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: Roberts.1.wpdOpenMr. Mark Roberts Dear Mr. Roberts: This responds to your letter asking whether it would be permissible for a member of the transit bus industry to replace a required passenger-side, flat unit magnification mirror installed on new buses having a gross vehicle weight rating (GVWR) of more than 4,536 kg (10,000 pounds) with a 40" to 60"-radius convex mirror. As discussed in a conversation with Eric Stas of my staff, your company manufactures the aftermarket mirrors in question, and you seek confirmation of "What is [a] legal and an illegal mirror once the buses are in revenue service?" We would like to begin by explaining that the National Highway Traffic Safety Administration (NHTSA) is authorized to issue Federal motor vehicle safety standards (FMVSSs) that set performance requirements for new motor vehicles and items of motor vehicle equipment. Manufacturers are required to certify that their products conform to our safety standards before they can be offered for sale. One of the safety standards we have issued is FMVSS No. 111, "Rearview Mirrors" (49 CFR 571.111). FMVSS No. 111 sets different requirements for buses depending on the GVWR. Buses, other than school buses, with a GVWR of more than 4,536 kg must meet the requirements of S7.1, which requires outside mirrors of unit magnification, each with not less than 323 cm2 of reflective surface, installed with stable supports on both sides of the vehicle. Vehicle manufacturers must install mirrors that comply with S7.1 in order to certify new buses covered under the standard. After the first sale of the vehicle, manufacturers, distributors, dealers, and repair businesses are prohibited from "knowingly making inoperative" any device or element of design installed on or in a motor vehicle in compliance with an applicable standard. 49 U.S.C. 30122. In general, the "make inoperative" prohibition requires businesses which modify motor vehicles to ensure that they do not remove, disconnect, or degrade the performance of safety equipment installed in compliance with an applicable standard. If NHTSA determines that a business has violated the "make inoperative" provision, it may assess a civil penalty in the amount of $5,000 per violation (not to exceed $15,000,000 in the aggregate). 49 U.S.C. 30165(a)(1). Thus, a manufacturer of new transit buses or other commercial entity repairing or modifying such buses could not replace a mirror complying with FMVSS No. 111 with another mirror that does not comply with the standard. However, it would be permissible to install your convex mirror on the passenger side of the bus as a supplement to a unit magnification mirror that meets all applicable requirements of FMVSS No. 111. The "make inoperative" provision does not apply to the actions of a vehicle owner in modifying his or her own vehicle. Consequently, NHTSA regulations do not prevent transit bus companies from making changes to their own used buses in their own garages or repair and maintenance facilities, even if they cause a vehicle to no longer comply with NHTSA safety standards. However, we urge vehicle owners not to degrade the safety of any system or device on their vehicles, including those required by FMVSS No. 111. Further, I note that the Departments Federal Motor Carrier Safety Administration (FMCSA) has jurisdiction over interstate motor carriers operating in the United States. Under FMCSA regulations, there is a provision related to "rear-vision mirrors" at 49 CFR 393.80, which provides in relevant part:
49 CFR 393.80(a). Thus, for vehicles covered under FMCSA regulations, there is an ongoing requirement for rear-vision mirrors that meet the requirements of FMVSS No. 111. You or transit bus owners should contact Larry Minor of the FMCSA at (202) 366-4009 for further information about this regulation and the vehicles to which it applies. In addition, States have the authority to regulate the use and licensing of vehicles operating within their jurisdictions. Therefore, you or transit bus owners should check with the Department of Motor Vehicles in any State in which the equipment will be sold or used regarding any such requirements. I hope you find this information useful. If you have further questions, please feel free to contact Eric Stas of my staff at this address or by telephone at (202) 366-2992. Sincerely, Jacqueline Glassman ref:111 |
2003 |
