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: aiam2904OpenMr. Walter J. Kulpa, Yankee Metal Products Corp., Norwalk, CT 06852; Mr. Walter J. Kulpa Yankee Metal Products Corp. Norwalk CT 06852; Dear Mr. Kulpa:#This is in response to your letter of September 18 1978, requesting a clarification of Federal Motor Vehicle Safety Standard No. 101-80, *Controls and Displays*. The National Highway Traffic Safety Administration concurs in your interpretation of S5.3.1 that any hand operated control which is mounted on the steering column does not have to meet the illumination requirements of Column 4 of Table 1.#Sincerely, Joseph J. Levin, Jr., Chief Counsel; |
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ID: aiam1781OpenHonorable William L. Scott, United States Senate, Washington, DC 20510; Honorable William L. Scott United States Senate Washington DC 20510; Dear Senator Scott: This is in response to your letter of January 28, 1975, requestin information concerning correspondence from the Virginia Automobile Dealers Association urging the issuance of a 2.5 mph bumper impact requirement by February 15, 1975.; On January 2, 1975, the National Highway Traffic Safety Administratio (NHTSA) published a Federal Register notice proposing to reduce the current 5-mph bumper impact requirements to 2.5 mph. The proposal was based primarily on the results of two agency- conducted studies which indicated that the cost and weight of many current production bumpers, in light of inflation and fuel shortages, made the bumpers no longer cost-beneficial. The aim of the proposed reduction in the bumper impact requirements is to allow manufacturers to produce lighter bumpers, which NHTSA studies indicate would have a favorable effect on the cost-benefit ratio.; No agreement was made with the motor vehicle industry concerning th proposal. The proposed reduction in the bumper requirements does not constitute a final statement of the NHTSA's position. All comments and data submitted in response to the proposal will be thoroughly considered before any final decision is reached.; Petitions have been received from various motor vehicle manufacturers insurance groups, and members of Congress requesting extensions of the period allowed for the submission of comments to the proposal. Although the motor vehicle manufacturers limited their request for an extension to that portion of the proposal that would not take effect until 1978, sufficient interest has been shown to indicate that more time is needed for the preparation of comments. Therefore, the comment period has been extended until March 3, 1975.; In addition, in order to allow the airing of all views, we have decide that a public hearing would be desirable. The hearing has been scheduled for February 18 and 19, 1975, at which time all interested persons are invited to present their views on the proposed amendment. I cordially invite the Virginia Automobile Dealers Association to attend and present its thoughts on this subject. We feel that the time schedule for the hearing and the comment closing date will permit the presentation of all sides of the questions involved, and enable the agency to make a final decision in time for the motor vehicle manufacturers to act with respect to the 1976 model year.; For your information, I have enclosed a copy of the Federal Registe notice scheduling the public hearing and extending the comment period. Your interest and that of the Virginia Automobile Dealers Association is greatly appreciated.; Sincerely, Barmin |
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ID: aiam4079OpenMr. M. Hayashibara, Managing Director, Certification Business Division, Mazda (North America), Inc., 24402 Sinacola Court, Farmington Hills, MI 48018; Mr. M. Hayashibara Managing Director Certification Business Division Mazda (North America) Inc. 24402 Sinacola Court Farmington Hills MI 48018; Dear Mr. Hayashibara: This responds to your letter seeking an interpretation of certain term used in Standard No. 110, *Tire selection and rims - passenger cars* (49 CFR S571.110). Specifically, you asked about the definitions of the terms 'curb weight', 'accessory weight', and 'production options weight'. These terms are defined in Standard No. 110 as follows.; The 'curb weight' of a vehicle is calculated by adding the weight o the vehicle with all of its standard equipment, including its maximum capacity of fuel, oil, and coolant to the weights of two optional items of equipment, *if the vehicle is equipped with these optional items*. The items whose weight is included in calculating the curb weight, if present on the vehicle, are air conditioning and the additional weight of an optional engine. No other optional items are included in calculating a vehicle's curb weight, even if the vehicle is equipped with such options.; The 'accessory weight' of a vehicle means the combined weight (i excess of the weight of the standard equipment items that may be replaced) of automatic transmission, power steering, power brakes, power windows, power seats, radio, and heater to the