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Proposed Rule

Federal Motor Vehicle Safety Standards; Accelerator Control Systems

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Start Preamble


National Highway Traffic Safety Administration (NHTSA), DOT.


Withdrawal of rulemaking.


In July 2002, NHTSA published an NPRM proposing to update Federal Motor Vehicle Safety Standard (FMVSS) No. 124, the agency's safety standard for vehicle accelerator control systems, to make explicit its applicability to new types of engines and throttle controls, particularly electronic ones. The proposal included a number of new test procedures to address different types of powertrain technology. One of those test procedures involved measurement of engine speed under realistic powertrain load conditions on a chassis dynamometer. That procedure was “technology-neutral” and was included to allow testing of vehicles that could not readily be tested by one of the other procedures included in the proposal that were technology specific.

As discussed in this document, the agency is withdrawing the NPRM while it conducts further research on issues relating to chassis dynamometer-based test procedures for accelerator controls.

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The following persons at the NHTSA, 400 7th Street, SW., Washington, DC 20590.

For non-legal issues, you may call Mr. Michael Pyne, Office of Crash Avoidance Standards (Telephone: 202-366-2720) (Fax: 202-366-7002).

For legal issues, you may call Ms. Dorothy Nakama, Office of Chief Counsel (Telephone: 202-366-2992) (Fax: 202-366-3820).

End Further Info End Preamble Start Supplemental Information


I. Background

Federal Motor Vehicle Safety Standard (FMVSS) No. 124, Accelerator Control Systems, provides for safe control of engine power by a vehicle's driver-operated accelerator. For vehicles that are operating with their accelerator controls intact, FMVSS No. 124 requires the rapid return of the throttle to the idle position (within one second for light vehicles and two seconds for heavy vehicles) when the accelerator pedal is released. For vehicles that experience disconnections in the linkage between their accelerator pedals and throttling devices, FMVSS No. 124 requires return to idle in an equally rapid fashion. By virtue of FMVSS No. 124's requirements, drivers are ensured that releasing the accelerator pedal will prevent the engine from continuing to power the drive wheels at a level greater than the idle level, even if the accelerator linkage breaks.

New engine control technology such as “throttle-by-wire” systems have significantly changed the nature of accelerator control functions and failure modes. Throttle linkages have become less common, and now “disconnections” or “severances” as referred to in the standard could just as easily involve electrical wires as they could rods, levers, and cables. In interpretation letters, NHTSA has stated that electrical wires and connectors in an electronic system are analogous to mechanical components in a traditional system and are therefore covered by FMVSS No. 124. However, complexity in electronic accelerator control systems is much greater than in mechanical ones, especially in terms of the powertrain responses that can result from failures in such systems.

In order to update FMVSS No. 124, NHTSA published a Request for Comments in 1995 (60 FR 60261) and, after consideration of comments received, issued an NPRM in 2002 (67 FR 48117).

The agency proposed that the standard specify explicitly the components and types of disconnections and severances to be covered in electronic accelerator control systems. NHTSA also proposed that the standard include new test procedures to better address different types of powertrains. A manufacturer could choose any one of the test procedures as a basis for compliance, and a “universal” chassis dynamometer test was included as a last resort in cases where the other procedures were inapplicable.

In making the proposal, NHTSA sought not to expand the scope of the existing Standard, but to merely clarify the standard's applicability to accelerator control systems associated with various powertrains including gasoline engines, diesel engines, electric motors, and hybrids. The new procedures in the proposal were all premised on return to a “baseline” idle condition measured on a normally operating vehicle, analogous to return of a throttle plate to the idle position.

The proposal included three technology specific test procedures plus a “universal” test procedure. The first of the proposed technology specific test procedures was essentially the existing air throttle plate position test of the current Standard, normally applicable to conventional gasoline engines. The second test procedure was measurement of fuel flow rate, normally applicable to diesel engines. The third test procedure was measurement of input current to a drive motor, applicable to electric vehicles. The last procedure was measurement of drivetrain output via engine speed, conducted on a chassis dynamometer. This was considered a universal test because it could be applied to gasoline, diesel, or electric vehicles.

II. Reason for Withdrawal

In commenting on the NPRM and in subsequent comments, the Alliance of Start Printed Page 65127Automobile Manufacturers (Alliance) suggested that FMVSS No. 124 should include a direct measurement of powertrain output to the drive wheels. [1,2] The Alliance stated that this would be a “technology-neutral” test and, thus, would be similar to NHTSA's proposed engine RPM test but with the advantage of being more easily applicable to hybrid powertrains in which engine RPM might not indicate drive torque. Subsequently, the Alliance suggested that the powertrain output test should measure vehicle driving speed, i.e., “creep speed,” rather than output horsepower or torque.[3] Toyota suggested a similar approach, but requested that the agency consider a somewhat different creep speed test procedure.[4]

While the agency regards these suggestions merely as variations on the dynamometer-based engine rpm test as proposed in the NPRM, we believe that additional research on the exact procedures for the suggested test is desirable. In particular, the agency wants to conduct its own tests to provide additional support for the use of a dynamometer for measurement of powertrain output (or possibly creep speed measurements), and demonstrate the feasibility of conducting compliance tests for all suggested approaches.

In addition, the Alliance suggested that the agency include air flow rate measurement as another optional test procedure in FMVSS No. 124. Many vehicles already have mass air flow sensors that can monitor air flow rate. For vehicles with sensors, the test would measure the air flow rate during the failsafe response for comparisons to the baseline idle condition. NHTSA plans to conduct research on the suggested air flow rate test procedure and decide on the appropriateness of including it in FMVSS No. 124.

Given the time it will take to conduct research on some of the issues involved, NHTSA has decided not to continue an active rulemaking on this issue during that research. Therefore, NHTSA is withdrawing the rulemaking to update FMVSS No. 124.

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Authority: 49 U.S.C. 322, 30111, 30115, 30117, and 30166; delegation of authority at 49 CFR 1.50.

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Issued: November 4, 2004.

Stephen R. Kratzke,

Associate Administrator for Rulemaking.

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1.  Docket NHTSA-2002-12845-10.

2.  Docket NHTSA-2002-12845-13.

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3.  Docket NHTSA-2002-12845-15.

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4.  Docket NHTSA-2002-12845-14.

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[FR Doc. 04-24978 Filed 11-9-04; 8:45 am]