22638 Federal Register / Vol. 77, No. 73 / Monday, April 16, 2012 / Proposed Rules 

1Accelerator pedal entrapment is a particular 

category of ‘‘unintended acceleration.’’ The latter is 

the general term we use to refer broadly to any 

vehicle acceleration that a driver did not purposely 

cause to occur. 2 49 CFR 571.124. 

DEPARTMENT OF TRANSPORTATION 

National Highway Traffic Safety 

Administration 

49 CFR Part 571 

[Docket No. NHTSA–2012–0038] 

RIN 2127–AK18 

Federal Motor Vehicle Safety 

Standards; Accelerator Control 

Systems 

AGENCY: National Highway Traffic 

Safety Administration (NHTSA), 

Department of Transportation (DOT). 

ACTION: Notice of proposed rulemaking 

(NPRM). 

SUMMARY: In this NPRM, we (NHTSA) 

propose to revise the Federal Motor 

Vehicle Safety Standard for accelerator 

control systems (ACS) in two ways. 

First, we propose to amend the Standard 

to address more fully the failure modes 

of electronic throttle control (ETC) 

systems and also to include test 

procedures for hybrid vehicles and 

certain other vehicles. This part of 

today’s proposal is related to an NPRM 

that NHTSA published in 2002. 

Second, we propose to add a new 

provision for a brake-throttle override 

(BTO) system, which would require that 

input to the brake pedal in a vehicle 

must have the capability of overriding 

input to the accelerator pedal. This BTO 

proposal is an outgrowth of NHTSA’s 

research and defect investigation efforts 

aimed at addressing floor mat 

entrapment and related situations.1 We 

propose to apply the requirement for 

BTO systems to new passenger cars, 

multipurpose passenger vehicles, trucks 

and buses that have a gross vehicle 

weight rating of 10,000 pounds (4,536 

kilograms) or less and ETC. 

DATES: Comments must be received on 

or before June 15, 2012. 

ADDRESSES: You may submit comments 

to the docket number identified in the 

heading of this document by any of the 

following methods: 

• Federal eRulemaking Portal: Go to 

http://www.regulations.gov. Follow the 

online instructions for submitting 

comments. 

• Mail: Docket Management Facility, 

M–30, U.S. Department of 

Transportation, West Building, Ground 

Floor, Rm. W12–140, 1200 New Jersey 

Avenue SE., Washington, DC 20590. 

• Hand Delivery or Courier: West 

Building Ground Floor, Room W12–140, 

1200 New Jersey Avenue SE., between 

9 a.m. and 5 p.m. Eastern Time, Monday 

through Friday, except Federal holidays. 

• Fax: (202) 493–2251. 

Regardless of how you submit your 

comments, you should mention the 

docket number of this document. 

You may call the Docket at 202–366– 

9324. 

Instructions: For detailed instructions 

on submitting comments and additional 

information on the rulemaking process, 

see the Public Participation heading of 

the SUPPLEMENTARY INFORMATION section 

of this document. Note that all 

comments received will be posted 

without change to http:// 

www.regulations.gov, including any 

personal information provided. 

Privacy Act: Please see the Privacy 

Act heading under Rulemaking 

Analyses and Notices. 

FOR FURTHER INFORMATION CONTACT: For 

non-legal issues, Mr. Michael Pyne, 

Office of Crash Avoidance Standards 

(telephone: 202–366–4171) (fax: 202– 

493–2990). Mr. Pyne’s mailing address 

is National Highway Traffic Safety 

Administration, NVS–112, 1200 New 

Jersey Avenue SE., Washington, DC 

20590. 

For legal issues, Mr. William Shakely, 

Office of the Chief Counsel (telephone: 

202–366–2992) (fax: 202–366–3820). 

Mr. Shakely’s mailing address is 

National Highway Traffic Safety 

Administration, NCC–112, 1200 New 

Jersey Avenue SE., Washington, DC 

20590. 

SUPPLEMENTARY INFORMATION: 

Table of Contents 

I. Executive Summary 

II. Introduction 

III. Safety Need for Brake-Throttle Override 

Systems 

A. Inability To Stop a Moving Vehicle in 

a Panic Situation 

B. How Trapped-Pedal Scenarios May Lead 

to Crashes 

C. Loss of Power Brake Boost Requires 

Greater Brake Pedal Force 

D. Description of Brake-Throttle Override 

IV. Technical Discussion of Accelerator 

Control System Safety Issues 

A. Accelerator Control System 

Disconnections 

B. Electronic Throttle Control 

C. Potential ETC Failures Not Covered 

V. Proposed Update of FMVSS No. 124 Test 

Procedures 

A. Purpose and Scope of FMVSS No. 124 

at Present 

B. Need for Update of FMVSS No. 124 

C. Applicability to Electronic Throttle 

Control Components 

D. Test Procedures of the 2002 NPRM 

E. Powertrain Output Test Procedures and 

‘‘Creep Speed’’ 

F. Comments on the 2002 NPRM 

VI. Notice of Proposed Rulemaking 

A. Definition of Electronic Throttle Control 

System 

B. Brake-Throttle Override Equipment 

Requirement 

C. Brake-Throttle Override Performance 

Requirement 

D. Update of FMVSS No. 124 

Disconnection Test Procedures 

E. Compliance Options for Various 

Vehicles 

VII. Safety Benefits and Crash Data 

A. Summary of Crash Data on Accelerator 

Control Issues 

B. Owner Complaint Data 

VIII. Cost, Lead Time, and Other Issues 

A. Cost of the Proposed BTO Requirement 

B. Proposed Lead Time and Phase-In 

C. Vehicles Over 10,000 lb GVWR 

D. Manual Transmission Vehicles 

E. Proposed New Title for FMVSS No. 124 

IX. Rulemaking Analyses and Notices 

A. Executive Orders 12866, 13563, and 

DOT Regulatory Policies and Procedures 

B. Regulatory Flexibility Act 

C. Executive Order 13132 (Federalism) 

D. National Environmental Policy Act 

E. Paperwork Reduction Act 

F. National Technology Transfer and 

Advancement Act 

G. Executive Order 12988 

H. Unfunded Mandates Act 

I. Executive Order 13045 

J. Executive Order 1211 

K. Plain Language 

L. Regulation Identifier Number (RIN) 

M. Privacy Act 

X. Public Participation 

I. Executive Summary 

NHTSA is proposing to amend 

Federal Motor Vehicle Safety Standard 

(FMVSS) No. 124, Accelerator Control 

Systems,2 in two ways. First, we are 

proposing to update the throttle control 

disconnection test procedures in 

FMVSS No. 124. This would apply to 

passenger cars, multipurpose passenger 

vehicles, trucks and buses, regardless of 

weight. Second, we propose to add a 

new requirement for a Brake-Throttle 

Override (BTO) system. The latter 

would be applicable to the same types 

of vehicles with 10,000 lbs. (4,536 

kilograms) gross vehicle weight rating 

(GVWR) or less and that have ETC. 

The first part of today’s proposal 

follows up on a previous rulemaking 

effort. In 2002, NHTSA published an 

NPRM to update FMVSS No. 124. That 

proposal was withdrawn in 2004 mainly 

because the agency concluded that 

further development was needed on 

some of the proposed test procedures. 

Today’s proposal revives that effort and 

resolves test procedure issues raised in 

the previous rulemaking. 

The second part of our proposal, a 

BTO system requirement, would require 

that the brake pedal in a vehicle have 


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3 In NHTSA’s February 2011 final report 

‘‘Technical Assessment of Toyota Electronic 

Throttle Control Systems,’’ the agency defined 

‘‘Unintended Acceleration’’ or ‘‘UA’’ very broadly 

as ‘‘the occurrence of any degree of acceleration that 

the vehicle driver did not purposely cause to 

occur.’’ Today’s proposal deals mainly with a subcategory of UA which is characterized by 

accelerator pedals that fail to return because they 

are stuck or trapped. 

4See Observation O–2 in section 7.2, page 173, 

of the NASA report at: http://www.nhtsa.gov/PR/ 

DOT-16-11. 

the capability of overriding input to the 

accelerator pedal when both are pressed 

at the same time. This action augments 

NHTSA’s ongoing research and defect 

investigation efforts aimed at addressing 

a serious safety situation where a pedal 

becomes entrapped by a floor mat or no 

longer responds to driver release of the 

pedal because of some other obstruction 

or resistance. 

In general, this proposal aims to 

minimize the risk that loss of vehicle 

control will be caused by either: (1) 

Accelerator control system 

disconnections; or (2) accelerator pedal 

sticking and entrapment. For both of 

these safety risks, which can affect 

vehicles with mechanical as well as 

ETCs, the purpose of this rulemaking is 

to ensure that stopping a vehicle is 

possible without extraordinary driver 

actions. Accordingly, we believe both 

aspects of this rulemaking to update 

FMVSS No. 124 are warranted. 

For measuring return-to-idle in the 

event of a disconnection, this proposal 

includes updated test procedures 

carried over from the 2002 proposal 

including a powertrain output test 

procedure which, under today’s 

proposal, would be based on 

measurement of vehicle creep speed. 

For situations where the accelerator 

pedal fails to return after release, this 

proposal incorporates a new BTO 

requirement which comprises: 

• An equipment requirement to 

ensure the presence of BTO in each 

vehicle; and 

• A performance requirement using a 

stopping distance criterion with the 

accelerator pedal applied. 

II. Introduction 

Controlling acceleration is one of the 

fundamental tasks required for safe 

operation of a motor vehicle. Loss of 

control of vehicle acceleration and/or 

speed, so-called ‘‘unintended 

acceleration’’ or ‘‘UA’’, can have serious 

safety consequences.3 It can arise either 

from driver error or for vehicle-based 

reasons including accelerator pedal 

interference and separation of throttle 

control components. 

To address loss of control of vehicle 

acceleration, FMVSS No. 124 requires 

an engine’s throttle to return to idle 

when the driver stops pressing on the 

accelerator pedal or when any one 

component of the accelerator control 

system is disconnected or severed at a 

single point. The standard was issued 

under 49 U.S.C. 30111(a), which directs 

NHTSA (by delegation from the 

Secretary of Transportation) to prescribe 

FMVSSs. Section 30111(a) also states 

that ‘‘Each standard shall be practicable, 

meet the need for motor vehicle safety, 

and be stated in objective terms.’’ This 

subsection is also the basis for this 

proposal. 

In recent years, NHTSA has been 

working to update FMVSS No. 124 to 

more directly address newer electronic 

engine control systems and also to 

address different types of accelerator 

control safety issues such as those that 

could be mitigated by BTO technology. 

We have evaluated BTO technology to 

understand its performance 

characteristics and how it differs among 

manufacturers using this technology. 

Based on that evaluation, we believe 

that light-vehicle manufacturers in the 

U.S. can implement BTO on vehicles 

having ETC without significant 

difficulty or cost. 

Currently, there are a few vehicle 

models that still have mechanical 

throttle controls, and the manufacturers 

of those vehicles may lack sufficient 

lead time at this point and probably 

would incur significant cost to change 

their manufacturing plans to install BTO 

systems within the next one or two 

model years. This is due to the need to 

change over from mechanical throttle 

control to ETC for implementation of 

BTO. However, we believe in the near 

future these mechanically-throttled 

vehicles will be discontinued or 

replaced with new models having ETC. 

Based on compliance information that 

NHTSA receives from vehicle 

manufacturers annually, almost all 

model year 2012 light vehicles sold in 

the U.S. will have a BTO system. Based 

on our experience with these BTO 

systems, we believe they will comply 

with this proposed rule without 

significant modification. Consequently, 

any manufacturer design, validation, 

and implementation costs associated 

with this proposal should be minimal. 

Furthermore, compliance testing costs 

are expected to be low since the 

proposed test procedure is nearly 

identical to existing brake performance 

test procedures. Tests could be 

conducted along with existing brake 

performance tests. 

Although we do not have a statistical 

estimate for the number of fatalities or 

injuries that could be prevented by 

brake-throttle override technology, we 

believe that BTO would prevent a 

significant number of crashes and thus 

have a positive impact on motor vehicle 

safety. In NHTSA’s complaint database, 

over a period of about ten years starting 

in January 2000, the agency identified 

thousands of reports of UA events of all 

types (see Section VIIB of this proposal). 

Based on NHTSA’s review and analysis 

of a subset of vehicle owner-provided 

narratives in the complaints, some UA 

incidents appear to have involved stuck 

or trapped accelerator pedals, and a 

portion of those resulted in crashes. We 

believe brake-throttle override would 

prevent most crashes where a stuck or 

trapped accelerator pedal was to blame 

because, with a BTO system, the driver 

would be able to maintain control 

through normal application of the 

vehicle’s brakes. We believe brakethrottle override also could prevent 

stuck-pedal incidents which do not 

result in a crash but which may require 

extraordinary driver actions to avoid a 

crash. 

III. Safety Need for Brake-Throttle 

Override Systems 

One of the specific observations of the 

NASA in its report to NHTSA on Toyota 

unintended acceleration stated: ‘‘When 

the brake can override the throttle 

command it provides a broad defense 

against unintended engine power 

whether caused by electronic, software, 

or mechanical failures.’’ 4 In Section A, 

below, we discuss actual incidents 

where a brake-throttle override system 

very likely would have provided a 

safety benefit. Of interest are driving 

emergencies in which drivers have 

extreme difficulty stopping or slowing 

their speeding vehicle because the 

accelerator pedal is prevented from 

returning to its normal rest position. 

Some of these incidents resulted in 

crashes and, in rare cases, deaths. These 

instances involve vehicles both with 

and without ETC systems. In Section B, 

we discuss how trapped pedal scenarios 

may lead to crashes. In Section C, we 

discuss how loss of power brake boost 

necessitates greater brake pedal pressure 

to stop a vehicle. Finally, in Section D, 

we discuss our conclusion that brakethrottle override systems can effectively 

prevent crashes involving trapped-pedal 

and sticking-pedal scenarios, and why 

we are proposing to require brakethrottle override systems on light 

vehicles with ETC. 

A. Inability to Stop a Moving Vehicle in 

a Panic Situation 

On August 28, 2009, there was a 

passenger car crash near San Diego, 

California that resulted in the deaths of 


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22640 Federal Register / Vol. 77, No. 73 / Monday, April 16, 2012 / Proposed Rules 

5Memorandum from B. Collins (Investigator and 

Interviewer, Vehicle Research and Test Center) to 

K. DeMeter (Director, Office of Defects 

Investigation), September 30, 2009, available in the 

docket cited in the heading at the beginning of this 

notice. 

four people. NHTSA’s Office of Defects 

Investigation (ODI) inspected the crash 

site on September 3, 2009, and 

subsequently both ODI and the NHTSA 

Vehicle Research and Test Center 

inspected the vehicle. A report was filed 

on September 30, 2009.5 The 

investigators noted the following: 

• The vehicle was a loaned Lexus 

ES350 traveling at a very high rate of 

speed that failed to stop at the end of 

Highway 125. 

• The driver was a 19-year veteran of 

the California Highway Patrol. 

• The cause of the crash was ‘‘very 

excessive speed.’’ 

• A customer who had previously 

used the same loaner car involved in 

this crash reported an unwanted 

acceleration event, experiencing speeds 

in excess of 80 mph. 

Investigating this crash, NHTSA 

inspectors and the San Diego County 

Sheriff’s Department discovered 

evidence that floor mats had trapped the 

accelerator pedal, as it was apparent 

that floor mats had been stacked in the 

driver footwell, the floor mat was 

unsecured, and the mat was not 

appropriate for the vehicle. 

The driver in this crash used the 

brakes during the prolonged event as 

evidenced by heat-related destruction of 

some brake components, but it is 

apparent that the brake application was 

insufficient to control the vehicle. It is 

unknown if the driver and occupants 

made attempts to use other means to 

stop the vehicle, including shifting the 

transmission to neutral and turning off 

the engine. The passenger car involved 

in the crash was equipped with a pushbutton keyless start system and a gated 

automatic transmission shifter with a 

manual shift mode. It did not have a 

BTO feature. 

NHTSA’s Office of Defect 

Investigation has received complaints 

through the Vehicle Owner’s 

Questionnaire (VOQ) of similar 

situations in which a driver attempted 

to stop a runaway vehicle. The 

following examples of this are excerpted 

from narrative descriptions in VOQs: 

Truck was in cruise control. Accelerated to 

pass slower traffic. Let off throttle. Truck 

went to full throttle. Could not get truck to 

decelerate. Had to stand on brakes to bring 

to a stop. Truck needs new rotors and pads. 

*The consumer stated the floor mat and gas 

pedal can interact. When the all weather mat 

is not clipped in place, and is moved under 

the gas pedal, it will become fully depressed. 

The mat can trap the pedal. *Updated 

[NHTSA–ODI ID# 10245488] 

and; 

I was accelerating on the highway and my 

car continued to accelerate after I took my 

foot off the gas. I tried to brake and the pedal 

was extremely hard to press on. The car was 

able to slow down a bit but once I took foot 

off brake pedal the car would speed up again. 

I took my car in for service and was told they 

could not duplicate the problem and maybe 

a floor mat caused the problem. My car 

continues to have trouble braking. [NHTSA– 

ODI ID# 10260682] 

and; 

While driving on a two-lane road * * * the 

accelerator became stuck. My car reached 

speeds of up to 80 mph. I could only reduce 

the speed to 60 mph by riding the brakes. I 

finally stopped the car by finding a safe pulloff and shifted into Neutral and then Park. 

My brakes were completely ruined and 

required replacement. My car was towed to 

a Toyota dealer. * * * The service 

department determined that the faulty 

acceleration was due to a rubber all-weather 

mat. The mat had been placed over the 

standard floor mat. [NHTSA–ODI ID# 

10200097] 

There are similar examples of these 

kinds of incidents, with and without 

crashes, in complaint narratives in the 

VOQ database. Given our evaluation of 

brake-throttle override technology and 

the impact it could have in these types 

of incidents, we believe a regulation is 

necessary. Furthermore, this can be 

done at low cost and with minimal 

vehicle design impact. Therefore, 

NHTSA has decided to proceed with 

this proposal to require brake-throttle 

override systems. 

B. How Trapped-Pedal Scenarios May 

Lead to Crashes 

The possibility of a trapped 

accelerator pedal has been widely 

acknowledged by NHTSA, vehicle 

manufacturers, consumer groups, and in 

the media as a key contributor to the 

problem of UA. Based on review of UA 

complaints in the agency’s VOQ data 

and other sources such as media 

accounts, we can reconstruct how a 

pedal entrapment event might lead to a 

crash. 

Based on VOQ narratives, when a 

pedal entrapment occurs, it often 

follows an acceleration event such as an 

overtaking maneuver or a merge onto a 

highway. Upon completion of such a 

maneuver, when the driver backs off or 

releases the accelerator pedal, the pedal 

may be trapped due to interference 

caused in many cases by stacked or outof-position floor mats, but it also can be 

caused by bunched or worn carpets or 

foreign objects in the driver footwell. In 

at least one case, a sharp edge on a 

plastic pedal snagged on the carpeting at 

wide-open throttle. We also have seen 

examples where internal friction in a 

pedal assembly prevented the 

accelerator pedal from springing back 

fully (i.e., to a neutral position). 

When pedal entrapment or sticking 

occurs, the driver is likely to be startled 

upon realizing that the vehicle is 

continuing to accelerate or is proceeding 

without an expected drop in speed, 

without any action on the driver’s part. 

One possible reaction is to re-apply the 

accelerator pedal, which may dislodge 

it. More likely, a driver will attempt to 

apply the brakes. In doing so, a driver’s 

conditioned expectation is that the 

brakes will produce quick and 

deliberate deceleration, responding with 

the same feel and feedback they provide 

in everyday driving. 

However, because the accelerator 

pedal is being held down and thus the 

vehicle is trying to accelerate or 

maintain speed, normal brake 

application usually will not result in the 

expected braking effect. This has been 

characterized as feeling like a ‘‘tug-ofwar’’ between the engine and brakes. 

The problem is exacerbated at higher 

vehicle speeds where increased 

stopping effort is necessary. Also, if the 

brakes are applied with light to 

moderate force for an extended period, 

i.e., if the driver ‘‘rides’’ the brakes, 

heat-induced brake fade can result 

which lessens braking effectiveness. The 

loss of braking effectiveness may be 

compounded further by a reduction in 

brake boost, as described in the next 

section. 

From the perspective of a driver in a 

vehicle that is accelerating 

unexpectedly or that fails to slow down 

in the usual manner when the brake is 

applied, this may amount to confusing 

and even frightening vehicle behavior. 

Depending on the duration of the event, 

many drivers in this situation may 

experience panic to some degree, and 

their subsequent actions may be 

unpredictable. 

