Federal Motor Vehicle Safety Standards; Accelerator Control Systems

DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

49 CFR Part 571

[Docket No. 95-93; Notice 01]

RIN 2127-AF76

Federal Motor Vehicle Safety Standards; Accelerator Control

Systems

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

ACTION: Request for comments.

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SUMMARY: NHTSA is considering issuing a proposal to amend the Federal

motor vehicle safety standard on accelerator control systems. The

standard was last revised in 1973, when only mechanical systems were

common on motor vehicles. In order to determine whether to propose

amending the standard to include requirements specifically tailored for

electronic accelerator control systems and to clarify possibly

ambiguous language, NHTSA poses a series of questions in this document.

NHTSA undertakes this action as part of its effort to implement the

President's Regulatory Reinvention Initiative to make regulations

easier to understand and to apply.

DATES: Comments must be received on or before February 2, 1996.

ADDRESSES: Comments must refer to the docket and notice numbers cited

at the beginning of this notice and be submitted to: Docket Section,

Room 5109, NHTSA, 400 Seventh Street SW., Washington, D.C. 20590. It is

requested, but not required, that 10 copies of the comments be

provided. The Docket Section is open on weekdays from 9:30 a.m. to 4

p.m.

FOR FURTHER INFORMATION CONTACT: For non-legal issues: Mr. Patrick

Boyd, Office of Vehicle Safety Standards, Office of Safety Performance

Standards, NHTSA, 400 Seventh Street SW., Washington, D.C. 20590. Mr.

Boyd's telephone number is (202) 366-6346, and his FAX number is (202)

366-4329.

For legal issues: Ms. Dorothy Nakama, Rulemaking Division, Office

of Chief

[[Page 62062]]

Counsel, NHTSA, 400 Seventh Street SW., Washington, D.C. 20590. Ms.

Nakama's telephone number is (202) 366-2992, and her FAX number is

(202) 366-3820. Please note that written comments should be sent to the

Docket Section rather than faxed to the above contact persons.

SUPPLEMENTARY INFORMATION:

President's Regulatory Reinvention Initiative

Pursuant to the March 4, 1995 directive ``Regulatory Reinvention

Initiative'' from the President to the heads of departments and

agencies, NHTSA undertook a review of its regulations and directives.

During the course of this review, the agency identified rules that it

could propose to eliminate as unnecessary or to amend to improve their

comprehensibility, application or appropriateness. As described below,

NHTSA has identified Federal Motor Vehicle Safety Standard (FMVSS) No.

124, Accelerator control systems, as one rule that may benefit from

amendments.

Background of Standard No. 124

Standard No. 124's purpose is to reduce deaths and injuries

resulting from loss of control of a moving vehicle's engine, due to

malfunctions in the vehicle's accelerator control system. Since 1972,

Standard No. 124 has specified requirements for ensuring the return of

a vehicle's throttle to the idle position under each of the following

two circumstances, (1) when the driver removes the actuating force

(typically, the driver's foot or cruise control) from the accelerator

control, and (2) when there is a severance or disconnection in the

accelerator control system. Standard No. 124 applies to passenger cars,

multipurpose passenger vehicles, trucks, and buses.

Paragraph S5.1 of Standard No. 124 requires that, under any load

condition, and within the time specified in S5.3, the throttle must

return to the idle position from any accelerator position or any speed

of which the engine is capable, whenever the driver removes the

actuating force. The standard defines the throttle as ``the component

of the fuel metering device that connects to the driver-operated

accelerator control system and that by input from the driver-operated

accelerator control system controls the engine speed.''

Standard No. 124 has two further requirements to provide safety in

the event of accelerator control failure. The first, specified at S5.1,

requires ``at least two sources of energy,'' each capable of returning

the throttle to idle position within the time limit for normal

operation, from any accelerator position or speed whenever the driver

removes the opposing actuating force. The second, specified at S5.2,

requires that the throttle return to idle ``whenever any one component

of the accelerator control system is disconnected or severed at a

single point'' and the driver releases the pedal.

Paragraph S5.3 requires that the throttle return to idle within 1

second for vehicles of 10,000 pounds or less gross vehicle weight

rating (GVWR) and within 2 seconds for vehicles with a GVWR greater

than 10,000. The maximum allowable time is increased to 3 seconds for

any vehicle that is exposed to ambient air at O degrees to -40 degrees

F. during the test or for any portion of a 12 hour conditioning period.

Standard No. 124 Applies to Electronic Accelerator Control Systems

When promulgated, the definitions and requirements of Standard No.

