ID: 11497AWKM

Mr. Kenneth W. Obrycki
2433 Arlington Street
Pittsburgh, PA 15209

Dear Mr. Obrycki:

This responds to your January 16, 1996 letter to this agency suggesting that tire safety would be improved if we were to require a yellow line approximately 1/4 of an inch wide across the width of tires at the 3/32 of an inch tread depth level. You stated that such a requirement could enable consumers to tell when tires are unsafe and could enable state police and inspection stations to readily observe dangerous tread levels. You believe that this would enhance passenger safety because worn tires would be replaced sooner.

We have carefully reviewed your letter, but do not agree that the requirement you suggest is warranted at this time. Our decision is explained below.

By way of background information, the National Highway Traffic Safety Administration (NHTSA) has the authority to issue Federal motor vehicle safety standards (FMVSSs) applicable to the manufacture and sale of new motor vehicles and new items of motor vehicle equipment. Among other things, such standards must be reasonable, practicable, and appropriate for the particular type of motor vehicle or motor vehicle equipment for which they are prescribed. Once a vehicle or item of equipment is sold to the consumer, NHTSA's authority generally terminates and with certain exceptions, use of that vehicle or item of equipment then becomes a matter of state jurisdiction.

NHTSA has issued a number of FMVSSs and related regulations applicable to tires, the pertinent ones here being FMVSS Nos. 109, New pneumatic tires, and 119, New pneumatic tires for vehicles other than passenger cars. Both standards require that all tires have treadwear indicators molded into the tread at the 2/32 of an inch tread depth level. This level was selected by NHTSA based on early studies that showed that when tread is worn to 2/32 of an inch, a tire rapidly loses its traction characteristics, thereby becoming unsafe. Although states, not NHTSA, have the authority to enforce tire removal when the tread depth becomes worn below a certain level, the agency has issued vehicle in use inspection standards at 49 Code of Federal Regulations, Part 570, for states to use as a guide in establishing their own vehicle inspection requirements.

You stated in your letter that Pennsylvania, and perhaps other states, has established minimum tread depth requirements at 3/32 of an inch. The state has the authority to do that, since it has jurisdiction over the use of vehicles and equipment. NHTSA has retained the 2/32 of an inch requirement for tread depth indicators, however, and recently denied a petition to raise the tread depth indicators to 3/32 of an inch because there was no proven safety need to do so. A copy of the denial notice is enclosed.

Although NHTSA has the authority to require a yellow line across the tire to highlight the tread depth indicators, the agency has no data suggesting a safety need for such action. The tread depth indicators currently required, even though unobtrusive from a distance, have been shown to be effective in alerting motorists, inspection stations, and law enforcement personnel to unsafe tire wear. Accordingly, without further data showing a safety need to do so, NHTSA does not believe that requiring yellow tread wear markings in addition to those already required would be reasonable at this time.

Thank you for your interest in motor vehicle safety.

Sincerely,

Samuel J. Dubbin Chief Counsel

Enclosure

Ref:109#119 ref:2/22/96

ID: 1984-2.46

TYPE: INTERPRETATION-NHTSA

DATE: 08/03/84

FROM: AUTHOR UNAVAILABLE; Frank Berndt; NHTSA

TO: Terry E. Teeter -- Transmission Division, Eaton Corp.

TITLE: FMVSS INTERPRETATION

TEXT:

Terry E. Teeter, P.E. Engineering Supervisor Transmission Division Eaton Corporation P.O. Box 4013 Kalamazoo, Michigan 49003

This responds to your May 14, 1984, letter to the National Highway Traffic Safety Administration regarding the transmissions that you manufacture for air brake equipped trucks. You stated that your transmissions use vehicle air pressure to accomplish gear changing and other transmission control functions. You stated your understanding that the transmission air system is an accessory similar to air powered wipers or air horns and therefore air lines connected to the system are exempt from Federal Motor Vehicle Safety Standard No. 106, Brake Hoses. As explained below, not all accessory lines are excluded from the standard, and the issue of whether your transmission lines are covered by the standard depends on whether a failure of the line would result in a loss of pressure in the brake system.

Federal Motor Vehicle Safety Standard No. 106, Brake Hoses, defines brake hose as:

a flexible conduit, other than a vacuum tubing connector, manufactured for use in a brake system to transmit or contain the fluid pressure or vacuum used to apply force to a vehicle's brakes.

