NHTSA Interpretation File Search
Overview
NHTSA's Chief Counsel interprets the statutes that the agency administers and the standards and regulations that it issues. Members of the public may submit requests for interpretation, and the Chief Counsel will respond with a letter of interpretation. These interpretation letters look at the particular facts presented in the question and explain the agency’s opinion on how the law applies given those facts. These letters of interpretation are guidance documents. They do not have the force and effect of law and are not meant to bind the public in any way. They are intended only to provide information to the public regarding existing requirements under the law or agency policies.
Understanding NHTSA’s Online Interpretation Files
NHTSA makes its letters of interpretation available to the public on this webpage.
An interpretation letter represents the opinion of the Chief Counsel based on the facts of individual cases at the time the letter was written. While these letters may be helpful in determining how the agency might answer a question that another person has if that question is similar to a previously considered question, do not assume that a prior interpretation will necessarily apply to your situation.
- Your facts may be sufficiently different from those presented in prior interpretations, such that the agency's answer to you might be different from the answer in the prior interpretation letter;
- Your situation may be completely new to the agency and not addressed in an existing interpretation letter;
- The agency's safety standards or regulations may have changed since the prior interpretation letter was written so that the agency's prior interpretation no longer applies; or
- Some combination of the above, or other, factors.
Searching NHTSA’s Online Interpretation Files
Before beginning a search, it’s important to understand how this online search works. Below we provide some examples of searches you can run. In some cases, the search results may include words similar to what you searched because it utilizes a fuzzy search algorithm.
Single word search
Example: car
Result: Any document containing that word.
Multiple word search
Example: car seat requirements
Result: Any document containing any of these words.
Connector word search
Example: car AND seat AND requirements
Result: Any document containing all of these words.
Note: Search operators such as AND or OR must be in all capital letters.
Phrase in double quotes
Example: "headlamp function"
Result: Any document with that phrase.
Conjunctive search
Example: functionally AND minima
Result: Any document with both of those words.
Wildcard
Example: headl*
Result: Any document with a word beginning with those letters (e.g., headlamp, headlight, headlamps).
Example: no*compl*
Result: Any document beginning with the letters “no” followed by the letters “compl” (e.g., noncompliance, non-complying).
Not
Example: headlamp NOT crash
Result: Any document containing the word “headlamp” and not the word “crash.”
Complex searches
You can combine search operators to write more targeted searches.
Note: The database does not currently support phrase searches with wildcards (e.g., “make* inoperative”).
Example: Headl* AND (supplement* OR auxiliary OR impair*)
Result: Any document containing words that are variants of “headlamp” (headlamp, headlights, etc.) and also containing a variant of “supplement” (supplement, supplemental, etc.) or “impair” (impair, impairment, etc.) or the word “auxiliary.”
Search Tool
NHTSA's Interpretation Files Search
| Interpretations | Date |
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ID: aiam1499OpenMr. E.J. Wagner, Manager, Director, American Retreaders' Assoc., Inc., P.O. Box 17203, Louisville, Kentucky 40217; Mr. E.J. Wagner Manager Director American Retreaders' Assoc. Inc. P.O. Box 17203 Louisville Kentucky 40217; Dear Mr. Wagner: This is in reply to your letters of April 7 and April 8, 1974 regarding Standard No. 117, 'Retreaded Pneumatic Tires.' Your April 7 letter asks whether Standard No. 117 requires treadwear indicators to be straight across the tread face. Your letter of April 8 encloses two sample rubber labels and asks whether each conforms to the requirements of S6.3 of Standard No. 117.; Paragraph S5.1.1(b) of Standard No. 117 does not specify configuration for treadwear indicators. Rather, it incorporates by reference the requirements for treadwear indicators of S4.2.1(d) of Standard No. 109, which calls only for a treadwear indicator that provides a 'visual indication that the tire has worn to a tread depth of 1/16 inch.' We do not construe this language to require a straight-across treadwear indicator and other configurations are therefore permitted.; With respect to the labeled you enclose in your letter of April 8, eac would conform to all of the requirements of S6.3 (which includes the requirements for both affixed (S6.3.1) and permanent (S6.3.2) labeling) if the tires to which they are affixed are of neither bias-belted or radial construction. If they are of either of these construction types, that information would have to be retention of the original casing labeling.; Yours truly, Richard B. Dyson, Assistant Chief Counsel |