124 were easy to understand and apply because their language was

strongly influenced by the design of mechanical accelerator control

systems and because all control systems were mechanical then. The

``throttle'' of a gasoline engine was the carburetor shaft that opened

and closed the air passages in the base plate. The ``throttle'' of a

diesel engine was the control rod, or rack that controlled fuel flow to

the high pressure injectors. The two energy sources were simply two

return springs acting on the linkages and/or cables between the

accelerator pedal and the throttle. If at least one of those springs

was connected directly to the carburetor or to the diesel fuel

injection rack, it would cause the throttle to return to idle in the

event of a disconnection of the linkage. And, if the single

contemplated failure occurred at one spring, the other would permit

continued driver control.

Subsequent to the promulgation of Standard No. 124, electronic

accelerator controls with on-board computer systems were introduced on

motor vehicles. Their use is steadily increasing, especially in heavy

trucks.

The introduction of electronic systems led to questions about their

status and treatment under the Standard. Stating that some of the

language in Standard No. 124 seemed more appropriate for mechanical

accelerator control systems than for electronic ones, Isuzu Motors

America, Inc., asked the agency a variety of questions concerning

electronic systems. Its central question was whether the Standard

applies to electronic systems. In an August 8, 1988 interpretation

letter to Isuzu, NHTSA stated that the Standard does apply to

electronic accelerator control systems. Among its other questions,

Isuzu asked whether a severance in electric wires in its electronic

accelerator control system is a severance within the meaning of S5.2 of

Standard No. 124. Isuzu expressed its belief that because the electric

wires were not a ``moving part,'' the answer should be ``no.'' NHTSA

disagreed.

It interpreted Standard No. 124's requirement that the throttle

return to idle ``whenever any one component of the accelerator control

system is disconnected or severed at a single point,'' to include all

severances or disconnections of any component of the accelerator

control system as within the standard, not just disconnections of

moving parts.

Need To Amend Standard No. 124

Most accelerator linkages on the largest classes of trucks (i.e.,

those over 33,001 lbs. GVWR) are now electronic. A mechanical

accelerator linkage controlling a fuel rack (i.e., a device that

controls fuel flow to the high pressure injectors) is now rare on the

largest classes of trucks. Most of today's heavy diesel trucks have no

mechanical connection between the accelerator pedal and the throttle.

Although the agency has been issuing interpretations about the

Standard's application to electronic accelerator control systems for

the last seven years, the flow of interpretation requests remains

unabated. Manufacturers continue to ask the basic question of whether

the Standard applies to electronic accelerator control systems. One

correspondent presumed that since those systems do not include springs

and linkages, as described in Standard No. 124, electronic accelerator

controls are not regulated. Another asked for a legal interpretation of

``throttle,'' as applied to electronic accelerator control systems.

Other correspondents have understood Standard No. 124 to mean simply

that two return springs should be placed on the treadle assembly. In

response, the agency has recited in its interpretation letters the

requirement that the sources of energy must be capable of returning the

throttle to idle in the event of a single severance or disconnection.

The correspondents did not submit sufficient information to enable the

agency to determine whether the proper mechanical operation of the

treadle was sufficient to assure return to idle in the event of an

electrical severance.

NHTSA notes that although the use of two springs on the treadle

assembly may

[[Page 62063]]

represent good treadle design, it does not intrinsically overcome a

disconnection anywhere within an electronic accelerator control system.

Thus, good treadle design does not provide an electronic accelerator

control system with the same degree of fail-safe operation provided a

mechanical system by redundant return springs on a traditional fuel

control rack. Those springs on a traditional rack could overcome an

accelerator control disconnection and return the throttle to idle.

Further, providing good treadle design does not solve the problem of

single point disconnection in electronic systems which now would

include connectors, wires, computer components and possibly even

software elements. Even parties recognizing the analogy between wire

severance and linkage severance have asked whether the standard applies

to subsequent short circuits as well as open disconnections.

NHTSA believes that the volume of requests for interpretation might

be reduced if, instead of answering these questions by drawing

analogies between traditional mechanical components and new electronic

systems, it amended the Standard to include provisions and language

specifically tailored to electronic systems. There are limitations to

the agency's ability to make regulatory language, which reflects the

design of mechanical systems, serve the purpose of regulating both

mechanical and electronic systems. NHTSA also believes that amending

the Standard not only to update it, but also possibly to redefine what

constitutes fail safe operation might give manufacturers more

flexibility in designing electronic systems and enable the agency to

better ensure that electronic systems function safely. In order to do

this, the agency must identify the most common predictable failures for

electronic systems and ascertain the most appropriate response to those

failures.

