off ESC but cannot be reset electronically). The manufacturer is required to provide an “ESC Off” control and a telltale that are mounted inside the occupant compartment in front of and in clear view of the driver and which are identified by the symbol or text shown for “ESC Off” in Table 1 of FMVSS No. 101 or the text “ESC Off.” Such telltale must remain continuously illuminated for as long as the ESC is in a mode that renders it unable to meet the performance requirements of the standard, whenever the ignition locking system is in the “On” (“Run”) position.

B. Lead Time and Phase-in

In order to provide the public as rapidly as possible with what are expected to be the significant safety benefits of ESC systems, NHTSA has decided to require all light vehicles covered by this standard to be equipped with a FMVSS No. 126-compliant ESC system by September 1, 2011 (with certain exceptions discussed below). This implementation date for full, mandatory compliance is the same as that proposed in the NPRM and is consistent with our stated intention to have 90 percent of the subject fleet equipped with ESC in the 2011 model year that starts September 1, 2010. The agency continues to believe that this schedule for full implementation of the safety standard for ESC is appropriate, in order to provide manufacturers adequate lead time to make necessary production changes. September 1, 2008 marks the start of a three-year phase-in period for FMVSS No. 126.

However, in response to public comments and upon further review of the production plans

voluntarily submitted by vehicle manufacturers, we have determined that it would be practicable to increase the percentage of new light vehicles that must comply with Standard No. 126 under the phase-in, thereby accelerating the benefits expected to be provided by ESC systems. Because ESC is so cost-effective and has such high benefits in terms of potential fatalities and injuries that may be prevented, the agency agrees that it is important to require ESC installation in light vehicles as quickly as possible. Accordingly, under this final rule, we are requiring the following phase-in schedule for FMVSS No. 126: 55 percent of a vehicle manufacturer's light vehicles manufactured during the period from September 1, 2008 to August 31, 2009 would be required to comply with the standard; 75 percent of those manufactured during the period from September 1, 2009 to August 31, 2010; 95 percent of those manufactured during the period from September 1, 2010 to August 31, 2011, and all light vehicles thereafter. (This compares to the NPRM's proposal for a 30/60/90/all phase-in schedule over the same time periods.)

In April 2006, NHTSA sent letters to seven vehicle manufacturers requesting voluntary submission of information regarding their planned production of ESC-equipped vehicles for model years 2007 to 2012. Six manufacturers responded with product plans containing confidential information. These agency letters and manufacturer responses (with confidential information redacted) may be found in Docket No. NHTSA-2006-25801.

In order to ensure the financial and technological practicability of the final rule (in keeping with our statutory mandate), while at the same time facilitating ESC installation in the light vehicle fleet as expeditiously as possible, the agency analyzed the product plans submitted by six vehicle manufacturers, whose combined production accounts for approximately 87 percent of the new light vehicle fleet.

As explained in Chapter VII of the FRIA, we examined three different potential phase-in schedules to find the right balance among these competing concerns. Based upon this product plan information and the desire to provide manufacturers with flexibility by having a carry forward provision, we have chosen the most aggressive phase-in alternative that we believe is reasonable (

i.e.,

55/75/95%).

We note that manufacturers' product plans have continued to evolve during the course of this rulemaking. For example, in a September 13, 2006 press release, Ford Motor Company announced that 100 percent of its light vehicle fleet would have ESC as standard equipment by MY 2010 (

see http://www.consumeraffairs.com/news04/2006/09/ford_stability.html

). The agency has carefully considered such developments in setting the phase-in schedule for this final rule.

Two factors were controlling in making the decision as to which alternative to choose: (1) The ability of manufacturers to change vehicles from being equipped with optional ESC to standard ESC for MY 2010 and MY 2011; and (2) Not forcing any manufacturer to install ESC in any make/model for which it was not planned to be at least an option. The agency did not believe there was enough lead time to redesign a make/model to include ESC by MY 2009. While there may be enough time to redesign such a make/model to include ESC by MY 2010, given the carry forward provisions this was not necessary for any of the six manufacturers for MY 2010. The second consideration became a factor once again in MY 2011, in not going beyond 95 percent (thereby obviating the costly need to redesign and develop tooling for a few vehicle lines which will not be produced in MY 2012).

In general, we anticipate that vehicle manufacturers will be able to meet the requirements of the standard by installing ESC system designs currently in production (

i.e.