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ID: aiam4361OpenMr. Thomas Baloga, Safety Engineering, Mercedes-Benz of North America, Inc., P. O. Box 350, Montvale, NJ 07645; Mr. Thomas Baloga Safety Engineering Mercedes-Benz of North America Inc. P. O. Box 350 Montvale NJ 07645; Dear Mr. Baloga: Thank you for your letter of May 12, 1987, to Stephen Oesch of my staf concerning the requirements of Standard No. 208, *Occupant Crash Protection.* You asked the agency to confirm that the 36 millisecond time interval be used in the calculation of the head injury criterion (HIC) applies both to the Part 572, Subpart B test dummy and to the Subpart E test dummy. This is to confirm that the 36 millisecond time interval should be uSed in the calculation of a HIC for both types of test dummies.; On October 17, 1986 (51 FR 37028), NHTSA published a final rule in th Federal Register amending Safety Standard No. 208, *Occupant Crash Protection*. One of the amendments modified the manner in which a HIC is calculated in the crash testing required by the standard. That amendment referred to S6.2 as the provision of the standard containing the HIC requirement. Instead, the notice should have amended S6.1.2, which sets out the HIC calculation for the Part 572, Subpart B test dummy, and S6.2.2, which sets out the HIC calculation to be used with the new Part 572, Subpart E test dummy. The agency will publish an amendment to adopt the necessary changes to S6.1.2 and S6.2.2 to make clear that the change to the calculation of the HIC criterion affects those two provisions.; If you need further information, please let me know. Sincerely, Erika Z. Jones, Chief Counsel |
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ID: aiam1163OpenMr. R. W. Harvey, Peterbilt Motor Truck Co., 300 Toland Street, San Francisco, CA 94124; Mr. R. W. Harvey Peterbilt Motor Truck Co. 300 Toland Street San Francisco CA 94124; Dear Mr. Harvey: This is in reply to your letter of May 22, 1973, in which you state yo are a distributor of Peterbilt trucks and ask whether certain operations you perform subject you to Federal requirements. These operations are modifications to air brake systems and the installation of used bodies on new truck chassis.; A company whose business includes the installation of used bodies o new truck chassis is a manufacturer under the National Traffic and Motor Vehicle Safety Act and, as such, has certain responsibilities under the Act and regulations issued by this agency. In response to your question regarding registration, you are required pursuant to NHTSA 'Manufacturers' Identification' regulations (49 CFR Part 566) to submit to the agency information regarding the manufacturing operations of your company and the types of vehicles that it manufacturers.; A manufacturer is also required, pursuant to NHTSA 'Certification regulations (49 CFR Part 567, 568) to ascertain and certify the conformity of each vehicle he manufacturers to applicable motor vehicle safety standards. Under these regulations the person who completes the vehicle (the 'final-stage manufacturer') is required to affix to the vehicle a label that contains the certification that the vehicle conforms to applicable standards, as well as other information. Our experience has been that most manufacturers who install truck bodies onto new chassis are final-stage manufacturers, who must affix this label. Persons whose manufacturing operations precede that of the final-stage manufacturer are required to provide documentation with the vehicle that indicates what steps will be necessary in order to bring the vehicle into conformity with applicable standards. You also ask if there are requirements for the making of periodic reports. NHTSA 'Defect Reports' regulations (49 CFR S 573.5(b)) do require manufacturers to furnish the NHTSA with quarterly production figures.; The other operation you describe is the modification of vehicle ai brake systems, including changes in valves, lines, spring brakes, air tanks, etc. If you merely modify an existing air brake system, there are presently no certification or reporting requirements applicable to you. The NHTSA has just issued certification requirements for persons who alter completed vehicles, and depending on the extent of the modification you