As you pointed out in your letter, the agency has previously determined that hoses connected to accessories such as air powered wipers or air horns need not comply with Standard No. 106. However, these hoses are only excepted from the standard if they do not transmit or contain the brake air pressure used to apply force to a vehicle's brakes. To determine whether the hoses of your transmission air system are excluded from Standard No. 106, you must determine whether a failure of such a hose would result in a loss of air pressure in the brake system. If this would be the case, the hoses transmit or contain the pressure used to apply force to the vehicle's brakes and therefore would have to comply with the standard. If you use a check valve or some other device to prevent loss of pressure, then the hose would not contain or transmit the air pressure and would not be required to comply with Standard No. 106.

Sincerely, Frank Berndt Chief Counsel

May 14, 1984

National Highway Traffic Safety Administration Office of Chief Counsel 400 7th Street, S.W. Washington, D.C. 20590

Attention: Frank Berndt

Gentlemen:

We manufacture heavy duty truck transmissions that are used in Class 7 and Class 8 highway trucks. These trucks typically use air braking systems that utilize air brake hoses subject to FMVSS-106. Various models of our transmissions use vehicle air pressure to accomplish gear changing and other transmission control functions (see attached typical transmission drawing). This basic system has been in use for over thirty years.

It is our understanding that the transmission air system is an accessory such as the air powered wipers or the air horn (previously clarified in "Preamble to Amendment to Motor Vehicle Safety Standard No. 106-74", Docket No. 1-5; Notice 10, Part 571; S106-74-Pre 6: copy attached), and therefore exempt from FMVSS-106. Please confirm that our understanding is correct.

If you wish to discuss this in more detail, or if you desire more information, please feel free to contact me at (616) 342-3400.

Sincerely,

Terry E. Teeter, P.E. Engineering Supervisor Preamble omitted.

ID: 1985-01.37

TYPE: INTERPRETATION-NHTSA

DATE: 02/26/85

FROM: AUTHOR UNAVAILABLE; Frank Berndt; NHTSA

TO: Mr. Giorgio Kirchner Federazione Italiana Fuoristrada

TITLE: FMVSS INTERPRETATION

TEXT:

AIR MAIL

Mr. Giorgio Kirchner Segreteria Generale Federazione Italiana Fuoristrada 20131 Milano Via Capranica, 4 ITALY

Dear Mr. Kirchner:

This responds to your letter asking for information about U.S. Federal laws covering tires. For your information, I have enclosed a copy of a letter I sent to a Brazilian tire manufacturer last year, explaining all of the requirements which must be satisfied by a foreign manufacturer selling tires in the United States and enclosing copies of the pertinent regulations.

You stated that you were particularly interested in knowing the meanings and the corresponding values of identification symbols required to appear an sidewalls of tires subject to Standard No. 119. You listed as examples of symbols you were interested in load range and "P.R."

The load range is a letter between "A" and "N", with an A being the lowest load range and N being the highest. Load ranges are designed to tires for use on motor vehicles other than passenger cars because such tires may have identical physical dimensions and, therefore, identical size designations, but widely differing load-carrying capabilities. To ensure that these tires are used only in situations where their load-carrying capability is sufficient, section S6.5(j) of Standard No. 119 requires a letter designating the load range to appear on the sidewall of each tire for use on motor vehicles other than passenger cars. If you are interested in learning the load-carrying capability of the load ranges assigned to a particular tire size, you should contact one of the standardization organizations listed in section S5.1(b) of the enclosed copy of Standard No. 119.

I believe that the symbol "P.R." refers to the ply rating for a tire. The ply rating is an older system which performed the same function now served by the load range. Under the ply rating system, tires were rated from 2 to 24 plies, with the lower numbers indicating a lesser load-carrying capability. Standard No. 119 does not require that a ply rating appear on the sidewall of tires. I have enclosed a copy of a page from the most recent yearbook published by the American standardization organization, the Tire a Rim Association, which shows how to convert a ply rating to the appropriate load range.

If you need further information or have any questions on the enclosed materials, please feel free to contact me.

Sincerely,

Original Signed By

Frank Berndt Chief Counsel

Enclosures

U.S. DEPARTMENT OF TRANSPORTATION 407 7th St. S.W. WASHINGTON D.C. 20580 (Stati Uniti)

Milano, 27.12.84

Re : U.S. Federal Laws covering Tires

Dear Sirs,

We should like to receive information covering the above mentioned U.S. Federal Laws and the one named FMVSS119.