Especially in cases involving a high 

level of throttle input, in order to 

overcome the racing engine, the driver’s 

application of the brakes has to be 

forceful and steady enough to produce 

a strong braking effect, ideally over a 

short duration to avoid brake fade. It is 

apparent from the complaint narratives 

that drivers sometimes do not apply 

steady, hard pressure to the brake pedal 

in these situations. Instead, they may 

‘‘ride’’ the brakes with insufficient pedal 

force. Or they may release the brakes 

and repeatedly try to re-apply them, 

sometimes stabbing at the brake pedal. 

This kind of driver reaction is evident 

in incidents investigated by NHTSA and 


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6The degree of this diminishment depends 

mainly on throttle position and engine speed. 

7Loss of brake boost is highly dependent on the 

type of vehicle propulsion and the design of its 

braking system. 

8We note that a BTO system fundamentally relies 

on brake pedal application. If the brake is not 

applied, even if all other necessary conditions are 

met, the BTO system will not engage and the 

vehicle accelerating force will not be suppressed. 

For this reason, pure pedal misapplication 

(meaning that a driver unintentionally steps on the 

accelerator pedal and does not apply the brake at 

all) is not addressed by installation of a BTO 

system. 

also in complaint narratives, and it may 

lead to or be a result of a loss of power 

brake boost, as described below. 

C. Loss of Power Brake Boost Requires 

Greater Brake Pedal Force 

Power brakes, as contrasted with 

manual brakes, provide boost to the 

brake pedal so that the force a driver 

must apply to the pedal in order to stop 

a vehicle is reduced. If the power assist 

fails, the brakes would still work, but 

the pedal force required to stop the 

vehicle would be multiplied. On 

vacuum-assisted power brake systems, 

which are by far the most common type 

in light vehicles, power assist is 

maintained by negative pressure (i.e., 

below atmospheric) in the engine’s 

intake manifold. 

When an accelerator pedal is stuck 

with the throttle open, manifold 

vacuum is diminished.6 In order to 

maintain brake boost until the throttle 

closes and restores vacuum in the 

manifold, many light vehicle brake 

systems have to rely on residual 

vacuum, which usually is very limited. 

If the brake pedal is pumped while 

the throttle is open, a loss of boost can 

ensue quickly for some vehicles. This 

depends on several factors including the 

rate of brake pedal application and how 

far the pedal is depressed. Brake booster 

volume and residual capacity are 

important factors that vary among 

different vehicles. Some vehicles have 

an auxiliary vacuum pump to maintain 

brake boost under low vacuum 

conditions, but even those systems have 

limitations. On vehicles with a 

hydraulic boost system, brake boost is 

unaffected by manifold vacuum, as are 

air brake systems in heavy vehicles. If 

a vehicle is equipped with an anti-lock 

brake system (ABS), engagement of the 

ABS provides brake hydraulic pressure 

to stop the vehicle, but sufficient brake 

pedal force still must be maintained by 

the driver, so having ABS does not 

always mitigate a loss of brake boost. 

Even with a loss of boost, a driver can 

usually bring a vehicle with a stuck 

accelerator to a stop. If a high enough 

brake pedal force is applied and held 

steadily, a vehicle’s brakes typically are 

capable of overpowering its engine, but 

the force necessary on the brake pedal 

can be many times greater than that 

used in daily driving. 

In some of the UA complaints in the 

ODI database, it was reported that the 

driver eventually was able to stop a 

vehicle with a stuck accelerator by 

holding down the brake pedal 

forcefully. However, presumably 

because the required pedal pressure was 

much greater than what those drivers 

were accustomed to, many 

complainants stated that the brakes 

seemed to have failed even in cases 

where the vehicle was successfully 

stopped without a crash. 

D. Description of Brake-Throttle 

Override 

A BTO is a feature that helps to 

address UA in trapped accelerator pedal 

situations and possibly in some other 

related situations. As reported in the 

press and to NHTSA, a number of 

vehicle manufacturers already have 

adopted brake-throttle override or will 

be incorporating BTO into their vehicle 

designs over the next few model years. 

Based on our technical review of the 

technology, brake-throttle override is an 

electronic function of the engine control 

system. Generally, it works by 

continuously checking the position of 

the brake and accelerator pedals and by 

recognizing when an acceleration 

command through the accelerator pedal 

is in conflict with a concurrent 

application of the brake pedal. If the 

BTO system identifies that a pedal 

conflict exists, it invokes the override 

function which causes the engine 

control system to ignore or reduce the 

commanded throttle input, thus 

allowing the vehicle to stop in a normal 

fashion. How this is accomplished 

depends on the design of the vehicle 

control system. In some vehicles, BTO 

engagement may partially close the 

throttle or return it to idle. In other 

types of powertrains, it may reduce fuel 

flow or, in the case of an electric drive 

system, attenuate the electric current 

driving the vehicle. Regardless of the 

specific means used, BTO intervention 

quickly reduces or eliminates the 

unintended vehicle propulsion. 

If a BTO system uses throttle closure 

to reduce power, this action may have 

the additional benefit of preventing loss 

of brake-boost by maintaining manifold 

vacuum (see discussion in the previous 

section).7

On a vehicle equipped with a BTO 

system, if for any reason an accelerator 

pedal fails to return after the driver 

stops pressing on it, BTO will engage as 

soon as the driver applies the brake 

pedal (there may be a delay built into 

the system on the order of one second; 

in some systems, other pre-conditions 

have to be met for the BTO to engage, 

as discussed below). By intervening in 

this way, the BTO system essentially 

gives the brake pedal priority over the 

accelerator pedal, allowing for normal 

braking. Thus, the vehicle can be 

brought to a stop with an amount of 

pedal effort that drivers are accustomed 

to, even though it may be clear that 

something out of the ordinary has 

occurred. Without a BTO system, the 

brakes would have to overcome the 

propulsive force of a racing engine, and 

the driver would have to ‘‘fight’’ the 

drivetrain as the vehicle is slowed and 

brought to a stop. 

Because it reduces or eliminates 

propulsive force and also has the 

potential to minimize loss of power 

brake boost, we believe that BTO would 

be very effective in scenarios like those 

described in the relevant VOQs where 

drivers apparently experienced trapped 

pedals. In those cases, BTO would 

ensure that normal application of the 

brake pedal would produce sufficient 

braking to stop the vehicle. This should 

minimize panic on the driver’s part and 

very likely would lower the risk of a 

crash following a trapped pedal event.8

Some manufacturers’ implementation 

of a BTO system may include checking 

for certain prerequisite conditions prior 

to actuation. The BTO system may 

check conditions such as vehicle speed, 

engine revolutions per minute (RPM), 

brake pedal travel, and pedal sequence 

(i.e., whether the brake was pressed first 

and then the gas pedal, or vice versa) to 

determine if the driver’s intention is to 

stop the vehicle. Based on these 

conditions, the BTO system may 

determine that the combined brake and 

gas pedal inputs are actually 

intentional, and it would not necessarily 

intervene in that case. This may occur, 

for example, if the vehicle is at very low 

speed and the driver presses on the 

brake first and then on the accelerator. 

This behavior is consistent with 

intentional driving maneuvers which 

may be used for such things as trailer 

positioning or similar situations. We 

believe there is no particular safety 

issue in these situations, and in fact this 

type of ‘‘two-footed’’ driving capability 

can be desirable and may be in 

widespread use. Since there is no reason 

for the BTO to intervene in this case, 

today’s proposal would not prohibit this 

kind of BTO design. In fact, our 

proposal intentionally avoids restricting 

the specific design aspects of BTO 

systems so that current BTO systems 


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9This may occur due to a malfunction in the 

moving parts of an accelerator pedal assembly 

causing the pedal to lose its ability to quickly spring 

back to its rest position. The assembly, after it has 

been in service, may develop excessive internal 

friction for a variety of possible reasons such as: 

internal springs or sensing elements can break; 

seating surfaces and housings can deform or 

fracture and fragments may lodge in moving parts; 

or foreign liquids can penetrate and coagulate 

inside the assembly. Manufacturing variation can 

play a role, as well as environmental factors like 

heat, cold, and moisture, which can lead to warping 

and corrosion. NHTSA has experience with pedal 

defects of this kind which have led to recalls, most 

notably the Jan. 2010 recall of accelerator pedal 

assemblies in Toyota vehicles [NHTSA Recall no. 

10V–017]. 

10For a fuller discussion of these letters of 

interpretation, please see NPRM of July 23, 2002 (67 

FR 48117). 

11The NASA report is available at: http:// 

www.nhtsa.gov/PR/DOT-16-11. After ten months of 

studying Toyota’s ETC system, NASA was not able 

to identify an electronic cause of large, unintended 

throttle openings. 

can be accommodated to the greatest 

extent possible, because we believe 

those systems (based on our testing) 

would address the safety issue at hand. 

Although often caused by floor mat 

interference, the failure of an accelerator 

pedal to return after release may also 

result from ‘‘sticky pedal’’ situations.9

Depending on the source of ‘‘stickiness’’ 

in an accelerator pedal, we believe that 

brake-throttle override will be an 

effective countermeasure in most 

instances as it would treat sticky pedals 

the same as trapped pedals, and thus 

would prevent any significant vehicle 

acceleration once the brake pedal is 

applied. 

We note that an ETC system may 

recognize when a pedal assembly is 

malfunctioning, and it may be able to 

invoke some fail-safe action without 

involving BTO. This would depend on 

the nature of the malfunction and the 

design of the control system. For 

example, an ETC could override the 

accelerator pedal assembly if signals 

from the pedal position sensor exceed 

design limits. This could occur without 

brake pedal application. This is a 

desirable response to a broken pedal 

assembly and meets the need for safety 

independent of any brake-throttle 

override capability. 

IV. Technical Discussion of Accelerator 

Control System Safety Issues 

A. Accelerator Control System 

Disconnections 

In the past, vehicles had mechanical 

throttle systems consisting of rods, 

levers, cables, and springs to translate 

movement of the driver-operated 

accelerator pedal into throttle plate 

rotation. These systems were subject to 

the possibility of disconnection or 

separation of its linkages. Without a 

safety countermeasure such as a springloaded throttle plate, a disconnection in 

a mechanical system could result in a 

throttle plate that remained open after 

the driver let off of the accelerator 

pedal. 

Similarly, return springs are 

susceptible to the possibility of 

disconnection or breakage, which could 

lead to an open throttle if the control 

system lacks a backup spring or other 

supplemental means of closing the 

throttle. 

There also is the possibility that an 

accelerator control system could have 

excessive friction between its moving 

parts, especially in very cold 

temperatures. This could inhibit the 

throttle from immediately rotating back 

to idle after release of the accelerator 

pedal. 

FMVSS No. 124 has been in place 

since the 1970s to ensure that 

disconnections, separations, or 

severances do not result in an open 

throttle and potentially a runaway 

vehicle. The Standard also prohibits 

ACSs that return the throttle to idle too 

slowly even with no disconnections, 

which could be hazardous in severe 

instances. 

These protections against 

disconnections and slow-returning 

throttles are carried forward in today’s 

proposal. 

B. Electronic Throttle Control 

Now that mechanical accelerator 

controls have been superseded by ETC, 

the kinds of failures that might occur are 

somewhat different. In an ETC or 

‘‘throttle-by-wire’’ system, the driver 

still uses an accelerator pedal to 

modulate drivetrain output. However, 

most of the mechanical components 

linking the pedal to the throttle on the 

engine now are supplanted by electronic 

components including sensors, electric 

motors, a control module, and 

connecting wires. Some mechanical 

parts, particularly springs, are still 

employed, but the primary connection 

between the pedal and the engine 

throttle is electronic. 

Disconnections of the kind covered by 

FMVSS No. 124 are possible in ETC 

systems, but would involve separation 

of electrical connectors or severance of 

connecting wires rather than 

disconnection of linkages or cables. In 

official letters of interpretation, NHTSA 

has asserted that disconnection of 

power and ground wires in ETC 

systems, as well as shorting of those 

wires, are to be considered among the 

faults covered by the Standard, and the 

agency has conducted compliance 

testing accordingly. However, none of 

these electrical disconnections are 

explicitly addressed in FMVSS No. 124 

currently.10 As such, today’s proposal 

updates FMVSS No. 124 to incorporate 

these interpretations so that the 

standard will now have specific 

regulatory language to address 

electronic ACSs. 

C. Potential ETC Failures Not Covered 

ETC systems generally are designed 

with fail-safe characteristics such as 

fault checking and control redundancy 

to prevent throttles from opening 

unintentionally. They often have ‘‘limp 

home’’ modes which restrict the throttle 

opening to a small range when a fault 

occurs. These fail-safe characteristics 

limit engine power so that the vehicle 

is incapable of abrupt acceleration. 

However, NHTSA understands that 

manufacturers and suppliers have 

implemented ETC systems in different 

ways and have incorporated different 

fail-safe characteristics in the design of 

these systems. 

Allegations of throttles failing to close 

after accelerator pedal release, or 

throttles opening unexpectedly without 

accelerator pedal input, have been 

widely publicized, and it has been 

alleged that some such incidents have 

been caused by electronic faults such as 

errant throttle control signals or ambient 

electrical disturbances. The agency has 

been carefully evaluating the safety of 

ETC systems through research and 

defect analysis, and we engaged the 

National Academy of Sciences (NAS), 

an independent scientific body, to study 

the problem of UA in motor vehicles. 

The NAS issued a report in January 

2012 to broadly address the issue of 

safety in electronic vehicle control 

systems. (Note that this study is 

different from the NASA report released 

in February 2011 which focused 

specifically on Toyota ETC systems.) 11

Until this work is complete, it is 

premature to propose additional safety 

requirements at this time. Therefore, the 

only ETC failures within the scope of 

this proposal are disconnections of ETC 

components and wiring which result in 

open or short circuits, which is 

consistent with NHTSA interpretations 

of the current language of FMVSS No. 

124. 

V. Proposed Update of FMVSS No. 124 

Test Procedures 

We believe that changes set forth in 

this proposal are necessary to ensure 

that the longstanding requirements in 

FMVSS No. 124 remain relevant for 

modern ACSs. 


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Although this proposal introduces 

new test procedures, we believe it does 

not impose a significant new burden on 

vehicle manufacturers. In fact, we 

expect it can relieve certification burden 

by providing test procedures for 

different kinds of accelerator control 

systems and also by accommodating 

fail-safe strategies other than return of a 

throttle to a mechanical stop. 

We note that this portion of today’s 

proposal is nearly the same as the 2002 

NPRM (July 23, 2002, 67 FR 48117), 

with two exceptions. First, an intake 

airflow rate criterion has been added to 

the other disconnection test procedures 

as a compliance option that may be 

useful for spark ignition engines. This 

criterion has been added in response to 

comments on the 2002 NPRM. 

Secondly, the powertrain output test we 

are proposing would use vehicle 

terminal speed or ‘‘creep speed’’ instead 

of some other parameter like engine 

speed or torque. This also has been 

added in response to comments on the 

2002 NPRM. 

A. Purpose and Scope of FMVSS No. 

124 at Present 

The scope of FMVSS No. 124 as it 

currently exists is limited to how 

quickly a throttle returns to idle, either 

in normal operation (i.e., without any 

disconnections) or in the event of a 

disconnection or severance in the 

control system. We have sought to 

maintain the scope of the existing 

Standard by limiting today’s proposal to 

what was designated in past agency 

interpretations as being within scope, 

and by limiting the additional test 

procedures to the minimum necessary 

for non-mechanical ACSs. For example, 

where the present Standard applies to 

single-point failures such as the 

disconnection of one end of a throttle 

cable, today’s proposal also is limited to 

single-point disconnections such as 

removal of a single electrical connector 

or severing a conductor at one location. 

The current language of the test 

procedure in FMVSS No. 124 is 

expressed in terms of the return of an 

observable moving part, i.e., the throttle 

plate, to a closed or nearly closed 

position. It does not prescribe other 

types of vehicle fail-safe responses 

besides throttle closure. This neglects 

the variety of ways in which powertrain 

output in a vehicle with a modern 

throttle control system can be reduced 

to an acceptably benign level, e.g., spark 

adjustment, even though the throttle 

plate may be at a non-idle position. It 

also leads to non-optimal test 

procedures for hybrid or electric 

vehicles and diesel-engine vehicles 

whose drive power may not be governed 

by throttle position. 

The current Standard’s stated purpose 

is to ‘‘prevent engine over-speed.’’ The 

sole performance criterion, expressed in 

terms of throttle plate closure, does 

indeed have the effect of limiting engine 

speed, or more specifically engine 

torque. That, in turn, limits power 

output to the drive wheels. 

FMVSS 124’s focus on control of the 

throttle was a convenient criterion at the 

time the Standard was adopted. 

However, NHTSA does not believe the 

intent of the Standard should be 

construed as merely setting a limitation 

on throttle position. Instead, it is 

evident that the fundamental safety 

purpose of the Standard is to prevent a 

vehicle’s powertrain from creating 

excessive driving force when there is no 

input to the accelerator pedal. There 

would be no safety reason whatsoever to 

require the throttle to close if that did 

not limit vehicle propulsion. 

B. Need for Update of FMVSS No. 124 

Even if it is well established that 

FMVSS 124 does apply to ETC systems, 

regulating ETC systems by drawing 

analogies to mechanical systems has 

undesirable outcomes. This can lead to 

situations, as we have mentioned, where 

safe engine responses are discounted, 

and test methods for some alternative 

types of vehicle propulsion are not 

clearly defined. 

There are important questions about 

exactly how the Standard should be 

applied to ETC. For example, in a 

request for interpretation, one vehicle 

manufacturer suggested that merely 

placing two return springs on the 

accelerator pedal assembly satisfied the 

requirement for ‘‘two sources of energy’’ 

capable of returning the throttle to idle. 

NHTSA responded that, while that 

approach might be enough to satisfy the 

need for pedal return, it could not 

ensure return of the engine throttle itself 

in the event of a disconnection beyond 

the pedal. 

Another reason that FMVSS 124 

needs updating is that powertrain 

responses that can result from failures 

in electronic systems are much more 

varied than with mechanical systems. 

Fuel injection and ignition timing are 

among factors that can be varied 

without any change in throttle position. 

For example, we have seen engines 

with spring-loaded throttles that do not 

close fully to idle when disconnected 

from the electrical harness. They 

assume a default position that is slightly 

more open than idle. This kind of 

‘‘limp-home’’ feature presents no safety 

hazard. In fact, it provides a safety 

benefit by avoiding engine stalling and 

allowing the vehicle to be moved out of 

traffic, which can be critical for 

preventing a crash. Engines with this 

kind of design may accomplish the 

essential fail-safe performance by 

retarding the ignition timing or 

restricting fuel delivery so that the 

engine torque output is limited to a 

level at or below what is normally 

provided at idle. A design of this kind 

thus is able to achieve an equivalent 

level of safety without full return of the 

throttle. 

Other technology also illustrates the 

need for this update of FMVSS 124. 

Modern engines routinely have variable 

valve lift and/or timing control. In at 

least one recent engine design, the level 

of valve control is great enough that the 

throttle plate no longer throttles the 

engine during at least part of the 

engine’s operating range. Instead, air 

intake is throttled to a large extent by 

the intake valves themselves while the 

throttle plate stays in an open position. 

In such a design, requiring ‘‘return of 

the throttle to the idle position’’ would 

be design restrictive without any safety 

justification. 

Furthermore, the reduced relevancy of 

the throttle plate removes the most 

easily observable component for 

verifying return-to-idle. For some 

engines such as electronically 

controlled diesel engines with unitized 

injectors, assessing compliance cannot 

be done by simply observing retraction 

of a traditional fuel rack to a set 

position. This means that some 

alternative method of verifying returnto-idle is needed. 

In spite of these facts, even the most 

advanced engines do have an idle state, 

and it is still possible to identify a 

measurement criterion for them and to 

expect these types of engines to return 

to a safe idle state. 

In order to recognize the advancement 

of engine technology, and to better 

regulate advanced vehicle propulsion 

systems, improved regulatory language 

is needed. This proposal addresses this 

need with revised regulatory language to 

include new test procedures that can be 

applied to a variety of vehicle 

propulsion systems. 

C. Applicability to Electronic Throttle 

Control Components 

NHTSA concluded in published 

interpretation letters that electrical 

wires and connectors in an electronic 

ACS are analogous to mechanical 

components in a traditional ACS and 

are therefore subject to the same safety 

requirements as their mechanical 

counterparts. We were able to conclude 

this because the regulatory language, 

although modeled on mechanical 


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features of carbureted engines, actually 

is stated in very general terms. It defines 

the ACS as ‘‘all vehicle components, 

except the fuel-metering device, that 

regulate engine speed in direct response 

to the movement of the driver-operated 

control and that return the throttle to 

the idle position upon release of the 

actuating force.’’ 

