ID: nht94-5.50

DATE: May 5, 1994

FROM: John Womack -- Acting Chief Counsel, NHTSA

TO: Tilman Spingler -- Robert Bosch GmbH

TITLE: None

ATTACHMT: Attached to letter dated 3/25/94 from Tilman Spingler to John Womack (OCC-9889)

TEXT:

This responds to your letter of March 25, 1994, asking for an interpretation of Motor Vehicle Safety Standard No. 108 with respect to integral beam headlighting systems.

You reference a letter of this office to Toyota in which we permit location of the light source control module outside the headlamp housing but permanently attached to it by a cable. You have asked whether there are "requirements for this cable concerning indivisibility and integration...."

There are no such requirements for the cable in Standard No. 108, and the headlamp manufacturer may adopt the construction that it has determined is most suitable for its design.

ID: nht94-5.6

TYPE: INTERPRETATION-NHTSA

DATE: December 9, 1994

FROM: Mr. R.E. Wareham -- Technical Director, Total Vehicle Security Ltd.

TO: J. Womack -- Acting Chief Council, NHTSA

TITLE: Re: Third Brake Light Conditions Sensor/SYNCRO LITE.

ATTACHMT: ATTACHED TO LETTER DATED 12/21/94 FROM PHILIP R. RECHT TO R. F. WAREHAM (A42; STD. 108); ALSO ATTACHED TO LETTER DATED 1/26/93 FROM JOHN WOMACK TO DAVID H. B. LEE

TEXT: I am writing to you with regards to discussions held between your office and Mr. David Lee of the Lee Family Corporation, together with correspondence on or around December 92 to January 93.

I am specifically wanting to re-confirm the status of your understanding with regards to the marketing and sale of this product into the US aftermarket. We have been granted the rights to distribute the product under our trade name of 'SYNCRO LITE' by t he Lee family and are wanting to commence a marketing campaign early in 95.

Specifically we intend to seek a 'licensee' who is able to drive sales of SYNCRO LITE through after market car accessory outlets, both via single and multiple 'chain store' outlets, the product will marketed as a D.I.Y. installation by the car owner.

We are intending to travel to Washington D C in late January 95 and would very much like the opportunity to meet with you or your associates in order to formalize our respective positions.

ID: nht94-5.7

TYPE: INTERPRETATION-NHTSA

DATE: December 12, 1994

FROM: Connie Mack -- U.S. Senate

TO: Department of Transportation, Intergovernmental & Consumer Affairs

TITLE: NONE

ATTACHMT: Attached to 1/17/95 letter from Philip R. Recht to Connie Mack (A43; Std. 109); Also related to 1/17/95 letter from Philip Recht to Bob Graham (A43; Std. 109); Also related to 12/15/94 letter from Bob Graham to John Womack

TEXT: Dear Sir:

Enclosed please find correspondence from my constituent.

I would appreciate your advising me of your action in this matter and returning the letter with your reply. Please respond to Helen Bina at my Fort Myers Regional Office, located at 1342 Colonial Boulevard, Suite 27, Fort Myers, Florida 33907, (813) 275-6252.

Thank you for your prompt attention.

Sincerely

ENCLOSURE 1:

December 5, 1994

The Honorable Connie Mack Constituent Service Center 1342 Colonial Blvd. Suite 27 Fort Meyers, FL 33907

Dear Senator Mack:

Thank You for your efforts on our behalf regarding the proposed bill before the Puerto Rican Senate regarding the importation of used tires. We have not as of yet received any response.

In these days of the NAFTA and G.A.T.T. Treaties this proposed bill seams like an attempt by the new tire manufactures for a restraint of trade that started in South America and has now spread to American Soil.

On November 3 we had written to the National Highway Traffic Safety Administration on the advise of the U.S. Department of Commerce but have not received a response as of today. We are trying to find out from them if Puerto Rico is under their jurisdict ion and what the laws are regarding tire tread depth.

With your help I am sure we will get the answers to our inquiries.

Sincerely,

Howard J. Levy -- Vice-President, USED TIRE INTERNATIONAL

enclosures

ENCLOSURE 2:

December 5, 1994

Dr. Ricardo Martinez Administrator National Highway Traffic Safety Administration 400 Seventh St. S.W. Washington, D.C. 20590

Dear Dr. Martinez:

On November 3, 1994 I wrote to you about the proposed bill before the Senate in Puerto Rico. As of this letter I have not heard from you or your agency. As I stated in my first letter to you this bills passage will mean the end of our industry in Puert o Rico.