We are particularly interested in knowing the readings (and the corresponding values) of identification symbols carried on tire sidewalls, i.e.:

Load Range, P.R., etc.

We thank you for your assistance.

We remain Yours faithfully Federazione Italiana Fuoristrada Segreteria Generale Giorgio Kirchner

ID: 2905yy

Ms. Jessie M. Flautt
4405 Lafayette Street
Bellaire, TX 77401

Dear Ms. Flautt

This responds to your letter to Mr. Steve Kratzke of my staff, requesting that the National Highway Traffic Safety Administration (NHTSA) grant permission to a repair business to modify your motor vehicle.

You explained that you are under five feet, two inches and legally blind in one eye. You further explained that, due to the increased size of headrests in recent years, you are unable to locate a 1991 automobile which does not have headrests which impede your field of vision. You wish to arrange to have the size of the headrests in a 1991 automobile reduced. You asked if you could obtain permission from this agency to permit this modification. I hope the following discussion explaining our regulation will be of assistance to you.

I would like to begin by clarifying that there is no procedure by which persons petition for and are granted permission from NHTSA to arrange to have a motor vehicle repair business modify their motor vehicle. Repair businesses are permitted to modify vehicles without obtaining permission from NHTSA to do so, but are subject to certain regulatory limits on the type of modifications they may make. In certain limited situations, we have exercised our discretion in enforcing our regulations to provide some allowances to a repair business which cannot conform to our regulations when making modifications to accommodate the special needs of persons with disabilities. Since your situation is among those given special consideration by NHTSA, this letter should provide you with the relief you seek.

Our agency is authorized to issue Federal Motor Vehicle Safety Standards (FMVSS) that set performance requirements for new motor vehicles and items of motor vehicle equipment. Manufacturers are required by the National Traffic and Motor Vehicle Safety Act (Safety Act) to certify that their products conform to our safety standards before they can be offered for sale. Manufacturers, distributors, dealers and repair businesses modifying certified vehicles are affected by 108(a)(2)(A) of the Safety Act. It prohibits those businesses from knowingly rendering inoperative any elements of design installed on a vehicle in compliance with a FMVSS. In general, 108(a)(2)(A) would require repair businesses which modify motor vehicles to ensure that they do not remove, disconnect or degrade the performance of safety equipment installed in compliance with an applicable safety standard. Violations of 108(a)(2)(A) are punishable by civil fines up to $1,000 per violation.

In situations such as yours where a vehicle must be modified to accommodate the needs of a particular disability, we have been willing to consider any violation of 108(a)(2)(A) a purely technical one justified by public need. I can assure you that NHTSA would not institute enforcement proceedings against a repair business that modifies the headrest on your vehicle to accommodate your condition. We caution, however, that only necessary modifications should be made to the headrest to accommodate your condition and we urge your dealer to modify your vehicle in such a manner that would not degrade from the safety currently provided by your vehicle. Many manufacturers are currently installing headrests in vehicles which exceed the minimum dimensions required by FMVSS No. 202, Head Restraints. I urge you not to have your headrest reduced below these dimensions if it is not necessary for your field of view.

If you have further questions or need some additional information in this area, please contact Mary Versailles of my staff at this address or by telephone at (202) 366-2992.

Sincerely,

Paul Jackson Rice Chief Counsel

/ref:VSA, 202 d:3/26/9l

ID: 2969yy

Ms. Jessie M. Flautt
4405 Lafayette Street
Bellaire, TX 77401

Dear Ms. Flautt

This responds to your letter to Mr. Steve Kratzke of my staff, requesting that the National Highway Traffic Safety Administration (NHTSA) grant permission to a repair business to modify your motor vehicle.

You explained that you are under five feet, two inches and legally blind in one eye. You further explained that, due to the increased size of headrests in recent years, you are unable to locate a 1991 automobile which does not have headrests which impede your field of vision. You wish to arrange to have the size of the headrests in a 1991 automobile reduced. You asked if you could obtain permission from this agency to permit this modification. I hope the following discussion explaining our regulation will be of assistance to you.

I would like to begin by clarifying that there is no procedure by which persons petition for and are granted permission from NHTSA to arrange to have a motor vehicle repair business modify their motor vehicle. Repair businesses are permitted to modify vehicles without obtaining permission from NHTSA to do so, but are subject to certain regulatory limits on the type of modifications they may make. In certain limited situations, we have exercised our discretion in enforcing our regulations to provide some allowances to a repair business which cannot conform to our regulations when making modifications to accommodate the special needs of persons with disabilities. Since your situation is among those given special consideration by NHTSA, this letter should provide you with the relief you seek.