NHTSA stated that the ACS does not 

consist only of the accelerator pedal 

assembly and the wiring harness 

connecting it to the engine control 

module (ECM), but extends beyond the 

ECM to include connections to the 

actual throttling device on the engine. 

We stated that the ACS must extend 

beyond the pedal assembly because 

those components are the only link 

between the engine throttle and the 

accelerator pedal. Otherwise, if the 

electrical connection between the ECM 

and throttle actuator was disconnected 

for example, no fail-safe action would 

be required, which would be contrary to 

the Standard’s primary purpose. 

There was also the issue of whether 

the ECM itself should be considered 

part of the ACS. We concluded in the 

interpretation letters that the ECM 

should be considered an ACS 

component for the purposes of the 

Standard because throttle control 

signals originate within it. We stated 

that the ECM as a whole unit, along 

with its associated external connective 

wires, are critical ‘‘linkages’’ that in 

effect form a connection from the gas 

pedal to the engine throttling device. 

On the other hand, it was less clear 

whether internal circuitry within the 

ECM or another enclosed electronic 

module should be subject to 

‘‘severances and disconnections.’’ If that 

were the case, the system might have to 

withstand disruption of internal 

electronic elements such as the 

microprocessor without causing loss of 

throttle control. Instead, we concluded 

that the internal elements of an ECM, 

besides serving functions unrelated to 

throttle control, are analogous to the 

internal fuel-metering parts of a 

carburetor, which the existing 

Standard’s ACS definition specifically 

excludes. Thus, the agency’s position 

has been that severances or 

disconnections of elements inside of the 

ECM or another enclosed module in the 

ACS are outside the scope of Standard 

No. 124. 

The 2002 proposal included new 

regulatory language to clarify FMVSS 

124’s applicability to electronic 

components. It included the following 

requirement for fail-safe performance: 

Severances and disconnections include 

those which can occur in the external 

connections of an electronic control module 

to other components of the accelerator 

control system and exclude those which can 

occur internally in an electronic control 

module. 

The interpretation letters (discussed in 

the July 2002 NPRM) also recognized 

that disconnections of wires between 

electronic components could result in 

short circuits, not just open circuits. For 

that reason, the proposed regulation also 

stated: 

The accelerator control system shall meet 

[these] requirements * * * when either open 

circuits or short circuits to ground result 

from disconnections and severances of 

electrical wires and connectors. 

These requirements are carried forward 

in today’s proposal. 

D. Test Procedures of the 2002 NPRM 

Of the several test procedures 

included in the 2002 NPRM, the first 

was essentially the air throttle plate 

position of the original Standard, 

normally applicable to conventional 

gasoline engines. 

A second proposed procedure, new to 

FMVSS 124, allowed for measurement 

of net fuel flow rate, and was included 

primarily for diesel engines, but could 

be applied to vehicles with other types 

of powertrains. 

A third proposed procedure, also 

new, allowed for measurement of 

electric current flow to an electric drive 

motor, and was intended for electric 

vehicles and for the electric driven 

portion of hybrid vehicles. 

Finally, the 2002 NPRM proposed a 

new procedure which would use engine 

speed to indicate idle state. As 

conceived, the procedure was to be 

conducted on a chassis dynamometer in 

order to simulate a realistic load on the 

drivetrain. RPM was thought to be a 

valid idle-state measurement as long as 

the appropriate amount of load was 

exerted on the drivetrain of the vehicle 

so that the engine speed response 

reflected actual driving conditions. The 

engine RPM test was considered a 

multi-purpose test because it could be 

applied to different powertrain types 

including those of gasoline, diesel, and 

possibly electric vehicles. 

Under the 2002 NPRM, a 

manufacturer could choose any one of 

the proposed test procedures as a basis 

for compliance, and the choice was to 

be irrevocable so that failure to comply 

under the selected procedure could not 

be negated merely by trying each of the 

other procedures in hopes of 

successfully complying. 

All of the procedures in the proposal 

were premised on return to a ‘‘baseline’’ 

idle condition which was the measured 

idle of the vehicle in normal operation, 

i.e., without any faults or 

disconnections in the ACS. Return to 

the ‘‘baseline’’ idle was treated as 

analogous to return of a throttle plate to 

the idle position. A tolerance was 

deemed appropriate to accommodate 

overshoot and/or fluctuation which are 

possible responses when disconnections 

are present in electronically controlled 

throttle systems. The proposal set the 

idle state tolerance at 50 percent above 

the measured baseline value. 

E. Powertrain Output Test Procedures 

and ‘‘Creep Speed’’ 

Early on in the effort to update 

FMVSS No. 124, comments from 

industry groups led to the idea that a 

performance test which measured 

engine output would be a useful 

alternative to a throttle position test. 

Among suggested measurement criteria 

were engine RPM and drive wheel 

torque. This idea evolved into using 

vehicle speed as a measurement 

criterion, and the term ‘‘creep speed’’ 

was applied to this because it would 

measure the speed that a vehicle has 

when it ‘‘creeps’’ along. Creep speed 

describes the condition of a vehicle 

moving under its own power when it is 

in gear and has no input to the driveroperated accelerator control. It is 

defined as the maximum or terminal 

speed that a vehicle can achieve in that 

condition both with its ACS intact and 

with disconnections. 

This test had the significant advantage 

of being ‘‘technology-neutral’’ meaning 

that it would be applicable to all forms 

of vehicle propulsion. However, 

measuring vehicle speed as a 

compliance criterion necessitates testing 

a vehicle under real or simulated 

driving conditions. That meant that a 

chassis dynamometer would be required 

for a creep speed test, or else the vehicle 

would have to be tested on a test track. 

At the time of the 2002 proposal, 

NHTSA was persuaded that the creep 

speed test had merit, but decided that 

further evaluation of the idea was 

necessary for a number of reasons. First, 

it was necessary to verify feasibility of 

using a dynamometer to measure creep 

speed since the agency did not have a 

similar procedure in any other 

regulation. Second, it would be 

necessary to determine whether creep 

speed was a useful and practical 

performance criterion. Lastly, we 

wanted to demonstrate the practicability 

of conducting compliance tests using 

that approach. 

Subsequent to the 2002 NPRM, 

NHTSA conducted a series of tests using 

a wheel-driven (chassis) dynamometer 

at the Transportation Research Center 

(TRC) in East Liberty, Ohio. A report 


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12Road force data is available for U.S. vehicles 

through the Environmental Protection Agency’s 

annual vehicle database which is available on the 

EPA Web site: http://www.epa.gov/otaq/crttst.htm. 

The EPA measurements are derived using a 

coastdown technique defined in SAE J2264 

‘‘Chassis Dynamometer Simulation of Road Load 

Using Coast Down Techniques’’ (APRIL 1995). 

13See docket NHTSA–2002–12845–0014, record 

of discussion and demonstration held on December 

10, 2002, with Toyota. 

14AIAM did not suggest a specific definition. 

describing the testing and results is 

available in the docket number cited in 

the heading of this notice. Tests were 

conducted using three ETC-equipped 

vehicles instrumented with torque 

wheels on their drive axles for 

measurement of the net acceleration or 

deceleration torque. As described in the 

report, the dynamometer was 

programmed so that its power 

absorption simulated the net road force 

of actual driving conditions, including 

the effects of tire rolling resistance and 

aerodynamic drag unique to each test 

vehicle.12

Dynamometer tests were conducted 

on each vehicle in a variety of 

operational conditions including both 

normal operation and with 

disconnection faults. The testing 

evaluated vehicle response to the types 

of disconnections that are possible in 

electronic ACS systems. Torque output, 

vehicle speed, and engine RPM were 

measured parameters of each test. 

Throttle plate position was also 

monitored. The latter was useful for 

determining if a vehicle’s design 

strategy to limit engine power during 

fail-safe operation was to use throttle 

control or some other factor. The 

following are key test results of 

NHTSA’s testing: 

ACS CREEP SPEED TEST RESULTS

Chevrolet pick-up, LT245/75R16 Buick Lacrosse sedan, 

P225/55R17 

Toyota Corolla sedan, 

P195/65R15 

Creep Speed at unfaulted idle ....... 3 mph–4 mph ............................... 5 mph ............................................ 4.9 mph. 

Maximum faulted creep speed ...... 9 mph ............................................ 23.5 mph ....................................... 23.6 mph. 

Fault condition where maximum 

creep speed occurs.

Disconnection at throttle actuator 

(whole connector).

Pedal harness disconnect at 40 

mph or greater.

Disconnection at throttle actuator 

(whole connector). 

This NHTSA testing indicated that 

drivetrain torque values were low 

following each sampled type of ACS 

disconnection. This was evident in that 

the test vehicles’ engines did not race to 

a high RPM level and the vehicles 

decelerated or gradually accelerated 

(depending on the initial test speed) to 

their terminal creep speeds. The 

vehicles behaved as if they were 

operating either in a normal idle or a 

‘‘high idle’’ condition, except in a few 

cases where the result was stalling or 

rough idling. The vehicles remained 

easily controllable in terms of being free 

of any abrupt acceleration. At any point 

in each test, it was possible to bring the 

test vehicles to a stop on the 

dynamometer with only light brake 

application (equivalent to or only 

marginally greater than that needed to 

prevent movement of an in-gear vehicle 

at a normal idle). 

The drivetrain output test procedure 

that we are proposing today as an 

alternative to throttle position, fuel 

delivery rate, air intake rate, or electric 

power delivery is based on this creep 

speed methodology. We are proposing 

that FMVSS No. 124 should allow a 

maximum creep speed for all vehicles of 

50 km/h (31 mph). This is a speed that 

we concluded would accommodate 

typical light vehicle responses to ACS 

disconnections including various limphome modes. This was based in part on 

a demonstration of vehicle response to 

pedal position sensor disconnection 

using a popular passenger vehicle with 

ETC. The demonstration was conducted 

as part of an ex-parte meeting and 

discussion with vehicle manufacturers 

as a follow-on to the 2002 NPRM.13

Our subsequent laboratory tests, as 

reported above, showed that this level of 

speed is equivalent to a relatively small 

amount of drivetrain torque output. 

Considering that this speed would be 

the ultimate terminal speed of a vehicle 

with an ACS disconnection, it 

represents a small and easily 

controllable amount of vehicle 

acceleration. We believe that it is a 

reasonable threshold that would ensure 

safety in the event of an ACS 

disconnection. 

The proposed procedure would 

measure terminal speed following an 

ACS disconnection from any initial 

vehicle speed. It is divided into two 

parts, corresponding to whether the 

initial test speed is greater or less than 

the required maximum of 50 km/h. For 

initial speeds lower than 50 km/h, the 

vehicle’s terminal speed following an 

ACS disconnection would have to stay 

below the 50 km/h threshold. For higher 

initial speeds, the terminal speed 

following a disconnection would have 

to drop to 50 km/h or lower within 

some specified period of time after the 

accelerator control is released. We call 

the latter case the ‘‘coastdown’’ 

procedure. The creep speed and 

coastdown procedures are discussed in 

more detail later in this document. 

F. Comments on the 2002 NPRM 

A number of comments were 

submitted in response to NHTSA’s 2002 

NPRM (before it was withdrawn). 

Commenters included The Alliance of 

Automobile Manufacturers (Alliance), 

The American Trucking Associations 

(ATA), The Association of International 

Automobile Manufacturers (AIAM), and 

The Truck Manufacturers Association 

(TMA). Some individual member 

companies of those organizations also 

submitted comments including Blue 

Bird Body Company, BMW Group, Ford 

Motor Company, American Honda 

Motor Company, and Volkswagen of 

America, Inc. 

The comments were generally 

supportive of NHTSA’s effort to update 

FMVSS 124, but raised a number of 

important issues. To a great extent, 

changes we have made in the current 

proposal vis-a`-vis the 2002 NPRM 

address those issues. The following is a 

brief point-by-point summary of the 

comments: 

AIAM 

• Cancellation of ‘‘limp-off-the-road’’ 

mode by brake pedal application is 

design restrictive. 

• 50 percent idle state tolerance is 

insufficient and could lead to stalling; 

range should be defined by 

manufacturer or some different way.14

• Favors having compliance options, 

but objects to ‘‘irrevocable selection.’’ 

• Suggests fuel delivery and air intake 

rate tests be done simultaneously 

(combine S6.2 and 6.3), i.e., measure 

both quantities at once; vehicle ‘‘passes’’ 

if either measurement meets the 

specification. 

• Recommends allowing optional 

early compliance with the new 

standard. 


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BMW 

• Favors deleting ‘‘normal operation’’ 

requirement or at least adding 

appropriate test procedures. 

• Increase delay time allowed for 

return of entire powertrain to idle state 

in the proposed RPM test. 

• Allow manufacturer to define an 

acceptable range for idle. 

• If NHTSA keeps tolerance, 50 

percent is not large enough. 

• Procedure in S6.2.5, S6.3.5, and 

S6.5.5 should say ‘‘remove actuating 

force after at least 3 sec. but before X 

sec.’’ 

• Concerned with use of 

‘‘indefinitely’’ with respect to 

maintaining idle following 

disconnection. 

• The dynamometer-based RPM test 

procedure would be overly burdensome 

because manufacturers would have to 

consider so many permutations of 

vehicle mass, final drive gearing, and 

drag. 

• Uncertainty in measurement of 

RPM return time by itself is probably 

greater than the specified 3 second 

allowance. 

Honda 

• Tolerance of 50 percent is too 

small—high altitude example given; 

suggests much larger tolerance since 

even twice the baseline (100 percent 

tolerance) would still be safe for drivers 

to handle. 

• With automatic transmissions, gear 

selection is modified after an ETC 

failure occurs, i.e., the vehicle cannot 

maintain same gears in failure-mode 

tests as in baseline tests. 

• Favors measuring vehicle speed, 

not engine speed, in RPM procedure. 

Volkswagen 

• Favors establishing an overall 

powertrain output test as main criterion 

in the safety standard. 

• Maximum idle should be defined 

according to manufacturer, not 

according to baseline measurement. 

Blue Bird 

• Supports the 2002 NPRM in full; 

two year lead-time relieves burden of 

compliance. 

Ford 

• Supports NHTSA effort; specific 

comments included with Alliance and 

TMA submittals. 

ATA 

• Recommends that the ‘‘idle state’’ 

definition be consistent throughout the 

standard. 

• Recommends performance-based 

test for cancellation of ‘‘limp-home’’ 

mode instead of specifying brake 

application which is too design 

restrictive. 

• Believes that the 50 percent 

tolerance should be adjusted to account 

for likely variation in fuel rate at or near 

idle. 

Alliance 

• Believes tolerance concept is 

impracticable and 50 percent is 

inadequate. 

• linking maximum idle to baseline is 

design restrictive and unnecessary for 

safety. 

• Fail-safe idle state varies too much 

to achieve stable conditions for 

comparison to baseline. 

• Stalling will result if fail-safe idle is 

restricted as proposed. 

• Standard 124 should be based on a 

manufacturer-specified maximum idle. 

• Suggests technology neutral 

‘‘powertrain torque output’’ test for failsafe operation. 

• Technology-neutral test should 

apply to normal operation as well as 

fail-safe (but not sure what compliance 

criterion should be used). 

• Return to idle should not be 

required before removal of pedal force 

after fault inducement. 

• Asks for confirmation that 

manufacturers will be allowed to make 

running changes in production to 

‘‘irrevocable selection’’. 

• Electronic ‘‘dashpots’’ should be 

treated the same as mechanical ones in 

current standard (however, this would 

be unnecessary if NHTSA allows 

manufacturer-specified maximum idle). 

• ‘‘Detection by powertrain control 

system’’ should be added to stop-lamp 

illumination as an allowable indicant of 

brake pedal application. 

• When air throttle percent-opening 

is close to zero at idle, 50 percent is 

meaningless. 

• Definition of ‘‘air throttle position’’ 

neglects non-rotating (slide type) 

throttles; suggests a simplified 

definition. 

TMA 

• Anticipates most trucks using fuel 

rate test to comply; suggests that fuel 

rate signal, not fuel delivery rate, is the 

appropriate criterion. 

• Severing power to the ECM shuts 

down processor, which means fuel rate 

signal goes away, which would 

necessitate observing some other 

compliance measure. 

• Wants to allow bench test of standalone engine instead of whole vehicle 

but not sure how ‘‘impose test load’’ as 

used in the procedures would apply to 

a test of a stand-alone engine, i.e., not 

mounted in a truck chassis. 

• Irrevocable selection wording too 

restrictive. 

• Recommends performance-based 

specification for removal of limp-home 

mode, not the design-restrictive ‘‘service 

brake apply’’ in the NHTSA proposal. 

• Wants return to or below the 

baseline to be an acceptable response. 

• Asks if the tolerance is based on 50 

percent of the average, maximum, 

minimum, or what? Also thinks the 

term ‘‘indefinitely’’ should be defined or 

quantified. 

Generally, these comments have been 

addressed in today’s proposal where 

appropriate or necessary. We have 

removed the procedure which specified 

that a limp-home mode would have to 

be cancelled by a light application of the 

service brake. Limp-home modes 

instead have to fall within the 50 

percent tolerance of the applicable idle 

state indicant, or cannot exceed the 

allowable creep speed of 50 km/h. 

We have not increased the tolerance 

but left it at 50 percent as proposed in 

2002 because commenters did not 

provide a specific alternative value or 

any rationale to support changing the 

tolerance. 

We have maintained the ‘‘irrevocable 

selection’’ stipulation given that we 

want to deter a manufacturer that fails 

to comply under their chosen test 

option from claiming compliance under 

another test option. 

In regard to determining the idle state 

for a test vehicle, we continue to believe 

that measuring a baseline value for the 

idle prior to executing any 

disconnections is a better alternative 

than requiring the vehicle manufacturer 

to provide idle state information for 

each test vehicle. This issue was 

discussed in the 2002 NPRM, and the 

reasoning has not changed. Essentially, 

we believe it is more expedient and 

practical to ascertain the baseline idle as 

part of the test methodology. 

Among other issues raised in 

comments on the 2002 proposal, and 

how we propose to address them, are 

the following: 

• We have elected to leave FMVSS 

No. 124’s ‘‘normal operation’’ 

requirement in today’s proposal because 

it has always been part of the Standard 

and no compelling reason for removing 

it was offered by any commenter. It may 

be relevant for vehicle operation in very 

cold temperatures. 

• Some commenters disagreed with 

our use of ‘‘indefinitely’’ to refer to the 

required duration of a vehicle’s returnto-idle following a disconnection. We 

believe it is necessary for safety to 

prohibit a design in which the throttle 

initially responds to an ACS 

disconnection by closing but re-opens 


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Federal Register / Vol. 77, No. 73 / Monday, April 16, 2012 / Proposed Rules 22647 

15This approach of combining an equipment 

requirement with a performance test is similar to 

the approach NHTSA used in establishing FMVSS 

No. 126, ‘‘Electronic Stability Control Systems.’’ In 

that rulemaking, NHTSA stated, ‘‘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.’’ [72FR17238]. In the case of brake-throttle 

override, whereas the proposed performance test is 

based on stopping distance requirements in FMVSS 

No. 135 which many vehicles can meet with a 

significant margin, it is likely that some vehicles, 

for instance those with high brake-torque-to-drivetorque ratios, could meet the proposed BTO 

performance test without actually having a BTO 

system. 

after a short time. We would consider 

alternative suggestions for how to 

ensure that idle is maintained following 

disconnection, and we request comment 

on this issue. 

• The tolerance of 50 percent may not 

be relevant when applied to a throttle 

position because it is not valid for a 

closed or nearly closed throttle. In 

general, engine output is not a linear 

function of ‘‘percent throttle opening.’’ 

NHTSA requests comment on the best 

way to evaluate throttle position as it 

relates to engine output (i.e., angular 

position, percent of full open, or some 

other measure) and how the 50 percent 

tolerance should be applied to throttle 

position. 

• Regarding the comment suggesting 

how to define throttle position for 

rotating air throttles, we note that the 

term ‘‘percent throttle opening’’ was not 

defined in the 2002 proposal even 

though it was used in one of the 

proposed compliance criteria. As above, 

we are requesting comment on how best 

to define throttle position so that it 

corresponds with drivetrain output. 

• Regarding the comment that, when 

measuring fuel rate or air intake rate, 

disconnection of the ECM power might 

cause the internal processor to stop 

functioning, and thus the fuel rate or air 

intake rate signal would cease: We do 

not view this as a significant difficulty 

because it can be assumed that the 

engine would shut down in this case, 

which would of course qualify as a 

complying vehicle response since 

powertrain output would go to zero. 