extent that these items are available as factory-installed options on that vehicle, *regardless of whether these options are actually present on the vehicle in question*. No other items of optional equipment are included in calculating the accessory weight, even if the vehicle is equipped with such options.; The 'production options weight' means the combined weight of all item of optional equipment that meet all of the following criteria:; (1) The weight of the item of optional equipment is more than fiv pounds greater than the weight of the item of standard equipment that it replaces,; (2) The optional equipment is present on the vehicle in question, and (3) The weight of the optional equipment has not previously bee considered in either the curb weight or the accessory weight.; Section S3 of Standard No. 110 lists the following examples of items o optional equipment whose weight might be considered when calculating the production options weight: heavy duty brakes, ride levelers, roof rack, heavy duty battery, and special trim. However, any item of optional equipment that meets the three criteria listed above *would* be included in calculating the production options weight, even if that item were not listed in the examples. Therefore, Mazda's understanding is correct that the weight of four-wheel drive components, aerodynamic accessories, special body styling panels, and sunroofs *are* included when calculating the production options weight.; If you have any further questions on this subject, or need mor information, please contact Steve Kratzke of my staff at this address or by telephone at (202) 426- 2992.; Sincerely, Erika Z. Jones, Chief Counsel |
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ID: aiam0893OpenMr. Thomas S. Pieratt, Jr., Executive Secretary, Truck Equipment & Body Distributors Association, 602 Main Street, Cincinnati, OH 45202; Mr. Thomas S. Pieratt Jr. Executive Secretary Truck Equipment & Body Distributors Association 602 Main Street Cincinnati OH 45202; Dear Mr. Pieratt: This is in reply to your letters of September 25 and October 19, 1972 In your letter of September 25, you ask whether persons performing intermediate manufacturing operations are subject to the Defect Reports regulations, specifically that part of the regulations which requires the quarterly reporting of production figures (S 573.5(b)). The defect reports regulations apply to all manufacturers of complete or incomplete motor vehicles. We consider intermediate manufacturers to be within the latter category, and the regulations therefore apply to them.; Your letter of October 19 asks whether a person who installs a fift wheel in a pickup truck is considered a 'remanufacturer.' Under existing regulations, we would not consider the installation of a fifth wheel on a pickup truck to be a significant enough alteration to constitute remanufacturing. Under the recently proposed amendment to the Certification Regulations regarding the certification of altered vehicles (37 F.R. 22600, October 25, 1972), whether such a person would be an alterer and required to affix a new label to the vehicle would depend upon whether the fifth-wheel is a readily attachable component.; Yours truly, richard B. Dyson, Assistant Chief Counsel |
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ID: aiam3246OpenMr. Earl H. Wright, Administrator, Department of Education, State of Florida, Tallahassee, FL 32304; Mr. Earl H. Wright Administrator Department of Education State of Florida Tallahassee FL 32304; Dear Mr. Wright: This responds to your recent letter requesting information concernin the legal ramifications of converting school buses with gasoline fuel systems to liquefied fuel systems.; I am enclosing a copy of a letter that we issued last year whic discusses the Federal requirements and implications of making such conversions of vehicle fuel systems. That letter should answer all of your questions. Please note that an individual or an entity such as a State agency or school board can make modifications to his or its own vehicles with impunity as far as Federal requirements are concerned, if that individual or entity performs the work. For example, district school board employees could make the conversion you desire without regard to Federal requirements, whereas a motor vehicle repair business or the L.P. gas dealer would be responsible for complying with all Federal requirements.; I hope this has been responsive to your inquiry. If you have an further questions, please contact Hugh Oates of my office at 202-426- 2992.; Sincerely, Frank Berndt, Chief Counsel |