, ones available in MY 2006). Except for possibly some low-production-volume vehicles with infrequent design changes (addressed below), NHTSA believes that most other vehicles can reasonably be equipped with ESC within three to four model years. We have determined that the majority of vehicle manufacturers would be able to meet the first two years of the revised phase-in schedule, without revising their current

production plans for ESC-equipped vehicles, given available phase-in credits under the rule. For the other manufacturers, they will have to increase production of ESC-equipped vehicles to comply with this accelerated phase-in schedule, but the available lead time is sufficient to allow for orderly planning for this increase and to achieve full implementation. Furthermore, we do not believe that the final rule's phase-in should pose ESC supply problems; public comments from vehicle manufacturers and ESC suppliers did not raise any such supply concerns, and our analysis of vehicle manufacturers' production plans suggest that the selected phase-in schedule will result in an installation rate increase of only a few percentage points in any year of the phase-in. Overall, we have determined that the final rule's phase-in schedule may be accomplished without disruptive changes in manufacturer and supplier production processes.

We note that the agency has considered the possibility that external forces (

e.g.

, increases in gasoline prices, changing consumer preferences) might affect demand for specific types of vehicles, such as SUVs, which have higher ESC penetration. Such concerns provided further reason for the agency to adopt a phase-in schedule that included a provision for carry-forward credits.

After outlining the general parameters of the phase-in for FMVSS No. 126, we now turn to a number of exceptions or exclusions from the phase-in intended to address certain classes of vehicle manufacturers that may require additional time to achieve compliance and to address certain ESC components that may pose problems for a broader range of manufacturers in the short term. As an initial matter, we now understand from the public comments that vehicle manufacturers currently employ a variety of approaches for ESC controls and telltales, many of which would not meet the requirements of the agency's proposal. As a complicating matter, vehicle manufacturers and their trade associations explained that even though most current ESC systems would largely meet the performance requirements of the proposed standard, manufacturers' inability to meet the proposed control and display requirements would prevent them from earning the carry-forward credits needed to comply with the NPRM's aggressive phase-in schedule. Vehicle manufacturers generally commented that they could bring their ESC systems into full compliance (including the control and telltale requirements) by the end of the phase-in, and they argued that it is the performance of the ESC systems themselves, not the messages provided by the controls and telltales, that impart safety benefits under the standard.

After consideration of the numerous manufacturer comments on this issue, we have decided to defer the standard's requirements related to the ESC telltales and controls until the end of the phase-in (

i.e.

, September 1, 2011 for most manufacturers; September 1, 2012 for final-stage manufacturers and alterers); however, at that point, all covered vehicles must meet all relevant requirements of the standard (

i.e.

, no additional phase-in for the control and telltale requirements). Manufacturers are encouraged to voluntarily install compliant ESC controls and displays prior to the mandatory compliance date. Our rationale for this change from our proposal is as follows.

We now understand that standardizing ESC controls and telltales will involve substantial design and production changes and that additional lead time will be required to effect those changes. In addition, our analysis demonstrates that the safety benefits associated with early introduction of ESC systems, even without standardized controls and displays, far outweigh the benefits of delaying the standard until all systems can fully meet the control and display requirements (

see

FRIA's lead time/phase-in discussion). We do not believe that implementation of the entire standard should be delayed until technical changes related to the ESC controls and telltales can be fully resolved, because they would deny the public the safety benefits of ESC systems in the meantime. Accordingly, we believe that it is preferable to move rapidly to implement the standard, but to delay the compliance date only for the ESC control and telltale requirements.

This final rule also excludes small volume manufacturers (

i.e.

, manufacturers producing less than 5,000 vehicles for sale in the U.S. market in one year) from the phase-in, instead requiring such manufacturers to fully comply with the standard on September 1, 2011. This exclusion should facilitate implementation for low-production-volume vehicles with infrequent design changes.

Consistent with the policy set forth in NHTSA's February 14, 2005 final rule on certification requirements for vehicles built in two or more stages and altered vehicles (70 FR 7414), final-stage manufacturers and alterers are excluded from the requirements of the phase-in and are permitted an additional one year for compliance (

i.e.

, until September 1, 2012). However, final-stage manufacturers and alterers may voluntarily certify compliance with the standard prior to this date.

Vehicle manufacturers may earn carry-forward credits for compliant vehicles, produced in excess of the phase-in requirements, which are manufactured between the effective date of the final rule and the conclusion of the phase-in period. (We note that carry-forward credits may not be used to defer the mandatory compliance date of September 1, 2011 for all covered vehicles.) The final rule also includes phase-in reporting requirements for ESC systems (contained in Subpart I of 49 CFR Part 585) which are consistent with the phase-in schedule discussed above.

C. Response to Public Comments by Issue

As noted previously, public comments on the September 2006 NRPM for ESC raised a variety of issues with the NPRM's proposed requirements. Each of these topics will be discussed in turn, in order to explain how these comments impacted the agency's determinations in terms of setting requirements for this final rule.