• To the extent that we have not 

addressed in today’s proposal comments 

that were made on the 2002 NPRM and 

remain relevant, we request further 

comment in response to this proposal. 

VI. Notice of Proposed Rulemaking 

This section explains how we propose 

to amend FMVSS No. 124 so that 

crashes and associated injuries or deaths 

as described previously can be 

minimized. 

Based in part on NHTSA’s VOQ data, 

we propose in this NPRM to address 

drivers’ inability to stop vehicles in 

stuck-accelerator emergencies by 

amending FMVSS No. 124 to require a 

brake-throttle override system on all 

light vehicles having ETC. 

With this requirement, we intend for 

the effect of the BTO system to be 

independent of the stopping capability 

provided by a vehicle’s service brakes. 

That is, even if stopping power alone is 

sufficient for a vehicle to meet the 

performance requirement under highspeed, open-throttle conditions, we are 

proposing that there still must be 

electronic intervention invoked by brake 

application to abate drive torque caused 

by a stuck accelerator pedal. 

A. Definition of Electronic Throttle 

Control System 

We propose to define electronic 

throttle control as an accelerator control 

system in which movement of a driveroperated control is translated into 

throttle actuation at least in part by 

electronic, instead of mechanical, 

means. Note that in this definition, 

‘‘accelerator control system,’’ ‘‘driveroperated accelerator control,’’ and 

‘‘throttle’’ are separately defined terms 

whose definitions are included in the 

regulatory text. This definition is 

necessary to identify vehicles to which 

the BTO requirements would apply, i.e., 

those having ETC. 

B. Brake-Throttle Override Equipment 

Requirement 

We also are proposing an equipment 

requirement for BTO. This would be 

included in addition to a BTO 

performance requirement as described 

in the next section. We are proposing 

the requirement in paragraph S5.4.1 of 

§ 571.124. 

The equipment requirement also 

would specify that a BTO system may 

be designed so that it does not engage 

at speeds below 10 mph, as discussed 

below. 

This equipment requirement is 

necessary to ensure that a brake-throttle 

override capability is installed on each 

vehicle, and that a manufacturer’s 

certification is not based only on brake 

system performance. Otherwise, it might 

be possible for a manufacturer whose 

vehicle meets the BTO performance test 

without engagement of a BTO system to 

avoid installing BTO altogether.15

Under this requirement, BTO must 

engage if the powertrain controller 

determines that inputs to the brake and 

accelerator pedals are conflicting. This 

means not just that the pedal inputs are 

overlapping but also that they probably 

are unintentional; are unlikely to occur 

in normal driving; and may create an 

unsafe operating condition. For 

example, if a vehicle is travelling at a 

high rate of speed, and the brake is 

forcefully applied while accelerator 

pedal input signal remains high, it is 

logical to conclude that the driver’s 

intent is to slow the vehicle and that the 

throttle command should be ignored. 

On the other hand, if overlap between 

the accelerator pedal and brake exists 

only briefly, such as for less than one 

second, there is no reason to engage an 

override feature since a vehicle could 

not accelerate much in such a short time 

span, and the potential for loss of 

control would be very small. 

This proposed equipment 

requirement makes BTO engagement 

optional below 16 km/h (10 mph). We 

believe this will accommodate most 

‘‘two-footed’’ driving situations which 

have legitimate purposes such as 

maneuvering trailers, pushing other 

vehicles (as police sometimes do to 

move stalled vehicles out of traffic), and 

in off-road driving. These driving 

scenarios are not considered to be 

unsafe, and there is no compelling 

safety reason to prohibit them. 

The proposed equipment requirement 

limits required BTO engagement to 

‘‘conflicts’’ between the accelerator 

pedal and brake, so that BTO systems 

can allow for left-foot braking and other 

two-footed driving situations as 

manufacturers see fit to accommodate 

their customers. For example, a brakefirst-then-accelerator sequence of pedal 

application would not necessarily be 

considered a ‘‘conflict’’ and so would 

not always have to engage the BTO. 

The 10 mph (16 km/h) cut-off is the 

speed below which initial engagement 

of BTO is not required. That is, if a 

pedal conflict initially occurs below 10 

mph, the onset of BTO intervention is 

not required until the vehicle speed 

reaches 10 mph. Once vehicle speed 

reaches 10 mph, BTO must engage at 

that point, assuming other conditions 

for engagement exist. This does not 

mean that, if BTO engages at a speed 

above 10 mph, the BTO can disengage 

as the vehicle slows to below 10 mph. 

It must remain engaged until the vehicle 

has been brought to a stop and remain 

engaged until either the pedal conflict 

no longer exists (for example, if the 

driver releases the brake, or the gas 

pedal becomes unstuck), or vehicle 

drive power is removed by another 

action such as turning off the ignition. 

We have considered whether it is 

appropriate to require that BTO 

activation be accompanied by a warning 

or alert to signal to the driver that BTO 

intervention has occurred. This could be 

in the form of either a visible or audible 

alert. We are not proposing that such an 


emcdonald on DSK29S0YB1PROD with PROPOSALS2
22648 Federal Register / Vol. 77, No. 73 / Monday, April 16, 2012 / Proposed Rules 

16See test summary ‘‘Results of NHTSA Stopping 

Distance Tests of Production Brake-Throttle 

Override Systems’’ at the beginning of the notice. 

alert be required, but we request 

comment on this issue, specifically if 

there is any safety data that would 

justify such a requirement. 

A related issue is whether it should be 

possible for a vehicle operator to 

manually turn off the BTO function. For 

example, a switch or control could be 

provided for that purpose, similar to on/ 

off switches for disabling Electronic 

Stability Control (ESC). Alternatively, a 

manufacturer might design an ‘‘ESC off’’ 

switch so that it also disables the BTO. 

We are not proposing to prohibit 

controls that turn off BTO. However, if 

a vehicle is equipped with a control for 

turning off BTO, we believe that the 

driver should be warned that the system 

is off, and the system should always 

default to a ‘‘BTO On’’ state whenever 

the ignition is cycled. We request 

comment on whether a BTO Off 

function should be allowed and, if so, 

how it should function. 

C. Brake-Throttle Override Performance 

Requirement 

As indicated previously, we are taking 

the approach in this proposal of 

including both a performance 

requirement and an equipment 

requirement for brake-throttle override 

systems. We considered establishing a 

design requirement as the sole 

requirement for BTO, but the differences 

among BTO systems currently available 

from different vehicle manufacturers are 

significant enough that a design 

requirement by itself cannot effectively 

accommodate them all without being 

overly complex and/or design 

restrictive. By combining a relatively 

simple performance test with the basic 

equipment requirement described 

above, we can achieve a robust standard 

which is largely performance-based and 

minimally costly or burdensome. 

We believe this approach is 

appropriate because, by all indications, 

existing BTO systems are effective for 

their intended purpose, and we would 

not be able to justify a BTO requirement 

that favors one design over another or 

compels some manufacturers to go to 

the expense of re-designing their 

systems. In fact, NHTSA recently 

sampled a number of current BTO 

systems in a brief series of high-speed, 

open-throttle braking tests.16 Those tests 

demonstrated that each of the different 

BTO designs was very effective. In each 

test, at speeds up to 99 mph, stopping 

distances of BTO-equipped vehicles 

with their accelerator pedal held to the 

floor typically were less than 5 percent 

to no more than 15 percent greater than 

normal (‘‘normal’’ meaning in a dropthrottle condition from the same test 

speed). That was contrasted with openthrottle stopping distances from similar 

speeds that were about 35 to 70 percent 

greater than normal for vehicles without 

BTO. The stopping distance 

improvement for vehicles with BTO 

compared to those without BTO was 

even larger in tests in which the brake 

pedal was modulated or ‘‘pumped’’. 

When combined with an open throttle, 

pumping of the brakes increases the 

pedal force needed to stop a vehicle, 

and this seems to be a fairly common 

occurrence in stuck accelerator pedal 

situations according to complaint 

narratives in the ODI database. 

In order to ensure the effectiveness of 

new BTO systems, we are proposing an 

open-throttle stopping distance test. The 

proposed requirement specifies a 

stopping distance measurement in 

which the accelerator pedal is applied at 

up to 100 percent of pedal travel for the 

duration of the braking event. The 

procedure would consist of 

conventional stopping distance 

measurements in accordance with 

specifications found in FMVSS No. 135, 

‘‘Light vehicle brake systems.’’ Where 

Standard No. 135 specifies that the 

throttle is released or the vehicle is 

placed in neutral, the vehicle would 

remain in gear with the accelerator 

pedal held down to as much as 100 

percent of its travel. This represents the 

situation when an accelerator pedal is 

trapped by a floor mat, with 100 percent 

pedal application being the worst-case 

scenario. For the purposes of these tests, 

we are proposing that the minimum 

accelerator pedal input would be 25 

percent because pedal inputs below that 

level may not produce significant 

vehicle acceleration and may not 

require intervention by the BTO system. 

(We note that this is merely to facilitate 

consistent BTO performance testing, 

and does not mean that BTO systems 

cannot engage at less than 25 percent 

accelerator pedal input.) 

Test speeds for the proposed BTO 

procedure would be any speed from 30 

km/h (18.6 mph) up to as much as 160 

km/h (99.4 mph). The latter is the 

maximum specified under FMVSS No. 

135. The procedure carries over the 

specification in S7.6 of FMVSS No. 135 

that limits test speed to 80 percent of a 

vehicle’s maximum speed, not to exceed 

160 km/h. 

The required stopping distance would 

be based on one of two requirements in 

FMVSS No. 135, depending on whether 

the test speed was greater or less than 

100 km/h, to reflect the fact that FMVSS 

No. 135 stopping distances are 

somewhat different for speeds above 

and below 100 km/h. For test speeds of 

100 km/h or below, the stopping 

distance requirement in S7.5, ‘‘Cold 

Effectiveness,’’ would apply. For speeds 

above 100 km/h, the stopping distance 

requirement in S7.6, ‘‘High-Speed 

Effectiveness,’’ would apply. 

We propose that the BTO performance 

test would be conducted at Lightly 

Loaded Vehicle Weight (LLVW) as 

defined in S6.3 of FMVSS No. 135. 

Although the Cold Effectiveness and 

High Speed Effectiveness procedures in 

FMVSS No. 135 specify conducting tests 

at both LLVW and GVWR, the stopping 

distance requirement is the same 

regardless of the loading condition. 

Consequently, we believe it is 

unnecessary to include the GVWR 

loading condition in the BTO 

performance test. We request comments 

with supporting data on whether there 

is any safety need for BTO performance 

to be measured at GVWR. 

Under S6.5.3.2 of FMVSS No. 135, for 

stopping distance procedures specifying 

multiple test runs, compliance is 

achieved if any one of the test runs is 

within the prescribed distance. This 

applies to the Cold Effectiveness and 

High Speed Effectiveness procedures, 

where six test runs are required for each 

set of test conditions. The vehicle is 

deemed to comply if at least one stop is 

within the required distance. We 

propose using this same methodology 

for the BTO performance tests. 

All other test conditions and 

procedures would be in accordance 

with FMVSS No. 135 specifications. 

This includes ambient environmental 

conditions, track conditions, and 

vehicle set-up. This would utilize 

existing practices to the greatest extent 

possible, thus reducing test burden and 

cost. 

We are proposing that the stopping 

distance of a vehicle in an open-throttle 

condition shall not be more than 5 

percent greater than the required 

stopping distance in FMVSS No. 135, 

specifically as set forth in S7.5 for test 

speeds up to 100 km/h and S7.6 for test 

speeds over 100 km/h. This 5 percent 

margin allows for any additional 

stopping distance resulting from the 

delay that may be needed for the BTO 

system to engage and during which the 

brakes have to work against the 

powertrain drive torque. The stopping 

distances in FMVSS No. 135 do not 

account for any such drive torque 

because they are measured with the 

vehicle in neutral or with the 

accelerator pedal released. The 

5 percent margin represents 

approximately the additional stopping 

distance NHTSA found was needed in 


emcdonald on DSK29S0YB1PROD with PROPOSALS2
Federal Register / Vol. 77, No. 73 / Monday, April 16, 2012 / Proposed Rules 22649 

17 ‘G’ or ‘g’ is a unit that refers to the average 

acceleration produced by gravity at the Earth’s 

surface. 18See http://www.epa.gov/otaq/crttst.htm. 

our tests of BTO-equipped vehicles (the 

same tests cited immediately above) 

comparing their wide-open throttle 

stopping distance to their drop-throttle 

stopping distance at maximum FMVSS 

No. 135 test speeds. 

D. Update of FMVSS No. 124 

Disconnection Test Procedures 

New Creep Speed and Coastdown Test 

Procedures 

We are proposing a new vehicle 

performance test of powertrain output 

as an optional test procedure for 

compliance with the FMVSS No. 124 

disconnection requirements. This 

procedure would measure vehicle speed 

following an ACS disconnection, socalled ‘‘creep speed,’’ as the criterion for 

compliance. Other criteria such as 

engine RPM were considered and 

rejected as a result of comments on the 

2002 rulemaking effort. By evaluating 

vehicle speed and acceleration, the 

creep speed test will directly measure 

the fundamental parameter that affects 

safety with respect to vehicle accelerator 

controls. 

Specifically, the compliance criterion 

we are proposing is vehicle terminal 

speed following an ACS disconnection 

and removal of force on the accelerator 

pedal. In order to comply, the measured 

creep speed obtained with no 

accelerator pedal input would have to 

fall below a maximum allowable value, 

which we are proposing should be 50 

km/h (31 mph). As mentioned 

previously in this proposal, this speed 

was suggested by a vehicle 

manufacturer and was confirmed as an 

appropriate level in NHTSA’s tests of 

two passenger cars and one light truck. 

It would accommodate typical 

responses of vehicle control systems to 

ACS disconnections, including limphome modes. Our tests also confirmed 

that this level of speed corresponds to 

a low level of drivetrain torque 

capability and thus is easily 

controllable. 

Under our proposed requirement, in 

the worst case of a vehicle whose torque 

output following an ACS disconnection 

allows the vehicle to reach a creep 

speed of exactly 50 km/h, the vehicle 

would accelerate at a rate only 

marginally greater than it would with no 

ACS faults. The vehicle’s acceleration 

would be limited to the equivalent of 

the aerodynamic and frictional drag 

forces on the vehicle at 50 km/h which, 

for light vehicles, is a small fraction of 

what the powertrain is capable of 

producing. 

Compliance with the creep speed 

requirement would be evaluated by 

selecting any accelerator pedal input 

(including zero input) that results in an 

initial test speed below 50 km/h. Then, 

following disconnection of the ACS and 

release of the accelerator pedal (if it was 

initially applied), the vehicle’s speed 

would have to remain below 50 km/h. 

We are proposing a time limit of 90 

seconds for this procedure, meaning 

that the vehicle would comply if its 

speed does not exceed 50 km/h before 

90 seconds have elapsed. If a vehicle is 

accelerating so slowly that it meets this 

requirement, then that is sufficient 

indication that it has an acceptable failsafe response. The average acceleration 

rate to reach 50 km/h in 90 seconds is 

approximately 0.015 g’s,17 which is a 

very low value considering that 

conventional passenger cars are capable 

of well over twenty times that value at 

low initial speeds. The 90-second time 

limit also will avoid unnecessarily 

prolonging the tests to wait for very 

slowly accelerating vehicles to finally 

reach a terminal speed. We request 

comment on whether 90 seconds is an 

appropriate value and, if not, what time 

limit should be substituted and why. 

For creep speed tests where the initial 

test speed is above 50 km/h, we are 

proposing a coastdown procedure 

which uses as a baseline the coastdown 

time of the test vehicle with its 

transmission in neutral. This 

compliance criterion was suggested by a 

vehicle manufacturer and appears to be 

a practical and appropriate 

specification. Under this procedure, 

each assessment of compliance would 

require two test runs as follows: 

• The first run would measure the 

elapsed time required for the test 

vehicle to coastdown from a selected 

target speed to exactly 50 km/h in 

neutral gear. The coastdown time 

measured in this way should constitute 

a worst-case since there would be no 

engine braking (resistance to vehicle 

motion resulting from engine friction 

and compression, independent of the 

vehicle brake system) to decelerate the 

vehicle. This elapsed time would be a 

‘‘baseline’’ for comparison to the result 

of the second test run. 

• In the second run, conducted at the 

same target speed but with the vehicle 

remaining in gear, coastdown would 

commence following an induced ACS 

disconnection and release of accelerator 

pedal. As in the first run, elapsed time 

for the vehicle to decelerate to 50 km/ 

h would be the measured value. 

Compliance would be determined by 

comparing the coastdown time in these 

two runs. The coastdown time in gear, 

from the second run, would have to be 

less than the coastdown time in neutral, 

from the first run. This comparison 

would verify that the powertrain output 

of the test vehicle in fact was reduced 

to a safe level, i.e., a level that produces 

less than a 50 km/h terminal speed, 

while at the same time establishing a 

time limitation to ensure that the rate of 

deceleration is not unreasonably low. 

As NHTSA has not had the 

opportunity to conduct trials using this 

methodology, we are requesting 

comment on any issues related to this 

proposed coastdown test procedure. 

We are proposing that the vehicle 

creep speed and coastdown time 

measurements would be conducted 

using a chassis dynamometer to impose 

road force through the vehicle’s drive 

wheels. The general test parameters for 

this type of dynamometer testing are 

available in an industry standard, SAE 

J2264, ‘‘Chassis Dynamometer 

Simulation of Road Load Using 

Coastdown Techniques.’’ We are 

proposing to incorporate by reference 

portions of that SAE standard. In 

NHTSA compliance testing, the 

vehicle’s terminal speed would be 

measured following an ACS 

disconnection when using the test 

procedures and environmental 

conditions specified in the SAE 

standard. For testing using a 

dynamometer, manufacturers would 

have the option of either measuring a 

vehicle’s road load characteristic 

directly by use of the procedure in SAE 

J2264, or by looking up the necessary 

road load coefficients in an 

Environmental Protection Agency 

database.18

A potential issue with creep speed 

and coast-down measurements 

conducted on a chassis dynamometer is 

that FMVSS No. 124 includes test 

temperatures down to as low as minus 

40 Celsius (equivalent to minus 40° F). 

To the best of our knowledge, existing 

vehicle dynamometer facilities normally 

cannot achieve ambient temperatures 

that low. Therefore, we specifically 

request comment on whether a different 

lower limit on environmental 

temperature should be specified in the 

FMVSS for tests of vehicle ACSs 

conducted using a dynamometer 

facility. 

We are proposing that the new creep 

speed test also could be conducted on 

a test track, to the extent that a suitable 

test area with adequate straightaway 

space is available. When starting from a 

high speed in the coastdown portion of 

the proposed test procedure, a vehicle 

may coast for a number of minutes. The 


emcdonald on DSK29S0YB1PROD with PROPOSALS2
22650 Federal Register / Vol. 77, No. 73 / Monday, April 16, 2012 / Proposed Rules 

required length of the test area could 

easily be on the order of a mile or more. 

This may limit the feasibility of 

substituting a track test for a 

dynamometer test. 

For a track test, the test area should 

meet a maximum slope specification 

since any significant grade could affect 

test outcome. Furthermore, in order for 

the test to be repeatable, wind 

conditions would have to be light, and 

air temperature should also be within a 

limited range because these factors 

influence aerodynamic drag. We are 

proposing the following conditions for 

creep and coastdown speed 

measurements conducted on a test track: 

• Straight course of dry, smooth, 

unbroken concrete or asphalt pavement 

with a continuous grade of not more 

than 0.5 percent in any direction; 

• Ambient temperature between 5 C 

(41 °F) and 32 C (90 °F); 

• Average wind speed no greater than 

16 km/h (10 mph) with gusts no greater 

than 20 km/h (12 mph) and with the 

wind velocity component perpendicular 

to the test direction no greater than 8 

km/h (5 mph). 

To the best of our knowledge, these 

conditions are consistent with current 

industry practice for this kind of testing. 

We request comment on these proposed 

conditions, specifically any information 

to support why NHTSA should consider 

different test conditions. 

We believe that this new method of 

compliance is a necessary addition to 

FMVSS No. 124 that fulfills the need for 

a ‘‘technology neutral’’ test that can be 

applied to any type of wheel-driven 

motor vehicle regardless of the type of 

propulsion system it uses. This 

procedure is performance-based and 

uses established vehicle test methods 

that should be familiar to the industry. 

Therefore, we believe that this new 

proposed procedure is both practicable 

and objective. 

New Air Intake and Fuel Delivery Rate 

Tests 

This proposal includes a fuel delivery 

rate test procedure as in the 2002 

NPRM. It also includes a new air intake 

rate test procedure that was not 

included in the 2002 NPRM. This 

procedure was suggested in comments 

as an alternative that will expedite 

testing of some vehicles. It is identical 

to the fuel rate test, but uses mass 

airflow rate rather than fuel flow rate to 

quantify the state of vehicle power 

output and whether the engine is at idle. 