Our agency is authorized to issue Federal Motor Vehicle Safety Standards (FMVSS) that set performance requirements for new motor vehicles and items of motor vehicle equipment. Manufacturers are required by the National Traffic and Motor Vehicle Safety Act (Safety Act) to certify that their products conform to our safety standards before they can be offered for sale. Manufacturers, distributors, dealers and repair businesses modifying certified vehicles are affected by 108(a)(2)(A) of the Safety Act. It prohibits those businesses from knowingly rendering inoperative any elements of design installed on a vehicle in compliance with a FMVSS. In general, 108(a)(2)(A) would require repair businesses which modify motor vehicles to ensure that they do not remove, disconnect or degrade the performance of safety equipment installed in compliance with an applicable safety standard. Violations of 108(a)(2)(A) are punishable by civil fines up to $1,000 per violation.

In situations such as yours where a vehicle must be modified to accommodate the needs of a particular disability, we have been willing to consider any violation of 108(a)(2)(A) a purely technical one justified by public need. I can assure you that NHTSA would not institute enforcement proceedings against a repair business that modifies the headrest on your vehicle to accommodate your condition. We caution, however, that only necessary modifications should be made to the headrest to accommodate your condition and we urge your dealer to modify your vehicle in such a manner that would not degrade from the safety currently provided by your vehicle. Many manufacturers are currently installing headrests in vehicles which exceed the minimum dimensions required by FMVSS No. 202, Head Restraints. I urge you not to have your headrest reduced below these dimensions if it is not necessary for your field of view.

If you have further questions or need some additional information in this area, please contact Mary Versailles of my staff at this address or by telephone at (202) 366-2992.

Sincerely,

Paul Jackson Rice Chief Counsel

/ref:VSA, 202 d:3/26/9l

ID: nht94-7.20

DATE: March 28, 1994

FROM: John Womack -- Acting Chief Counsel, NHTSA

TO: Richard Kreutziger -- Executive Director, New York State Bus Distributor Association, Inc.

TITLE: None

ATTACHMT: Attached to faxes dated 2/14/94 and 1/12/94 from Richard Kreutziger to Walter Myers (OCC 9559); Also attached to letter dated 2/20/87 from Erika Z. Jones to Martin V. Chauvin

TEXT:

This responds to your Fax of January 12, 1994, requesting an information on the extent to which a state can adopt requirements for school buses which exceed the Federal motor vehicle safety standards. This also responds to your FAX of February 14, 1994, requesting an explanation of the location requirements for a side emergency door exit in Standard No. 217, Bus Emergency Exits and Window Retention and Release (as amended at 57 FR 49413; November 2, 1992).

Your January 12, 1994 FAX requested clarification of when a state could impose requirements on school buses which exceeded the requirements of the Federal motor vehicle safety standards (FMVSS). Specifically, you asked whether the state could impose such requirements on (1) a public school and (2) a contractor providing transportation for a public school. Section 103(d) of the National Traffic and Motor Vehicle Safety Act (the Safety Act; 15 U.S.C. 1392(d)) provides that:

Whenever a Federal motor vehicle safety standard ... is in effect, no State or political subdivision of a State shall have any authority either to establish, or to continue in effect, with respect to any motor vehicle or item of motor vehicle equipment any safety standard applicable to the same aspect of performance of such vehicle or item of equipment which is not identical to the Federal standard. Nothing in this section shall be construed to prevent ... any State or political subdivision thereof from establishing a safety requirement applicable to motor vehicles or motor vehicle equipment procured for its own use if such requirement imposes a higher standard than that required to comply with the otherwise applicable Federal standard.

Section 103 (d) preempts state requirements for school buses covering the same aspect of performance as an applicable FMVSS that are different from the applicable FMVSS, except to the extent that the requirements impose a higher level of performance and apply only to vehicles procured for the State's use. A state law imposing higher requirements would be preempted under S103(d) to the extent that the law requires ALL school buses manufactured for use in the state to comply with the law. The law would not be preempted to the extent that it applies to public school buses. In addition, the agency has previously interpreted the phrase "vehicles procured for (the State's) own use" to include public school buses and school buses operated and owned by a private contractor under contract to transport children to and from public school. See, for example, February 20, 1987 letter to Mr. Martin Chauvin (copy enclosed).