perform, these requirements may apply to you. They are effective February 1, 1974. All trucks manufactured after September 1, 1974, that are manufactured with air brakes will be required to conform to requirements specified in Federal Motor Vehicle Safety Standard No. 121. The law would not allow you to modify the air brake system of any truck manufactured on or after that date, before the sale of the truck to a purchaser for a purpose other than resale (a user), if the modification you performed would cause the vehicle to no longer comply with the standard.; I have only summarized the requirements that, based on the facts yo have provided, would be applicable to you. Your responsibilities are stated specifically in the regulations we have referred to, and you may obtain copies of these requirements as indicated on the enclosed, 'Where to Obtain Motor Vehicle Safety Standards and Regulations.'; Yours truly, Richard B. Dyson, Assistant Chief Counsel |
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ID: aiam5659OpenJeffrey S. Bakst, Esq. Attorney at Law 2406 Auburn Avenue Cincinnati, OH 45219-2702; Jeffrey S. Bakst Esq. Attorney at Law 2406 Auburn Avenue Cincinnati OH 45219-2702; "Dear Mr. Bakst: This responds to your request for the views of th National Highway Traffic Safety Administration (NHTSA) on two questions related to litigation in which you are currently involved, that refer to Federal Motor Vehicle Safety Standard No. 124, Accelerator control systems. The two questions and our responses are set out below. You advise us that you are 'dealing with a 1988 Dodge Ram 50 truck manufactured by Mitsubishi in Japan, sold in July, 1988.' You informed Dorothy Nakama of my staff that in December 1990, your client was injured while driving the Dodge Ram truck. You further informed Ms. Nakama that our October 26, 1995 interpretation letter to Hugh Bode, Esq. addressed Mr. Bode's questions stemming from the same accident and lawsuit as yours. Question 1. If the manufacturer discovers a safety-related problem after the vehicle has been sold to the first purchaser in good faith, does the manufacturer have a legal duty to notify NHTSA and/or the purchaser of this problem? If yes, what must a manufacturer do for the purchaser? The answer to the first part of this question is yes. Pursuant to 49 U.S.C. 30118(c): A manufacturer of a motor vehicle . . . shall notify NHTSA by certified mail, and the owners, purchasers, and dealers of the vehicle . . . if the manufacturer -- (1) learns the vehicle contains a defect and decides in good faith that the defect is related to motor vehicle safety . . . Under 49 U.S.C. 30120, where such notification is required, the manufacturer 'shall remedy the defect . . . without charge when the vehicle is presented for remedy.' The vehicle manufacturer may choose to remedy the defect by repairing the vehicle, replacing it with an identical or reasonably equivalent vehicle, or refunding the purchase price, less a reasonable allowance for depreciation. The requirement that the remedy be provided without charge does not apply if the vehicle was bought by the first purchaser more than eight years prior to the manufacturer's defect determination. Question 2. Assume there is a safety-related defect in a brand new carburetor that results in engine overspeed. If the 'two sources of energy' are not sufficient to return the throttle to idle position when the driver removes the actuating force from the accelerator control in use, does the carburetor fail to comply with FMVSS 124? The relevant portion of FMVSS No. 124 (S5.1) provides as follows: There shall be at least two sources of energy capable of returning the throttle to the idle position within the time limit specified by S5.3 from any accelerator position or speed whenever the driver removes the opposing actuating force. In the event of failure of one source of energy by a single severance or disconnection, the throttle shall return to the idle position within the time limits specified by S5.3, from any accelerator position or speed whenever the driver removes the opposing actuating force. Under the standard, with either energy source severed or disconnected, the standard requires that the remaining energy source return the throttle to the idle position within the specified time from any accelerator position or speed whenever the driver removes the opposing actuating force. NHTSA's Office of Vehicle Safety Compliance, (at (202) 366-2832), is the office within NHTSA which has the authority to investigate whether there is a noncompliance with the Federal Motor Vehicle Safety Standards. We are not in a position to render an opinion as to whether the facts you describe indicate the existence of a safety-related defect. For your information, I am enclosing a copy of our October 26, 1995 letter to Hugh J. Bode, Esq. If you have any further questions, please contact Dorothy Nakama of my staff at this address or at (202) 366-2992. Sincerely, Samuel J. Dubbin Chief Counsel Enclosure"; |