These test procedures are logical 

extensions of the traditional throttle 

position test. For most existing gasoline 

engines, throttle position indicates (and 

in fact controls) the rate of intake of air/ 

fuel mixture into the engine which, in 

turn, determines engine power output. 

Since the air/fuel ratio stays relatively 

constant over the engine’s operating 

range, observing either the fuel intake 

rate or air intake rate also provides a 

valid indicant of engine output, and 

either quantity can substitute for throttle 

position. In effect, fuel rate, air intake 

rate, and throttle position are equivalent 

for FMVSS 124 purposes in that they 

each can indicate whether the engine is 

at idle. 

For diesel engines, the traditional 

FMVSS 124 test indicant is the fuel rack 

position which determines fuel flow. 

(The fuel rack is the mechanical linkage 

on older diesel engines that moves back 

and forth when the accelerator pedal is 

pressed and released; its operation is 

analogous to a mechanical throttle 

linkage on a gasoline engine.) Fuel rack 

position corresponds to fuel intake rate, 

so we are proposing that, on modern 

diesels without a fuel rack, the net fuel 

delivery rate is the appropriate engine 

power indicant. Diesels operate on 

excess intake air unlike a gasoline 

engine, so power output cannot 

necessarily be gauged by air intake rate 

alone. We request comment as to the 

appropriateness of air intake rate as a 

measurement criterion for diesel 

engines, and also whether there are 

other possibilities for diesels besides 

those we have considered here. 

Components Included in an Accelerator 

Control System 

In interpretation letters on FMVSS 

No. 124 which responded to questions 

about which parts of an ETC system are 

considered ACS components, we treated 

an ACS as a series of linked components 

extending from the driver-operated 

control to the throttling or fuel-metering 

device on the engine or motor. 

Electronic systems using wires, relays, 

control modules, and electric actuators 

joining the accelerator pedal to the 

throttle or injectors on the engine are 

analogous to mechanical systems in 

which levers, cables, and springs serve 

the same purpose. We indicated that a 

severance at any one point in the system 

should not result in a large increase in 

engine power, and that this also applies 

to an ACS that mixes mechanical and 

electronic components. 

Nevertheless, an ETC system is less 

easily defined than a mechanical one 

because a variety of components can 

influence engine speed without being in 

the direct line of action between the 

accelerator pedal and the throttling 

device on the engine. As in the 2002 

NPRM, we see two basic approaches for 

defining the items included in an 

electronic ACS. 

One approach would be to list in the 

regulatory text of the Standard each and 

every component, including each 

conductor, connector, module, etc., 

which is subject to the fail-safe 

requirements. This explicit approach 

would provide a high degree of 

specificity, but would lack flexibility. It 

carries a significant risk that a 

connective component omitted from 

specific mention in the standard would 

be excluded from regulation, even if the 

omission was unintentional. 

An alternative approach, and the one 

that we have chosen to adopt in this 

proposal, is to specify in general terms 

the connective components that are 

regulated. This approach lends a greater 

degree of flexibility and leaves open the 

possibility that the regulatory language 

can be adapted to new technology. The 

covered ACS parts still would be 

limited to ‘‘connective components’’ 

only, so we believe that using this 

general approach does not diverge from 

the scope of the existing Standard. 

We are listing here some common 

components of an ACS to illustrate the 

intent of the proposed Standard and to 

make it widely acknowledged that these 

components are considered connective 

components of an ACS. This is not 

intended to be an all-inclusive list. The 

following enumerates some of the 

connective components for both 

mechanical and electronic systems that 

we believe must comply with the 

disconnection requirements of FMVSS 

No. 124: 

• Components of an Air- or FuelThrottled Engine 

The critical connective components of 

the ACS are: (1) The springs or other 

sources of stored energy that return the 

driver-operated control and the throttle 

to their idle position; (2) the linkages, 

rods, cables or equivalent components 

which are actuated by the driveroperated control; (3) the linkages, rods, 

cables or equivalent components which 

actuate the throttle; (4) the hoses which 

connect hydraulic or pneumatic systems 

within an ACS; (5) the connectors and 

individual conductors in the electrical 

wiring which connect the driveroperated control to the engine control 

processor; (6) the connectors and 

individual conductors in the electrical 

wiring which connect the ECM to the 

throttle or other fuel-metering device; 

and (7) the connectors and individual 

conductors in the electrical wiring 

which connect the ECM to the electrical 

power source and electrical ground. 

The ECM itself is also included as a 

single component of an electronic ACS. 

However, as before, we treat the fail-safe 

(i.e., disconnection) requirements of the 


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Federal Register / Vol. 77, No. 73 / Monday, April 16, 2012 / Proposed Rules 22651 

Standard as pertaining to the external 

connections to and from the ECM. We 

consider the internal elements of the 

ECM to be like the internal elements of 

a carburetor or throttle body injector, 

which are not subject to the fail-safe 

requirements of the Standard. The 

wiring and connectors between the 

pedal position sensor and the ECM, the 

wiring and connectors between the ECM 

and the fuel or air throttling device on 

the engine, and the power and ground 

connections to the ECM all qualify as 

connective elements rather than internal 

ones. 

• Components of an Electric Propulsion 

System’s ACS 

For an electric motor-driven vehicle, 

the critical connective components of an 

ACS are: (1) Springs or other sources of 

energy that return the driver-operated 

control and the motor speed controller 

to the idle position; (2) linkages, rods, 

cables or equivalent components which 

are actuated by the driver-operated 

control; (3) linkages, rods, cables or 

equivalent components which actuate 

the motor speed controller; (4) hoses 

which connect hydraulic or pneumatic 

actuators and components within the 

ACS; (5) connectors and individual 

conductors in electrical wiring 

connecting the driver-operated control 

to the motor speed controller or motor 

control processor; (6) connectors and 

individual conductors which connect 

the motor control processor to the motor 

speed controller (if they are separate 

modules); (7) connectors and individual 

conductors in the electrical wiring 

which connect the motor control 

processor to electrical power and 

ground; and (8) the connectors and 

individual conductors in the electrical 

wiring from the motor speed controller 

to the electric traction motor. 

Definition of Idle State 

Based on comments NHTSA received 

on the 2002 NPRM, manufacturers 

would prefer that the Safety Standard 

allow the manufacturers to determine 

what is an acceptable idle state. 

Manufacturers consistently commented 

that the idle state varies according to a 

number of factors such as engine 

temperature, accessory load, emission 

controls, and altitude. It may not be 

possible to specify fixed values for 

throttle position, engine speed, fuel rate, 

etc., because those characteristics can 

change according to many conditions 

without any input from the accelerator 

pedal. They pointed out that limp-home 

modes can adjust engine operation to 

prevent stalling and to provide enough 

power for a vehicle to be moved from 

an unsafe location in the event of a 

malfunction. 

The current Standard accommodates a 

range of idle state values by allowing 

any throttle position ‘‘appropriate for 

existing conditions.’’ In a traditional airthrottled engine which has a mechanical 

throttle stop that designates the idle 

position of the throttle, the throttle stop 

can change position as dictated by 

operating conditions. For example, it 

may move to a position of increased 

throttle opening when the engine is 

cold. In testing, the throttle stop 

provides a convenient reference 

position that makes determination of 

compliance a simple matter. 

Vehicle manufacturers recommended 

that idle state should be a manufacturerspecified data item provided to NHTSA 

for each compliance test. Under this 

approach, each manufacturer would 

specify a value or range of values for the 

applicable idle state indicant for each of 

its vehicles. 

After considering the comments, we 

are not persuaded that this approach is 

the best solution to the question of how 

to define an appropriate idle state value. 

We believe it would be burdensome to 

have to obtain idle state data from 

manufacturers for each test vehicle, 

potentially for numerous possible 

operating conditions. 

Instead, we believe it is easier and 

more practical to establish a baseline 

idle state simply by measuring the 

initial value of the applicable idle state 

indicant (throttle position, fuel delivery 

rate, electrical power input, etc.) at the 

beginning of a compliance test (i.e., 

immediately before any fault is 

induced). This initial value would be an 

appropriate baseline because it would 

account for whatever operating 

conditions exist at the time a test takes 

place. It is convenient because it is 

measured directly as part of the test 

procedure, and it does not depend on 

information provided by vehicle 

manufacturers. 

Once the baseline is established, the 

value of the idle state indicant at the 

end of the test is expected to be the 

same as or close to the baseline value 

established at the start of the test 

(within a tolerance range, as defined 

below). Compliance is indicated by 

whether or not the idle state returns to 

the baseline value within the elapsed 

time specified in S5.3 of the regulatory 

text. 

This approach is valid only if 

operating conditions such as engine 

temperature, accessory load, etc., are 

fairly constant during a test since 

adjustments made by an electronic 

control system to compensate for 

changes in conditions would not be 

observable but rather would take place 

within the ECM. Consequently, it could 

be difficult to distinguish between a 

permissible increase in idle state and a 

noncomplying one. 

In order to address this, NHTSA’s 

proposal specifies that operating 

conditions must be held constant to the 

greatest extent possible during fail-safe 

tests in order to minimize variations in 

engine idle that are not due to an ACS 

disconnection. In a compliance test, the 

engine must be stabilized and all 

accessory controls fixed so that 

conditions that affect idle state do not 

change significantly during the course 

of the test. This includes operating the 

engine long enough to deactivate cold 

start features as well as to stabilize 

emission controls. We have specified 

that the engine must be operated for at 

least 5 minutes prior to any 

measurement of idle, as this should be 

sufficient to achieve a reasonably steady 

idle state. We request comment whether 

5 minutes is an appropriate value. 

For some operating characteristics 

such as ‘‘variable displacement’’ or 

cylinder de-activation modes, we 

recognize that maintaining a constant 

operating condition may not be 

straightforward. It would be acceptable 

to either prevent engagement of these 

kinds of features during testing or to 

ensure that they do not change the idle 

state during testing. We request 

comment on what means are available 

to ensure that features like cylinder 

deactivation do not influence test 

results. 

Under today’s proposal, the baseline 

value is established by observing the 

idle state indicant for an engine with a 

normally functioning ACS. For the 

‘‘normal operation’’ requirement, the 

compliance criterion would be the time 

to return to the baseline value from the 

moment of release of the accelerator 

pedal from any position within its full 

range of movement. For the ‘‘fail-safe’’ 

requirement, the idle state following a 

disconnection in the ACS is compared 

to the baseline value to ensure that it is 

close to (i.e., within the tolerance) or 

below the baseline. The time elapsed 

from the moment of the disconnection 

and pedal release for the measured 

value to return to the baseline value 

must be within the Standard’s specified 

time spans (1 second for light vehicles). 

With the engine operating in a steady 

state with accessory controls at fixed 

settings, any difference in the ‘‘before 

and after’’ idle states should be 

attributable to the induced 

disconnection. 


emcdonald on DSK29S0YB1PROD with PROPOSALS2
22652 Federal Register / Vol. 77, No. 73 / Monday, April 16, 2012 / Proposed Rules 

Two Sources of Energy for Returning 

Throttle to Idle 

At present, FMVSS No. 124 states in 

S5.1, ‘‘there shall be at least two sources 

of energy capable of returning the 

throttle to the idle position’’ within the 

specified time limits from any 

accelerator position or speed, whenever 

the driver removes the actuating force 

on the accelerator pedal. It also specifies 

that, whenever one source of energy 

fails, the other shall be able to return the 

throttle to idle. In the past, springs have 

been the predominant sources of energy 

for return to idle. That appears to still 

be the case for accelerator pedal 

assemblies of vehicles with electronic 

accelerator controls and for throttle 

bodies. These assemblies usually 

incorporate multiple springs, and 

testing of fail-safe operation would still 

include disconnection of each single 

spring. 

However, because the standard 

requires return-to-idle regardless of 

whether there are two sources of energy 

present, this requirement may be 

considered superfluous. Most if not all 

manufacturers will continue to provide 

two or more return springs on 

accelerator pedal assemblies and 

throttle bodies whether or not there is 

an explicit requirement for it because it 

is a simple way of meeting the ‘‘singlepoint disconnection’’ requirement when 

one of the springs is disconnected. 

As we have noted elsewhere in this 

proposal, our letters of interpretation 

have stated that, although having two or 

more springs on a pedal assembly is a 

good idea, that alone is not sufficient to 

ensure compliance with the FMVSS No. 

124 fail-safe requirements. For example, 

dual springs on the pedal assembly 

would be irrelevant if the assembly’s 

electrical connector was disconnected. 

For these reasons, we believe it may 

be appropriate to delete the requirement 

for two sources of energy which return 

the throttle to idle. We request comment 

on this issue. 

Under today’s proposal, the singlepoint disconnection requirement is 

applicable to any source of throttle 

return energy connected to the ACS. 

This includes electric motors and 

actuators, solenoids, and other 

electrically powered devices. The 

electric power source for these 

components would be considered a 

‘‘source of energy’’ for closing the 

throttle, and thus the power and ground 

leads for these components would be 

subject to disconnection. 

Criteria for Return to Idle in Normal 

Operation 

Engines With a Traditional Throttle 

Plate 

Like the previous NPRM, this 

proposal retains return of a throttle plate 

to the idle position as the criterion for 

normal operation of air-throttled 

engines with a traditional throttle. This 

criterion is still valid for many gasoline 

engines with either mechanical or 

electronic accelerator controls, and 

probably will continue to be for the 

foreseeable future. 

Diesel Engines 

For diesels (and other fuel-throttled 

engines), this proposal provides fuel 

delivery rate (gallons/hour of fuel 

entering the combustion chambers of 

the engine) as a measure of idle state. It 

requires return of the fuel rate to the 

idle fuel rate as a measure of return-toidle. For diesel engines, power is 

controlled directly by controlling fuel 

flow. The result of rapidly releasing the 

accelerator control is a rapid return of 

the fuel rate to the steady idle rate, and 

there is no need to account for the time 

lag required for the engine speed to 

return to idle. In this respect, the fuel 

rate of fuel-throttled engines is 

analogous to the throttle position of airthrottled engines. 

Engines With Unitized Injectors 

An engine with self-contained, 

integrated fuel injectors (called ‘‘HEUI’’ 

injectors for High Energy Unit Injector), 

now commonplace in commercial 

trucks, is potentially problematic with 

respect to return to idle criteria because 

it has multiple ‘‘throttles,’’ those being 

its individual injectors, which can 

operate independently of each other. 

However, fuel flow rate for these 

engines generally can still be used to 

quantify the operational state of the 

engine. The fuel rate combines the 

action of the individual injectors and 

represents the steady effect of all the 

injectors’ dynamic duty cycles (percent 

open time or pulse width and 

frequency). It also avoids the problem of 

the lack of a visibly observable throttle 

reference position. Fuel rate thus 

provides a satisfactory return-to-idle 

indicant for modern diesel engines with 

electronic fuel systems. 

For light vehicles, similar fuel control 

arrangements may become more 

prevalent as diesels become more 

common and direct-injection gasoline 

engines enter the marketplace. We 

believe these vehicles will be able to 

comply by either the fuel rate test or one 

of the other available test procedures 

described in this proposal. 

For many heavy vehicles, we 

understand that a fuel rate signal which 

consolidates the effect of fuel pressure 

and fuel injector duty cycle is available 

as a standardized diagnostic channel. 

For engines without this diagnostic 

signal, direct measurement of fuel flow 

in the supply and return lines would be 

necessary to ascertain the net fuel rate. 

Electric Motors 

For vehicles which use electric motor 

propulsion, the electric power input at 

the drive motor (computed from voltage 

and current) would be used as the 

indicant idle state. This measurement 

responds directly to the operation of the 

motor controller which, like a unitized 

electronic fuel injector, is a throttle 

without a measurable reference 

position. Since drive torque is directly 

proportional to the drive motor input 

current and voltage, this indicant is 

equivalent to throttle position. 

Alternative measurement criteria used 

for non-electric vehicles such as fuel 

delivery rate are not applicable to 

electric vehicles, but we request 

comment on whether there are any other 

measurement criteria that would be 

appropriate for electric vehicles. 

No Normal Operation Test 

Corresponding to Creep Speed Method 

Unlike the test procedures for throttle 

position, fuel delivery rate, air intake 

rate, and electric power delivery, the 

creep speed test does not have a 

corresponding normal operation 

criterion. This was the subject of at least 

one comment on the 2002 NPRM that 

suggested that an engine output 

criterion should be provided for normal 

as well as fail-safe operation. However, 

establishing a normal operation 

requirement based on creep speed 

would require restricting aspects of 

vehicle performance such as engine 

braking effect that have never been part 

of FMVSS No. 124 or any other NHTSA 

regulation. For example, a normal 

operation requirement for creep speed 

might specify that a vehicle has to 

coastdown to a speed of ‘X’ from an 

initial test speed of ‘Y’ in ‘Z’ seconds. 

This would place restrictions on vehicle 

rolling resistance and engine-braking 

that are unrelated to safety. Therefore, a 

creep speed-based normal operation 

requirement is not feasible under 

FMVSS No. 124. 

Consequently, if a manufacturer 

selects the creep speed procedure to 

certify to the fail-safe requirement, a 

different procedure would have to be 

selected to certify to the normal 

operation requirement. 


emcdonald on DSK29S0YB1PROD with PROPOSALS2
Federal Register / Vol. 77, No. 73 / Monday, April 16, 2012 / Proposed Rules 22653 

Response Time for Normal Operation 

This proposal maintains the existing 

requirement that, in normal operation 

(i.e., without faults in the ACS), return 

to idle must occur within 1 second after 

release of the accelerator pedal for light 

vehicles, and within 2 seconds for 

heavy vehicles (over 10,000 lb. GVWR). 

The required response time is 3 seconds 

if the test vehicle is exposed to 

temperatures of minus 18 Celsius or 

lower during any portion of the 24-hour 

conditioning period, for both light and 

heavy vehicles. 

Fail-Safe Performance Criteria 

Because electronic ACSs can use 

various means to reduce vehicle power 

in response to an ACS disconnection, 

our intent in this proposal is to allow 

manufacturers to take advantage of 

those possibilities by establishing failsafe criteria that are performanceoriented rather than design-oriented. 

Powertrain Output ‘‘Creep Speed’’ Test 

Option 

We have included in S6.5 of the 

proposed regulatory text a new 

‘‘technology-neutral’’ powertrain output 

test performed on a dynamometer or test 

track, as described previously in this 

document (see ‘‘New Creep Speed and 

Coastdown Test Procedures’’ under 

section VI D, above). This test of failsafe response is performance-based and 

independent of powertrain design, i.e., 

it is valid for any type of powertrain in 

any wheel-driven vehicle. It provides a 

universal measurement criterion, i.e., 

maximum vehicle terminal speed, that 

has direct relevance to the safety 

purpose of FMVSS 124. The new creep 

speed and coastdown procedures 

require that a test vehicle cannot 

accelerate appreciably if its initial speed 

is below 50 km/h and must decelerate 

if its initial speed is above 50 km/h 

upon release of the accelerator pedal 

following an ACS disconnection. The 

new creep speed and coastdown 

procedures appear in section S6.5 of the 

regulatory text of this rule which 

specifies controlled test conditions for 

accurate exertion of road load on the 

drivetrain. 

Fail-Safe Performance Test for AirThrottled Engines 

For air-throttled engines, return of the 

throttle plate to the idle position is the 

least burdensome test for many vehicles 

in current production. This alternative 

is identical to the procedure of the 

present Standard. A second alternative 

is return of the fuel rate to the idle state. 

For air-throttled engines, engine power 

cannot vary substantially from the idle 

state if the fuel rate is constrained to the 

value observed at the idle state. Thus, 

fuel delivery rate is a reliable indicant 

that engine power is constrained. 

Similarly, a third alternative is mass 

airflow rate through the intake 

manifold. Air intake rate behaves like 

fuel delivery rate for vehicles whose 

fuel-air ratio stays relatively constant as 

operating conditions vary. Thus, air 

intake rate is also an acceptable indicant 

of engine power output. 

Fail-Safe Performance Test for FuelThrottled Engines 

Since fuel-throttled engines such as 

diesel engines may operate with excess 

intake airflow, neither the position of an 

air throttle, if one is present, nor the air 

intake rate would be an accurate 

indicant of engine power. Fuel delivery 

rate, on the other hand, is an accurate 

and sufficient indicant of engine power 

for these engines in most cases. The 

same fuel delivery rate criterion 

specified for evaluating compliance in 

normal operation of fuel-throttled 

engines is included in this proposal as 

an optional test for fail-safe 

performance. 