WE NEED YOUR HELP IN THIS MATTER!!!!!

Would it also be possible for you to send a copy of the laws pertaining to tread depth in the U.S. and it's territories.

Sincerely,

Howard J. Levy Vice-President, USED TIRE INTERNATIONAL

ID: nht94-5.8

TYPE: INTERPRETATION-NHTSA

DATE: December 15, 1994

FROM: Bob Graham -- U.S. Senate

TO: John Womack -- Chief Council, Legislation Division, NHTSA

TITLE: NONE

ATTACHMT: Attached to 1/17/95 letter from Philip Recht to Bob Graham (A43; Std. 109); Also related to 1/17/95 letter from Philip Recht to Connie Mack (Std. 109; A43); Also related to 12/12/94 letter from Connie Mack to the DOT

TEXT: Dear Mr. Womack:

Enclosed is a letter from Mr. Howard Levy, who has concerns regarding guidelines used by states regarding tire tread requirements and whether they also apply to Puerto Rico.

I would appreciate your reviewing this situation and providing me with your comments. Please send your response to my state office: Post Office Box 3050, Tallahassee, Florida 32315, Attention: Sharon McLanahan.

I am grateful for your cooperation and assistance. I look forward to hearing from you soon.

With kind regards,

Sincerely

Enclosure 1:

December 6, 1994

The Honorable Bob Graham Post Office Box 3050 Tallahasse, FL 32315

Dear Senator Graham:

On October 6, 1994 I wrote to you about the proposed bill before the Senate in Puerto Rico, with the regards to the importation of used tires.

In these days of the N.F.T.A. and G.A.T.T. agreements it seams that the new tire manufacturers are pressing for a restraint of trade by pressing for the passage of this bill.

We have contacted the U.S. Department of Commerce they in turn have directed us to the National Highway Safety & Traffic Administration. We had written them on November 6, but as of today we have not gotten any response. We would like to get a copy of the laws regarding tire tread depth here in the U.S. and in Puerto Rico and we would like to know if they have jurisdiction in Puerto Rico. We need your help in getting this vital information.

If this bill passes it will surely mean the end of our industry in Puerto Rico

WE URGE YOUR HELP IN THIS MATTER!!!!

Sincerely,

Howard J. Levy Vice-President, Used Tire International

Enclosure 2:

November 3, 1994

DR. Ricardo Martinez Administrator National Highway Traffic Safety Administration 400 Seventh St. S.W. Washington, D.C. 20590

Dear Dr. Martinez:

Used Tire International, INC. is an Exporter of Quality Used Tires Worldwide. There is a very serious situation that has arisen in Puerto Rico in regards to the importation of Used Tires, a proposed bill is before the senate there that would require all Used Tires being imported to have a minimum 5/32" tread depth and a tax of $ 10.00 each. The tread depth of 5/32" is 3/32" more than the 2/32" that is required by U.S. law. Does the NHTSA have jurisdiction over these laws in Puerto Rico or does the Pue rto Rican Senate control the regulations over highway safety.

If this proposed Bill is passed this would mean the end of the Used Tire industry on the island. This is an industry that many people count on there because many people cannot afford to purchase new tire which I will add some new tires only have 4/32" t read. To inact a law that would require a Used Tire to have more or as much tread as a new tire would further hurt our industry.

WE URGE YOUR AGENCIES HELP IN THIS MATTER!!!!!

Sincerely,

Howard Levy Vice President

Enclosure 3:

10/28/94

Mr. Howard J. Levy Vice-President Used Tire International 837 S.E. 8th Ave., Suite 202 Deerfield Beach, FL 33441

Dear Mr. Levy: On behalf of Secretary Brown, I am pleased to respond to your letter regarding a proposed bill in Puerto Rico which would change tread depth regulations for selling used tires.

The U.S. Government agency responsible for developing guidelines used by states regarding tread requirements is the National Highway Traffic Safety Administration (NHTSA). The NHTSA would also be able to respond to your concerns regarding Puerto Rico. You may wish to contact directly the NHTSA:

Mr. Ricardo Martinez, M.D. Administrator National Highway Traffic Safety Administration (NHTSA) 400 Seventh Street, S.W. Washington, D.C. 20590 tel: (202) 366-1836

Thank you for your interest in this matter.