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ID: aiam2466OpenMr. William G. Mathews, III, Vice President, Universal Imports, 14622 Southlawn Lane, Rockville, Maryland 20850; Mr. William G. Mathews III Vice President Universal Imports 14622 Southlawn Lane Rockville Maryland 20850; Dear Mr. Mathews: #This is in reply to your November 5, 1976, lette concerning antique tires. You have asked whether it is permissible to import 6.70 x 15 tires, an original equipment size on several classic Mercedes-Benz, that are not marked in accordance with Federal Motor Vehicle Safety Standard No. 109, *New Pneumatic Tires*. #Standard No. 109 applies to 'new pneumatic tires for use on passenger cars manufactured after 1948' (S2). The 6.70 x 15 tire size designation appears in Table I-A of Appendix A of the standard. While this tire may have been original equipment on several classic cars, it is also for use on passenger cars manufactured since 1948. As such, it is subject to all the requirements of Standard No. 109. Therefore, a 6.70 x 15 tire that is not marked according to the standard may not be imported into the United States. #Sincerely, Frank A. Berndt,Acting Chief Counsel; |
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ID: aiam5209OpenMr. Dale Moore, CIC Hagan Hamilton Insurance and Financial Services 448 South Baker Post Office Box 847 McMinnville, OR 97128; Mr. Dale Moore CIC Hagan Hamilton Insurance and Financial Services 448 South Baker Post Office Box 847 McMinnville OR 97128; "Dear Mr. Moore: This responds to your letter addressed to Walter Myer of this office in which you asked whether 15-passenger vans used by Linfield College to transport high school-age students to the college must comply with the Federal motor vehicle safety standards applicable to school buses. You explained in your letter and its enclosure that Linfield College sponsors an 'Upward Bound' program, in which selected high school-age students from disadvantaged families are transported to the college campus for academic tutoring and other activities, including field trips, counseling, etc. You have been advised that the college's 15-passenger vans 'may have to meet federal requirements in order to be leased or purchased from an automobile dealer.' Let me begin by stating that the National Highway Traffic Safety Administration's (NHTSA's) requirements for new school buses regulate the manufacture and sale or lease of new vehicles used for transporting students. The Federal requirements do not, however, regulate what bus may be used for particular student transportation purposes. The requirements that apply to the use of school vehicles are set by the State. Thus, if there are regulations about what buses an Oregon college must use to transport Oregon high school students, such regulations are administered by the State of Oregon, not the Federal government. Some background information on our requirements might be helpful to your inquiry. The National Traffic and Motor Vehicle Safety Act, 15 U.S.C. 1381 to 1431, as amended (Safety Act) authorizes NHTSA to issue Federal motor vehicle safety standards (FMVSSs) applicable to the manufacture and sale of new motor vehicles, including school buses. The Safety Act defines a school bus as 'a passenger motor vehicle which is designed to carry more than 10 passengers in addition to the driver, and which . . . is likely to be significantly used for the purpose of transporting primary, preprimary, or secondary school students to or from such schools or events related to such schools.' It is a violation of the Safety Act for any person to sell or lease any new motor vehicle as a school bus that does not comply with all Federal school bus safety standards. It is not a violation of Federal law, however, to sell any noncomplying used vehicle as a school bus, even if the seller knows the vehicle will be significantly used as a school bus. Similarly, it is not a violation of Federal law to use a noncomplying vehicle to transport school children. As noted above, that is because individual states, not the Federal government, regulate the use of motor vehicles. In the situation described in your letter, several issues must be addressed to determine whether the vans are subject to our school bus safety standards. The first issue is whether the vans are 'buses.' Since the vans are designed to carry more than 10 persons, the answer to that question is yes. The second issue is whether Upward Bound activities are considered 'school related events.' Although Oregon