Some modern diesel and gasoline 

direct injection engines may inject 

additional small amounts of fuel during 

a single injection cycle. This extra fuel 

does not contribute to propulsion, but is 

intended to smooth engine operation or 

to meet emissions requirements. If 

vehicles with these types of engines 

could not be adequately tested using the 

fuel delivery rate procedure, then the 

optional creep speed procedure would 

be an appropriate alternative since that 

test is not sensitive to any particular 

fuel delivery characteristics. 

Fail-Safe Performance Test for Electric 

Vehicles 

For vehicles driven solely by electric 

motors, we are proposing that an 

optional test of fail-safe performance be 

the same as the normal operation 

criterion, i.e., return of the drive motor 

electric power input to the idle state. 

This procedure can also be applied to 

the electric drive motor of a hybrid 

vehicle. 

Fail-Safe Performance Test for Hybrid 

Vehicles 

For a hybrid vehicle that combines 

more than one type of propulsion 

system, the most applicable test 

procedure would be the creep speed test 

which would evaluate the net driving 

effect of the various propulsion systems 

working together. Alternatively, fail-safe 

performance of each separate engine’s or 

motor’s accelerator controls could be 

demonstrated independently using test 

options appropriate for each type of 

propulsion system. For example, on a 

gas-electric hybrid, the gas engine might 

be tested by measuring the throttle 

position while the electric motor is 

tested by measuring current and voltage. 

Response Time Requirements for FailSafe Operation 

The required response times for the 

idle state indicant to return to or near 

the baseline value following an ACS 

disconnection are the same as those 

given in the current Standard and also 

for normal operation of the ACS. For 

light vehicles (under 10,000 lb GVWR), 

return to idle must occur within 1 

second after ACS disconnection and 

release of the accelerator pedal, or, 

within 2 seconds for heavy vehicles 

(over 10,000 lb. GVWR). The required 

response time is 3 seconds if the test 

vehicle is exposed to temperatures of 

minus 18 Celsius or lower during any 

portion of the 24-hour conditioning 

period, for both light and heavy 

vehicles. 

For the proposed creep speed 

procedure, compliance is not based 

directly on the time required for an idle 

state indicant to return to idle. Instead, 

for test speeds at or below 50 km/h, 

compliance is based on whether the 

vehicle’s terminal speed remains below 

50 km/h for at least 90 seconds after an 

ACS disconnection; for test speeds 

greater than 50 km/h, compliance is 

based on whether the time required to 

coast down to 50 km/h is greater or less 

than the coastdown time in neutral from 

the same test speed. 

E. Compliance Options for Various 

Vehicles 

Our proposal would require 

manufacturers to specify one of the 

following criteria as the basis for 

certifying a vehicle to the requirements 

of S5.1 (normal operation) and S5.2 

(fail-safe operation) of the standard: 

Throttle position, fuel delivery rate, air 

intake rate, electric power delivery, and 

creep speed/coastdown performance. 

The selection would be at the option of 

the manufacturer. However, while one 

of the criteria, creep speed/coastdown 

performance, could be used for any 

vehicle, the appropriateness of the other 

criteria would depend on the nature of 

the vehicle. For example, an electric 

vehicle could be certified based on 

electric power delivery in addition to 

creep speed/coastdown performance, 

and a vehicle with a gasoline engine 

could be certified based on throttle 

position, fuel delivery rate, and air 

intake rate, as well as creep speed/ 

coastdown performance. We believe it is 

appropriate to permit multiple options 

to manufacturers so long as each option 


emcdonald on DSK29S0YB1PROD with PROPOSALS2
22654 Federal Register / Vol. 77, No. 73 / Monday, April 16, 2012 / Proposed Rules 

would meet the relevant safety need. We 

request comments on the 

appropriateness of each of the proposed 

options; the possibility of a 

manufacturer seeking to use an option 

that might not be appropriate for a 

vehicle given the characteristics of the 

vehicle and, if so, the safety 

consequences; and whether there is a 

need for the regulation to limit any of 

the options to vehicles with particular 

characteristics. 

VII. Safety Benefits and Crash Data 

A rule based on today’s proposal 

would be expected to prevent most 

crashes resulting from accelerator pedal 

entrapment, including floor mat 

incidents. The accidents that could be 

avoided are similar to highly publicized 

crashes that have played a key role in 

the escalation of UA as a nationally 

recognized safety problem. 

With regard to the ACS disconnection 

requirements, any benefits associated 

with the original FMVSS No. 124 safety 

standard would be unchanged by this 

proposal. 

A. Summary of Crash Data on 

Accelerator Control Issues 

Three of NHTSA’s crash datasets were 

identified as potential sources of 

information about possible accelerator 

control issues in passenger vehicles: 

Fatality Analysis Reporting System 

(FARS), National Motor Vehicle Crash 

Causation Survey (NMVCCS), and 

National Automotive Sampling 

System—Crashworthiness Data System 

(NASS–CDS). FARS is an annual census 

of fatal traffic crashes based upon 

secondary data sources such as the 

police accident report. NMVCCS was a 

one-time three year special study of 

crashes involving at least one passenger 

vehicle towed due to damage and 

investigated by NHTSA with an 

emphasis on pre-crash factors. NASS– 

CDS is an annual sample of crashes 

involving at least one passenger vehicle 

towed due to damage and investigated 

by NHTSA with an emphasis on 

crashworthiness factors. Overall these 

databases each contain cases involving 

an allegation of a stuck accelerator or 

throttle, and the available information is 

summarized below. However, each of 

these sources also has limitations that 

should be considered when using the 

results. 

Fatality Analysis Reporting System 

(FARS) 

FARS is a nationwide census 

providing yearly data regarding fatal 

injuries suffered in motor vehicle traffic 

crashes. FARS records when a preexisting vehicle defect or condition is 

noted in police accident report (PAR) as 

a vehicle related factor. According to the 

FARS Coding and Validation Manual, 

‘‘the report may indicate that a 

component is inadequate, inoperative, 

faulty, damaged or defective.’’ The 

FARS Manual also cautions that the 

presence of a vehicle related factor 

‘‘only indicates the existence of the 

condition(s)’’ and that the condition 

‘‘may or may not have played a role in 

the crash.’’ 

The most relevant vehicle related 

factor in FARS to identify possible 

accelerator control issues is ‘‘power 

train.’’ The code for ‘‘power train’’ 

includes the following components: 

universal joint, drive shaft, 

transmission, engine, clutch and gas 

pedal. In the 2009 data there were seven 

light passenger vehicles with the 

presence of a power train related factor 

involved in seven fatal crashes resulting 

in ten fatalities. 

Because of the inclusion of many 

different components and situations in 

the category of powertrain, researchers 

must request the PAR from the State and 

review the narrative sections to extract 

additional information. However, in this 

case, analysis of these seven PARs 

indicated that the police reports did not 

typically contain useful information for 

understanding whether the accelerator 

control was a factor in the crash. Our 

analysis also indicated that many of the 

reports with this designation involve 

vehicles that stalled. 

National Motor Vehicle Crash Causation 

Survey (NMVCCS) 

NMVCCS was a nationwide survey of 

crashes involving light passenger 

vehicles, with a focus on the factors 

related to pre-crash events. A total of 

6,949 crashes were investigated between 

January 1, 2005, and December 31, 2007. 

Of these, 5,470 cases comprise a 

nationally representative sample. The 

remaining 1,479 cases are suitable for 

clinical study. Each investigated crash 

involved at least one light passenger 

vehicle that was towed due to damage. 

The advantage of NMVCCS over 

FARS for identifying possible 

accelerator control issues is twofold. 

The first is that the data in NMVCCS are 

based upon the investigation of a 

researcher trained to focus on pre-crash 

events rather than exclusively on 

secondary sources such as the PAR. The 

second is that NMVCCS contains a more 

specific vehicle related factor. 

According to the NMVCCS SAS 

Analytical Users Manual, the vehicle 

related factor of ‘‘engine’’ in NMVCCS 

‘‘documents if the vehicle experienced 

an engine related problem during the 

pre-crash phase. Examples of engine 

related problems include stalling, 

missing, and throttle problems.’’ There 

were 26 cases that included a vehicle 

with an engine related problem—20 in 

the nationally representative sample 

and 6 among the case studies. After 

reading the crash narratives associated 

with these cases, most of them involved 

engines that stalled or overheated. Only 

three cases involved a problem with the 

accelerator control: Case numbers 

2005074596262, 2007008450848 and 

2007079486127. The first case involved 

a 1984 Oldsmobile Cutlass that was 

known to have an accelerator problem 

before the crash. The driver reported 

that ‘‘the vehicle would not remain 

running unless [he] held [his] foot on 

the gas and then [put] the vehicle into 

gear’’ and that while doing this right 

before the crash ‘‘the accelerator stuck at 

full throttle.’’ The second case involved 

a 1994 Chevrolet Corvette that the driver 

reported was not running properly. The 

driver ‘‘tried to feather the gas, upon 

doing so the gas pedal stuck down.’’ The 

driver lost control while braking and 

steering. The third case involved a 1965 

Ford Mustang where the ‘‘accelerator 

became stuck and the vehicle 

accelerated to approximately 129 km/h 

(80 mph).’’ The driver lost control and 

left the roadway after applying the 

brakes. Only two of these three cases 

were part of the nationally 

representative sample, and there are not 

enough cases to accurately estimate a 

sample size for the problem. 

National Automotive Sampling 

Survey—Crashworthiness Data System 

(NASS–CDS) 

NASS–CDS is an annual nationally 

representative sample of traffic crashes 

involving at least one passenger vehicle 

towed due to damage. The advantage of 

NASS–CDS is that many years of data 

can be examined, and this analysis 

focuses on the most recent ten years 

(2000 through 2009). A limitation, 

however, is that NASS–CDS does not 

have a coded variable to search for 

possible accelerator control factors. 

Instead, the identification of potentially 

relevant cases is based upon searching 

the crash narrative for key words. A 

caveat associated with this search is that 

the potential accelerator control issue 

must be mentioned in the crash 

narrative and the key words must be 

able to identify these cases. 

A search of the crash narrative for 

‘‘throttle,’’ ‘‘accelerator’’ or ‘‘gas pedal’’ 

resulted in 44 cases from 2000 through 

2009. However, in many of these cases 

the person applied the gas pedal rather 

than the brake. In a few cases the 

driver’s foot struck the accelerator 

usually because of a medical condition 


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19The VOQ form and other information about 

filing a complaint can be found at the following 

NHTSA-administered Web site: www.safercar.gov 

20See Observation O–1 in section 7.2, page 172, 

of the NASA report at: http://www.nhtsa.gov/PR/ 

DOT-16-11. 

such as a seizure but sometimes because 

of the foot becoming trapped or wedged. 

However, eleven cases during the tenyear period indicated an accelerator 

control issue. Additional searches were 

conducted for ‘‘racing,’’ ‘‘acceleration’’ 

and ‘‘runaway’’ to find cases related to 

racing engines, sudden or UA and 

runaway vehicles. However, these 

searches did not produce any additional 

relevant cases. 

The following table summarizes the 

results, including a brief recap of the 

accelerator control issue as described in 

the narrative: 

Make Model MY Notes 

Chevrolet ............................ Corvette .............................. 1995 The PAR reported the throttle had stuck open for some reason. 

Oldsmobile .......................... Cutlass ............................... 1989 Vehicle throttle stuck open. 

Oldsmobile .......................... Ciera ................................... 1990 The driver of the vehicle has indicated that his accelerator pedal stuck 

causing the loss of vehicle control. 

Ford .................................... F-Series Pickup .................. 1997 The driver stated the accelerator stuck. 

Chevrolet ............................ C/K/R/V-Series Pickup ....... 1988 The driver experienced a problem with the accelerator, attempted to stop 

at the marked intersection, but was unable to stop. 

Buick ................................... LeSabre .............................. 1989 The driver stated that the accelerator stuck and he could not stop the vehicle. 

Pontiac ................................ Bonneville ........................... 2002 The PAR related the driver was driving in lane one of the three-lane, oneway street when the accelerator stuck and the driver took evasive action 

and steered the vehicle to the left so he would not run out into traffic. 

But the interview stated the driver was parked on the right side of the 

road and when he started up the vehicle it took off. 

Chevrolet ............................ Cavalier .............................. 1990 The vehicle’s accelerator stuck depressed. 

Chevrolet ............................ Blazer ................................. 1996 A portable oxygen tank fell onto the accelerator. 

Ford .................................... Bronco ................................ 1985 The accelerator of vehicle got stuck. 

Infiniti .................................. J30 ...................................... 1993 The driver claimed the accelerator stuck. 

Overall it appears that the claims of 

accelerator control issues span a variety 

of vehicle models and model years. 

Also, in most cases, the only 

information available about the nature 

of the problem is a claim that an 

accelerator or throttle ‘‘stuck’’ while the 

vehicle was in motion. In some cases 

the narrative explicitly mentioned that 

the driver tried to stop but could not. 

Two of the eleven cases do not fit the 

general pattern of a stuck accelerator 

with little additional information. In 

one case an oxygen tank fell on the 

accelerator, and the driver was unable to 

stop the vehicle. In another case, there 

were conflicting reports of whether the 

driver could not stop a moving vehicle 

or whether the vehicle suddenly 

accelerated from a stopped position. 

There are several reasons that NASS– 

CDS is not particularly useful for 

providing national estimates of the 

incidence of accelerator control issues. 

As mentioned previously, searching for 

key words in the narrative requires that 

the information be recorded in the 

narrative and that the key words are 

capturing all of the appropriate cases. A 

second reason is that the information 

available in the narrative is usually just 

the claim of a stuck accelerator or 

throttle with little additional 

information to understand the nature of 

the problem. A final reason is that the 

sample size of eleven cases over ten 

years is not sufficient for accurately 

estimating the problem size. 

Nevertheless, to the extent that we are 

able to identify in NASS–CDS some 

cases where an accelerator pedal 

became stuck, along with out test track 

assessment of vehicles with the 

technology, we believe brake-throttle 

override would be a solution for 

mitigating the subsequent crashes that 

occurred. 

Because the FARS, NASS, and 

NMVCSS data are of limited usefulness 

for estimating harm caused by ACSrelated failures, we cannot estimate the 

safety problem on a national level. 

However, based on media reports, our 

analysis of recent ODI complaint data, 

observations from NASA’s review of 

certain Toyota vehicles, and NHTSA’s 

history with floormat issues and other 

types of problems that prevent an 

accelerator pedal from responding 

normally, we believe this rulemaking is 

necessary. 

B. Owner Complaint Data 

The Office of Defects Investigation 

(ODI) is the office within NHTSA 

responsible for conducting defect 

investigations and administering safety 

recalls in support of NHTSA’s mission 

to improve safety on our nation’s 

roadways. One important means by 

which ODI discovers vehicle safetyrelated defects is self-reporting by 

vehicle owners. By relating the 

information over a toll-free hotline or by 

filling out a VOQ on-line,19 vehicle 

owners can provide complaint 

information that is entered into ODI’s 

vehicle owner complaint database. This 

information is used with other 

complaints and information to 

determine if a safety-related defect trend 

exists. 

Our analysis and discussion of stuck 

and trapped accelerator pedals in 

today’s notice is exemplified by ODI 

VOQs because consumers have 

described crashes or incidents involving 

a vehicle speeding out of control with 

a stuck accelerator pedal. These 

incidents cannot be identified readily 

from data elements in NHTSA’s 

traditional crash data sources (as 

discussed in the previous section) or 

there are too few cases available in those 

databases. In addition, one of the 

specific observations made by the 

NASA in its report to NHTSA on Toyota 

unintended acceleration stated that 

some VOQs indicate that drivers may 

not know or understand the vehicle 

response when they attempt to control 

a runaway vehicle, i.e., that the high 

engine speed resulting from a shift to 

neutral will not harm the vehicle, or 

that pumping vacuum-assisted brakes 

can decrease their effectiveness.20

There are important qualifications in 

the use of VOQs as a data source for 

conducting rulemaking. Among them 

are: 

• VOQs are self-reported data, 

meaning that the information they 

contain is dependent on the description 

of an incident provided by the driver, 

another involved party, or someone 

related. 


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21The report is available on the internet at: 

http://nhtsa.gov/staticfiles/nvs/pdf/NHTSAUA_report.pdf. 

• There may be no follow up 

investigation to verify what actually 

happened or to make an objective 

analysis of the root cause of a crash. 

However, in the case of complaints 

involving UA, ODI did do extensive 

follow-up work, mostly in connection 

with defect investigations that were 

opened, and attempted to confirm, for 

example, if there was evidence of floor 

mat interference contributing to a UA 

incident. 

• Important facts about other possible 

contributing factors in these incidents 

may be unavailable. 

• The crashes and incidents reported 

are not randomly selected (random 

selection is a normal prerequisite for 

statistical analysis.) In the case of UA 

incidents, selection depended partly on 

which vehicles were involved in ODI 

investigations. 

• Many relevant incidents may be 

unreported because the driver or other 

party chose not to file a complaint or 

did not know how or where to do so. 

• The numbers of complaints relating 

to any safety problem may either underrepresent or over-represent the extent of 

the problem on a national level. 

VOQs can, however, help to identify 

emerging safety issues and problems 

that drivers are having, which is 

appropriate for what we are trying to 

address with this proposal. NHTSA’s 

analysis and breakdown of UA 

complaints is available in the February 

2011 NHTSA report, ‘‘Technical 

Assessment of Toyota Electronic 

Throttle Control (ETC) Systems,’’ 21

Section 2. Using a broad keyword search 

and manual review of the results, 

NHTSA identified a total of 9,701 UA 

incidents of all types involving model 

year 1998–2010 vehicles reported in 

VOQs between January 1, 2000, and 

March 5, 2010. It was possible to 

identify the UA initiation speed in 5,512 

of those incidents, and a crash was 

indicated in 2,039 of the 5,512. Of those 

crashes, 16 percent had either medium 

or high initiation speed (defined as at 

least 15 mph or 45 mph, respectively). 

Although we do not know how many 

of those complaints are attributable to 

UA resulting from stuck or trapped 

accelerator pedals, there are many 

examples of VOQs which indicate that 

the accelerator pedal was stuck, or 

something to that effect, including some 

that specifically mention floor mat 

entrapment. A few of these go into 

greater detail, describing harrowing 

incidents that exceed a minute in 

duration, include swerving in and out of 

traffic, and are accompanied by severe 

heat damage to the brakes. While these 

are relatively uncommon compared to 

overall crash/incident risk, they often 

pose extra danger because of the longer 

duration of the events and the freeway 

environment where they often occur 

which may include evasive action by 

surrounding vehicles, therefore 

exposing more people to crash risk. 

In any case, it appears that stuck or 

trapped accelerator pedals present a 

serious safety problem and occur 

frequently enough to warrant regulatory 

action, even if accurate quantification of 

the problem is not possible at the 

present time. 

VIII. Cost, Lead Time and Other Issues 

A. Cost of the Proposed BTO 

Requirement 

We expect the cost of a brake-throttle 

override requirement for light vehicles 

to be close to zero for the following 

reasons. As of model year 2012, all but 

two light vehicle manufacturers have 

incorporated brake-throttle override in 

the ETC-equipped vehicle models that 

they produce for sale in the U.S. This 

is based on manufacturer-supplied 

information that NHTSA receives as 

part of our annual safety compliance 

testing program. There are a few specific 

ETC-equipped models currently without 

BTO because they are at the end of their 

product design cycle and which either 

will be discontinued or will be 

equipped with BTO in the next design 

cycle, prior to the effective date of any 

final rule which results from this 

proposal. 

The proposed BTO regulation would 

set minimum requirements for existing 

as well as future light vehicle BTO 

systems. Based on our experience with 

them, existing systems will meet the 

proposed standard without 

modification. However, if some systems 

do require changes to meet the proposed 

standard, we believe the changes would 

be minimal. 

Because of the nearly 100 percent 

market penetration of the technology, 

the fact that most if not all systems 

already would meet the rule, and given 

that a final rule would not take effect for 

at least one or two years from the date 

of today’s notice, we expect that 

manufacturer design, validation, and 

implementation costs attributable to the 

proposed brake-throttle override 

requirement for light vehicles would be 

close to zero. 

Compliance testing costs also are 

expected to be low since the proposed 

test procedure is nearly identical to 

existing brake performance test 

procedures and could be conducted 

along with existing brake performance 

tests. 

B. Proposed Lead Time and Phase-In 

As discussed in Section V, we believe 

that current vehicles should be able to 

comply with the ACS disconnection 

requirements in this proposal without 

significant lead time because the 

updated procedures in this proposal do 

not change the basic return-to-idle 

requirement that has applied to motor 

vehicles for as long as the current 

standard has been in effect. We are 

proposing the following lead time for 

compliance with the disconnection 

requirements in this proposal as 

follows: 

• Each vehicle shall comply within 

one year from the next September 1 

following the date of publication of the 

final rule. 