NHTSA is also concerned that regulating electronic systems by

drawing analogies to mechanical systems may have the effect of limiting

the permissible responses to failures in electronic systems to the

fail-safe modes of mechanical systems. At present, the failure modes

(i.e., disconnection and severance) specified in Standard No. 124 are

the predictable failure modes of a mechanical system. The agency

believes that the regulation of electronic systems in a manner tailored

to them can be beneficial to manufacturers, vehicle users, and the

public. For example, with electronic systems, there may be failure

modes in which it is wiser to either shut down the engine or to provide

for a fail-safe mode in which the engine has just enough power to

permit the vehicle to be driven to the side of the road, than to

require that the engine be returned to idle. Since such choices were

not feasible with mechanical controls, they were not included in

Standard No. 124.

Through this request for comments, NHTSA wishes to determine

whether it can propose amendments which identify the predictable

failure modes of electronic systems and specify an acceptable safe

response for each mode.

Normal v. Failure Modes

On many trucks, locking hand controls are necessary for the

operation of engine-driven vocational equipment, i.e., work-performing

equipment such as garbage compactors or cement mixers, when the vehicle

is parked. Similar locking hand controls are also provided to

facilitate engine warm-up. Obviously, locking hand controls can be

thought of as preventing the return to normal idle speed when the

accelerator pedal is released (defined in the Standard as a failure).

Several requests for interpretation have resulted. However, locking

hand controls do not affect highway safety because the locking controls

are not meant to be used to drive vehicles. Explicit specification in

the standard of what is or is not permissible with respect to the

operation of locking hand controls could eliminate a source of

ambiguity.

Likewise, the lack of absolute repeatability in the normal

operation of some electronic accelerator controls results in the return

to a range of idle speeds instead of a single idle speed. While this

range is narrow enough to permit safe operation of a vehicle, the

return to a range of speeds instead of a single speed nevertheless

introduces questions about whether a range is narrow enough to be

regarded as complying with the requirements of the standard for return

to idle speed. A revision of the standard offers an opportunity to

adopt language that distinguishes between normal safe characteristics

of accelerator controls and instances of failure.

Questions for Comment

In order to determine whether the agency should propose to amend

Standard No. 124 and to obtain a better idea of technology that is

presently available, NHTSA asks the following questions to clarify

engineering issues. Sections A and B apply to electronic systems only.

Sections C, D, E and F are of general applicability.

A. Industry Consensus

The Society of Automotive Engineers (SAE) has developed recommended

practices for electronic signal interfaces for heavy diesel vehicle

engine control processors and for some aspects of accelerator pedal

position sensor performance. The SAE's recommended practice specifies

that the accelerator position sensor (APS) assembly shall comply with

all appropriate Federal motor vehicle safety standards.

A1. Has the SAE or other industry consensus standards organizations

considered fail-safe provisions for electronic accelerator controls? Is

there industry agreement (informal or formal) concerning what fail-safe

provisions should be adopted for electronic accelerator control

systems?

A2. What fail-safe strategies are now being employed by vehicle and

component manufacturers?

B. Technical Considerations of a Fail-Safe Electronic Accelerator

Control System

NHTSA believes that the potential points of failure of an

electronic accelerator control system are:

--the mechanical linkage and return springs between the pedal and the

accelerator position sensor (APS);

--the electrical connections between the APS and the engine control

processor;

--the electrical connections between the engine control processor and

other critical sensors;

--the electrical connections between the engine control processor and

fuel or air metering devices which determine engine speed;

--power to the engine control processor, the APS and critical sensors;

and

--the integrity of the engine control processor, APS, and other

critical sensors.

A single point disconnection would mean the severance of a single

wire or the disconnection of all the terminals housed in a single

connector. The consequences both of an open circuit or a short circuit

would ordinarily be relevant, but NHTSA does not exclude the

possibility that some designs could prevent either a short circuit or

an open circuit in the event of a disconnection. Critical sensors are

those whose malfunction or disconnection could cause a significant

uncontrolled engine overspeed. The agency is not aware that sensors

other than the APS are critical in a safety sense.

With this background, NHTSA asks the following questions:

B1. Are there other predictable points of failure of an electronic

control system?

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B2. Are sensors other than the APS critical to safety on either

gasoline or diesel engines?

B3. Are engine development trends pushing other sensors toward

safety critical operation (i.e., to become a sensor whose malfunction

or disconnection could cause a significant uncontrolled engine

overspeed)?

B4. Is it practical (from an engineering standpoint) to expect a

fail-safe design of a unitary electronic accelerator control system,

even in the limited sense of ensuring fail-safe performance in the case

of single point failures at predictable locations? Would it be more

practical (and still meet the need for safety) to use a redundant,

simplified APS and engine controller, active only at the idle position

of the pedal? Is the use of redundant systems more practical than a

single system to achieve fail-safe performance?

B5. Do any currently produced vehicles with electronic accelerator

control systems use redundancy to achieve fail-safe operation?