Major Issues

1. Approach of the ESC NPRM

Subject to the phase-in schedule set forth in S8, the NPRM for ESC proposed to require new vehicles covered by Standard No. 126 to 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 (

see

S5,

Requirements

). The proposed standard would apply to passenger cars, multipurpose passenger vehicles, trucks, and buses with a gross vehicle weight rating of 4,536 kilograms (10,000 pounds) or less (

see

S3.1,

Application

NHTSA also noted that the ESC proposal would implement the provision in section 10301 of SAFETEA-LU, which requires the Secretary of Transportation to “establish performance criteria to reduce the occurrence of rollovers consistent with stability enhancing technologies” and to issue a final rule by April 1, 2009.

A number of commenters on the NPRM raised issues regarding the general approach taken by the agency in terms of its proposal for ESC. These comments are discussed immediately below.

(a) ESC Mandate vs. ESC Standardization

Mr. Kiefer urged NHTSA to adopt specifications for standardization of ESC systems that manufacturers voluntarily choose to install, rather than mandating

installation at this time. The commenter stated that this approach would provide a trial period during which the ESC requirements could be evaluated, prior to fleet-wide installation.

We believe Mr. Kiefer's suggested approach falls short in light of the advanced state of development of ESC systems. Moreover, our analysis of the real-world experience with ESC to date indicates that a rulemaking mandate for it will save thousands of lives each year on American roadways. Our analyses also indicate that a mandate for ESC will be among the most cost-effective of NHTSA's rules ever. Moreover, the agency is not aware of any significant operational problems for ESC systems now in millions of vehicles on the American roads, nor have ESC suppliers or vehicle manufacturers indicated that there are such problems. Under these circumstances, there is no reason to delay proceeding to a mandate for this life-saving technology to be on all light vehicles.

(b) ESC as Part of a Comprehensive Rollover Safety Program

The comments of Advocates for Highway and Auto Safety (Advocates) included a lengthy discussion of what it perceives to be the agency's failure to carry out a comprehensive rollover crash safety plan. Public Citizen similarly argued that the ESC rulemaking should be part of a comprehensive rollover plan, and in particular, it objected to the proposal's failure to include a requirement for roll stability control (cited as currently in production on the Volvo XC-90). According to Public Citizen, a requirement for roll stability control would lead SUVs to be equipped with roll sensors, which it argued would in turn enhance safety features critical for ejection mitigation such as seatbelt pretensioners, advanced window glazing, and side impact airbags.

As we have stated in the past and in the NPRM for this rule, the agency adopted such a comprehensive plan in June 2003, which envisions agency efforts (several of which are currently underway) to improve vehicle stability, ejection mitigation, roof crush resistance, as well as road improvements and behavioral strategies aimed at consumer education. The relevant legislative provisions contained in SAFETEA-LU are fully consistent with the agency's ongoing efforts to prevent rollover crashes and to reduce their severity when they do occur.

Our analysis demonstrates that ESC systems can have a major positive impact in terms of preventing loss of control and keeping the vehicle on the roadway, thereby preventing rollovers. Regarding our decision not to propose a requirement for roll stability control, the agency made this determination because there is little data available to assess whether that feature actually provides any additional safety benefits, given that it appears that some current systems add this feature to ESC. Note that we believe that current systems that include roll stability control will satisfy the requirements for ESC. Under 49 U.S.C. 30111, a safety standard must be practicable, meet the need for motor vehicle safety, and be stated in objective terms; in setting the standard, relevant, available motor vehicle safety information must be considered. In this case, the dearth of information about roll stability control effectively precludes the agency from adopting a roll stability requirement, because it is not possible to determine whether this technology meets the need for safety. At the same time, this rule does not establish any barriers to automakers' adding roll stability control to ESC systems, nor to customers' demanding it. The issue of roll stability control and other ESC features is discussed in further detail in Section IV.C.3 of this document.

Impact on Other NHTSA Rulemakings

Advocates argued that the ESC NPRM and accompanying PRIA should take into account that rulemaking's impact on the agency's proposal

to upgrade FMVSS No. 216,

Roof Crush Resistance.

The commenter stated that the ESC benefits assessment is incomplete because it does not discuss how some unknown portion of fatalities due to roof crush will not occur as a result of ESC intervention to keep the vehicle on the road (

i.e.

, by preventing the rollover crash entirely), and it makes essentially the same point regarding the roof crush NPRM.

70 FR 49223 (August 23, 2005).

The agency agrees that the ESC rule would impact the agency's rulemaking to amend FMVSS No. 216,

Roof Crush Resistance.

The benefits estimated in the PRIA for FMVSS No. 216, which accompanied the NPRM published on August 23, 2005 (70 FR 49223), reflect the impacts of ESC penetration into the fleet at that time. As a general matter, the impact of ESC on FMVSS No. 216 should be addressed in the regulatory analyses for FMVSS No. 216 rather than in the ESC rule. Generally, the agency's approach for estimating the actual benefits of any rulemaking is to adjust the benefits of a later rule to take into account the impacts of earlier rules. Therefore, for the ESC rulemaking, the PRIA and this FRIA estimated the overall benefits of the ESC rule and only address the impacts of prior rulemakings on this current rule. The impact of ESC on other future rulemakings would be addressed in those future rules respectively. The benefits of future rules, including the roof crush rulemaking, will reflect the installation of ESC in the vehicle fleet.