We are not proposing a phase-in period 

for the disconnection requirements 

because the proposed rule codifies the 

positions taken by the agency on those 

requirements that have been 

promulgated in interpretation letters 

available for a number of years to 

industry and the public. Also, our 

compliance testing of vehicles with ETC 

has not demonstrated significant 

compliance issues to date. 

We are proposing that lead time for 

compliance with the new brake-throttle 

override requirements should be as 

follows: 

• Each vehicle subject to the 

requirements shall comply within two 

years from the next September 1 of the 

date of publication of the final rule. 

For example, if a final rule were 

published on October 1, 2012, the 

disconnection requirements in the final 

rule would take effect on September 1, 

2013, and the brake-throttle override 

requirements would take effect on 

September 1, 2014. We believe that this 

would give vehicle manufacturers 

ample time to implement the new 

requirements at minimal cost. 

For the brake-throttle override 

requirements, we believe a phase-in is 

unnecessary because a significant 

portion of new vehicles already are 

either equipped with a BTO system or 

will be by the coming model year. 

We request comment on the proposed 

lead time, including specific safety 

issues or cost and production issues that 

might influence the effective date of the 

rule. 

C. Vehicles Over 10,000 lb GVWR 

In addition to covering light vehicles, 

FMVSS No. 124 also applies to heavy 

vehicles, i.e., trucks and buses. Many 

heavy trucks are diesel-powered. For 


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[1] Department of Transportation, Adoption of 

Regulatory Policies and Procedures, 44 FR 11034 

(Feb. 26, 1979). 

throttle system disconnection testing on 

those vehicles, the fuel rate compliance 

option would be applicable. The creep 

speed procedure on a dynamometer or 

test track would be an option also. 

However, since heavy truck powertrains 

and chassis often are produced 

separately by different manufacturers, a 

given powertrain might have to be 

certified for several different chassis. 

Responsibility for certification 

(assuming it is a multi-stage 

manufacturing situation) typically 

would fall to the chassis manufacturer. 

For heavy vehicles, a brake-throttle 

override requirement may or may not be 

necessary. Trucks and buses already are 

subject to compliance with FMVSS No. 

105, Hydraulic and electric brake 

systems and FMVSS No. 121, Air brake 

systems, so performance tests based on 

braking distance are practicable. In 

addition, NHTSA’s complaint and crash 

data reports do not indicate a trapped 

pedal problem in heavy vehicles. 

Furthermore, trucks and buses often 

operate at full throttle during normal 

driving, and the acceleration rate of 

trucks and buses is significantly lower 

than for light vehicles. Additionally, 

most trucks have manual transmissions 

for which the clutch functions as an 

available countermeasure in the case of 

a stuck throttle in a truck. 

Since there is no apparent safety need 

for brake-throttle override systems to 

apply to heavy vehicles, we are 

proposing that the brake-throttle 

override requirement would apply only 

to passenger cars, multipurpose 

passenger vehicles, trucks, and buses 

with GVWRs of 10,000 pounds or less. 

However, we seek comment on this 

issue, specifically any data related to 

pedal entrapment or similar issues 

where BTO might be an effective 

safeguard. 

D. Manual Transmission Vehicles 

In the proposed brake-throttle 

override system regulation, we have not 

made any distinction for vehicles with 

GVWRs of 10,000 pounds or less 

equipped with manual transmissions. 

There are cogent reasons why manual 

transmission-equipped vehicles might 

be less susceptible to crashes resulting 

from trapped pedals. Primarily, these 

vehicles have a clutch pedal which 

disengages the engine from the drivewheels. This provides an expedient 

countermeasure for a driver in the event 

of a trapped accelerator pedal. 

Furthermore, clutch operation is not 

influenced by a stuck throttle the way 

that brake operation may be. 

Compared to vehicles with automatic 

transmissions, pedal placement in a 

manual transmission vehicle may be 

different and the brake pedal typically 

is smaller. We do not know if these 

factors influence trapped pedal 

incidents, either positively or 

negatively. 

NHTSA invites comments on this 

issue. If comments include sufficient 

justification for excluding manual 

transmission vehicles from the BTO 

requirements, and we are convinced 

that there will be no safety-related 

consequences, we will consider 

adopting that exclusion. Otherwise, we 

would not have any basis for excluding 

vehicles from the brake-throttle override 

system requirements based on their 

having a manual transmission. 

E. Proposed New Title for FMVSS No. 

124 

To reflect the addition of a BrakeThrottle Override requirement, we are 

proposing that the title of FMVSS No. 

124 be changed from ‘‘Accelerator 

control systems’’ to ‘‘Accelerator control 

and brake-throttle override systems.’’ 

We invite comment on this proposed 

change. 

IX. Rulemaking Analyses and Notices 

A. Executive Orders 12866 and 13563 

and DOT Regulatory Policies and 

Procedures 

The agency has considered the impact 

of this rulemaking action under 

Executive Orders 12866 and 13563 

(January 18, 2011, ‘‘Improving 

Regulation and Regulatory Review’’) the 

Department of Transportation’s 

regulatory policies and procedures (44 

FR 11034; February 26, 1979). OMB has 

advised us that this NPRM is not 

significant. This action was not 

reviewed by the Office of Management 

and Budget under these executive 

orders. It is not considered to be 

significant under the Department’s 

Regulatory Policies and Procedures.[1]

This NPRM includes the following 

proposed changes to FMVSS No. 124: 

Adds language so the Standard 

explicitly applies to ETC systems; 

includes test procedures for hybrids and 

other vehicles whose propulsion is not 

governed by throttling of combustion air 

intake; and adds a new requirement for 

a brake-throttle override system. We 

believe that the cost of implementing 

this proposal, if adopted, would be 

relatively small. Given the 

interpretations issued by NHTSA, 

manufacturers should have been aware 

for a long time of the applicability of 

FMVSS No. 124 to ETC-equipped 

vehicles. Since this proposal does not 

change the scope of the ACS 

disconnection requirements and only 

defines specific test procedures for ETC 

systems, all vehicles should be able to 

comply without costly re-design. Also, 

since this proposal allows new 

alternative methods of compliance for 

ACS disconnections, vehicles should 

not have significant compliance issues. 

There would likely be costs associated 

with certification testing. Those costs 

might vary somewhat depending on 

which procedure a manufacturer selects, 

but they should be similar to the costs 

of certifying to the current standard. In 

the case of the powertrain output (i.e., 

creep speed) test option, we expect the 

cost would be comparable to that for a 

single test run conducted for EPA 

emission or fuel economy purposes in a 

dynamometer facility or on a test track. 

These are tests that vehicle 

manufacturers conduct routinely either 

in their own facilities or through a 

commercially available source. 

For Brake-Throttle-Override systems, 

we believe the cost of the rule would be 

minimal because manufacturers already 

are incorporating BTO in their light 

vehicle fleets, and those systems are 

likely to meet the new safety 

requirement without modification. This 

would minimize any costs attributable 

to a NHTSA rule. There would be 

compliance testing costs. 

B. Regulatory Flexibility Act 

Pursuant to the Regulatory Flexibility 

Act (5 U.S.C. 601 et seq., as amended by 

the Small Business Regulatory 

Enforcement Fairness Act (SBREFA) of 

1996), whenever an agency is required 

to publish a notice of rulemaking for 

any proposed or final rule, it must 

prepare and make available for public 

comment a regulatory flexibility 

analysis that describes the effect of the 

rule on small entities (i.e., small 

businesses, small organizations, and 

small governmental jurisdictions). The 

Small Business Administration’s 

regulations at 13 CFR Part 121 define a 

small business, in part, as a business 

entity ‘‘which operates primarily within 

the United States.’’ (13 CFR 121.105(a)). 

No regulatory flexibility analysis is 

required if the head of an agency 

certifies that the rule will not have a 

significant economic impact on a 

substantial number of small entities. 

The SBREFA amended the Regulatory 

Flexibility Act to require Federal 

agencies to provide a statement of the 

factual basis for certifying that a rule 

will not have a significant economic 

impact on a substantial number of small 

entities. 

NHTSA has considered the effects of 

this rulemaking action under the 


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22The issue of potential preemption of state tort 

law is addressed in the immediately following 

paragraph discussing implied preemption. 

Regulatory Flexibility Act. According to 

13 CFR 121.201, the Small Business 

Administration’s size standards 

regulations used to define small 

business concerns, manufacturers of 

passenger vehicles would fall under 

North American Industry Classification 

System (NAICS) No. 336111, 

Automobile Manufacturing, which has a 

size standard of 1,000 employees or 

fewer. Using the size standard of 1,000 

employees or fewer, NHTSA estimates 

that there are fewer than 20 small 

business manufacturers of passenger 

vehicles subject to the proposed 

requirements. 

The Head of the Agency hereby 

certifies that this proposed rule would 

not have a significant economic impact 

on a substantial number of small 

entities. The basis for this certification 

is that if made final, none of the 

proposed changes will require the 

addition of new systems or equipment 

on existing vehicles that manufacturers 

are not already putting on vehicles (i.e., 

brake-override systems), and costs 

associated with the proposal will be 

minimal for all manufacturers, 

including small businesses. 

C. Executive Order 13132 (Federalism) 

NHTSA has examined today’s 

proposal pursuant to Executive Order 

13132 (64 FR 43255; Aug. 10, 1999) and 

concluded that no additional 

consultation with States, local 

governments, or their representatives is 

mandated beyond the rulemaking 

process. The agency has concluded that 

the proposal would not have sufficient 

federalism implications to warrant 

consultation with State and local 

officials or the preparation of a 

federalism summary impact statement. 

The proposal would not have 

‘‘substantial direct effects on the States, 

on the relationship between the national 

government and the States, or on the 

distribution of power and 

responsibilities among the various 

levels of government.’’ 

NHTSA rules can have preemptive 

effect in two ways. First, the National 

Traffic and Motor Vehicle Safety Act 

contains an express preemption 

provision: 

When a motor vehicle safety standard is in 

effect under this chapter, a State or a political 

subdivision of a State may prescribe or 

continue in effect a standard applicable to 

the same aspect of performance of a motor 

vehicle or motor vehicle equipment only if 

the standard is identical to the standard 

prescribed under this chapter. 

49 U.S.C. 30103(b)(1). It is this statutory 

command that preempts any nonidentical State legislative and 

administrative law 22 addressing the 

same aspect of performance. 

The express preemption provision 

described above is subject to a savings 

clause under which ‘‘[c]ompliance with 

a motor vehicle safety standard 

prescribed under this chapter does not 

exempt a person from liability at 

common law.’’ 49 U.S.C. 30103(e). 

Pursuant to this provision, State 

common law tort causes of action 

against motor vehicle manufacturers 

that might otherwise be preempted by 

the express preemption provision are 

generally preserved. However, the 

Supreme Court has recognized the 

possibility, in some instances, of 

implied preemption of State common 

law tort causes of action by virtue of 

NHTSA’s rules—even if not expressly 

preempted. 

This second way that NHTSA rules 

can preempt is dependent upon the 

existence of an actual conflict between 

an FMVSS and the higher standard that 

would effectively be imposed on motor 

vehicle manufacturers if someone 

obtained a State common law tort 

judgment against the manufacturer— 

notwithstanding the manufacturer’s 

compliance with the NHTSA standard. 

Because most NHTSA standards 

established by an FMVSS are minimum 

standards, a State common law tort 

cause of action that seeks to impose a 

higher standard on motor vehicle 

manufacturers will generally not be 

preempted. However, if and when such 

a conflict does exist—for example, when 

the standard at issue is both a minimum 

and a maximum standard—the State 

common law tort cause of action is 

impliedly preempted. See Geier v. 

American Honda Motor Co., 529 U.S. 

861 (2000). 

Pursuant to Executive Order 13132, 

NHTSA has considered whether this 

rule could or should preempt State 

common law causes of action. The 

agency’s ability to announce its 

conclusion regarding the preemptive 

effect of one of its rules reduces the 

likelihood that preemption will be an 

issue in any subsequent tort litigation. 

To this end, the agency has examined 

the nature (e.g., the language and 

structure of the regulatory text) and 

objectives of today’s rule. NHTSA does 

not intend that this rule preempt state 

tort law that would effectively impose a 

higher standard on motor vehicle 

manufacturers than that established by 

today’s rule. Establishment of a higher 

standard by means of State tort law 

would not conflict with the proposal 

announced here. Without any conflict, 

there could not be any implied 

preemption of a State common law tort 

cause of action. 

D. National Environmental Policy Act 

NHTSA has analyzed this NPRM for 

the purposes of the National 

Environmental Policy Act. The agency 

has determined that implementation of 

this action would not have any 

significant impact on the quality of the 

human environment. 

E. Paperwork Reduction Act 

Before a Federal agency can collect 

certain information from the public, it 

must receive approval from the Office of 

Management and Budget (OMB). Under 

the Paperwork Reduction Act of 1995, a 

person is not required to respond to a 

collection of information by a Federal 

agency unless the collection displays a 

valid OMB control number. NHTSA has 

carefully examined this notice of 

proposed rulemaking and has 

determined that there are no Paperwork 

Reduction Act consequences on motor 

vehicle manufacturers or any other 

members of the public if this NPRM is 

made final. 

F. National Technology Transfer and 

Advancement Act 

Under the National Technology 

Transfer and Advancement Act of 1995 

(NTTAA) (Pub. L. 104–113), ‘‘all Federal 

agencies and departments shall use 

technical standards that are developed 

or adopted by voluntary consensus 

standards bodies, using such technical 

standards as a means to carry out policy 

objectives or activities determined by 

the agencies and departments.’’ In 

today’s NPRM, NHTSA proposes to 

incorporate by reference, in whole or in 

part, two voluntary consensus standards 

developed by the Society of Automotive 

Engineers (SAE): SAE J2264 (APR 95) 

‘‘Chassis Dynamometer Simulation of 

Road Load Using Coastdown 

Techniques’’ and in SAE J1263 

(JAN2009), ‘‘Road Load Measurement 

and Dynamometer Simulation Using 

Coastdown Techniques,’’ the following 

test conditions: S7.1, ‘‘Ambient 

Temperature’’; S7.2 ‘‘Fog,’’ S7.3 

‘‘Winds,’’ and S7.4 ‘‘Road Conditions.’’ 

G. Executive Order 12988 

With respect to the review of the 

promulgation of a new regulation, 

section 3(b) of Executive Order 12988, 

‘‘Civil Justice Reform’’ (61 FR 4729, 

February 7, 1996) requires that 

Executive agencies make every 

reasonable effort to ensure that the 

regulation: (1) Clearly specifies the 

preemptive effect; (2) clearly specifies 


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the effect on existing Federal law or 

regulation; (3) provides a clear legal 

standard for affected conduct, while 

promoting simplification and burden 

reduction; (4) clearly specifies the 

retroactive effect, if any; (5) adequately 

defines key terms; and (6) addresses 

other important issues affecting clarity 

and general draftsmanship under any 

guidelines issued by the Attorney 

General. This document is consistent 

with that requirement. 

Pursuant to this Order, NHTSA notes 

as follows. The issue of preemption is 

discussed above in connection with E.O. 

13132. NHTSA notes further that there 

is no requirement that individuals 

submit a petition for reconsideration or 

pursue other administrative proceeding 

before they may file suit in court. 

H. Unfunded Mandates Reform Act 

The Unfunded Mandates Reform Act 

of 1995 requires agencies to prepare a 

written assessment of the costs, benefits 

and other effects of proposed or final 

rules that include a Federal mandate 

likely to result in the expenditure by 

State, local or tribal governments, in the 

aggregate, or by the private sector, of 

more than $100 million annually 

(adjusted for inflation with base year of 

1995). This NPRM, if made final, would 

not result in expenditures by State, local 

or tribal governments, in the aggregate, 

or by the private sector in excess of $100 

million annually. 

I. Executive Order 13045 

Executive Order 13045 (62 FR 19885, 

April 23, 1997) applies to any rule that: 

(1) Is determined to be ‘‘economically 

significant’’ as defined under E.O. 

12866, and (2) concerns an 

environmental, health, or safety risk that 

NHTSA has reason to believe may have 

a disproportionate effect on children. 

This rulemaking is not subject to the 

Executive Order because it is not 

economically significant as defined in 

E.O. 12866. However, since this NPRM, 

if made final, would require an updated 

ACS on passenger cars, multipurpose 

passenger vehicles, trucks and buses, 

and would require a brake-throttle 

override system on passenger cars, 

multipurpose passenger vehicles, trucks 

and buses with a GVWR of 10,000 

pounds or less, it should have a 

beneficial safety effect on children 

riding in such vehicles. 

J. Executive Order 13211 

Executive Order 13211 (66 FR 28355, 

May 18, 2001) applies to any 

rulemaking that: (1) Is determined to be 

economically significant as defined 

under E.O. 12866, and is likely to have 

a significantly adverse effect on the 

supply of, distribution of, or use of 

energy; or (2) that is designated by the 

Administrator of the Office of 

Information and Regulatory Affairs as a 

significant energy action. This 

rulemaking is not subject to E.O. 13211. 

K. Plain Language 

The Plain Writing Act of 2010 (Pub. 

L. 111–274) and Executive Order 12866 

require each agency to write all rules in 

plain language. Application of the 

principles of plain language includes 

consideration of the following 

questions: 

• Have we organized the material to 

suit the public’s needs? 

• Are the requirements in the rule 

clearly stated? 

• Does the rule contain technical 

language or jargon that is not clear? 

• Would a different format (grouping 

and order of sections, use of headings, 

paragraphing) make the rule easier to 

understand? 

• Would more (but shorter) sections 

be better? 

• Could we improve clarity by adding 

tables, lists, or diagrams? 

• What else could we do to make the 

rule easier to understand? 

If you have any responses to these 

questions, please include them in your 

comments on this proposal. 

L. Regulation Identifier Number (RIN) 

The Department of Transportation 

assigns a regulation identifier number 

(RIN) to each regulatory action listed in 

the Unified Agenda of Federal 

Regulations. The Regulatory Information 

Service Center publishes the Unified 

Agenda in April and October of each 

year. You may use the RIN contained in 

the heading at the beginning of this 

document to find this action in the 

Unified Agenda. 

M. Privacy Act 

Anyone is able to search the 

electronic form of all comments 

received into any of our dockets by the 

name of the individual submitting the 

comment (or signing the comment, if 

submitted on behalf of an association, 

business, labor union, etc.). You may 

review DOT’s complete Privacy Act 

Statement in the Federal Register 

published on April 11, 2000 (Volume 

65, Number 70; Pages 19477–78). 

X. Public Participation 

How do I prepare and submit 

comments? 

Your comments must be written and 

in English. To ensure that your 

comments are correctly filed in the 

Docket, please include the docket 

number of this document in your 

comments. 

Your comments must not be more 

than 15 pages long. (49 CFR 553.21.) We 

established this limit to encourage you 

to write your primary comments in a 

concise fashion. However, you may 

attach necessary additional documents 

to your comments. There is no limit on 

the length of the attachments. 

Comments may also be submitted to 

the docket electronically by logging onto 

the Docket Management System Web 

site at 

http://www.regulations.gov. Follow the 

online instructions for submitting 

comments. 

Please note that pursuant to the Data 

Quality Act, in order for substantive 

data to be relied upon and used by the 

agency, it must meet the information 

quality standards set forth in the OMB 

and DOT Data Quality Act guidelines. 

Accordingly, we encourage you to 

consult the guidelines in preparing your 

comments. OMB’s guidelines may be 

accessed at http://www.whitehouse.gov/ 

omb/fedreg_reproducible. 

How can I be sure that my comments 

were received? 

If you wish Docket Management to 

notify you upon its receipt of your 

comments, enclose a self-addressed, 

stamped postcard in the envelope 

containing your comments. Upon 

receiving your comments, Docket 

Management will return the postcard by 

mail. 

How do I submit confidential business 

information? 

If you wish to submit any information 

under a claim of confidentiality, you 

should submit three copies of your 

complete submission, including the 

information you claim to be confidential 

business information, to the Chief 

Counsel, NHTSA, at the address given 

above under FOR FURTHER INFORMATION

CONTACT. In addition, you should 

submit a copy, from which you have 

deleted the claimed confidential 

business information, to the docket at 

the address given above under 

ADDRESSES. When you send a comment 

containing information claimed to be 

confidential business information, you 

should include a cover letter setting 

forth the information specified in our 

confidential business information 

regulation. (49 CFR Part 512.) 

Will the agency consider late 

comments? 