C. Vehicle Drive Functions v. Vocational Functions

NHTSA legal interpretations regarding hand throttle controls view

their operation as setting a new idle speed to which the throttle

should return in the prescribed time limits ``upon release of the

driver-operated accelerator control system.'' This view is accurate for

traditional ``fast idle'' setting devices for cold engine operation.

But, it may also have resulted in interpretations that do not

distinguish between accelerator control systems that drive the vehicle,

and auxiliary accelerator controls meant to allow the operation of

vocational equipment (such as the compactor on a garbage truck) on a

parked vehicle.

C1. How is the cold engine fast idle function accomplished with

electronic accelerator controls?

C2. How is the engine of a parked vehicle held at the appropriate

speed to operate vocational equipment when the vehicle is equipped with

an electronic accelerator control system?

C3. Is there a general way to distinguish between accelerator

controls affecting the driving of the vehicle and those affecting only

the vehicle's operation as a power source for vocational equipment,

presumably without effect on highway safety?

D. Initial Idle Speed

Manufacturers have been concerned with the question of how

consistently a vehicle's engine must return to exactly the same idle

speed to meet Standard No. 124. Apparently, the resolution and

hysteresis of the various sensors and the discrete nature of digital

systems create idle speed variations that do not in any way indicate

failure.

D1. Would it be practical to designate a range about a vehicle's

initial idle speed to clarify the difference between normal and

abnormal performance of an accelerator control system? Please describe

the desirable extent of such a range and provide a rationale for that

range.

E. Public Technical Meeting

NHTSA believes that the development of any proposal to amend

Standard No. 124 may benefit from a direct, oral exchange of ideas

among NHTSA, vehicle manufacturers, and other affected parties.

Reliance solely on written public comments may not be the most

effective means of assessing the appropriate steps for ensuring the

safe operation of electronic accelerator control systems.

E1. Once the agency has analyzed the written comments submitted in

response to this document, should it hold a public technical meeting to

discuss possible proposals for amending the Standard No. 124? If so, on

which issues should such a public technical meeting focus?

F. Other Issues

F1. Should the agency propose to amend Standard No. 124 in any

other respect that has not been discussed above? If so, please describe

how the agency should propose to amend the Standard, and provide a

rationale for the recommended change.

Rulemaking Analyses and Notices

1. Executive Order 12866 and DOT Regulatory Policies and Procedures

This request for comment was not reviewed under Executive Order

12866 (Regulatory Planning and Review). NHTSA has analyzed the impact

of this request for comment and determined that it is not

``significant'' within the meaning of the Department of

Transportation's regulatory policies and procedures. The agency

anticipates if a proposal and ultimately a final rule should result

from this request for comment, new requirements would not be imposed on

manufacturers with respect to the currently regulated systems. The

request for comment seeks to find cost effective means to make Standard

No. 124 more understandable when applied to electronic accelerator

control systems. If NHTSA decides to initiate rulemaking, it is NHTSA's

intent that the rulemaking not impose any additional costs.

Procedures for Filing Comments

Interested persons are invited to submit comments on this request

for comment. It is requested but not required that 10 copies be

submitted.

All comments must not exceed 15 pages in length. (49 CFR 553.21).

Necessary attachments may be appended to these submissions without

regard to the 15-page limit. This limitation is intended to encourage

commenters to detail their primary arguments in a concise fashion.

If a commenter wishes to submit certain information under a claim

of confidentiality, three copies of the complete submission, including

purportedly confidential business information, should be submitted to

the Chief Counsel, NHTSA, at the street address given above, and seven

copies from which the purportedly confidential information has been

deleted should be submitted to the Docket Section. A request for

confidentiality should be accompanied by a cover letter setting forth

the information specified in the agency's confidential business

information regulation. 49 CFR part 512.

All comments received before the close of business on the comment

closing date indicated above for the proposal will be considered, and

will be available for examination in the docket at the above address

both before and after that date. To the extent possible, comments filed

after the closing date will also be considered. Comments received after

the comment due date will be considered as suggestions for any future

rulemaking action. Comments on the request for comment will be

available for inspection in the docket. The NHTSA will continue to file

relevant information as it becomes available in the docket after the

closing date, and it is recommended that interested persons continue to

examine the docket for new material.

Those persons desiring to be notified upon receipt of their

comments in the rules docket should enclose a self-addressed, stamped

postcard in the envelope with their comments. Upon receiving the

comments, the docket supervisor will return the postcard by mail.

Authority: 49 U.S.C. 322, 30111, 30115, 30117, and 30166;

delegation of authority at 49 CFR 1.50.

Issued on: November 28, 1995.

Barry Felrice,

Associate Administrator for Safety Performance Standards.

[FR Doc. 95-29453 Filed 12-1-95; 8:45 am]

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