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
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ID: aiam5492OpenMr. Scott E. Peters Director, Regulations & Compliance U.S. Electricar 5355 Skylane Boulevard Santa Rosa, CA 95403; Mr. Scott E. Peters Director Regulations & Compliance U.S. Electricar 5355 Skylane Boulevard Santa Rosa CA 95403; "Dear Mr. Peters: This responds to your letter to me in which you aske whether Federal Motor Vehicle Safety Standard (FMVSS) No. 110, Tire selection and rims (49 CFR 571.110), applies to your Electricar sedan. You explained that your Electricar sedan (Electricar), a converted Geo Prizm, is being built under NHTSA Exemption No. 92-3 for low-emission vehicles. You stated that the Electricar's speed and endurance limitations are substantially below those of internal combustion-powered vehicles. You further stated that it is your understanding that 'the purpose of Standard No. 110, S4.4.2 (I assume you meant paragraph S4.2.2, since there is no S4.4.2 in the standard) is to ensure against tire failure due to prolonged operation at speeds in the range of 75 mph or higher.' Thus, you interpret FMVSS No. 110 as not applying to the Electricar or other electric passenger cars 'in which it is physically impossible to operate at high speeds for an extended duration.' You asked this agency, therefore, to review paragraph S4.2.2 and provide you our opinion as to its applicability to your Electricar. As discussed below, the requirements of S4.2.2 are applicable to electric passenger cars. By way of background information, the National Highway Traffic Safety Administration issues safety standards for motor vehicles and motor vehicle equipment. The agency does not provide approvals of motor vehicles or motor vehicle equipment. Instead, manufacturers are required to certify that their vehicles and equipment meet applicable safety standards. Federal Motor Vehicle Safety Standard No. 110 specifies requirements for tire selection to prevent overloading. Section S2 of the standard provides that the standard applies to passenger cars. S4.2 of the standard specifies the following tire load limits: S4.2.1 The vehicle maximum load on the tire shall not be greater than the applicable maximum load rating as marked on the sidewall of the tire. S4.2.2 The vehicle normal load on the tire shall not be greater than the test load used in the high speed performance test specified in S5.5 of section 571.109 of that tire. The test load used in the high speed performance test specified in S5.5 of Standard No. 109 is 88 percent of the tire's maximum load rating as marked on the tire sidewall. With respect to your question whether S4.2.2 applies to electric passenger cars, the answer is yes. That section applies on its face to all passenger cars, and does not include an exception for electric passenger cars. Your understanding that the purpose of S4.2.2 is limited to ensuring against tire failure due to prolonged operation at speeds in the range of 75 mph or higher is incorrect. The reference in that requirement to Standard No. 109's high speed performance test is for the sole purpose of specifying a load and not to indicate that the requirement is limited to high speed operation. As indicated above, Standard No. 110 seeks to ensure that tires are not overloaded. One way Standard No. 110 does this is by requiring in S4.2.1 that the vehicle maximum load on the tire not exceed the maximum load rating of the tire. Another way Standard No. 110 does this is by limiting the vehicle normal load on the tire, so that the tire will have some reserve load carrying capacity available to handle safely cargo and other kinds of added loading the car may experience. S4.2.2 does this by limiting the normal load on a tire to 88 percent of the tire's maximum load rating, which ensures that 12 percent of the tire's load rating will be available to bear cargo and other added loads. I hope this information is helpful to you. Should you have any further questions or need additional information, please feel free to contact Walter Myers of my staff at this address or at (202) 366-2992. Sincerely, Philip R. Recht Chief Counsel Enclosure"; |