Sincerely,

Walter Bastian Director Office of Latin America and the Caribbean U.S. Dept. of Commerce

Enclosure 4:

December 5, 1994

Dr. Ricardo Martinez Administrator National Highway Traffic Safety Administration 400 Seventh St. S.W. Washington, D.C. 20590

Dear Dr. Martinez:

On November 3, 1994 I wrote to you about the proposed bill before the Senate in Puerto Rico. As of this letter I have not heard from you or your agency.

As I stated in my first letter to you this bills passage will mean the end of our industry in Puerto Rico.

WE NEED YOUR HELP IN THIS MATTER!!!!!

Would it also be possible for you to send a copy of the laws pertaining to tread depth in the U.S. and it's territories.

Sincerely,

Howard J. Levy Vice-President

ID: nht94-5.9

TYPE: INTERPRETATION-NHTSA

DATE: December 15, 1994

FROM: Gerard Bonvin -- Automobile Cheyenne USA, Inc

TO: Philip Recht -- Chief Council Office, NHTSA

TITLE: NONE

ATTACHMT: Attached to 2/2/95 letter from Philip R. Recht to Gerard Bonvin (A43; Part 555)

TEXT: Dear Mr. Recht

Automobile Cheyenne USA, INC, is a California corporation, and an affiliate of Automobile Cheyenne S.A. (France) a successful manufacturer of small passenger and utility Vehicles with a proven ten years track record.

Automobile Cheyenne's main product is the "Cheyenne", a small Jeep type, a lightweight, front-wheel drive utility vehicle which is stylish, reliable, very economical, and inexpensive. Automobile Cheyenne USA, has been formed for the purpose of distri bution in North America. Our preliminary schedule has our first year of production beginning July 1996.

After our brief conversation dated the December 14, I would like to take the opportunity to ask you questions about DOT regulations.

- What are the procedure to follow in order to be categorize Small Volume manufacturer?

- Is there really a big difference on the test in order to certified between small volume and over 10000 vehicles?

- Is there any difference between two seaters or four seaters on crash test?

- Is there a rear crash impact?

- Do we need Air Bags if we have Seat belts?

- Do we need a buzzer for the Seat Belt?

- Is the dashboard need to be padded?

- Is there any specific ways on how to install the windshield?

- What is the surface of the windshield that need to wiped?

- As far as Windshield Wipers, how many cycles and how many different speed?

I hope that these questions will not infringe on your time, and I would like to thank in advance for your help. I wish you a happy holidays.

Truly Yours

ID: nht94-6.1

DATE: May 5, 1994

FROM: John Womack -- Acting Chief Counsel, NHTSA

TO: Randolph Schwarz

TITLE: None

ATTACHMT: Attached to letter dated 9/30/93 Est. from Randolph Schwarz to John Messera (OCC-9211)

TEXT:

This responds to your letter to Mr. John Messera of NHTSA, requesting an interpretation of Federal Motor Vehicle Safety Standard No. 116; Motor vehicle brake fluids. Your letter has been referred to my office for a response. As a consumer retrofitting your vehicle with DOT 5 brake fluid, you had several questions concerning the possible effects that an ingredient in the brake fluid might have on elastomers used in brake systems. Your questions are answered below.

You described "seal swelling additives" added to DOT 5 brake fluid, that contact various elastomers in the brake system. Your first question was, when brake fluid manufacturers combine additives with brake fluid, should consumers be concerned with the combined fluids' compatibility with various elastomers used in braking systems?

Standard No. 116 defines, at S4. Definitions, brake fluid as a liquid designed for use in a motor vehicle hydraulic brake system where it will contact elastomeric components made of: styrene and butadiene rubber (SBR); ethylene and propylene rubber (EPR); polychlorophene (CR) brake hose inner tube stock; or natural rubber (NR). In order to minimize failures in hydraulic braking systems, Standard No. 116 specifies minimum performance standards for brake fluids. These performance standards include tests for styrene and butadiene rubber cups,the most common type of elastomer in a hydraulic brake system. The brake fluid manufacturer must certify that the brake fluid complies with Standard No. 116. (See S5.2.2(d).)

While DOT 5 brake fluid must meet Standard No. 116, the specific ingredients in the fluid are not regulated by the standard. However, in addition to compliance with Standard No. 116, brake fluid manufacturers must ensure that the fluid is free of safety-related defects under the National Traffic and Motor Vehicle Safety Act. Sections 151-159 of the Safety Act concern the recall and remedy of products with defects related to motor vehicle safety. In the event that the brake fluid manufacturer or NHTSA determines that the brake fluid contains a safety related defect, the brake fluid manufacturer would be responsible for notifying purchasers of the defective brake fluid and remedying the problem free of charge.