may have a specific definition of 'school related event' for the purpose of determining whether Linfield College must use certified school buses, with regard to Federal law, we conclude the answer is yes. That is, if a new bus were sold or leased to the college, we would consider the new vehicle as being sold or leased for a school related event. The goal of Upward Bound is to prepare the participating students for post- secondary education. That is also, of course, one of the goals of the secondary schools in the program. Your enclosure states that Upward Bound staff 'visit each high school on a weekly basis doing counseling and follow-up work with each student.' These regular ongoing visits could not happen without the cooperation of the secondary schools in the program. Accordingly, it appears to us that the Upward Bound program is an 'event related to' the secondary schools concerned, within the meaning of the Safety Act. The final issue is whether transporting Upward Bound students constitutes a significant use for the vans. Linfield College need not purchase certified new school buses for its general purpose vehicles, even though such vehicles may be used occasionally to transport Upward Bound students. On the other hand, if Linfield College purchases or leases the vans knowing that they will be significantly used to transport Upward Bound students, the seller who knows of such anticipated use must sell only properly certified school buses. For information regarding state requirements on the use of school buses, you may contact Mr. Donald Forbes, 135 Transportation Building, Salem, OR 97310, telephone (503) 378-6388. I hope this information is helpful to you. Sincerely, John Womack Acting Chief Counsel"; |
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ID: aiam2036OpenMr. R.W. Hildebrandt, Group Director of Engineering, The Bendix Corporation, 901 Cleveland Street, Elyria, Ohio 44035; Mr. R.W. Hildebrandt Group Director of Engineering The Bendix Corporation 901 Cleveland Street Elyria Ohio 44035; Dear Mr. Hildebrandt: #This responds to your letter of July 14, 1975 requesting an interpretation of the labeling requirements of Federal Motor Vehicle Safety Standard No. 106-74, *Brake Hoses*, as applied to brake hose end fittings. #S5.2.3 of the standard requires (with an exception not relevant here) that one component of a multi-piece end fitting be labeled with certain information. You have pointed out that many end fittings designated for use with nylon brake hose include components identical to those found in fittings used with copper tubing, which is not covered by the standard. Labeling of one of these common components would satisfy the standard. You have interpreted Standard No. 106-74 as permitting an end fitting manufacturer to label his full stock of such components, even though some of them would appear in copper tubing assemblies. Your interpretation is correct. #Sincerely, Frank A. Berndt, Acting Chief Counsel; |
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ID: aiam4048OpenMr. William Frank Mitchell, 4228 Floyd Road, Austell, GA 30001; Mr. William Frank Mitchell 4228 Floyd Road Austell GA 30001; Dear Mr. Mitchell: This is in response to your letter of February 5, 1986, concernin Federal odometer disclosure requirements.; In 1972, Congress enacted Title IV of the Motor Vehicle Information an Cost Savings Act, 15 U.S.C. SS 1981-1991, seeking to eliminate odometer tampering and to establish certain safeguards for the protection of motor vehicle purchasers. This law is applicable in all fifty states, the District of Columbia, Puerto Rico, Guam, the Virgin Islands, the Canal Zone and American Samoa.; Section 1988(a) of the Act requires the Secretary of Transportation t prescribe rules relating to written odometer disclosures. These powers have been delegated to the National Highway Traffic Safety Administration (NHTSA). 49 C.F.R. S 1.50(f). To carry out the Congressional mandate, this Agency promulgated rules for the disclosure of odometer information, 49 C.F.R. S 580.4, and specified the form to be filled out by transferors of motor vehicles, 49 C.F.R. S 580.6. In addition, NHTSA exempted transferors of certain vehicles from the disclosure requirements. 49 C.F.R. S 580.5.; The portion of the regulation you question, 49 C.F.R. S 580.5(a)(1) exempts the transferors of motor vehicles having a gross vehicle weight rating (GVWR) of more than 16,000 pounds from the odometer disclosure requirements. The phrase 'gross vehicle weight rating' is defined as 'the value specified by the manufacturer as the loaded weight of a single vehicle.' 