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ID: aiam4583OpenThe Honorable Robert C. Smith U.S. House of Representatives Washington, DC 20515; The Honorable Robert C. Smith U.S. House of Representatives Washington DC 20515; "Dear Mr. Smith: Thank you for your letter to Secretary Skinner o behalf of your constituent, Mrs. Maureen Andrews, of Derry. You expressed concern about the absence of safety belts for school bus passengers and about the number of persons to occupy a school bus seat. I've been asked to respond to your letter since the National Highway Traffic Safety Administration (NHTSA) is responsible for administering Federal programs relating to school bus safety. The National Traffic and Motor Vehicle Safety Act of 1966 authorizes NHTSA to issue motor vehicle safety standards for new motor vehicles, including school buses. In 1974, Congress amended the Act to direct NHTSA to issue motor vehicle safety standards addressing various aspects of school bus safety, such as seating systems, windows and windshields, emergency exits, and fuel system integrity. Pursuant to that authority, NHTSA issued a comprehensive set of motor vehicle safety standards to make school buses, already a safe mode of transportation, even safer. We have considered the safety belt issue in connection with our safety standard for school bus passenger crash protection, Federal Motor Vehicle Safety Standard No. 222. Standard No. 222 requires that large school buses provide passenger crash protection through a concept called 'compartmentalization.' Providing compartmentalization entails improving the interior of the school bus with protective seat backs, additional seat padding, and better seat spacing and performance. These interior features are intended to keep occupants in their seating area and protect them during a crash. They ensure that a system of crash protection is provided to passengers independent of whether these passengers use safety belts. For your information, I have enclosed a copy of our notice terminating a rulemaking proceeding to decide whether Standard No. 222 should be amended to specify certain requirements for safety belts voluntarily installed on new large school buses. We decided not to amend the standard since these belts appear to be currently installed in a manner that ensures adequate safety performance. The notice provides a thorough discussion of the safety belt issues raised by Mrs. Andrews. As explained in the notice, school buses in this country have compiled an excellent safety record. In addition to meeting compartmentalization requirements, large school buses differ from small school buses in that they have greater mass, higher seating height and high visibility to other motorists. For all of these reasons, the need for safety belts to mitigate against injuries and fatalities in large school buses is not the same as that for smaller vehicles, such as small school buses. Thus, although Standard No. 222 does require safety belts for passengers in small school buses, we conclude that a Federal requirement for the installation of safety belts in large school buses is not justified at this time. Mrs. Andrews also asks about requirements that apply to the number of children that are allowed to sit on a bench seat. We are not authorized by Congress to regulate the number of persons that may occupy a school bus seat. However, for the purpose of ensuring that school bus manufacturers properly design their large school buses, we do specify the method for establishing the number of designated seating positions on a bench seat. The number of seating positions on a bench seat is calculated under Standard No. 222 by dividing the bench width in inches by 15 and rounding the result to the nearest whole number. Under this formula, a 39 inch bench seat has three seating positions. (39 divided by 15 = 2.6, which is rounded to 3) For small school buses, the determination of the number of positions ensures that the bench seat would have sufficient restraint systems for the maximum number of persons that should ever occupy the seat, and that the seat provides crash protection to all these persons. For large school buses, the determination ensures that the forces applied to the seat during compliance tests are reasonable reflections of the number of occupants and of the crash forces that would be involved in a real-world crash. It should be noted, however, that the number of seating positions derived from the Standard No. 222 formula is not meant to be an absolute measure of the seating capacity of the bus, irrespective of occupant size. We recognize that, in practice, school buses transport a tremendously wide variety of student sizes. For example, while a bus that may be capable of easily accommodating 65 preschool or elementary students, it may be capable of carrying only 43 high school students. When the bus is used to transport students of widely varying ages and sizes, the appropriate capacity of the bus will fall somewhere between those two values. The decision on how many passengers may be comfortably and safely accommodated, therefore, is a decision that must be reached by the bus operator, in light of the ages and sizes of passengers involved, and in accordance with state and local requirements. Since NHTSA does not have the authority to regulate how States use school buses, the agency could not preclude a State from allowing the number of passengers on a bench seat to exceed the number of designated seating positions on that seat. However, we agree with Mrs. Andrews that a student should not stand while riding in a school bus. We agree further that a student should not sit on a seat unless the student can sit fully on the seat instead of sitting only partially on the seat and thus only being partially protected by the compartmentalization. We believe that Mrs. Andrews' concerns as they apply to public schools would be best addressed by her working with the local school board and state officials. I hope this information is helpful. If you have any further questions, please do not hesitate to contact me. Sincerely, Diane K. Steed Enclosure"; |