In your letter, you stated that you are retrofitting a vehicle with DOT 5 brake fluid. If your vehicle contained a brake fluid other than DOT 5 in its brake system, we recommend that the old fluid be flushed completely out of the brake system, before being replaced with DOT 5. This is necessary to ensure that the DOT 5 brake fluid does not mix with any other brake fluid type.

Your second question was whether DOT 5 brake fluid's compliance with

Standard No. 116 ensures compatibility with elastomers. The answer is yes, for SBR elastomers. Further, besides Standard No. 116, the brake fluid manufacturer is subject to sections 151-159 of the Safety Act, that were previously discussed. At this time, NHTSA is not aware of safety related defects resulting from other ingredients used with brake fluid.

Your third question was whether Standard No. 116 only addresses SBR compatibility with brake fluid. Standard No. 116, at S4, addresses brake fluid that contacts four elastomer types. However, the tests specified in the standard are only of the most commonly used SBR cups.

Your fourth question was, if Standard No. 116 only mentions SBR elastomer, would it be advisable to add other elastomers to the specification, or to discuss elastomer compatibility on the brake fluid container?

Information discussing the elastomer compatibility of the brake fluid, or other ingredients, may be voluntarily placed on brake fluid containers. Standard No. 116 specifies information that brake fluid containers must carry. However, Standard No. 116 does not prohibit manufacturers from noting on brake fluid containers, compatibility of the silicone brake fluid, or other ingredients, with various elastomers.

Finally, you asked what Standard No. 116 specifies as the maximum viscosity for DOT 5 brake fluid, at -40 degrees Fahrenheit. Standard No. 116 specifies, at S5.1.3 (o), that the maximum viscosity is 900 centistokes (cSt).

I hope that this information is helpful. If you have any further questions, please contact Dorothy Nakama of my staff at (202) 366-2992.

ID: nht94-6.10

DATE: April 26, 1994

FROM: John Womack -- Acting Chief Counsel, NHTSA

TO: Michael E. Klima -- Managing Engineer, Failure Analysis Associates, Inc.

TITLE: None

ATTACHMT: Attached to letter dated 3/29/94 from Michael E. Klima to Edward Jettner (OCC-9832)

TEXT:

This responds to your letter of March 29, 1994, to Mr. Edward Jettner of this agency concerning the dynamic testing requirements of Standard No. 208, Occupant Crash Protection. Your questions concern the application of this standard to a pickup truck manufactured in April 1988 with a gross vehicle weight rating (GVWR) of 4,400 pounds. You asked whether the injury criteria in S6 apply to this truck, whether a 35 mph fixed barrier crash test is required, and which sections of Standard No. 208 apply to this truck.

The safety belt installation requirements for all vehicle types are set forth in Standard No. 208. Section S4.2.1 of standard No. 208 gives vehicle manufacturers a choice of three options for providing occupant crash protection in trucks and multipurpose passenger vehicles with a GVWR of 10,000 pounds or less, manufactured on or after January 1, 1976 and before September 1, 1991. Option 1, set forth in S4.1.2.1, requires vehicle manufacturers to provide automatic protection at the front outboard seating positions, and either meet the lateral crash protection and rollover requirements by means of automatic protection systems or have manual safety belts at the front outboard seating positions such that those positions comply with the occupant protection requirements when occupants are protected by both the safety belts and the automatic protection. Option 2, set forth in S4.1.2.2, requires vehicle manufacturers to provide a lap or lap/shoulder safety belt at every seating position, have automatic protection for the front outboard seats, and have a warning system for the safety belts provided. Option 3, set forth in S4.1.2.3, requires the manufacturer to install lap or lap/shoulder safety belts at every seating position and to have a warning system for those belts.

According to your letter, the manufacturer installed Type 2 seat belt assemblies at the front outboard seating positions. This suggests that the manufacturer chose to comply with Option 3. Under this option, the only requirements in Standard No. 208 that those belts were required to comply with were S7.1, S7.2, and S7.3. The belts were also required to comply with the requirements of Standard No. 209, Seat Belt Assemblies. The manufacturer was not required to certify that the vehicle complied with the dynamic testing requirements of Standard No. 208. The injury criteria in S6 of the standard are applicable only to vehicles which must comply with the dynamic testing requirements.