Your February 14, 1994 FAX asked whether the November 2 final rule permits a right side emergency exit door to be to the rear of the passenger compartment.

The answer is yes. Except for a left side emergency exit door installed as the first additional emergency exit on a bus with a rear emergency door, there are no fore and aft location requirements for side emergency exit doors. I have attached for your information an appendix which lists all the location requirements for additional emergency exits.

I hope you find this information helpful. If you have any other questions, please contact us at this address or by phone at (202) 366-2992.

(Appendix omitted.)

ID: nht74-2.5

DATE: 11/04/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Todco Division

TITLE: FMVSS INTERPRETATION

TEXT: This responds to Todco's September 27, 1974, question whether Standard No. 121, Air brake systems, 49 CFR 571.121, requires a spring brake system on Todco's "Jifflox converter dolly." You describe the Jifflox dolly as a trailer converter dolly which may also be used as a "third axle attachment" on a two-axle truck.

Standard No. 121 applies to vehicles, and specifies separate requirements for trucks, buses, and trailers. It appears that the Jifflox is subject to separate requirements under the standard depending on its use.

If Todco manufactures (Illegible Word) sells the Jifflox for use as a "trailer converter dolly" (defined in 49 CFR 571.3 as a trailer equipped with one or more axles, a lower half of a fifth wheel, and a drawbar), it constitutes a vehicle subject to Standard No. 121. As such it is exempted from the parking brake system requirements (S5.6) and its emergency braking capability is not required to be applied by an emergency source, such as a spring brake, that is not affected by loss of air pressure or brake fluid pressure in the service brake system.

If a truck manufacturer utilizes the Jifflox as an additional axle in the suspension of its vehicle, the truck manufacturer must assure that the truck meets the requirements applicable to it with the Jifflox incorporated in it. This means that, if the truck is manufactured to accept the Jifflox dolly and the truck is rated for a gross vehicle weight rating that depends on inclusion of the axle, the truck must comply with all applicable requirements of the standard with the Jifflox attached. If the truck manufacturer determines that parking brakes are required on the Jifflox axle to meet S5.6.1 or S5.6.2, those parking brakes would have to be applied by an energy source that is not affected by loss of air pressure or brake fluid pressure in the service brake system.

Yours truly,

ATTACH.

September 27, 1974

Richard Dyson -- Chief Council, National Highway Traffic Safety Administration

Dear Mr. Dyson:

This is a second request regarding a ruling on the Jifflox Converter Dolly. This letter is in lieu of our first request of which our copy has been misplaced.

The Jifflox Converter Dolly has been manufactured, sold and licensed as a converter dolly. As stated in F.M.V.S.S.-121 paragraph S.5.8 a converter dolly need not have spring brakes. However, the Jifflox is unique in the fact that it can also be used as a third axle attachment.

In previous conversations with Mr. Sid Williams it has been his opinion that since the Jifflox is sold and licensed as a converter dolly it would be exempt from spring brakes. He reffered us to your office for an official ruling.

Since we deal directly with the truck manufacturers they are obviously concerned with this ruling. They have in fact requested from us an official ruling from your office.

I would think that since the Jifflox is sold throughout the United States, an ammendment to F.M.V.S.S.-121 would be in order. However an official ruling from your office in letter form would suffice.

Since we are a member of the T.T.M.A., I am forwarding a copy of this letter to Mr. Bert Weller, in hopes that research in this matter may be expedited.

If you have any questions regarding this matter, do not hesitate to contact me.

Sincerely

Frank L. Wigand, Eng. Dept. -- TODCO Division

cc: Joseph J. Cunha; Bert Weller

ID: nht94-2.3

TYPE: Interpretation-NHTSA

DATE: March 28, 1994

FROM: John Womack -- Acting Chief Counsel, NHTSA

TO: Richard Kreutziger -- Executive Director, New York State Bus Distributor Association, Inc.

TITLE: None

ATTACHMT: Attached to faxes dated 2/14/94 and 1/12/94 from Richard Kreutziger to Walter Myers (OCC 9559); Also attached to letter dated 2/20/87 from Erika Z. Jones to Martin V. Chauvin

TEXT:

This responds to your Fax of January 12, 1994, requesting an information on the extent to which a state can adopt requirements for school buses which exceed the Federal motor vehicle safety standards. This also responds to your FAX of February 14, 1994, requesting an explanation of the location requirements for a side emergency door exit in Standard No. 217, Bus Emergency Exits and Window Retention and Release (as amended at 57 FR 49413; November 2, 1992).