We will consider all comments 

received before the close of business on 

the comment closing date indicated 

above under DATES. To the extent 


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possible, we will also consider 

comments that the docket receives after 

that date. If the docket receives a 

comment too late for us to consider in 

developing a final rule (assuming that 

one is issued), we will consider that 

comment as an informal suggestion for 

future rulemaking action. 

How can I read the comments submitted 

by other people? 

You may read the comments received 

by the docket at the address given above 

under ADDRESSES. The hours of the 

docket are indicated above in the same 

location. You may also see the 

comments on the Internet. To read the 

comments on the Internet, go to http:// 

www.regulations.gov. Follow the online 

instructions for accessing the dockets. 

Please note that even after the 

comment closing date, we will continue 

to file relevant information in the docket 

as it becomes available. Further, some 

people may submit late comments. 

Accordingly, we recommend that you 

periodically check the Docket for new 

material. You can arrange with the 

docket to be notified when others file 

comments in the docket. See http://

www.regulations.gov for more 

information. 

List of Subjects in 49 CFR Part 571 

Imports, Motor vehicle safety, Motor 

vehicles, and Tires. 

Proposed Regulatory Text for FMVSS 

No. 124 

In consideration of the foregoing, 

NHTSA proposes to amend 49 CFR Part 

571 as set forth below. 

PART 571—FEDERAL MOTOR 

VEHICLE SAFETY STANDARDS 

1. The authority citation for Part 571 

continues to read as follows: 

Authority: 49 U.S.C. 322, 30111, 30115, 

30117 and 30166; delegation of authority at 

49 CFR 1.50. 

2. Section 571.5 is amended by 

adding paragraphs (k)(50) and (k)(51) to 

read as follows: 

§ 571.5 Matter incorporated by reference. 

* * * * * 

(k) * * * 

(50) SAE 1263 (JAN2009) ‘‘Road Load 

Measurement and Dynamometer 

Simulation Using Coastdown 

Techniques,’’ Sections S7.1 ‘‘Ambient 

Temperature,’’ S7.2 ‘‘Fog,’’ S7.3 

‘‘Winds,’’ and S7.4 ‘‘Road Conditions.’’ 

(51) SAE J2264 (APR 1995) ‘‘Chassis 

Dynamometer Simulation of Road Load 

Using Coastdown Techniques.’’ 

* * * * * 

3. Section 571.124 is revised to read 

as follows: 

§ 571.124 Standard No. 124; Accelerator 

control and brake-throttle override systems. 

S1. Scope. This standard establishes 

requirements for each engine, electric 

motor, and other motive power source 

connected to a vehicle’s drive wheels to 

return to idle, within a specified time 

and a specified tolerance, whenever 

actuating force on the driver-operated 

accelerator control is removed and 

whenever there is a severance or 

disconnection in the accelerator control 

system. This standard also establishes 

requirements for brake-actuated throttle 

override systems. 

S2. Purpose. The purpose of this 

standard is to reduce deaths and injuries 

resulting from uncontrolled vehicle 

propulsion caused by malfunctions or 

disconnections in accelerator control 

systems and from conflicting inputs to 

the brake and accelerator controls in a 

vehicle. 

S3. Application. This standard 

applies to passenger cars, multipurpose 

passenger vehicles, trucks, and buses. 

Section S6.6 does not apply to vehicles 

having a GVWR greater than 10,000 lb 

(4545 kg), or to vehicles without 

Electronic Throttle Control. 

S4. Definitions. 

Accelerator control system means all 

vehicle components, including both 

mechanical and electrical/electronic 

components and modules, that operate 

a vehicle’s throttle in response to 

movement of the driver-operated 

accelerator control and that, upon 

removal of actuating force on the driveroperated control, return both the throttle 

and the driver-operated control to their 

idle or rest positions. For the purposes 

of this standard, an electronic control 

module is considered a single 

component, and the external wiring and 

connections of each module to other 

accelerator control system components 

and to other vehicle components 

including power and ground 

connections are subject to severance or 

disconnection. 

Air intake rate means the rate at 

which combustion air is supplied to an 

engine. 

Air-throttled engine means an internal 

combustion engine in which output 

power is controlled primarily through 

regulation of the air intake rate. 

Ambient temperature means the 

temperature of air surrounding a test 

vehicle measured at a sufficient distance 

to not be significantly affected by heat 

from the test vehicle. 

Coastdown means vehicle 

deceleration which occurs when there is 

no input to either the brake or 

accelerator pedals. 

Creep speed means the maximum 

terminal speed that can be achieved 

when a vehicle in a lightly loaded 

condition, starting from a standstill or 

any speed of which the vehicle is 

capable, is driven in any gear with no 

input to its driver-operated accelerator 

control. 

Driver-operated accelerator control 

means any device on a vehicle, such as 

an accelerator pedal, that a driver uses 

to modulate engine or motor power, but 

not including cruise control, locking 

hand throttles, or any engine or motor 

control not intended for regulating 

vehicle propulsion. 

Electric power delivery means a power 

computation (such as wattage) derived 

from the current and voltage input to an 

electric motor that drives a vehicle. 

Electronic throttle control means an 

accelerator control system in which 

movement of the driver-operated control 

is translated into throttle actuation, at 

least in part by electronic, instead of 

mechanical, means. 

Engine or motor means any source of 

motive power in a vehicle, including 

internal combustion engines and 

electric motors, connected to the drive 

wheels and capable of propelling the 

vehicle. 

Fuel delivery rate means the net rate 

of fuel use (supply minus return) in an 

engine. 

Fuel metering device means the 

internal parts of a carburetor, fuel 

injector, fuel distributor, or fuel 

injection pump, and the internal 

elements of electronic modules in the 

accelerator control system such as 

circuit boards and discrete electrical 

components contained inside an engine 

control module, which adjust engine or 

motor operating variables such as fuelair ratio and ignition timing. 

Fuel-throttled engine means an 

internal combustion engine in which 

output power is controlled primarily 

through regulation of fuel delivery rate. 

Idle or idle state means the normal 

running condition of a vehicle’s engine 

or motor with no faults or malfunctions 

affecting engine or motor output when 

there is no input to the driver-operated 

accelerator control. 

Idle state conditions are conditions 

which influence idle state during 

normal operation of a vehicle, including 

but not limited to engine temperature, 

air-conditioner load, emission control 

state, and the use of speed setting 

devices such as cruise control. 

Idle state indicant means a vehicle 

operating parameter which varies 

directly with engine or motor output, 

including: throttle position, fuel 

delivery rate, air intake rate, electric 

power delivery, and creep speed. 

Throttle means the component of an 

accelerator control system which, in 


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response to movement of the driveroperated accelerator control, modulates 

vehicle propulsion by varying throttle 

position, fuel delivery rate, air intake 

rate, electric power delivery, or other 

means by which powertrain output is 

regulated. 

S5. Requirements. Each vehicle shall 

meet the requirements of S5.1 through 

S5.3 when tested in accordance with 

applicable procedures in S6, at any 

ambient temperature between minus 40 

and plus 50 degrees Celsius and after 12 

hours of conditioning at any 

temperature within that range unless 

otherwise specified, and with its engine 

or motor running under any load 

condition and at any speed of which the 

engine or motor is capable. 

S5.1 Normal Operation. The throttle 

shall return to idle within the time limit 

specified in S5.3 whenever the driveroperated accelerator control is released 

from any position when the vehicle is 

tested in accordance with S6.3. 

S5.2 Fail-safe Operation. Each 

vehicle shall meet S5.2.1 or S5.2.2. A 

fuel metering device is not subject to 

disconnection or severance under this 

test procedure. 

S5.2.1 In the event of a 

disconnection or severance at a single 

point of any one component of the 

accelerator control system, including 

disconnection or severance of an 

electrical component that results in an 

open circuit or a short circuit to ground, 

but not a disconnection or severance 

inside of an electronic module, the 

throttle shall return to or below idle 

plus a tolerance of 50 percent, within 

the time limit specified in S5.3 after 

release of the driver-operated 

accelerator control from any position, 

when tested in accordance with S6.4; or 

S5.2.2 When tested in accordance 

with S6.5, each vehicle’s maximum 

creep speed shall be no greater than 50 

km/h (31 mph), and the vehicle shall 

decelerate continuously from any initial 

speed greater than 50 km/h of which the 

vehicle is capable until its speed is 

reduced to 50 km/h or lower, and the 

time required to coast down to 50 km/ 

h shall not exceed the time required to 

coast down to 50 km/h from the same 

speed in neutral gear without faults in 

the accelerator control system. 

S5.3 Response Time. When tested in 

accordance with S6.3 and S6.4, the 

maximum time to return to idle as 

indicated by the throttle position or 

other selected idle state indicant shall 

be 

(a) Not greater than 1 second for 

vehicles of 4536 kilograms (10,000 

pounds) or less gross vehicle weight 

rating (GVWR), 

(b) Not greater than 2 seconds for 

vehicles of more than 4536 kilograms 

(10,000 pounds) GVWR, and 

(c) Not greater than 3 seconds for 

vehicles, regardless of GVWR, that are 

exposed to ambient air at minus 18 to 

minus 40 degrees Celsius during a test 

or any portion of the 12-hour 

conditioning period. 

S5.4 Brake-Throttle Override. 

S5.4.1 Each motor vehicle under 

10,000 lb GVWR having electronic 

throttle control shall meet the 

performance requirement of S6.6 and 

shall be equipped with a throttleoverride system that is engaged by 

application of the vehicle’s service 

brake and that meets the following 

requirements: 

(a) The system shall consist of 

hardware and/or software components 

on the vehicle which have the capability 

of identifying and reacting to conflicts 

between accelerator pedal and brake 

pedal inputs; 

(b) At vehicle speeds greater than 16 

km/h (10 mph), when a conflict exists 

between the vehicle’s accelerator and 

brake pedals, the override system must 

engage and must substantially reduce 

propulsive force delivered to the driving 

wheels to a controllable level by means 

of a change in throttle opening, fuel 

delivery rate, air intake rate, electric 

power delivery, or an equivalent means; 

(c) Once engaged, the override must 

remain engaged at any speed as long as 

brake pedal application is maintained at 

or above the force level or travel which 

initially engaged the override, and as 

long as accelerator pedal input is in 

conflict with the brake application. 

S5.4.2 When tested in accordance 

with the brake-throttle override 

performance test in S6.6, a vehicle is 

deemed to comply if at least one of the 

six stops is made within the prescribed 

distance. However, in all of the six 

stops, the brake-throttle override must 

engage if the system identifies a conflict 

between the accelerator pedal and 

brake. 

S5.4.3 If a means is provided for the 

vehicle operator to turn off the brakethrottle override system— 

(a) There must be an illuminated alert 

or message that remains in view of the 

driver as long as the system is turned off 

and the vehicle ignition is on, and 

(b) The system must default to an 

active state whenever the vehicle 

ignition is started. 

S6. Test Procedures. 

S6.1 Irrevocable Selection. The 

manufacturer shall select one of the 

following criteria upon which it bases 

its certification to the requirements in 

section S5.1 and S5.2 in this standard: 

throttle position, fuel delivery rate, air 

intake rate, electric power delivery, or 

creep speed/coastdown performance. 

This selection is irrevocable and shall 

be made prior to or at the time of 

certification of the vehicle pursuant to 

49 CFR Part 567, ‘‘Certification.’’ 

S6.2 General. For the test 

procedures in sections S6.3 and S6.4, 

the ‘‘baseline’’ value is the value of the 

selected idle state indicant measured for 

an engine or motor operating at idle 

without accelerator control system 

faults under the conditions that exist at 

the beginning of a test and which are 

held constant during the test. 

(a) For idle state conditions that 

provide a means of driver control, for 

example air-conditioner setting, the 

selected setting for testing may be any 

point within the control range, 

including ‘‘off.’’ 

(b) The engine or motor is operated 

for not less than 5 minutes to stabilize 

the idle state prior to testing. 

(c) Vehicles are conditioned and 

tested at any ambient temperature 

between minus 40 and plus 50 degrees 

Celsius, except as specified for creep 

speed and coastdown test procedures in 

S6.5. 

(d) The time to return to idle in S6.4 

is measured first from the instant that a 

severance or disconnection occurs and 

then, if necessary, from the instant of 

release of the driver-operated 

accelerator control. 

S6.3 Test Procedure for Evaluating 

Return-to-Idle in Normal Operation 

S6.3.1 Condition the test vehicle to 

a selected ambient temperature for up to 

12 hours. 

S6.3.2 Start the vehicle, set controls 

such as for the air-conditioner, and 

operate the engine for not less than 5 

minutes. 

S6.3.3 Measure the baseline value of 

one of the following idle state indicants 

identified by the vehicle manufacturer 

for the test vehicle: throttle position, 

fuel delivery rate, air intake rate, or 

electric power delivery. 

S6.3.4 Set engine speed and 

powertrain loading condition by shifting 

the transmission to neutral or any gear 

and moving the driver-operated 

accelerator control to any position, with 

or without resistance applied to the 

vehicle’s drive wheels. 

S6.3.5 After at least 3 seconds, 

release the driver-operated accelerator 

control. 

S6.3.6 Verify that the measured idle 

state indicant returns to or below its 

baseline value determined in S6.3.3 

following release of the driver-operated 

accelerator control within the response 

time specified in S5.3. 


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6.4 Test Procedure for Evaluating 

Return-to-Idle Following a 

Disconnection or Severance 

6.4.1 Condition the test vehicle to a 

selected ambient temperature for up to 

12 hours. 

S6.4.2 Start the vehicle, set controls 

such as for air-conditioning, and operate 

the engine for not less than 5 minutes. 

S6.4.3 Measure the baseline idle 

value of one of the following idle state 

indicants identified by the vehicle 

manufacturer for the test vehicle: 

throttle position, fuel delivery rate, air 

intake rate, or electric power delivery. 

S6.4.4 Set engine speed and 

powertrain loading condition by shifting 

the transmission to neutral or any gear 

and moving the driver-operated 

accelerator control to any position, with 

or without resistance applied to the 

vehicle’s drive wheels. 

S6.4.5 While continuing to measure 

the idle state indicant, disconnect one 

component of the accelerator control 

system by removing one connector or 

severing a wiring harness or individual 

wire, leaving the disconnected or 

severed component in either an open 

circuit condition or shorted to ground. 

S6.4.6 If there is no change in the 

idle state indicant after at least 3 

seconds, release the driver-operated 

accelerator control. 

S6.4.7 Verify that, following either 

S6.4.5 or S6.4.6, the idle state indicant 

returns to and remains at or below a 

value that is no more than 50 percent 

greater than its baseline value as 

measured in S6.4.3, within the response 

time specified in S5.3. 

S6.5 Alternative Procedure for 

Evaluating Return-to-Idle Following a 

Disconnection or Severance, Using 

Creep Speed and Coastdown 

S6.5.1 This test procedure measures 

creep speed and coastdown time on a 

chassis (wheel-driven) dynamometer 

configured to simulate the correct road 

load as a function of speed for the test 

vehicle as determined in accordance 

with SAE J2264 (APR 95), ‘‘Chassis 

Dynamometer Simulation of Road Load 

Using Coastdown Techniques.’’ 

(Incorporated by reference, see § 571.5.) 

This test procedure also may be 

performed on a straight road course 

consisting of dry, smooth, unbroken 

asphalt or concrete pavement with a 

continuous grade of not more than 0.5 

percent in any direction. 

S6.5.2 The test vehicle is lightly 

loaded (driver-only with no cargo and 

fuel tank level between one-quarter and 

full.) Tires are set at cold inflation 

pressures provided on the vehicle 

placard and/or the tire inflation label, 

and all vehicle windows are fully 

closed. For track tests, ambient 

conditions are as specified in SAE J1263 

(JAN 2009), ‘‘Road Load Measurement 

and Dynamometer Simulation Using 

Countdown Techniques’’ in section 7, 

‘‘Test Conditions’’ at S7.1 ‘‘Ambient 

Temperatures’’, S7.2 ‘‘Fog,’’ S7.3 

‘‘Winds,’’ and S7.4 ‘‘Road Conditions’’ 

(incorporated by reference, see § 571.5). 

S6.5.3 Time intervals measured in 

S6.5.5 and S6.5.6 begin at the instant 

that a disconnection or severance is 

induced in the accelerator control 

system, or from the instant that the 

accelerator pedal is released or the 

transmission is shifted to neutral, as 

applicable, depending on which of 

those actions initiates a vehicle 

response. Test vehicle speed versus time 

are recorded continuously during test 

runs. 

S6.5.4 Start up the test vehicle, set 

accessory controls such as for airconditioning, and operate the vehicle 

for not less than 5 minutes. 

S6.5.5 Creep Speed Measurement 

Procedure 

(a) With the vehicle’s drive wheels on 

the dynamometer roller(s) or with the 

vehicle positioned on the road test 

course, place the transmission selector 

in the ‘‘drive’’ position. For manual 

transmissions, select the highest gear 

(lowest numerical gear ratio) which 

allows the vehicle to coast without 

stalling if the clutch is gradually 

released when there is no input to the 

accelerator pedal. 

(b) With the vehicle operating at idle 

or at any target speed up to 50 km/h (31 

mph), simultaneously release the 

accelerator pedal (if applied) and 

disconnect one component of the 

accelerator control system by removing 

one connector or severing a wiring 

harness or individual wire, leaving the 

disconnected or severed component in 

either an open circuit condition or 

shorted to ground. 

(c) Note the speed of the test vehicle 

at 90 seconds after the disconnection 

and verify that it does not exceed 50 

km/h. 

S6.5.6 Coastdown Time 

Measurement Procedure 

(a) With the vehicle’s drive wheels on 

the dynamometer roller(s) or with the 

vehicle positioned on the road test 

course, place the transmission selector 

in the ‘‘drive’’ position and drive the 

vehicle up to any selected target speed 

greater than 50 km/h. For manual 

transmissions, select any gear 

appropriate for the selected target speed. 

(b) At the target speed, release the 

accelerator pedal and simultaneously 

shift the vehicle into neutral. Allow the 

vehicle to coast without any brake 

input. 

(c) Verify that the vehicle decelerates 

to or below 50 km/h and record the 

elapsed time needed for the vehicle to 

reach 50 km/h. 

(d) Repeat the step in S6.5.6(a) and, at 

the same target speed, simultaneously 

release the accelerator pedal and 

disconnect one component of the 

accelerator control system by removing 

one connector or severing a wiring 

harness or individual wire, leaving the 

disconnected or severed component in 

either an open circuit condition or 

shorted to ground. 

(e) Record the elapsed time needed for 

the vehicle to decelerate to 50 km/h, 

and verify that it does not exceed the 

elapsed time in the step in S6.5.6(c). 

S6.6 Performance Test for BrakeThrottle Override Systems. 

Measure vehicle stopping distance 

with the test vehicle’s accelerator pedal 

applied as specified in the following 

procedure: 

S6.6.1 Select a target speed which is 

greater than or equal to 30 km/h and 

less than or equal to 160 km/h and 

which, if greater than 100 km/h, does 

not exceed 80 percent of the test 

vehicle’s maximum speed. ‘‘Maximum 

speed’’ is used as defined in section S4 

of 49 CFR 571.135, ‘‘Light Vehicle Brake 

Systems,’’ (FMVSS No. 135). 

S6.6.2 Conduct stopping distance 

measurements in accordance with the 

general procedures and test conditions 

specified in S6 of FMVSS No. 135, and 

as follows: 

(a) Accelerate the test vehicle and, 

while still in gear, hold the accelerator 

pedal in any fixed position between 25 

and 100 percent of the full range of 

pedal travel. 

(b) At the target speed, without 

releasing the accelerator pedal from the 

position as selected in S6.6.2(a), apply 

the service brake and bring the vehicle 

to a stop using a brake pedal force of not 

less than 65N (14.6 lbs) and not more 

than 500N (112.4 lbs).; 

(c) Repeat six times for a total of six 

test runs at each target speed. 

S6.6.3 Verify that the stopping 

distance ‘S’ (in meters) for each vehicle 

speed ‘V’ (in km/h) is no more than 5 

percent greater than the stopping 

distance specified in either S7.5.3(b) or 

S7.6.3 of FMVSS No. 135 by meeting 

one of the following requirements: 

(a) For test speeds up to and including 

100 km/h: S ≤ 1.05(0.10V + 0.0060V2). 

(b) For test speeds greater than 100 

km/h: S ≤ 1.05(0.10V + 0.0067V2). 

Issued on: March 28, 2012. 

Christopher J. Bonanti, 

Associate Administrator for Rulemaking. 

[FR Doc. 2012–9065 Filed 4–12–12; 11:15 am] 

BILLING CODE 4910–59–P 


emcdonald on DSK29S0YB1PROD with PROPOSALS2