49 C.F.R. S 571.3.; In explaining the exemption for heavier vehicles, NHTSA stated: >>>A new section, 49 C.F.R. S 580.5, has been added in response to number of comments that objected to the application of the requirements to categories of vehicles for which the odometer is not used as a guide to value. Buses and large trucks, for example, are routinely driven hundreds of thousands of miles, and their maintenance records have traditionally been relied on by buyers as the principal guide to their condition. The NHTSA is in agreement with the position taken by Freightliner Corp. , White Motor Corp. , and the National Association of Motor Bus Operators, and has therefore created an exemption for larger vehicles. The exemption applies to vehicles having gross weight ratings of more than 16,000 pounds.<<<; 38 *Federal Register* 2978 (1973) While some courts have determined that NHTSA's authority to creat exemptions may be limited, we believe that NHTSA has the authority to create exemptions for transfers of vehicles for which the odometer reading is not relied upon as an indicator of vehicle mileage or condition. Consequently, the exemption remains a part of the odometer disclosure regulations.; Sincerely, Kathleen DeMeter, Assistant Chief Counsel for General Law |
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ID: aiam3277OpenHonorable Samuel S. Stratton, House of Representatives, Washington, D.C. 20515; Honorable Samuel S. Stratton House of Representatives Washington D.C. 20515; Dear Mr. Stratton: This responds to your recent correspondence requesting information o behalf of the Schenectady County Traffic Safety Board. The Safety Board is concerned that many new or converted propane-powered vehicles carry no identification indicating that the vehicles contain propane fuel instead of gasoline. The Safety Board states that this creates a dangerous situation for firemen, policemen or other emergency personnel who respond to accidents involving propane-powered vehicles. You were asked to initiate legislative action to require such identification on these vehicles.; The National Highway Traffic Safety Administration issues safet standards and regulations governing the manufacture of new motor vehicles and motor vehicle equipment. Therefore, if there were a demonstrated safety need for identification on propane vehicles, the agency would have authority under the National Traffic and Motor Vehicle Safety Act (15 U.S.C. 1381, *et seq*.) to require a label or tag as was suggested by the Safety Board. Please inform the Safety Board that it should petition the agency to initiate rulemaking action to establish such a requirement if it has information or evidence indicating that a safety problem does indeed exist. I have enclosed a copy of the regulation which explains what must be included in a Petition for Rulemaking.; The agency has no authority under the Vehicle Safety Act to regulat used motor vehicles and, therefore, could not require an identification label on a used vehicle that is converted to propane fuel. Congress left this jurisdiction to the individual States. Consequently, Congressional action or action at the State level would be required to mandate identification labels on used vehicles.; I am also enclosing a copy of a letter of interpretation the agenc issued last August which discusses the implications under Federal law of installing auxiliary fuel tanks in motor vehicles and of converting vehicles to the use of propane gas. Although not directly related to the Safety Board's concern, it might be of interest.; I hope this has been responsive to your inquiry. If you have an further questions, please contact Hugh Oates of my staff at 2020-426-2992.; Sincerely, Frank Berndt, Chief Counsel |
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ID: aiam4418OpenMr. Gary W. Rossow, Director, Government Technical Affairs, Mercedes-Benz Truck Company, Inc., 4747 N. Channel, P.O. Box 3849, Portland, OR 97208; Mr. Gary W. Rossow Director Government Technical Affairs Mercedes-Benz Truck Company Inc. 4747 N. Channel P.O. Box 3849 Portland OR 97208; Dear Mr. Rossow: This responds to your request for an interpretation of Federal Moto Vehicle Safety Standard No. 121, *Air Brake Systems*. Section S6.2.1 of that standard specifies for certain tests conducted on a dynamometer that '(t)he dynamometer inertia for each wheel is equivalent to the load on the wheel with the axle loaded to its gross axle weight rating.' According to your letter, you have interpreted the term 'equivalent' in this section to 'authorize compliance testing by reference to axle loads under actual stopping conditions.' You requested confirmation of this interpretation. As discussed below, we disagree with your suggested interpretation.; By way of background information, the National Highway Traffic Safet Administration (NHTSA) 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 or equipment