ID: Roseman_ltrOpen Mr. Robert A. Roseman Dear Mr. Roseman: This responds to your letter to Stephen P. Wood of my staff asking two questions about Federal Motor Vehicle Safety Standard (FMVSS) No. 106, Brake Hoses (49 CFR 571.106). Both of your questions are answered below. You explain that your company manufactures boat trailers and that you have questions about a brake hose assembly "that does not meet Standard No. 106." You ask for confirmation of information you were given that "DOT doesn't apply to boat trailers because they are not for commercial use." As explained below, the information you were provided is incorrect. Question 1: Does 49 CFR 571.106 apply to boat trailers that are used on the public highways for non-commercial use? The answer is yes. All trailers, including boat trailers, manufactured for use on the public highways and all brake hoses, brake hose assemblies, and end fittings used on trailers and boat trailers must comply with FMVSS No. 106. (See S3 of FMVSS No. 106 regarding the applicability of the standard.) The term "boat trailer" is defined in 49 CFR 571.3, as "a trailer designed with cradle-type mountings to transport a boat and configured to permit launching of the boat from the rear of the trailer." (Emphasis added.) As a subcategory of "trailers," boat trailers must comply with all Federal motor vehicle safety standards applicable to trailers, including FMVSS No. 106. We note that our answer would be the same even if the boat trailers you manufacture were used on the public roads for commercial rather than non-commercial purposes. Question 2: What would my exposure for correction be if I simply began using the lower cost brake hose assemblies until the issue is clarified? Would I have to replace all those that I supplied? Under 49 U.S.C. 30101 et seq. (the Safety Act), you must use brake hose, end fittings and assemblies that comply with Standard No. 106. 49 U.S.C. 30112. Under 30115 of the Safety Act, manufacturers are required to certify that their motor vehicles and/or motor vehicle equipment comply with all applicable Federal motor vehicle safety standards in effect at the time of manufacture. Section 30115 prohibits any person from issuing such certification "if, in exercising reasonable care, the person has reason to know the certificate is false or misleading in a material respect." Persons who knowingly certify compliance of vehicles containing non-compliant equipment are subject to the Act's civil penalty provisions. 49 U.S.C. 30165. Under 30165, anyone who violates 30112 or 30115 is subject to a civil penalty up to $5,000 per violation, up to a maximum penalty of $15,000,000 for a series of related violations. In addition, the Act prohibits the sale of non-compliant vehicles or equipment. The statute also requires manufacturers to notify consumers that a motor vehicle or item or equipment they purchased fails to comply with the FMVSSs or contains a safety-related defect, and requires manufacturers to remedy such noncompliances and defects without charge. We have enclosed an information sheet that briefly describes these and other manufacturer responsibilities. I hope this information is helpful. If you have any questions, please contact Robert Knop of this office at (202) 366-2992. Sincerely, Jacqueline Glassman Enclosure |
2002 |
ID: RUSHFORD.RBMOpen Ms. Lisa Rushford Dear Ms. Rushford: This is to acknowledge your letter concerning the problems with air bags. Please be assured that your comments and concerns will be taken into consideration as the agency develops a solution to these problems. Enclosed is a list of Questions and Answers regarding air bags that I hope will be helpful to you. Sincerely, John Womack Acting Chief Counsel Enclosure cc: The Honorable Charles W. Stenholm ref:208 d:11/27/96 |
1996 |
ID: RVIA-MonacoCoach.ekmyOpenLawrence F. Henneberger, Esq. Dear Mr. Henneberger: This is in response to your August 26, 2003 letter on behalf of the Recreational Vehicle Industry Association (RVIA) and Monaco Coach Company (Monaco), addressed to Mr. Kenneth N. Weinstein of this agency, in which you raised issues dealing with the submission of field reports under the National Highway Traffic Safety Administrations Early Warning Reporting (EWR) regulations. As you are aware, these issues were previously discussed during an August 5, 2003 meeting between NHTSA officials and representatives of RVIA and Monaco. You asked whether Pre-Delivery Inspection (PDI) forms, Dealer Acceptance forms (DAF), and any other pre-retail sale documents "related to recreational vehicles which are still in the direct control of the manufacturer or dealer" fall under the definition of "field reports" and therefore subject to the requirements of the EWR regulations. In your letter, you explained