According to Consumers Union, vehicle manufacturers currently utilize a variety of acronyms and proprietary trade names to identify their ESC systems, which in turn make it more difficult for consumers to know what to ask for when shopping for a vehicle. To limit consumer confusion, Consumers Union urged NHTSA to require uniform terminology for how ESC systems are identified, so as to facilitate vehicle-to-vehicle comparisons. The organization recommended use of the nomenclature “ESC” and the term “Electronic Stability Control,” which presumably already have broad consumer recognition. A similar comment was provided by Mr. Petkun. These commenters also argued that the agency should require the automobile industry and dealerships to provide training for sales staff so that they may better educate and more accurately advise potential buyers about the value of an ESC system.

The agency appreciates the importance of providing consumers with clear information regarding vehicle safety features to use when deciding which vehicle to purchase, because we believe that such information serves a safety need (consistent with the agency's motor vehicle information mandate under 49 U.S.C. Chapter 323,

Consumer Information

). However, we do not believe it is necessary to pursue the use of common terminology for ESC, for the following reasons. The primary concern engendering calls for common terminology involved a consumer's ability to know whether a given vehicle is equipped with ESC or some other similar-sounding device (

e.g.

, a manufacturer's name for traction control), but that concern has essentially been eliminated by this final rule, which mandates installation of a compliant ESC system on all light vehicles by the end of the phase-in period. Absent that concern, there is no need for NHTSA to dictate how companies market their products.

2. The Definition of “ESC System” as the Basis of the Standard

As noted above, the NPRM proposed to require installation of an ESC system

that meets the definition contained in paragraph S4 of the standard, as well as the requirements of S5.1,

Required Equipment.

The proposed definition of “ESC System” specified certain features that must be present on that equipment, including that it be capable of applying all four brakes individually and have a computer using a closed-loop algorithm to limit vehicle oversteer and to limit vehicle understeer when appropriate. In addition, the system must have a means to determine the vehicle's yaw rate and to estimate its side slip, as well as a means to monitor driver steering inputs. Furthermore, the ESC system must be operational during all phases of driving including acceleration, coasting, and deceleration (including braking), except when the driver has disabled ESC or the vehicle is below a low speed threshold where loss of control is unlikely, and it must remain operational when the antilock brake system or traction control system is activated. The ESC system must also meet the proposed performance requirements for lateral stability and vehicle responsiveness (

see

S5.2).

BorgWarner Torq Transfer Systems, Inc. (BorgWarner) stated that the proposed standard should not mandate a specific solution in terms of how an ESC system would operate (

i.e.

, requiring a brake-base system), but instead it should adopt a performance standard that would encourage development of new and potentially improved technologies, ones which may provide more benefits and/or be more cost-effective than brake-based ESC systems. The commenter stated that it is ultimately the forces at the road/tire interface that are adjusted by the ESC, regardless of how that is accomplished. Accordingly, BorgWarner stated its opposition to the definition of “ESC System” as the basis of the standard because “* * * other systems such as effective design of suspension and steering geometry, active steering, active suspension, AWD active yaw control, torque vectoring yaw control, [and] electronically controlled axle differentials may increase the vehicle's stability threshold such that loss of control is not imminent within the scope of the proposed testing procedure.”

Delphi Corporation (Delphi) stated that there are currently various alternative technologies in various stages of development that may substitute for brake-based ESC systems. According to the commenter, these include active steering systems (Active Front Steer, Active Rear Steer, Steer by Wire, Electric Power Steering), active drivetrains (Active Differentials, Electronic Limited Slip Differentials, Electric Motor/Generator Devices for Propulsion/Braking), and active suspensions (Active Stabilizer Bars, Active Dampers, Active Springs). Delphi added that while brake-based ESC systems are usually restricted to limit-handling conditions, other technologies (such as those mentioned above) can operate across a range of linear-handling to limit-handling (

i.e.

, nonlinear-handling) conditions.

The commenter stated that alternative technologies such as Active Front Steer and Active Rear Steer may actually prevent the vehicle's tires from reaching total saturation in the first place, thereby avoiding unstable and unresponsive situations.

“Linear-handling” describes the conditions that average drivers usually face. Drivers are accustomed to a range of lateral acceleration in which a given steering wheel movement produces a proportional change in the vehicle's heading, so that one knows with some degree of certainty where the vehicle will go when the wheel is turned a certain amount.

“Nonlinear-handling” is at the edge of, and beyond, the range of lateral acceleration to which drivers are normally accustomed (

i.e.

, above about one-half “g” on dry pavement for ordinary vehicles). In such situations, the relationship between the driver's steering input and the vehicle's response changes, and the lag time of the vehicle's response can lengthen.