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ID: aiam3231OpenMr. Raymond J. Salehar, Highway Safety Engineer, Motor Vehicle Administration, Maryland Department of Transportation, 6601 Ritchie Highway NE, Glen Burnie, MD 21062; Mr. Raymond J. Salehar Highway Safety Engineer Motor Vehicle Administration Maryland Department of Transportation 6601 Ritchie Highway NE Glen Burnie MD 21062; Dear Mr. Salehar: This responds to your February 8, 1980, letter asking whether it i permissible for a State to transport children to and from school on regular city transit buses. The answer to your question is yes, if the buses are on their scheduled transit routes and are transporting both school children and adults.; The National Highway Traffic Safety Administration has defined schoo bus in a way that allows buses sold for use as common carriers in urban transportation to transport school children without complying with school bus standards. This definition is located in Title 49 of the Code of Federal Regulations, Part 571.3. The agency permitted this exemption from the school bus safety standards in acknowledgment of the high costs involved in maintaining dual fleets of buses, one for school children and one for adults. Accordingly, the agency permitted cities with operating bus lines to transport children on those city buses. The agency also believes that joint bus fleets can help to conserve fuel.; The agency has made one restriction on the use of city buses t transport school children. The buses must be operating on their regular passenger routes and schedules and must not be operating on special school bus routes. Any vehicle that is operating exclusively as a school bus should be constructed in accordance with the school bus safety standards.; Sincerely, Frank Berndt, Chief Counsel |
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ID: aiam3661OpenMr. John C. Dobbs, Project Manager, E-Z-Go Textron, P.O. Box 388, Augusta, GA 30913-2699; Mr. John C. Dobbs Project Manager E-Z-Go Textron P.O. Box 388 Augusta GA 30913-2699; Dear Mr. Dobbs: This is in reply to your letter of February 4, 1983, telling of you wish to build a four-wheeled light weight traffic enforcement vehicle similar to a three-wheeled machine manufactured by Cushman. You have asked whether you have to meet passenger car safety standards 'or can we obtain a waiver for this vehicle only to comply with motorcycle safety standards?' You have enclosed a brochure on the vehicle you propose to modify, Textron's GX-800.; I am sorry to say that only vehicles with three wheels or less ar defined as 'motorcycles' for purposes of compliance with the Federal motor vehicle safety standards. Years ago, the agency totally excluded from the application of those standards four-wheeled vehicles with a curb weight of 1000 pounds or less such as the GX-800. However, that exclusion was terminated in the early 1970's.; A manufacturer of 10,000 vehicles or less per year may petition for temporary exemption from any safety standard where immediate compliance would cause substantial economic hardship. However, he must make a good faith effort to bring the vehicle into compliance during the exemption period. Although this would appear impossible with your vehicle because of its physical limitations, the agency has in the past exempted replicas of 1900-style vehicles where full compliance was manifestly not feasible. I enclose a copy of Title 49 Code of Federal Regulations Part 555 which sets out the exemption procedures. If your planned vehicle would have a cargo box, similar to the one on the Cushman vehicle, your vehicle could be considered a 'truck' for compliance purposes.; As a car or truck, your vehicle would also have to comply with Federa fuel economy and emissions standards. Exemptions from fuel economy standards may be sought under 49 CFR Part 525. As to the emissions standards, you should write the Environmental Protection Agency.; Sincerely, Frank Berndt, Chief Counsel |