that recreational vehicle manufacturers, prior to retail sale of a recreational vehicle, typically require dealers to complete and provide back to the manufacturer what are known in the industry as PDIs, DAFs and similar materials. You further clarified that these "form documents . . . are essentially checklists for dealer completion which are intended to detect and correct, under warranty, any product deficiencies prior to retail sale of a recreational vehicle." As we explained in the preamble to the EWR Final Rule, the term "field report" was not intended to cover every dealer-to-manufacturer communication. See 67 Fed. Reg. 45,855 (July 10, 2002). In response to requests to clarify the Final Rule, we amended the definition of "field report" in an April 15, 2003 Final Rule to exclude vehicles that are still within the control of the manufacturer. As amended, a "field report" is defined as "[a] communication in writing, including communications in electronic form . . . with respect to a vehicle or equipment that has been transported beyond the direct control of the manufacturer . . . regarding the failure, malfunction, lack of durability, or other performance problem of a motor vehicle or motor vehicle equipment, or any part thereof, produced for sale by that manufacturer, regardless of whether verified or assessed to be lacking in merit . . ." 49 C.F.R. 579.4(c), 68 Fed. Reg. 18,136 at 18,142 (April 15, 2003). Based upon your description of the documents identified in your letter, we confirm your understanding that those documents do not fall within the ambit of the EWR regulatory requirements. While vehicles in the possession of dealers are considered to be "beyond the direct control of the manufacturer" for recall purposes, NHTSA does not consider documents prepared by dealers that address particular vehicle prior to their first retail sale to be field reports for purposes of the EWR regulations. We also note that deficiencies would be corrected under warranty and therefore reported to NHTSA under the EWR provision pertaining to warranty claims. Should you have any further questions, please contact Andrew J. DiMarsico of my staff at (202) 366-5263. Sincerely, Jacqueline Glassman ref:579 |
2003 |
ID: schaub.ztvOpenMr. Frank A. Schaub Dear Mr. Schaub: We are replying to your e-mails of February 27 and March 4, 2003, with reference to your citation by local authorities who concluded that the modulating headlamp on your motorcycle was a flashing light and prohibited under the laws of Connecticut. You have asked for our assistance. We have not reviewed Connecticut Department of Motor Vehicles Regulation Section 14-137-99 which you reference, as we do not provide interpretations of State laws. However, I am enclosing a copy of a letter from this Office, dated June 20, 2000, to Michael L. Wagner which, based on facts you present, is squarely on point with your situation. In brief, we informed Mr. Wagner that, under Federal law, modulating headlamps are not flashing headlamps; modulating headlamps that comply with applicable Federal motor vehicle safety standards adopted by the National Highway Traffic Safety Administration (NHTSA) are permissible for use on motorcycles; and a State (or a political subdivision of a State) is preempted by Federal law from having a local law that has the effect of prohibiting a motorcycle headlamp modulating system meeting Federal specifications. The letter to Mr. Wagner contains appropriate legal citations. This interpretation of June 20, 2000, remains in effect today. As you requested, I am enclosing a copy of S7.9.4, Motorcycle headlamp modulation system, which is part of 49 CFR 571.108, Federal Motor Vehicle Safety Standard No. 108, Lamps, Reflective Devices, and Associated Equipment. I am also enclosing a copy of the section of the Federal statute governing the relationship of the Federal motor vehicle safety standards with State motor vehicle safety standards, 49 U.S.C. 30103(b), Preemption. If there are any questions, please contact Taylor Vinson, Senior Attorney, NHTSA, at (202)-366-5263. Sincerely, Jacqueline Glassman Enclosures |
2003 |