Your January 12, 1994 FAX requested clarification of when a state could impose requirements on school buses which exceeded the requirements of the Federal motor vehicle safety standards (FMVSS). Specifically, you asked whether the state could impose suc h requirements on (1) a public school and (2) a contractor providing transportation for a public school. Section 103(d) of the National Traffic and Motor Vehicle Safety Act (the Safety Act; 15 U.S.C. 1392(d)) provides that:

Whenever a Federal motor vehicle safety standard ... is in effect, no State or political subdivision of a State shall have any authority either to establish, or to continue in effect, with respect to any motor vehicle or item of motor vehicle equipment any safety standard applicable to the same aspect of performance of such vehicle or item of equipment which is not identical to the Federal standard. Nothing in this section shall be construed to prevent ... any State o r political subdivision thereof from establishing a safety requirement applicable to motor vehicles or motor vehicle equipment procured for its own use if such requirement imposes a higher standard than that required to comply with th e otherwise applicable Federal standard.

Section 103 (d) preempts state requirements for school buses covering the same aspect of performance as an applicable FMVSS that are different from the applicable FMVSS, except to the extent that the requirements impose a higher level of performance and apply only to vehicles procured for the State's use. A state law imposing higher requirements would be preempted under S103(d) to the extent that the law requires ALL school buses manufactured for use in the state to comply with the law. The law would n ot be preempted to the extent that it applies to public school buses. In addition, the agency has previously interpreted the phrase "vehicles procured for (the State's) own use" to include public school buses and school buses operated and owned by a pri vate contractor under contract to transport children to and from public school. See, for example, February 20, 1987 letter to Mr. Martin Chauvin (copy enclosed).

Your February 14, 1994 FAX asked whether the November 2 final rule permits a right side emergency exit door to be to the rear of the passenger compartment.

The answer is yes. Except for a left side emergency exit door installed as the first additional emergency exit on a bus with a rear emergency door, there are no fore and aft location requirements for side emergency exit doors. I have attached for your i nformation an appendix which lists all the location requirements for additional emergency exits.

I hope you find this information helpful. If you have any other questions, please contact us at this address or by phone at (202) 366-2992.

(Appendix omitted.)

ID: nht91-2.49

DATE: March 26, 1991

FROM: Paul Jackson Rice -- Chief Counsel, NHTSA

TO: Jessie M. Flautt

TITLE: None

ATTACHMT: Attached to letter from Jessie M. Flautt to Steven Kratzske (OCC 5813)

TEXT:

This responds to your letter to Mr. Steve Kratzke of my staff, requesting that the National Highway Traffic Safety Administration (NHTSA) grant permission to a repair business to modify your motor vehicle.

You explained that you are under five feet, two inches and legally blind in one eye. You further explained that, due to the increased size of headrests in recent years, you are unable to locate a 1991 automobile which does not have headrests which impede your field of vision. You wish to arrange to have the size of the headrests in a 1991 automobile reduced. You asked if you could obtain permission from this agency to permit this modification. I hope the following discussion explaining our regulation will be of assistance to you.

I would like to begin by clarifying that there is no procedure by which persons petition for and are granted permission from NHTSA to arrange to have a motor vehicle repair business modify their motor vehicle. Repair businesses are permitted to modify vehicles without obtaining permission from NHTSA to do so, but are subject to certain regulatory limits on the type of modifications they may make. In certain limited situations, we have exercised our discretion in enforcing our regulations to provide some allowances to a repair business which cannot conform to our regulations when making modifications to accommodate the special needs of persons with disabilities. Since your situation is among those given special consideration by NHTSA, this letter should provide you with the relief you seek.

Our agency is authorized to issue Federal Motor Vehicle Safety Standards (FMVSS) that set performance requirements for new motor vehicles and items of motor vehicle equipment. Manufacturers are required by the National Traffic and Motor Vehicle Safety Act (Safety Act) to certify that their products conform to our safety standards before they can be offered for sale. Manufacturers, distributors, dealers and repair businesses modifying certified vehicles are affected by S108(a)(2)(A) of the Safety Act. It prohibits those businesses from knowingly rendering inoperative any elements of design installed on a vehicle in compliance with a FMVSS. In general, S108(a)(2)(A) would require repair businesses which modify motor vehicles to ensure that they do not remove, disconnect or degrade the performance of safety equipment installed in compliance with an applicable safety standard. Violations of S108(a)(2)(A) are punishable by civil fines up to $1,000 per violation. In situations such as yours where a vehicle must be modified to accommodate the needs of a particular disability, we have been willing to consider any violation of S108(a)(2)(A) a purely technical one justified by public need. I can assure you that NHTSA would not institute