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ID: aiam2357OpenRoderick H. Willcox, Esq., Messrs. Chester, Hoffman, Park, Willcox, & Rose, 16 East Broad Street, Columbus, OH, 43215; Roderick H. Willcox Esq. Messrs. Chester Hoffman Park Willcox & Rose 16 East Broad Street Columbus OH 43215; >>> Re: W.B. Marvin Manufacturing Co.<<< Dear Mr. Willcox: This is in reply to your letter of June 16, 1976, asking severa questions with respect to the applicability of 15 USC 1397(a)(2)(A) of the National Traffic and Motor Vehicle Safety Act and Federal Motor Vehicle Safety Standard No. 108 (49 CFR 571.108) to a product manufactured by your client, the W.B. Marvin Manufacturing Company. This product is 'a screen which fits on the front part of the automobile and protects the radiator, headlamps and other lower parts of the car' from bugs.; W.B. Marvin would not be in violation of either the Act or Standard No 108 by manufacturing and selling these screens. Such liability as may exist centers on the installation of them. Standard No. 108 establishes requirements for lighting equipment on new motor vehicles, and for replacement equipment. One of the requirements of SAE Standard J580a, *Sealed Beam Headlamp*, June 1966, incorporated by reference in Standard No. 108, is that ' a headlamp, when in use, shall not have any styling or other feature, such as a glass cover or grille in front of the lens.' Since the screen is positioned in front of the headlamps it would be an 'other feature' of the type intended to be prohibited by the standard if, as appears likely, it affects compliance with headlamp photometrics (SAE Standard J579) or headlamp aim (SAE Standard J580). If installation results in a noncompliance, the screen could not, therefore, be legally installed by a vehicle manufacturer, distributor, or dealer as original equipment on a motor vehicle.; As for replacement equipment, under Section 1397 (a)(2)(A) of the Ac an automobile owner may himself modify his vehicle in any manner he chooses, but modifications performed at his request by others may not 'render inoperative in whole or part, any device or element of design installed on . . . a motor vehicle . . . in compliance with an applicable Federal motor vehicle safety standard.' If installation of the screen affects compliance with headlamp photometrics or other requirements, then it would appear to 'render inoperative' a lighting device installed in accordance with a Federal motor vehicle safety standard, within the meaning of Section 1397(a)(2)(A). Installation by the auto service center of the retailer would therefore be prohibited, since such a facility is deemed a 'motor vehicle repair business.'; There are no Federal motor vehicle safety standards that directly appl to the screen as an item of motor vehicle equipment, nor do I know of any other Federal regulation affecting it.; I hope this letter is responsive to your questions. Yours truly, Frank Berndt, Acting Chief Counsel |
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ID: aiam2642OpenMr. Robert Rubenstein, Chief Engineer, Alderson Research Laboratories, Inc., 390 Ludlow Street, Stamford, CT 06904; Mr. Robert Rubenstein Chief Engineer Alderson Research Laboratories Inc. 390 Ludlow Street Stamford CT 06904; Dear Mr. Rubinstein (sic): This responds to Alderson Research Laboratory's July 15, 1977, reques for confirmation that Part 572, *Anthropomorphic Test Dummy* (49 CFR 572), neither requires nor prohibits venting of the abdominal insert specified in drawing No. ATD 3250-2. The agency proposed the addition of leak test specifications to the drawing in August 1975 (40 CFR 33462, August 5, 1975) but they were not made final (42 CFR 7148, February 7, 1977).; Your interpretation that Part 572 neither requires nor prohibit venting of the abdominal insert is correct. The language you cite from the preamble to our February 1977 rulemaking is misleading in suggesting the requirement for venting. The agency more clearly described the requirement in its most recent amendment of Part 572 (42 FR 34299, July 5, 1977), stating that the Part does not 'specify an abdominal sealing specification.' Agency testing demonstrated conforming results both with and without venting (DOT HS-020875) and sees no reason to control this aspect of dummy design.; Sincerely, Joseph J. Levin, Jr., Chief Counsel |
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ID: aiam5187OpenMs. Laura J. Platter 6662 Mohawk Court Columbia, MD 21046; Ms. Laura J. Platter 6662 Mohawk Court Columbia MD 21046; "Dear Ms. Platter: This responds to your letter to Senator Barbar Mikulski about the Federal government's classification of minivans for safety purposes. You were concerned that classifying minivans as trucks rather than passenger vehicles would permit these vehicles to be equipped with fewer safety features. Congress has authorized this agency, the National Highway Traffic Safety Administration (NHTSA), to issue Federal motor vehicle safety standards that are applicable to new motor vehicles and items of motor vehicle equipment. In the last few years, NHTSA has extended nearly all the passenger car safety standards to cover light trucks and multipurpose passenger vehicles (MPVs). (Minivans are typically considered to be MPVs under our safety standards.) The only significant safety requirement for passenger cars that the agency has not extended to light trucks and MPVs is dynamic side impact protection. This is a new requirement that is being phased in for passenger cars beginning this September. NHTSA is currently in rulemaking to consider whether the dynamic side impact protection requirements should be extended to light trucks and MPV's, and published an advance notice of proposed rulemaking on this subject in June 1992. I hope this information is helpful to you. Sincerely, Howard M. Smolkin Acting Administrator cc: The Honorable Barbara A. Mikulski"; |