ID: RVIA-MonacoCoach_new.ekmyOpenLawrence F. Henneberger, Esq. Dear Mr. Henneberger: This is in response to your August 26, 2003 letter on behalf of the Recreational Vehicle Industry Association (RVIA) and Monaco Coach Company (Monaco), addressed to Mr. Kenneth N. Weinstein of this agency, in which you raised issues dealing with the submission of field reports under the National Highway Traffic Safety Administrations Early Warning Reporting (EWR) regulations. As you are aware, these issues were previously discussed during an August 5, 2003 meeting between NHTSA officials and representatives of RVIA and Monaco. You asked whether Pre-Delivery Inspection (PDI) forms, Dealer Acceptance forms (DAF), and any other pre-retail sale documents "related to recreational vehicles which are still in the direct control of the manufacturer or dealer" fall under the definition of "field reports" and therefore subject to the requirements of the EWR regulations. In your letter, you explained that recreational vehicle manufacturers, prior to retail sale of a recreational vehicle, typically require dealers to complete and provide back to the manufacturer what are known in the industry as PDIs, DAFs and similar materials. You further clarified that these "form documents . . . are essentially checklists for dealer completion which are intended to detect and correct, under warranty, any product deficiencies prior to retail sale of a recreational vehicle." As we explained in the preamble to the EWR Final Rule, the term "field report" was not intended to cover every dealer-to-manufacturer communication. See 67 Fed. Reg. 45,855 (July 10, 2002). In response to requests to clarify the Final Rule, we amended the definition of "field report" in an April 15, 2003 Final Rule to exclude vehicles that are still within the control of the manufacturer. As amended, a "field report" is defined as "[a] communication in writing, including communications in electronic form . . . with respect to a vehicle or equipment that has been transported beyond the direct control of the manufacturer . . . regarding the failure, malfunction, lack of durability, or other performance problem of a motor vehicle or motor vehicle equipment, or any part thereof, produced for sale by that manufacturer, regardless of whether verified or assessed to be lacking in merit . . ." 49 C.F.R. 579.4(c), 68 Fed. Reg. 18,136 at 18,142 (April 15, 2003). Based upon your description of the documents identified in your letter, we confirm your understanding that those documents do not fall within the ambit of the EWR regulatory requirements. While vehicles in the possession of dealers are considered to be "beyond the direct control of the manufacturer" for recall purposes, NHTSA does not consider documents prepared by dealers that address particular vehicle prior to their first retail sale to be field reports for purposes of the EWR regulations. We also note that deficiencies would be corrected under warranty and therefore reported to NHTSA under the EWR provision pertaining to warranty claims. Should you have any further questions, please contact Andrew J. DiMarsico of my staff at (202) 366-5263. Sincerely, Chief Counsel |
2003 |
ID: Sealing_screen000519OpenMs. Erika Z. Jones Dear Ms. Jones: This responds to your January 7, 2005, letter asking about Federal Motor Vehicle Safety Standard (FMVSS) No. 302, Flammability of interior materials. You ask if a sealing screen attached to an exterior door panel would be subject to FMVSS No. 302. Our answer is no. In your letter, you state that the sealing screen is installed between the door trim panel and the exterior door panel. It does not adhere to the door trim panel at any point, and is physically attached only to the exterior door panel. You state that the sealing screen serves the purpose of protecting the space behind the exterior door panel from moisture leaks and is not designed to absorb energy from an occupant in a crash. The sealing screen is within 13 millimeters (mm) of the occupant compartment air space. FMVSS No. 302 applies to new motor vehicles, and specifies burn resistance requirements for particular components, listed in S4.1 of the standard, used in the vehicle occupant compartment. Of those components, any portion of a single or composite material which is within 13 mm of the occupant compartment air space must meet the burn limit requirements of S4.3 of the standard. The components listed in S4.1 are:
The question presented by your letter is whether we would consider the screen you described as a "trim panel, including door, front, rear, and side panels". Our answer is no. The screen is attached solely to the exterior door panel and is not incorporated into the interior door trim panel. We therefore conclude that it is not part of a "trim panel". Since the screen would not be part of a component listed in S4.1, it is excluded from FMVSS No. 302. If you have any additional questions please contact Mr. Chris Calamita of my staff at (202) 366-2992. Sincerely, Jacqueline Glassman ref:302 |
2005 |