enforcement proceedings against a repair business that modifies the headrest on your vehicle to accommodate your condition. We caution, however, that only necessary modifications should be made to the headrest to accommodate your condition and we urge your dealer to modify your vehicle in such a manner that would not degrade from the safety currently provided by your vehicle. Many manufacturers are currently installing headrests in vehicles which exceed the minimum dimensions required by FMVSS No. 202, Head Restraints. I urge you not to have your headrest reduced below these dimensions if it is not necessary for your field of view.

If you have further questions or need some additional information in this area, please contact Mary Versailles of my staff at this address or by telephone at (202) 366-2992.

ID: nht76-4.27

DATE: 09/03/76

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: Freightliner Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your July 23, 1976, question whether the "no lockup" requirement of S5.3.1 of Standard No. 121, Air Brake Systems, requires wheel sensors on both axles of a tandem axle system in those cases where the "no lockup" performance is provided by means of an antilock system. Sections S5.3.1 (trucks and buses) and S5.3.2 (trailers) specify that the vehicle shall, under various load, road surface, and speed conditions, be capable of stopping

. . .without lockup of any wheel at speeds above 10 mph, except for:

(a) Controlled lockup of wheels allowed by an antilock system. . .

(b) * * * * *

This basic requirement is stated in performance terms, permitting a manufacturer to choose any brake system design that will ensure that the wheels do not lock up under the specified conditions.

The exception to the "no lockup" requirement set forth above permits "controlled lockup of wheels allowed by an antilock system." Manufacturers demonstrated, during the course of rulemaking, that properly functioning antilock systems might be designed to allow wheel lockup for a fraction of a second, and that antilock design should not be inhibited by a prohibition on all lockup. The agency made the "controlled lockup" exception a part of the standard (36 FR 3817, February 27, 1971) and has subsequently interpreted the term to permit manufacturers latitude in the design of their systems.

In compliance with the basic requirement, most manufacturers have equipped each axle of a vehicle with a valve to regulate the air pressure that applies the brakes, sensors at each wheel to send a signal when a wheel is locking up, and a logic module that receives the signals and instructs the valve when to release air pressure to prevent lockup ("axle-by-axle control"). Recently, some manufacturers have simplified their systems by utilizing only one valve and logic module to modulate the air supply to both axles of the typical tandem axle system found on many trucks and trailers ("tandem control"). Two approaches to wheel sensor placement have been used for tandem control systems. If it is possible to predict which of the two axles will lock first during braking, sensors may be placed on this axle only, knowing that reduced air pressure in response to a signal from the "sensed" axle will also release the brakes on the "unsensed" axle. In other cases, where it is not possible to predict which axle will lock first, tandem control systems may have sensors on all four wheels of the tandem.

In November 12, 1974, and March 7, 1975, letters of interpretation to Dana Corporation, the NHTSA confirmed that a manufacturer may choose the number of wheel speed sensors and logic modules that he includes in his antilock system. Thus, tandem control is not prohibited by the standard, regardless of the number of wheel speed sensors provided. When Dana asked if lockup on the unsensed axle of a single-axle sensor system would qualify for the "controlled lockup" exception of the requirement, the agency said that it would not, reasoning that the logic module would not exert effective control over the lockup of the unsensed axle without benefit of input signals from wheels on that axle. Therefore, according to the Dana interpretation, the unsensed axle in a single-axle sensor system could not be allowed to lock at all, even momentarily, during the service brake stopping test. No data of actual performance was submitted with the Dana letter.

Your letter argues that the NHTSA's interpretation of "controlled lockup" (to Dana Corporation) creates an anomalous and unjustified restriction on the use of "tandem control." Your submission, and data received by the agency from other interested persons, demonstrate that the Dana interpretation does not adequately reflect the degree of control which a single-axle sensor system actually can exert over the unsensed axle of a tandem system. Based on analysis of the submitted data, it appears that the amount of lockup permitted on unsensed axles is closely controlled by the permitted on unsensed axles is closely controlled by the available antilock systems. While there is a measurable difference in stopping performance between "axle-by-axle" control and "tandem control," the standard already permits either of these means to satisfy the requirements. When the narrower question of the performance difference between sensors on one or both axles is analyzed, it is apparent that virtually no difference exists in the stopping distance of vehicles equipped these two ways. The effective lateral stability available during a stop also appears comparable regardless of placement of sensors on one or both axles. A technical report summarizing these findings will be placed in the public docket as soon as possible.