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ID: aiam3950OpenMr. Charles E. Gillipsie, President, Salem Quality Equipment, Inc., 501 East 8th Street, Salem, VA 24153-6385; Mr. Charles E. Gillipsie President Salem Quality Equipment Inc. 501 East 8th Street Salem VA 24153-6385; Dear Mr. Gillipsie: This responds to your April 30, 1985 letter asking if your leasin company is allowed to occasionally rent 10- and 15-passenger vans to schools for special school activity trips. As Ms. Hom of my staff informed you in a telephone conversation on April 26, 1985, you are not prohibited by Federal statute or regulations from renting vans to schools on a one-time or very occasional basis.; The National Highway Traffic Safety Administration (NHTSA) has th authority under the National Traffic and Motor Vehicle Safety Act to issue motor vehicle safety standards that apply to the manufacture and sale of new motor vehicles. The parties directly affected by the Vehicle Safety Act are manufacturers of new school buses and persons selling new school buses. The Vehicle Safety Act prohibits those parties from selling new buses for use as school buses if those vehicles do not comply with the Federal school bus safety standards.; When Congress passed the 1974 amendments to the Vehicle Safety Act Congress adopted the following definition of a 'school bus': 'Schoolbus means a passenger motor vehicle which is designed to carry more than 10 passengers in addition to the driver, and which the Secretary determines 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...' (Emphasis added.); Two basic considerations are relevant, therefore, to the Vehicle Safet Act's definition of a 'school bus' and the applicability of the Act's requirements to school bus sellers. The first is the vehicle's passenger capacity, and second, its intended use. If you buy a new 12- or 15-passenger van to rent to schools on a regular basis, that van would be a 'school bus,' since it would have the passenger capacity of a 'bus' and is 'likely to be significantly used' to carry school children. A dealer or distributor who sells you the new van would have to ensure that the van meets our school bus safety standards. Conversely, the less frequently a bus is used for school service, the less likely it is that its use is 'significant.' If you use your van to carry students on a very infrequent basis, as the case appears to be, then it would not be considered a 'school bus,' and the van would not have to meet the school bus safety standards.; In your letter, you referred to a Federal Register notice (40 FR 60033 December 31, 1975) that amended NHTSA's regulatory definition of a 'school bus' and discussed leasing arrangements. NHTSA's definition of a school bus covers buses 'sold or introduced in interstate commerce for purposes that include carrying students to and from school or related events.' The notice explained that NHTSA's definition includes buses 'introduced in interstate commerce' in order to account for those situations where buses are leased to schools for transporting students. You asked for clarification of this discussion.; The term 'introduction in interstate commerce' and the reference in th Federal Register notice to leasing arrangements addressed those situations where a new bus is leased by a manufacturer, distributor or dealer directly to a school or school district. In those situations, there is no sales transaction involved. When a new bus is leased to a school or school district directly from its manufacturer, distributor or dealer, the Vehicle Safety Act requires that the bus must comply with the school bus safety standards.; If you have further questions, do not hesitate to contact my office. Sincerely, Jeffrey R. Miller, Chief Counsel |