comply with all applicable standards. The following represents our opinion based on the facts provided in your letter.; As indicated in your letter, your request for an interpretation wa submitted in light of recent correspondence between your company and NHTSA's Office of Vehicle Safety Compliance (OVSC). OVSC requested you to submit information on the compliance with Standard No. 121 of the Mercedes-Benz model L-1317, a two axle straight truck. You responded to that request by submitting a compliance certification and interpretation concerning section S6.2.1. In letter dated April 9, 1987, OVSC informed you that it did not agree with your interpretation.; Standard No. 121's dynamometer tests are set forth in section S5.4 That section specifies that brake assemblies must meet the requirements of S5.4.1 (brake retardation force--relevant only to towed vehicles), S5.4.2 (brake power), and S5.4.3 (brake recovery), under the conditions of S6.2. One of those conditions, set forth in S6.2.1, is as follows:; >>>S6.2.1 The dynamometer inertia for each wheel is equivalent to th load on the wheel with the axle loaded to its gross axle weight rating. For a vehicle having additional gross axle weight ratings specified for operation at reduced speeds, the GAWR used is that specified for a speed of 50 mph, or, at the option of the manufacturer, any speed greater than 50 mph.<<<; In support of your suggested interpretation, you noted that axle load of a decelerating vehicle vary under different deceleration conditions, i.e., as a vehicle travelling forward decelerates, the load on the axles shifts so that the front axle load rises and rear axle load falls. You stated that it is your reading of Standard No. 121 that the manufacturer 'can assess compliance by either using a static load value or determining which of the varying values of the axle load should be considered in view of actual vehicle behavior.' With respect to gross axle weight rating (GAWR), you suggested that when used in the context of Parts 567 and 568, the GAWR is properly measured in a static manner, to permit determination of whether the load carrying capacity of a vehicle axle in actual use has been reached. For dynamometer tests of service brakes under dynamic conditions, however, you argued that such tests should properly take into account the dynamic effects of deceleration.; You then stated the following: >>>The language of S6.2.1, setting dynamic test conditions, indicate that the dynamometer inertia for each wheel is to be set at the 'equivalent' to the load on the wheel, when the axle is loaded to its GAWR (i.e., its load-carrying capacity). This language is not restrictive and grants a manufacturer the flexibility of determining an 'equivalent' loading in consideration of the dynamic phenomena in conducting the tests required by S5.4. Thus, the static GAWR is permitted to be linked to dynamic conditions by the word 'equivalent.'<<<; We disagree with your suggested interpretation, which we believe i inconsistent with the language of S6.2.1, past interpretations of that provision, and the compliance test procedures the agency has long followed with respect to this provision. As indicated above, S6.2.1 specifies that the dynamometer inertia for each wheel is 'equivalent to the load on the wheel with the axle loaded to its gross axle weight rating.' The phrase 'equivalent to the load' uses the singular 'load,' instead of the plural 'loads,' to show that the dynamometer inertia has only a single value. By itself, this suggests that S6.2.1 was not intended to provide multiple options for the dynamometer inertia setting, depending on the dynamic conditions simulated.; Further, the overall language of S6.2.1 shows how the singl dynamometer inertia setting is to be determined. The term 'GAWR' is defined in 49 CFR Part 571.3 as 'the value specified by the vehicle manufacturer as the load-carrying capacity of a single axle system, as measured at the tire-ground interfaces.' When an axle is loaded to its load-carrying capacity, there is one 'load on the wheel,' at whose 'equivalent' the dynamometer inertia must be set.; While we believe that the language of section S6.2.1 is clear on th issue raised by your letter, we also note that agency guidance in the form of past interpretation letter and OVSC's laboratory procedures for Standard No. 121 are also clear. In an interpretation letter to Wagner Electric, dated May 26, 1972, the agency stated:; >>>In the dynamometer test conditions of S6.2.1, the dynamomete inertia for each brake assembly is based on 1/2 the GAWR of the axle. The rating for each axle is required to be stated separately. If, in the example you give, you choose to give 17,000 pounds as the rating for each axle, then the dynamometer inertia would be at 8,500 pounds for each brake assembly.; <<>>Section S5.1.1 does not specify whether or not the vehicle is movin as a test condition for the requirement. In view of the absence of this test condition, the NHTSA will resolve differences in this test condition in the manufacturer's favor if they affect the outcome of testing.