Standards No. 208 does not include a 35 mph fixed barrier crash test requirement. The dynamic crash test in Standard No. 208 is barrier crash test at any speed up to 30 mph. NHTSA does perform some 35 mph barrier

crash tests as part of the New Car Assessment Program (NCAP). NCAP is a consumer information program, not a safety compliance test. NHTSA does not test every vehicle under this program. In the 1993 model year program, NHTSA tested 37 new vehicles and released results on 68 additional vehicles which had been tested previously and had not changed significantly in model year 1993.

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

ID: nht94-6.11

DATE: April 25, 1994

FROM: John Womack -- Acting Chief Counsel, NHTSA

TO: Richard Kreutziger -- Executive Director, New York State Bus Distributors Ass'n.

TITLE: None

ATTACHMT: Attached to letter dated 4/13/94 from Richard Kreutziger to John Womack (OCC-9865)

TEXT:

This responds to your request of April 13, 1994, for an interpretation of Motor Vehicle Safety Standard No. 108.

You reference paragraphs S5.5.7(a) and (b) which apply to vehicles of less than 80 inches overall width and ask whether there are similar requirements for wider vehicles.

Paragraph S5.5.7(a) requires that "(w)hen the parking lamps are activated, the tail lamps, license plate lamps, and side marker lamps shall also be activated." There is no similar requirement for vehicles whose overall width is 80 inches or more because these vehicles are not required to have parking lamps (see Table I of Standard No. 108).

Paragraph S5.5.7(b) requires that "(w)hen the headlamps are activated in a steady-burning state, the tail lamps, parking lamps, license plate lamps and side marker lamps shall also be activated." Paragraph S5.5.3 requires tail lamps on all vehicles, regardless of width, to be activated when the headlamps are activated in a steady burning state. As noted in the preceding paragraph, wide vehicles are not required to have parking lamps.

This leaves the question of license plate lamps and side marker lamps. As you have surmised, there is no specific requirement in Standard No. 108 that these lamps be simultaneously activated with the headlamps on vehicles whose overall width is 80 inches or greater. However, we understand that it is industry practice to wire its large vehicles in this manner. We also believe that those who do not wire the side marker lamps to operate with the headlamps include them in the separate switch that activates the clearance and identification lamps.

ID: nht94-6.12

DATE: April 25, 1994

FROM: John Womack -- Acting Chief Counsel, NHTSA

TO: Christopher S. Spencer -- Engineering

TITLE: None

ATTACHMT: Attached to letter dated 9/8/93 from Christopher S. Spencer to R. C. Carter (OCC-9128)

TEXT:

This responds to your letter about the brake reservoir requirements of Federal Motor Vehicle Safety Standard No. 121, Air Brake Systems (49 CFR S571.121). I apologize for the delay in our response. You stated that you are developing a new reservoir design to improve reservoir volume without increasing the need for space. You asked how to test your reservoirs since you believe that "(t)he safety standard does not clarify the test criteria specifically how the reservoir is to be sealed."

By way of background information, the National Highway Traffic Safety Administration does not provide approvals of motor vehicles or motor vehicle equipment. Under the National Traffic and Motor Vehicle Safety Act, it is the responsibility of the manufacturer to ensure that its vehicles and equipment meet applicable requirements. The following represents our opinion based on the facts provided in your letter.

Standard No. 121 establishes performance and equipment requirements for braking systems on vehicles equipped with air brakes. The Standard's reservoir requirements for trucks and buses are set forth in section S5.1.2. That section requires these vehicles to be equipped with one or more service reservoir systems that meet specified performance requirements. Section S5.1.2.2 specifies the following:

Each reservoir shall be capable of withstanding an internal hydrostatic pressure of five times the compressor cutout pressure or 500 psi, whichever is greater, for 10 minutes.

The purpose of this requirement is to ensure that an air brake system reservoir has a minimum level of structural integrity. NHTSA has long interpreted the term "withstand" to require that there be no rupture or permanent circumferential deformation of the reservoir exceeding one percent. At one point, the agency issued an interpretation concluding that the term "withstand" meant that a reservoir can deform only slightly and must contain the applied pressure with only a limited pressure drop at any time during the test. However, NHTSA later withdrew that interpretation because it inadvertently increased the severity of the requirement. See 42 FR 64630, December 27, 1977, and 43 FR 9149, March 6, 1978.