ID: SEMAOpenMr. Stephen B. McDonald Vice President, Government Affairs Specialty Equipment Marketing Association 1317 F Street, NW, Suite 500 Washington, DC 20004 Dear Mr. McDonald: This responds to your letter requesting clarification of our notice of interpretation of Federal Motor Vehicle Safety Standard (FMVSS) No. 108, published in the Federal Register (70 FR 65972) on November 1, 2005. The interpretation addressed how FMVSS No. 108 applies to replacement equipment. The issues you asked about are addressed below. In our interpretation, we noted that FMVSS No. 108s current requirement for replacement equipment, set forth in paragraph S5.8.1 of the standard, reads as follows: Except as provided below, each lamp, reflective device, or item of associated equipment manufactured to replace any lamp, reflective device, or item of associated equipment on any vehicle to which this standard applies shall be designed to conform to this standard. We explained: This language is relatively straightforward. For any particular item of lighting equipment, e.g., a lamp, FMVSS No. 108 states only that if a lamp is manufactured to replace a lamp on a vehicle to which the standard applies, it must be designed to conform to the standard. It does not say anything about the replacement lamps being required to have the same type of light source as the OE lamp. Moreover, while it is true that, unlike other lamps, FMVSS No. 108 specifically regulates headlamp systems including their light sources, neither the language of S5.8.1 nor any other language in the standard requires replacement headlamps to use the same light sources as the OE headlamps. 70 FR at 65974. In your letter, you stated that you agreed with this language, but asked for clarification of the immediately following paragraph, which reads as follows: Under our revised interpretation, it is our opinion that a lamp (or other item of lighting equipment, as relevant) manufactured to replace a lamp on a vehicle to which the standard applies is permitted under S5.8.1 so long as the vehicle manufacturer could have certified the vehicle to FMVSS No. 108 using the replacement lamp instead of the lamp it actually used. To the extent the vehicle manufacturer could have certified the vehicle using the replacement lamp, instead of the lamp it actually used, we believe the replacement lamp should be viewed as being designed to conform to FMVSS No. 108. This includes, but is not limited to, replacement headlamps using different light sources than the OE headlamps. You expressed concern that this paragraph could be construed as preventing new technologies from being used as replacement equipment, even though such equipment was in compliance with FMVSS No. 108. You stated, as an example, that if a technology could not have been certified in a new vehicle prior to 2005 because the technology was not yet developed, but was available in 2005, an unreasonably strict reading could limit the technology for use only in 2005 model year and subsequent model year vehicles. We confirm that the language was not intended to be so narrowly applied so as to prevent new technologies from being used as replacement equipment on earlier model year vehicles. With reference to your example, to the extent the manufacturer of the pre-2005 model year vehicle could have certified the vehicle using the later replacement lamp incorporating the new technology (had that technology been available at the time of vehicle manufacture), instead of the lamp it actually used, we believe the replacement lamp should be viewed as being designed to conform to FMVSS No. 108. You also asked to confirm that while the paragraph only references the vehicle manufacturer, it is not intended to exclude other segments of the industry that could have certified the vehicles lighting system using a replacement lamp. You stated that this could include a lighting manufacturer, dealer or alterer. As discussed below, for the sentence at issue, we agree that alterers (persons who make changes to vehicles prior to first sale) would be included along with vehicle manufacturers. However, lighting manufacturers and dealers would not be included unless they were also alterers. As indicated above, in the sentence at issue, we stated that it is our opinion that a lamp (or other item of lighting equipment, as relevant) manufactured to replace a lamp on a vehicle to which the standard applies is permitted under S5.8.1 so long as the vehicle manufacturer could have certified the vehicle to FMVSS No. 108 using the replacement lamp instead of the lamp it actually used. We referenced vehicle manufacturer because