Delphi also stated that systems using a combination of steering and braking actuation are more responsive and are not necessarily more objectionable to drivers because they are more predictive in their operation. Accordingly, Delphi recommended modifying the ESC definition in the regulatory text to permit any actuator device that can influence the tire/road forces to achieve improvements in vehicle stability and responsiveness.

Specifically, the commenter suggested modifying paragraphs S4 and S5.1.1 of the proposed standard to read as follows:

S4 Definitions (1) “* * * augments vehicle directional stability by applying and adjusting the wheel forces to induce correcting yaw torques to a vehicle;”

S5.1.1 “Is capable of

dynamically adjusting all four wheel forces

and has a control algorithm that utilizes this capability.”

RLP Engineering expressed concern that the NPRM's “equipment requirements” (

i.e.

, definition of an “ESC system”) is based upon current component technology and methodology, which could become outdated. Instead of specifying components, the commenter recommended that the agency state certain objectives and required outcomes, namely requiring means and methods of detecting impending vehicle instability and subsequent means and methods for actively engaging appropriate countermeasures. RLP Engineering argued that such an approach would allow for advancement in the state of the art and elimination of obsolete vehicle componentry (with the potential for cost reduction).

According to the Alliance of Automobile Manufacturers (Alliance) and the Association of International Automobile Manufacturers (AIAM), for some electric or hybrid vehicles, the industry expects that the appropriate ESC braking torques could be provided directly through the vehicle's propulsion system (regenerative braking) without the need to apply the friction brake, as done by current ESC systems. The commenters stated that such systems would potentially provide enhanced safety benefits in terms of more rapid and precise applied braking intervention, as well as longer service life for the vehicle's friction brakes.

In order to accommodate such technology, the Alliance/AIAM recommended modifying S4 (definition of “ESC system”) and S5.1.1 of the proposal to read as follows:

S4,

Electronic Stability Control System or ESC System

* * *

(1) That augments vehicle directional stability by applying and adjusting vehicle brake

torques

individually to induce a correcting yaw

moment

to a vehicle.

S5.1.1 Is capable of applying brake

torques

individually to

all four wheels

and has a control algorithm that utilizes this capability.

After careful consideration of the comments, we have decided to retain the approach set forth in the NPRM (with certain modifications), which would make the requirements associated with the definition of “ESC System” the primary basis of the standard. Our reasoning for this decision is as follows.

The agency's intention in the context of this ESC rulemaking has been to spread the proven safety benefits of current ESC systems across the light vehicle fleet. Available information shows that current brake-based ESC systems are effective and meet the need for motor vehicle safety. The agency is not aware of and commenters have not provided any information to demonstrate the efficacy of the ESC-related technologies specified in their comments as an alternative to brake-based ESC systems.

Furthermore, it is possible for a vehicle without ESC to be optimized to avoid spin-out in the narrowly defined conditions of the ESC oversteer intervention test (especially if the standard is silent on understeer) but to lack the advantages of ESC under other conditions. The agency has determined that it is not currently feasible to develop a comprehensive battery of tests that could substitute for the knowledge of what equipment constitutes ESC, and it remains to be seen if such approach

would ever be practical to set a purely performance-based standard that would ensure that manufacturers provide at least current ESC systems. Therefore, we have concluded that the standard's definition of “ESC System” is necessary in order to ensure that light vehicles have the attributes of ESC systems that produced the large reduction of single-vehicle crashes and rollovers in our crash data study (as discussed in detail in Section II.D). We note that a similar approach of defining heavy truck ABS, rather than depending solely on performance requirements, has been successful under FMVSS No. 121, Air Brake Systems. The following discussion explains the identified obstacles to a strictly performance-based approach.

Among the challenges associated with developing a performance test for ESC, the agency notes that manufacturers develop ESC algorithms using tests whose conditions are generally not repeatable (

e.g.

, icy surfaces which change by the minute, wet/slippery surfaces which are not repeatable day-to-day) and through simulation. Manufacturers also use hundreds of conditions requiring weeks of testing for a given vehicle. However, it is not practicable to use these approaches as part of a safety standard. Furthermore, the agency cannot use subjective tests to determine compliance with a safety standard.

It is possible to overcome these limitations by adopting the standard's definition of “ESC System,” which is based on a Society of Automotive Engineers definition of what ESC is, and which includes those elements that account for the cost of those systems. There is no reason to believe that manufacturers will incur all the costs of the ESC equipment and capabilities required by the standard's definition and then just program the system to achieve limited operation restricted to the test conditions of the standard. The standard's definitional requirement for “ESC System” requires, at a minimum, the equipment and capabilities of existing ESC system designs. This translates into the substantial fatality and injury benefits provided by existing ESC systems.