<<<; We do not agree that this letter supports your suggeste interpretation. The letter addressed only the issue of how a requirement should be read in view of the absence of a particular test condition. As explained at length above, we conclude that section S6.2.1 clearly specifies the particular test conditions to be followed for this section. Therefore, the Oshkosh letter is not relevant to requests for interpretation of S6.2.1.; You also argued that in order to provide an appropriate braking system with proper distribution of brake forces between the axles, its design must take into account the transfer of weight from the rear axle to the front axle during normal and emergency braking conditions. You stated that such a design and compliance test leads to a significant reduction in premature lockup of the rear axle. You also argued that NHTSA has recognized your braking system as 'a safe and effective system' in its research testing.; We agree that a manufacturer must take into account the transfer o weight from the rear axle to the front axle when designing an appropriate braking system. This is necessary to provide safe brake performance during varying loading conditions, for normal and emergency brake applications on varying road conditions, and it is so for all kinds of vehicles. However, the requirements of Standard No. 121 do not require vehicles to have too much rear braking, as you appear to imply. The requirements of S5.4.2 (Brake Power), and S5.4.3 (Brake Recovery), are minimum performance requirements intended to help ensure that brakes retain adequate stopping capacity during and after exposure to conditions caused by prolonged or severe use, such as long, downhill driving. In practice, in order to perform well in such conditions, both front and rear brakes must have a minimum capacity, and this capacity is related to GAWR despite the fact that the actual loads borne by the front and rear axles vary during different brake applications. The agency therefore referred to GAWR in section S6.2.1, because this is an objective value that is readily ascertainable for every vehicle, and performance based on this value meets the particular safety need provided for by the requirements of section S5.4. These minimum requirements are not intended, nor do they operate, as a restriction on the design decisions that manufacturers must make independently to distribute braking capacity to meet anticipated load distributions.; Contrary to your assertion, NHTSA has not concluded that your brak system is 'safe and effective.' We also note that the quotations of the agency's research report cited in your letter address only limited aspects of braking performance and are taken out of context. We note that you stated that '(t)he Agency reported finding that the subject vehicle's front and rear axles were '. . .well balanced and tended to lock at close to the same pedal effort level.' (p. 19).' A more complete quotation is as follows:; >>>. . . In the empty driver best effort stops the driver was also abl to utilize this peak friction, although not as effectively as the antilock, because the brakes on front and rear axles of the vehicle were well balanced and tended to lock at close to the same pedal effort level. In the loaded case, however, the front axle tended to lock prematurely and it was not possible for the driver to maintain all four wheels near the peak friction level. He could keep the front tires near the peak but when this occurred rear braking was relatively low. If he applied more braking, the front axle locked and he lost steering control due to lack of lateral traction at the front tires.'<<<; Based on the information before the agency, OVSC is continuing it investigation concerning the compliance of your vehicles with Standard No. 121.; Sincerely, Erika Z. Jones, Chief Counsel |
Request an Interpretation
You may email your request to Interpretations.NHTSA@dot.gov or send your request in hard copy to:
The Chief Counsel
National Highway Traffic Safety Administration, W41-326
U.S. Department of Transportation
1200 New Jersey Avenue SE
Washington, DC 20590
If you want to talk to someone at NHTSA about what a request for interpretation should include, call the Office of the Chief Counsel at 202-366-2992.
Please note that NHTSA’s response will be made available in this online database, and that the incoming interpretation request may also be made publicly available.