it is the vehicle manufacturer, rather than the equipment manufacturer, that is responsible for certifying new vehicles to FMVSS No. 108. The only entities other than vehicle manufacturers that could be certifying new vehicles to FMVSS No. 108 would be alterers. Under our regulations, alterers are persons who make changes to certified motor vehicles prior to first retail sale. Part 567.7, Requirements For Persons Who Alter Certified Vehicles, requires alterers to certify that the vehicle, as altered, complies with all applicable safety standards affected by the alteration. Since alterers may be certifying a new vehicle to FMVSS No. 108, it would be correct to reference them along with vehicle manufacturers in the above-quoted sentence. However, it would not be correct to include any entities that would not be certifying a new vehicle to FMVSS No. 108. Therefore, lighting manufacturers and dealers would not be included unless they were also alterers. I hope this information is helpful. If you have any further questions, please feel free to contact Edward Glancy of my staff at (202) 366-2992. Sincerely, Anthony M. Cooke Chief Counsel ref:108 d.8/24/06 |
2006 |
ID: Senator Collins2OpenThe Honorable Susan M. Collins United States Senate Washington, DC 20510 Dear Senator Collins: This responds to the letter from your office regarding the National Highway Traffic Safety Administrations (NHTSAs) interpretation of the term motor vehicle for the purposes of the National Traffic and Motor Vehicle Safety Act (Safety Act) and, in particular, the application of this interpretation to certain very small trucks, including Japanese mini Kei trucks, imported by B&M Mini Trucks and Tractors LLC, of Madawaska, Maine. Your offices letter says that any changes to NHTSAs interpretation of what is a motor vehicle could substantially impact this company, which has relied on this guidance in its business. Accordingly, your office enclosed a letter from Mr. Harvey B. Fox further detailing these concerns. The question of whether certain non-traditional vehicles, such as the Kei trucks at issue, are motor vehicles for the purposes of the Safety Act, and therefore subject to regulation under its provisions, is currently before NHTSA in the form of several letters requesting interpretive guidance on whether various non-traditional vehicles fall within this definition. NHTSAs legal interpretations are written with the intent to clarify the meaning of the statutes and regulations it administers. In making an interpretation, NHTSA seeks above all to promote vehicle safety, after due consideration of all relevant factors, including the impact of alternative interpretations. Changes in the marketplace and in the motor vehicle population, however, may cause an established agency position to become inconsistent with achieving the goal of protecting drivers, their passengers, and other roadway users. As such, refinements to our guidance is periodically indicated to consider and address new or emerging trends or developments in transportation. The agency has not made any decision yet to seek a change in its existing interpretation of motor vehicle, as that term might relate to certain non-traditional vehicles such as very small trucks. If we decide to consider a change, we would follow our common process for the consideration of significant changes to established interpretations - we would publish a draft new interpretation in the Federal Register, solicit public comment, and then publish a notice setting forth our final conclusions. Page 2 The Honorable Susan M. Collins I hope this explanation responds to the concerns of you constituent. Please let me know if I can be of any further assistance. Sincerely yours, Anthony M. Cooke Chief Counsel cc: Phillip R. Bosse ref:VSA d.12/18/06 |
2006 |
ID: Sens_a_brake003065OpenMr. Gregory Gibb Dear Mr. Gibb: This responds to your inquiry regarding the regulations applicable to a trailer brake system that relies on a combination of air and hydraulics. You asked if a system manufactured by your company, the "Sens-a-Brake" system, would be classified as an air brake system under Federal Motor Vehicle Safety Standard (FMVSS) No. 121, Air brake systems. As explained below, the "Sens-a-Brake" system would be defined as an air-over-hydraulic brake subsystem, and therefore would be an airbrake system under FMVSS No. 121. I am pleased to have this opportunity to explain our regulations to you. FMVSS No. 121 specifies performance requirements for trucks, buses and trailers equipped with air brake systems. S4 of the standard defines "air brake system" as follows:
S4 of the standard defines "air-over-hydraulic brake subsystem" as:
In your letter you explained that the "Sens-a-Brake" system consists of an electronic brake controller and an air compressor mounted on a trailer, which supplies air for the application of the trailers braking mechanism. Your companys web site states that the electric brake controller incorporates a "pressure sensitive film that enables accurate measurement of the force being applied to the towing vehicles brake pedal."The website further explains that this pad attaches directly to the brake pedal of the tow vehicle. The pedal controller then modulates the air pressure supplied by the air compressor based on the pressure applied to the brake by the vehicle driver. The air pressure then transmits a force to the mechanism used to apply or release the hydraulic trailer brakes. Based on the description you provided in your letter and the information on your companys website, the "Sens-a-Brake" system comes within definition of "air-over-hydraulic brake subsystem." The "Sens-a-Brake" system transmits a force applied by a vehicle driver to the brake pedal, first through an electrical signal and then through compressed air, to a hydraulic brake system. While the system does not use air as the initial means for transmitting force from the driver control to the hydraulic system, compressed air is used in the system to transmit force from the driver control. Therefore, the "Sens-a-Brake" system would be an "air-over-hydraulic system," which is regulated as an air brake system under FMVSS No. 121. In your letter, you referenced a previous interpretation letter the agency issued to Mr. Tom Brunson, in which the agency concluded that a system with some similarities to the "Sens-a-Brake" system was not an air brake system (April 4, 2000). However, the system addressed by the letter to Mr. Brunson had one significant difference; the air pressure in that system was controlled primarily through an inertial controller mounted on the back of the tow vehicle. The system in the Brunson letter permitted a driver to control braking through a dash-mounted switch, but the switch was not intended to modulate the pressure applied to the brake mechanism. The primary control for actuating the air compressor in the Brunson letter system was the inertial controller mounted on the rear of the tow vehicle and not the vehicle driver. In contrast, the "Sens-a-Brake" system relies on force generated at the driver control (the force applied to the brake pedal pad) to modulate the application of compressed air to a hydraulic brake. Similarly, in an October 22, 2001 letter to Mr. Gary Rudnik the agency concluded that a trailer brake system was not an air brake system under FMVSS No. 121 if a trailers brakes activated as a result of the tow vehicles brake lamps illuminating (copy enclosed). Under the system described in the Rudnick letter, the brake pedal would function solely as an on-off switch for the trailer braking system, with the trailers brakes being activated upon illumination of the tow vehicles brake lamps when the driver pressed the tow vehicles brake pedal. However, the system would not transmit force applied by the driver via air to modulate the brakes; the brake pedal merely served as an on-off switch for the trailer braking system. Again in contrast, the "Sens-a-Brake" system relies on force applied to the brake pedal to modulate the application of compressed air to a hydraulic brake. Thus, if a system were to modulate the amount of air pressure applied to a hydraulic trailer brake mechanism in relation to force applied to a driver control, then that system would be an air brake system. If, however, a driver control were merely to function as an on-off switch, then that system would not be an air brake system under FMVSS No. 121. We note that when the agency incorporated the definition of "air-over-hydraulic brake subsystem" into FMVSS No. 121, we did not anticipate its application to light duty trailers. At that time, the agency indicated that air-over-hydraulic brake subsystems were installed exclusively on single-unit vehicles with a gross vehicle weight rating greater than 19,500 pounds (See 60 Federal Register 36741; July 18, 1995; copy enclosed). Unless the standard were amended through the rulemaking process, the Sens-a-Brake system is an air brake system under FMVSS No. 121. If you have any further questions, please contact Mr. Chris Calamita, of my staff at (202) 366-2992 Sincerely, Jacqueline Glassman Enclosures |
2004 |
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.