Without the definition of “ESC System,” it would not be feasible to comprehensively assess the operating range of resulting devices, particularly for understeer intervention, that might be installed in compliance with the safety standards. If manufacturers were to only optimize the vehicle so as to pass only a few highly-defined tests, there public would not receive the full safety benefits provided by current ESC systems.

The U.S. Environmental Protection Agency (EPA) experienced problems with heavy duty diesel manufacturers' production of engines that met EPA standards during laboratory testing under EPA procedures but were turned off under highway driving conditions. On October 22, 1998, the Department of Justice and EPA announced a settlement with seven major diesel engine manufacturers. Accordingly, we do not believe that the industry's ability to circumvent the requirements of the standard is a theoretical one, as would permit us to forgo a definition for “ESC System.”

Under this topic, we also note the comment from the Alliance/AIAM about test variability (in the responsiveness portion of the oversteer intervention test). Even under test conditions chosen for high repeatability, these commenters maintain that the performance requirements must be decreased to allow a larger margin of compliance. Such margins of compliance would make a very weak standard if based solely on tests that would be considerably less repeatable than those we are using.

The Delphi comment also lists a number of systems and components that can influence wheel forces and suggests that it should be permissible for the definition of ESC to be satisfied by systems that can generate wheel force (

i.e.

, a requirement more open than compelling a system that must operate through brake forces). However, the commenter did not provide any data to show the effectiveness of such systems, as would demonstrate that they meet the need for motor vehicle safety and that it would be appropriate to substitute them for proven brake-based ESC systems. We believe there are good reasons for the safety standard at least initially to be based on braking forces (noting that we have changed the definition to include all “braking” torques at the wheels (

i.e.

, regenerative braking by an electric motor as well as the action of friction brakes)). While some of the devices mentioned by BorgWarner and Delphi could create yaw moments (for ESC interventions) by driving torques,

yaw moments created by braking torques have an advantage in critical situations because they also cause the vehicle to slow down.

“Driving torque” is a force applied by the engine through the drive train in order to make a particular wheel turn faster than the others—similar to “braking torques” which brakes one wheel to make it turn slower than the others. Either force can be utilized by an ESC system to change the heading of the vehicle, although braking torque has the added benefit of helping slow the vehicle down.

These commenters also mention a number of steering-related concepts as an alternative means of meeting the standard's requirements. Specifically, Delphi stated that active steering interventions (in a vehicle that combines steering and braking in its ESC) could operate at driving conditions well below critical levels of tire saturation (where steering interventions lose their power) and produce a more responsive vehicle. While active steering may be useful in certain situations, the steering interventions may not be very helpful at or near the limit of traction, which is arguably the critical situation at the heart of this rulemaking. Again, braking forces have an advantage over steering forces because they can create a more powerful yaw intervention when the vehicle is at the limit of traction.

Liebemann

et al.

, Safety and Performance Enhancement: The Bosch Electronic Stability Control (ESP), 2005 ESC Conference.

We understand that manufacturers of a small number of luxury cars are beginning to add active steering to ESC, as described by Delphi, which are very refined vehicle systems that are carefully designed so as to not annoy their drivers. We clarify that the standard in no way prohibits the addition of refinements to vehicles that retain the ability to create yaw moments with brake torques when necessary. The vehicles in question retain the brake-based ESC as the backstop for stability, because the brake interventions which are more noticeable to drivers retain their power in situations where the transparent steering interventions might not be powerful enough. Without data to assess the effectiveness of these potential alternative operating features for ESC (which commenters did not provide), we have decided that it would not be appropriate at this time to abandon the requirement for brake torque-based systems which have proven benefits, in favor of concepts that have not yet demonstrated any safety benefits, much less the enormous benefits associated with current brake torque-based ESC systems.

We acknowledge that in requiring ESC as it now exists and has proven to be beneficial, we may be indirectly impacting hypothetical future technological innovations. We have to balance the benefits of saving thousands of lives a year by requiring ESC systems with the capabilities of current ESC systems, against the loss of savings in the future provided by some even more advanced ESC technologies. In this case, we believe that the opportunity to save this many lives must be selected. Should new advances lead to forms of ESC different than those currently required by this standard, interested parties can petition the agency to modify the regulation. We also note that

the vehicle manufacturers who are the directly regulated parties have not opposed using the definition for “ESC System” as the primary requirement of the standard, and some have actively supported it. We interpret this to mean that the vehicle manufacturers are not aware of any feasible alternative approach for providing efficacious electronic stability control in the near future, other than the approach described in the definition.

3. Stringency of the Standard

The NPRM proposed in S4 to require installation of an ESC system that: (1) Is capable of applying all four brakes individually and has a control algorithm that utilizes this capability; (2) is operational during all phases of driving including acceleration, coasting, and deceleration (including braking), except when the driver has disabled ESC or the vehicle is below a low speed threshold where loss of control is unlikely, and (3) remains operational when the antilock brake system or traction control system is activated (

see

S5.1). The ESC system also would have to meet the proposed performance requirements for lateral stability and vehicle responsiveness (

see

S5.2).