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ID: aiam0385OpenMr. Nathan Sagan, 949 Central Avenue, Albany, NY (sic); Mr. Nathan Sagan 949 Central Avenue Albany NY (sic); Dear Mr. Sagan: This is in further reply to your request made to the Regiona Administrator of the National Highway Traffic Safety Administration concerning the applicability of the Tire Identification and Record Keeping regulation (49 CFR Part 574) to tires on Cushman golf carts.; As we indicated in our letter of June 23, golf carts are not considere to be motor vehicles within the meaning of the regulation or the National Traffic and Motor Vehicle Safety Act. Therefore, the regulation is not applicable to tires sold with or for golf carts.; Sincerely, Lawrence R. Schneider, Acting Chief Counsel |
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ID: aiam2212OpenMr. Tommy Watson, Engineer of Codes and Standards, Leisure Time Products, Inc., P.O. Box 232, Nappanee, Indiana 46550; Mr. Tommy Watson Engineer of Codes and Standards Leisure Time Products Inc. P.O. Box 232 Nappanee Indiana 46550; Dear Mr. Watson: This is in response to your letter of January 29, 1976, requesting a interpretation of the requirements of S.6 of Federal Motor Vehicle Safety Standard No. 111 , *Rearview Mirrors*, as they apply to the manufacture of mobile homes with a GVWR of greater than 10,000 pounds.; The standard requires that these vehicles be equipped with outsid mirrors of unit magnification, *each with not less than 50 square inches of reflective surface*, on both sides of the vehicle. While you are free to provide additional mirrors, the standard clearly requires two mirrors each of which has at least 50 square inches of reflective surface. Substitution of a number of small mirrors for one or both of the 50 square inch mirrors is impermissible, even if a total reflective area of 50 square inches is provided.; If you require any further assistance, do not hesitate to write. Sincerely, Richard B. Dyson, Assistant Chief Counsel |
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ID: aiam4796OpenMr. Satoshi Nishibori Vice President Industry-Government Affairs 750 17th Street, NW Suite 902 Washington DC 20006; Mr. Satoshi Nishibori Vice President Industry-Government Affairs 750 17th Street NW Suite 902 Washington DC 20006; "Dear Mr. Nishibori: This responds to your request for a interpretation of Standard No. 114, Theft Protection (49 CFR 571.114). You were uncertain whether your shift lock emergency override system, your emergency key release, and your transmission park lock system comply with S4.2 and S4.3, as amended by a May 30, 1990 final rule (55 FR 21868). On June 29, 1990, you submitted a petition for reconsideration which the agency is currently considering. Under the revised requirements, section S4.2 provides that: 'Each vehicle shall have a key-locking system that, whenever the key is removed, prevents: (a) the normal activation of the vehicle's engine or motor, and (b) either steering or forward self-mobility of the vehicle or both. For a vehicle equipped with an automatic transmission with a 'park' position, the key-locking system shall prevent removal of the key unless the transmission or transmission shift lever is locked in 'park' or becomes locked in 'park' as the direct result of removing the key.' As explained below, we have made the following interpretations concerning your systems based on our understanding of them from your petition for reconsideration, your July 25, 1990 letter, and your discussions with agency staff. By way of background, the National Traffic and Motor Vehicle Safety Act, ('Vehicle Safety Act,' 15 USC 1381 et seq.) requires every new motor vehicle sold in the United States to be certified as complying with all applicable Federal motor vehicle safety standards. The Vehicle Safety Act specifies that the manufacturer must certify that each of its vehicles complies with all applicable safety standards in effect on the date of manufacture. Because of this statutory requirement, this agency does not approve any manufacturer's vehicles or offer assurances that the vehicles comply with the safety standards. Any person violating the Vehicle Safety Act by manufacturing or selling new noncomplying vehicles may be liable for potential penalties of $1,000 per violation up to $800,000. Shift Lock Emergency Override You explained that your shift lock emergency override system is operable by depressing a button on the lower, rear portion of the shift lever. By depressing the button, the transmission may be shifted out of 'park,' independent of the ignition key position or the key being in the ignition switch. You expressed your opinion that the transmission remains 'locked' in 'park' until it is 'unlocked,' either by turning the ignition key to the 'on' position and depressing the brake pedal or by operating the emergency shift release override. This led you to conclude that your emergency shift override would be permissible under S4.2(b). We disagree with your suggested interpretation. Under S4.2(b), the key-locking system