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ID: aiam2973OpenMr. Charles D. Hylton, III, Director, Editorial Services, National Tire Dealers & Retreaders Association, Inc., 1343 L Street, N.W., Washington, DC 20005; Mr. Charles D. Hylton III Director Editorial Services National Tire Dealers & Retreaders Association Inc. 1343 L Street N.W. Washington DC 20005; Dear Mr. Hylton: This is in response to your letter of February 27, 1979, asking whethe tire dealers are responsible for supplying point-of-sale information concerning the Uniform Tire Quality Grading Standards (UTQG) (49 CFR 575.104) to prospective tire purchasers.; Subpart A of Part 575, *Consumer Information Regulations*, provides i section 575.6(c) (49 CFR 575.6(c)) that,; >>>'Each manufacturer of motor vehicles, each brand name owner o tires, and each manufacturer of tires for which there is no brand name owner shall provide for examination by prospective purchasers, at each location where its vehicles or tires are offered for sale by a person with whom the manufacturer or brand name owner has a contractual, proprietary, or other legal relationship, or by a person who has such a relationship with a distributor of the manufacturer or brand name owner concerning the vehicle or tire in question, the information specified in Subpart B of this part that is applicable to each of the vehicles or tires offered for sale at that location ...'<<<; The UTQG Standards, contained in Subpart B of Part 575, specify th information which must be furnished to prospective purchasers by vehicle manufacturers, tire manufacturers, and tire brand name owners (49 CFR 575.104(d)(1)(ii)).; Thus, the Consumer Information Regulations place the responsibility fo providing UTQG point-of-sale information to prospective tire purchasers on manufacturers and brand name owners rather than directly on tire dealers. The means by which tire manufacturers and brand name owners assure that UTQG information is provided for examination will be determined between these suppliers and their dealers and distributors.; You should also note that, in light of the 30-day stay granted by th U.S. Court of Appeals for the Sixth Circuit in the case of *B.F. Goodrich Co. v. Department of Transportation*, the effective dates for all requirements of the UTQG regulation, with the exception of paragraphs (d)(1)(i)(A) and (d)(1)(iii) (49 CFR 575.104(d)(i)(A) and (d)(1)(iii), are now March 31, 1979 for bias-ply tires and October 1, 1979 for bias- belted tires. Paragraph (d)(1)(i)(A), the sidewall molding requirement, and paragraph (d)(1)(iii), the first purchaser requirement, now become effective October 1, 1979 for bias-ply tires and March 31, 1980 for bias-belted tires.; Sincerely, Frank A. Berndt, Acting Chief Counsel |
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ID: aiam2420OpenMr. G. B. Craig, Commissioner, Department of California Highway Patrol, P.O. Box 898, Sacramento, CA 95804; Mr. G. B. Craig Commissioner Department of California Highway Patrol P.O. Box 898 Sacramento CA 95804; Dear Commissioner Craig: Thank you for your August 12 and September 28, 1976, letters to ou Office of Standards Enforcement concerning possible noncompliance of certain air- braked school buses with Standard No. 121, *Air Brake Systems*. At issue is the functioning of a 'double check valve' between the two tanks of an air brake system designed to meet S5.7.2 of the standard (as it was in effect prior to September 1, 1976). The valve serves to provide air pressure from either supply reservoir to hold off the spring brakes while guarding the air brake system from air loss through either one of the reservoirs. The identified problem stems from construction or installation of the valve such that it does not necessarily operate to seal off the brake system from a loss of air in one of the tanks, permitting loss of air from both reservoirs unless the rate of air loss is substantial. Your letter advises that the State of California is permitting the continued operation of the school buses in question pending receipt of a response from the National Highway Traffic Safety Administration (NHTSA).; I would like to address the findings you raise in the order in whic they are listed on page two of your letter. I interpret your first finding to be that the 'split system' designs used in compliance with Standard No. 121 may be incapable of meeting the stopping distance requirements set forth in S5.7.2. You question whether S5.7.2 adequately specifies a 'back up' braking capability that is not cancelled out by a single failure of air pressure components, citing cases where a substantial rate of loss from one tank (introduced as a failure in accordance with S5.7.2.3) draws down the air pressure in both halves of a split system.; The general requirement of S5.7.2.3 (of the now superseded text) i that the vehicle, in one out of six attempts under specified conditions, must be capable of stopping from 60 mph within a distance of 613 feet 'with a single failure in the service brake system of a part designed to contain compressed air or brake fluid. . . .' To provide this performance (and meet the other requirements of S5.7.2) manufacturers have provided 'split systems' modulated by the service brake control. As a matter of general compliance with this requirement, you have asked if any single failure (other than failure of common components) can be introduced into the system as a test of its compliance. The answer to your question is yes. The NHTSA does not know the basis of Ford Motor Company's contention that the 'failure' introduced in the system must be