Advocates expressed strong support for a mandate that ESC be provided on all light vehicles, but it urged the agency to adopt a more stringent standard in the final rule. Specifically, Advocates argued that the proposed requirements for ESC intervention to increase lateral stability and to restore proper directional heading are sub-optimal. The commenter also objected to what it characterized as the “minimal standard” that would be set by the proposal, one which effectively accommodates the lowest level of all existing ESC system designs and performance, rather than pushing for state-of-the-art technology. According to the commenter, the proposal would grandfather in all existing ESC designs, even though not all ESC systems have the same level of capabilities.

Advocates also requested that the rule require certain operating functions present on many current ESC systems (

e.g.

, automatic speed reduction achieved by automatic braking and engine de-powering/engine control, traction control, automatic steering, roll stability control), even though the agency based its benefits assessment in the PRIA by “piggybacking” onto these more robust ESC systems. The commenter stated that these additional features, which the agency suggests have some positive safety value, make some unknown (

i.e.

, unquantified) contribution to the anticipated reduction in deaths, injuries, and crash severity associated with the ESC rulemaking. Advocates added that the PRIA's estimated benefits may be inflated because, given the more truncated requirements of the proposed standard, there is no assurance that manufacturers will continue to install more complex ESC systems, a result that would detract from ESC as an advanced safety technology.

In addition, Advocates urged that the agency continue its efforts to reconcile ESC intervention with effective roll stability control systems, characterizing the latter as the only means to directly intervene to prevent imminent rollover (as compared to ESC's indirect contributions through oversteer and understeer intervention). Although the commenter seemed to acknowledge that incorporation of roll stability control requirements may not be possible immediately, it stated that the agency should eventually include performance specifications for this function as part of FMVSS No. 126.

Consumers Union expressed general support for the ESC rulemaking, stating that stability control systems should be standard equipment on all vehicles, especially sport utility vehicles (SUVs). It further stated that, since 1998, it has conducted tests on 179 vehicles equipped with ESC systems, but it has found considerable variability in the level of performance across the systems provided. The commenter stated that better ESC systems act decisively but not prematurely, whereas other systems can be slow to react, help only in certain situations, and intervene too frequently during normal driving. Accordingly, Consumers Union recommended that NHTSA's standard should be modeled after the ESC systems found to be “best performers,” which it characterized as ones that are intrusive and very evident in “at the limit” testing (

i.e.

, at the point at which loss of vehicle control may be imminent), but less so during routine driving.

In addition, Consumers Union stated that ESC calibration should be adjusted to match the type of vehicle for which the system has been developed so that it complements vehicle and driver characteristics (

e.g.

, a more intrusive system for a minivan than for a sports sedan).

Specifically, Consumers Union stated that the NPRM's proposed steering response 1.07 seconds after the initiation of steering (minimum of 6 feet from the center line) is not aggressive enough, and accordingly, the commenter reasoned that it could allow manufacturers to fit low grip tires and slow steering to improve performance under the standard's test procedures. Consumers Union expressed concern that manufacturers may seek to reduce costs by developing cheaper, less sophisticated ESC systems which may pass all the requirements of the standard, but which may be relatively less effective in terms of saving lives.

Public Citizen commented that the agency's ESC proposal is incomplete because it does not deal with the full set of technologies which make up many current ESC systems, instead proposing a more limited yaw stability standard. (Public Citizen also argued that the agency assessed benefits in the PRIA on these more advanced ESC systems). For example, Public Citizen noted that the Alliance of Automobile Manufacturers made a presentation to NHTSA in which it described a number of current features

on ESC systems, including yaw stability,

traction control, ABS,

brake assist, active steering, body roll control,

vehicle roll stability control, corner brake control,

and electronic damping control.

Public Citizen specifically asked why the agency considered traction control to be only a “convenience feature.”

We note that many of the ESC-related features cited by the commenters may serve similar or complementary functions, which may vary to some extent from vehicle to vehicle. However, to the extent possible, we have tried to generally explain our understanding of these technologies either in footnotes or the textual discussion of this document.

“Yaw stability” means an electronic stability control system of the type required by new FMVSS No. 126 and explained in section II.D of this preamble.

“ABS” means anti-lock braking system, a system that controls rotational wheel slip in braking by sensing individual wheel speeds and adjusting brake actuating forces in response to those signals. ABS provides many of the components necessary for ESC.

“Body roll control” is a utilization of electronic damping control to stiffen the body roll resistance in a curve to provide a more level ride.

“Corner brake control” (CBC) is designed to improve vehicle stability

during a braking event

by adjusting the brake line pressure applied to the individual wheels. It is a refinement of ABS with some similarity to ESC, except that CBC intervention requires the driver to apply force to the brake pedal, whereas ESC interventions occur regardless of whether the driver has applied the brakes.