must prevent removal of the key unless the transmission or transmission shift lever is locked in 'park' or becomes locked in 'park' as the direct result of removing the key. Given the presence of the emergency shift release override, we do not believe the transmission or transmission shift lever would ever be 'locked' in park, since it could be released without regard to the key used to operate the vehicle's key-locking system. Your alternative shift lock system in which the manual override would be operable only after removing a cover over the override lever would also not appear to comply with S4.2 because the presence of a cover would not affect one's ability to release the transmission shift lever without regard to the key used to operate the vehicle's key-locking system. Emergency Key Release You explained that your emergency key release system facilitates removal of the ignition key in the event of an electrical system failure. That system permits overriding the ignition key lock, so that the ignition key can be removed from the vehicle and the driver can lock the vehicle. You explained that the emergency key release override is activated by removing a cover over the ignition switch and then using a screw driver to activate a hidden lever located inside the exposed ignition switch compartment. We do not concur with your suggested interpretation of S4.2. That requirement provides that 'the key-locking system shall prevent removal of the key unless the transmission or transmission shift lever is locked in 'park.' The regulatory text does not refer to alternative methods of key removal such as the procedure you describe. While you state that virtually any key locking system can be overriden through some form of lock disassembly and associated procedures, we do not consider the simple override you describe to be similar to lock disassembly. Therefore, an emergency key release system in which the key could be removed in a position other than 'park' would not comply with S4.2, regardless how the key could be removed. Nevertheless, such an emergency key release would be permissible if it were operable only while the transmission or transmission shift lever were locked in the 'park' position. You should be aware that we are evaluating such systems in our review of the petitions for reconsideration to the final rule. Park Lock System You explained that your park lock system prevents drivers from inadvertently depressing the accelerator pedal rather than the brake pedal when shifting out of 'park'. This is accomplished by permitting the transmission lever to be moved out of 'park' only if the ignition key is in the 'on' position and the brake pedal is depressed. You further explained that if the transmission is placed in 'park,' the shift lever locks in that position when the ignition key is turned to the 'off' position. You expressed your belief that your park lock system complies with S4.3, as amended. I agree that your park lock system appears to comply with S4.3. That provision requires that the prime means for deactivating the vehicle's engine or motor, typically the ignition key, shall not activate the key-locking system described in S4.2(b). Based on our understanding of your key-locking system, it appears to comply with S4.3 because that provision refers to the key-locking system and not a transmission shift lock. As you correctly note, the purpose of S4.3 is to prevent the potentially dangerous situation in which the ignition key of a moving vehicle is turned to the 'off' position causing the steering column to lock. You asked that we continue to consider your petition for reconsideration, if, as we have done, we concluded that some of your suggested interpretations were incorrect. We will notify you of our response to that petition as soon as we complete our review of it. I hope this explanation is helpful. Please contact Mr. Marvin Shaw of my staff at (202) 366-2992 if you have any further questions. Sincerely, Paul Jackson Rice Chief Counsel Enclosure"; |
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ID: aiam3053OpenMr. Stephen E. Mulligan, International Harvester, Law Department, 401 North Michigan Avenue, Chicago, IL 60611; Mr. Stephen E. Mulligan International Harvester Law Department 401 North Michigan Avenue Chicago IL 60611; Dear Mr. Mulligan: This responds to your June 4, 1979, letter asking several question relating to manufacturer's responsibilities to maintain first purchaser lists and to certify vehicles in compliance with the safety standards.; Your first question asks whether a manufacturer is permitted to replac its first purchaser lists with lists of most recent purchasers when that information comes to a manufacturer's attention. You