You asked about this requirement in connection with a reservoir design that includes a bushing on the inside of an endcap. A weld is placed around the bushing. You describe two different procedures you have used to seal the reservoir.

In what you describe as "Test Criteria 1," a socket head plug is put into

the bushing with 3 full wraps of tape. With this first method, you state that as the pressure is applied to the reservoir, the endcap starts to expand out. The bushing stretches with the endcap, and as the bushing stretches the threads are pulled away from the plug. The plug must therefore be retightened several times before the required pressure is reached. In your "Test Criteria 2," you state that a rubber grommet or washer is placed on the inside of the bushing and forced to expand to seal the bushings from the inside. You stated that this method checks the weld but removes the threads from the test. With the second method, you state that there was no failure at over five times the working pressure.

While Standard No. 121 does not specify a particular test procedure for this requirement, the language of S5.1.2.2 makes it clear that a reservoir must "withstand" for 10 minutes a condition where the reservoir is pressurized at the specified level. Therefore, in conducting a compliance test, NHTSA would pressurize a reservoir to the specified level. This would necessitate sealing the reservoir.

In considering how a particular reservoir would be sealed, it is important to bear in mind that the purpose of the test is to evaluate the reservoir's structural integrity and ability to withstand pressurization. I can offer you the following comments on the two alternative test methods you described. The first method (Test Criteria 1) would appear to evaluate a reservoir's ability to withstand pressurization. The threaded plug would appear to reasonably approximate how the reservoir would be sealed in an actual use situation. I note that the mere fact that the plug needs to be tightened during the test to achieve the specified level of pressure would not indicate a failure but would simply reflect minor air leakage around the plug.

The second method (Test Criteria 2) would not fully evaluate a reservoir's ability to withstand pressurization, since it would, as you recognized, remove the threads from the test, thereby creating an artificial seal. It is our opinion that a reservoir would not be capable of "withstanding" the specified hydrostatic internal pressure if the threads failed under such pressurization. This would represent a structural failure equivalent to a rupture.

I hope this information is helpful. If you have any questions about NHTSA's safety standards, please feel free to contact Marvin Shaw at this address or by telephone at (202) 366-2992.

ID: nht94-6.13

DATE: April 25, 1994

FROM: John Womack -- Acting Chief Counsel, NHTSA

TO: Ken Simons -- Esq.

TITLE: None

ATTACHMT: Attached to letter dated 6/25/93 from Kenneth P. Simons to Department of Transportation, Trucking Division (OCC-8877)

TEXT:

This responds to your letter asking about brake requirements for trailers used in tractor trailer combinations. I apologize for the delay in our response. You asked whether all such trailers are required to be equipped with "maxi" brakes on one or both axles. You state that a "maxi" brake is found on all road tractors and "sets the brakes automatically when the air pressure gets down to a minimum level." Please note that the term "maxi" brakes ordinarily refers to spring brakes used in parking and emergency brake applications. I further note that most, but not all, trailers are equipped with spring brakes. I am pleased to have this opportunity to explain our requirements.

By way of background information, under the National Traffic and Motor Vehicle Safety Act ("Safety Act," 15 U.S.C. S1392), the National Highway Traffic Safety Administration (NHTSA) is authorized to issue Federal motor vehicle safety standards applicable to new motor vehicles and items of motor vehicle equipment. NHTSA does not approve vehicles or equipment. Instead, manufacturers are required to certify that their vehicles or equipment meet all applicable standards.

Standard No. 121, Air Brake Systems (49 CFR S571.121, copy enclosed), specifies performance requirements for trucks, buses and trailers equipped with air brake systems. The purpose of the standard is to insure safe braking performance of vehicle under normal and emergency conditions.

While Standard No. 121 does not require manufacturers to use spring brakes or any other particular type of brake system, many manufacturers use spring brakes to comply with the standard's requirements concerning parking brake performance (truck, buses and trailers; see S5.6), emergency brake performance (trucks and buses only; see S5.7), and trailer pneumatic system failure performance (see S5.8). I note that while the requirements of S5.65 and S5.8 apply to most air-braked trailers, S3 of Standard No. 121 excludes some trailers from all of the standard's requirements. In addition, S5.6 and S5.8 specify alternative requirements for some trailers.

I hope this information is helpful. If you have any further questions about NHTSA's safety standards, please feel free to contact Marvin Shaw of my staff at this address or by telephone at (202) 366-2992.