For this reason, and based on review of test unavailable at the time of the Dana interpretation, the agency concludes that its interpretation of "controlled lockup" in response to the question posed by Dana should be, and is hereby, withdrawn. It is the agency's interpretation that the "controlled lockup" exception is not dependent on the number or location of sensors used in an antilock installation.

Sincerely,

ATTACH.

FREIGHTLINER CORPORATION

July 23, 1976

LEGAL COUNSEL -- National Highway Traffic Safety Administration

Re: Motor Vehicle Safety Standard No. 121 (49CFR571.121)

Dear Sir:

Freightliner Corporation, a manufacturer of light-weight heavy-duty air braked vehicles, is vitally affected by the requirements of FMVSS-121. Therefore, we are requesting a clarification of the exemption contained in S5.3.1, for "controlled lockup of wheels allowed by an antilock system." In reading the requirements of Standard No. 121, the exemption to the "no wheel lockup" requirement contained in S5.3.1 clearly applies to any wheel of a tractor, truck or bus which is subject to the control of an antilock system. But in a previous interpretation on this subject (March 7, 1975, letter of James C. Shultz to Harold D. Shall, Dana Corporation), the Acting Chief Cousel appeared to limit this exemption only to wheels which are equipped with antilock wheel speed sensors. Clearly, this interpretation is design restrictive in that it is stated in design rather than performance terms. Further, this interpretation does not take into consideration the possibility of alternate means for achieving controlled wheel lockup, such as mechanical drives which interlock both tandem axles.

The results of recent tests conducted by Freightliner show that the wheels on both tandem axles of a tandem axle vehicle can be effectively controlled through the use of one antilock system sensing wheel speeds from only one axle, and demonstrate that "controlled lockup" typical of that provided by axle-by-axle antilock systems can be achieved through a combination of suspension design, controlled brake actuation timing, and antileck system design. The test results (see attachment) indicate that the vehicle equipped with only one antilock controller meets the stopping distance requirements of FMVSS-121 with performance equivalent to that of vehicles equipped with the more complex and costly axle-by-axle antilock systems currently employed.

Since tractors and trucks, such as those manufactured by Freightliner Corporation, are subject to stopping distance requirements under a variety of road and load conditions, efficient utilization of available traction for braking is already a requirement of the standard for powered vehicles. Therefore, we believe that requiring the use of axle-by-axle antilock systems is unnecessary to ensure efficient utilization of available traction for braking of powered vehicles. Accordingly, we request interpretation of the requirements of S5.3.1 which is:

1. Stated in performance rather than design criteria.

2. Which does not impose a more strigent requirement for axles which are not equipped with wheel speed sensors (but subject to the control or an antilock system) than the "controlled lockup" requirement applicable to wheels which are equipped with wheel speed sensors.

If further information is necessary or desirable, we would be pleased make a technical presentation to you and appropriate members of the NHTSA staff, which would include a discussion of our test results along with movies of the tests.

Respectfully submitted,

Ray W. Murphy -- Director, Research and Development

Attach. FMVSS-121 STOPPING DISTANCE TEST DATA

Vehicle - Three Axle COE Tractor, 138" Wheelbase Control Axle Loads (lbs.) Steering Drive Trailer Loaded 10,480 34,110 33,290 Bob tail 7,550 6,040 -

Brakes Size Actuation Power Linings Steering Axle 15x4 14 degrees x9 ABB-551D Drive Axle 15x7 12 degrees x12 (Dual) ABB-551D

Average service brake stopping distances in ft., vehicle equipped with tandem control antilock system (numbers in parenthesis are values from tests of similarly configured vehicle equipped with axle-by-axle antilock control system)* Loaded Bobtail FMVSS-121 Requirement 20 MPH Dry Asphalt 33.6 27.6 35 (SN 75) Test Surface (34.0) (26.4) 60 MPH Dry Asphalt 259.8 251.2 293 (SN 75) Test Surface (253.7) (225.5) 20 MPH Wet Slippery 58.8 60.2 ** (SN 20) Test Surface (71.3) (57.3)

* Freightliner CTC Report No. T081-75/12, November 20, 1975

** 60 ft. on SN 30 test surface