point out that Part 577, *Defect and Noncompliance Notification*, requires manufacturers to notify vehicle owners or the most recent purchaser known to the manufacturer.; The National Traffic and Motor Vehicle Safety Act of 1966 (as amended (15 U.S.C. 1381 *et seq*.) requires in section 158 (15 U.S.C. 1418) that manufacturers maintain lists of first purchasers of their vehicles. The purpose of this requirement is to facilitate the issuance of defect and noncompliance notifications to vehicle owners. Lists of the most recent purchasers of a manufacturer's vehicles would be even more efficient for recall purposes than would first purchaser lists. Accordingly, the National Highway Traffic Safety Administration has determined that maintaining lists of most recent purchasers of a manufacturer's vehicles satisfies the statutory requirement to maintain first purchaser lists.; In your second question, you ask about the labeling requirements o individuals that modify incomplete vehicles. IN the fact situation you present, International Harvester (IH) certifies a chassis-cab in accordance with the agency's certification regulations and transfers it to an IH dealer who performs some minor modifications on the chassis-cab prior to its delivery to a final-stage manufacturer. The IH dealership is either owned or controlled by IH. You ask what type of certification label the IH dealer should attach.; You suggest that an alterer's label might be the appropriate label t use. The other possibilities that you recommend are the use of an intermediate manufacturer's label or merely removing and amending the chassis-cab label attached to the incomplete vehicle. You suggest that the latter is more appropriate since the dealer modifying the chassis-cab is owned by IH, and therefore, it constitutes the same manufacturer that constructed the chassis- cab. You state further that to require an intermediate manufacturer's label appears to be inappropriate since that label would show that the chassis-cab and the intermediate manufacturer are both the same corporation.; Alterer's labels are only used by individuals or businesses modifyin vehicles that have been certified by a final-stage manufacturer. Therefore, an alterer's label would be inappropriate in this instance since the chassis- cab has not been certified as a completed vehicle.; The agency concludes that in the case where a manufacturer's wholl owned dealership is modifying a certified chassis, the label on the chassis-cab should be removed and a correct label should be added. In these instances, the chassis-cab is still within the control of the original manufacturer. Therefore, it is appropriate for that manufacturer to assume the responsibility for the modification made by its dealers. The dealer is not an independent business of the type that must attach an intermediate manufacturer's label. Accordingly, your dealer may amend the incomplete vehicle label as a result of its modifications.; Sincerely, Frank Berndt, Chief Counsel |
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ID: aiam1594OpenMr. A.J. Burt, Sales Engineer, Highway Products, B.F. Goodrich Aerospace and Defense Products, P.O. Box 340, Troy, OH 45373; Mr. A.J. Burt Sales Engineer Highway Products B.F. Goodrich Aerospace and Defense Products P.O. Box 340 Troy OH 45373; Dear Mr. Burt: This responds to your June 4 and June 20, 1974, letters asking if parking brake system which locks mechanically after the brake is applied by any emergency air supply acting through the service air brake chamber would comply with Standard No. 121, *Air brake systems*. The parking brake provisions require in part:; >>>S5.6.3 *Application and holding*. The parking brake shall be applie by an energy source that is not affected by loss of air pressure or brake fluid pressure in the service brake system. Once applied, the parking brakes shall be held in the applied position solely by mechanical means.<<<; The arrangement described would not meet this requirement because th energy source to apply the brakes (the emergency air supply) would be affected by loss of air pressure in the service brake system. For example, any failure in the service brake piston diaphragm would cause a loss of air pressure that would in turn 'affect' the energy source that applies the parking brakes. The brake chamber housing assembly is an element which is not considered to be part of the service brake system for this requirement.; I would like to point out that the provisions of Standard No. 121 d not apply to trailers manufactured before January 1, 1975.; Yours truly, Richard B. Dyson, Acting Chief Counsel |
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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.