“Electronic damping control” is an electronic system of shock absorbers having electrically-controllable damping rates (stiffness) and a control module to operate them as a system.

According to Public Citizen, the ESC equipment requirements are already out-of-date and will be obsolete by the time a final rule is published. The commenter argued that the proposal would mislead consumers into thinking that they are purchasing a true ESC system using the latest technology. Public Citizen stated that because the agency's proposal would accept the

least extensive of current ESC technologies, it would merely ratify the

status quo

and not “reduce” rollover deaths as Congress required under SAFETEA-LU. The organization stated that the agency cannot rely upon an unenforceable expectation that vehicle manufacturers will continue to provide advanced ESC systems, and it expressed concern that some vehicle manufacturers might actually strip out certain ESC-related features on low-cost vehicles, thereby actually degrading vehicle safety. In contrast, Public Citizen argued that the agency should exert a “technology forcing” influence with respect to vehicle safety improvements. Thus, Public Citizen argued that the ESC proposal would not go far enough to improve vehicle safety.

Public Citizen stated that the two studies of the effectiveness of ESC system prepared by NHTSA, which used Fatality Analysis Reporting System (FARS) data for 1997-2004 and State registration data for 1997-2003, surveyed a time period during which ESC technology was a relatively new technology. As a result, Public Citizen argued that those studies were confounded by small sample sizes and that the results, therefore, make it nearly impossible to support statistically significant claims regarding specific ESC configurations or to separate out the components which the agency decided not to include in its proposal. Again, Public Citizen commented that the PRIA for the ESC NPRM counts the benefits of more extensive ESC technologies, without counting the full costs for those systems. It argued that more properly, the agency should have measured the benefit of a yaw control system, which is more in line with the requirements of the agency's proposal.

In response to these comments requesting that the agency require additional features found on some ESC systems, we have decided to incorporate a requirement for ESC engine control but not to require other system components at this time. Although discussed in detail immediately below, the following summarizes our rationale for this decision.

As a preliminary matter, we find no merit in Public Citizen's arguments that the NPRM's proposed ESC requirements fail to satisfy the requirements of the statutory mandate under SAFETEA-LU. As discussed previously, the statute provided the agency with discretion to adopt performance criteria for technologies consistent with stability enhancing technologies. Our research identified ESC systems as the most effective of these technologies, and our proposal was based upon the definition for “ESC System” promulgated by the Society of Automotive Engineers, a group which is broadly representative of industry experts. Furthermore, the Verband der Automobilindustrie (VDA), an association of German vehicle manufacturers, acknowledged that NHTSA's definition corresponds to modern “state-of-the-art” ESC systems. The proposal also established performance criteria in the form of tests for lateral stability and vehicle responsiveness (

see

Section IV.C.4 and the Appendix for a discussion of the agency's efforts to develop a performance test for understeer). Accordingly, this final rule meets the requirements of SAFETEA-LU.

As discussed above, under 49 U.S.C. 30111, a safety standard must be practicable, meet the need for motor vehicle safety, and be stated in objective terms; in setting the standard, relevant, available motor vehicle safety information must be considered. With the exception of engine control, all of the other ESC-related components lack supporting data to assess their effectiveness and to determine whether such technologies meet the need for safety. The commonality of design for ESC systems that were represented in the agency's crash data study focused on individual brake application and engine control, and we note that in its comments, VDA stated that the agency's proposed definition for “ESC system” captures the state-of-the-art. Again, even though certain later ESC designs incorporate some additional features, it was not possible to determine the safety benefits, if any, of these features because these features were not available on any of the ESC-equipped vehicles in the crash data study. Also, some of those features are directed at comfort and convenience rather than safety (as explained below). We do not believe that there is good reason to postpone the proven life-saving benefits of basic ESC systems until such time as the agency can conduct the necessary research to assess the panoply of related components. Accordingly, we believe that it is not necessary to specify additional components as part of the standard's definition for “ESC system,” but instead, we leave it to the discretion of vehicle manufacturers to tailor the features of their individual ESC systems to the needs of a given vehicle. We note that the rule does not limit manufacturers' ability to develop, install, and advertise stability control systems that go beyond its requirements.

At the time of the agency's analysis, the U.S. crash data available to NHTSA to evaluate the benefit of ESC did not include vehicles newer than 2003. However, the ESC systems of the vehicles that were part of the agency's analysis proved extraordinarily effective, reducing single-vehicle crashes from 34 to 59 percent and reducing rollover in single-vehicle crashes (the crash type leading to over 80 percent of rollovers) from 71 to 84 percent. The results were statistically significant and in agreement with studies by other parties worldwide as cited in the NPRM. The rule requires ESC systems at least as capable as those that produced this extremely high level of demonstrated, real-

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