at least 50 psi/min from an initial reservoir pressure of 120 psi.; A noncompliance with S5.7.2.3 occurs only if the vehicle, with th failure introduced, is incapable of stopping within the prescribed distance in one out of six attempts. Thus, an extremely small failure which is easily overcome by compressor pressure would be one way of testing for compliance with S5.7.2.3, but it would not, in all likelihood, result in the demonstration of a noncompliance. As you noted in the second paragraph of page 3 of your letter, a noncompliance with stopping distance requirements may depend (largely because of a compressor's ability to overcome air loss) on the rate of leakage introduced and the time allowed between introduction of the failure and application of the emergency brake. The standard does not (except for the provision of S6.1.14 for towing vehicles manufactured on or after September 1, 1976) provide detailed specification of procedures, particularly the time between failure and brake application. The agency therefore must utilize a reasonable procedure that does not unfairly test the system. In this case, the agency considers the introduction of any size leak, followed by brake application as soon as the low pressure warning activates, to be a reasonable procedure, approximating what would occur in the event of actual failure on the highway. The agency would find a noncompliance with S5.7.2.3 if the school buses are incapable of stopping within the required distance when the described procedure is followed.; Your second finding is that a particular double check valv installation can cause noncompliance with S5.7.2.3. Consistent with our general discussion of compliance with S5.7.2.3, stopping tests are the means to discover whether the buses in question comply. We are analyzing your data, and a noncompliance investigation has been opened. We have notified Ford Motor Company of its commencement. We have also forwarded data to our Office of Defects Investigation to see if the check valve problem constitutes a safety-related defect apart from the issue of compliance.; Your last three findings address the separate question of whether th concept of a split system is adequately interfaced with the parking brake requirements of Standard No. 121. First you make the general point that, if S5.7.2.3 permits a substantial loss of air from both sides of a split system, the benefit of redundant lines is negated and the split system requirement is unjustified. The agency understands your position and believes that a stricter control on the amount of permissible leakage (perhaps by means of a limitation on compressor replenishment or a longer period before emergency brake application) may be justified. Particularly important is your point that a compressor loses capability as it grows older, and that this is not accounted for in new-vehicle tests. At the same time, however, larger failures do occur and we continue to view the split system as extremely important for these cases. The split system provides extremely good protection against failures such as rupture of a line or brake chamber diaphragm.; With regard to your point that split systems do not guard agains failure of components common to the two systems as they are presently constructed (such as the compressor drive belt), I must agree with your point that no brake system can guard against every conceivable failure completely. It is for these cases, in fact, that the agency considers the automatic application of the parking brake system beneficial following loss of the other two capabilities.; You make the further point that, in cases of marginal compliance (i.e. the compressor can replace most but not all air loss from both sides of the split system), the gradual loss of system pressure permits parking brake application that interferes with modulation of the emergency capability. While S5.7.2 was designated as '*Modulated emergency braking system*', no specification for modulation was set forth in its requirements. The agency intended that a system conforming to S5.7.2 would be controlled by the driver instead of by automatic application. Our review of the systems you tested indicates that they are 'modulated systems' as contemplated by the agency.; The present emergency brake requirements only state that the system 'b applied and released, and be capable of modulation, by means of the service brake control.' While further specification of this requirement may be in order, I believe it is the early application of the parking brake that actually concerns you, as it affects the application and release of the emergency braking capability.; You make the observation that early application of the spring brakes i response to air pressure loss permits them to drag, become overheated, and fade, making them useless before they can be utilized. A related issue is that the spring brakes will apply shortly after emergency brake availability (even before activation of the low air pressure warning), immobilizing the vehicle with no capability to release the parking brakes. You suggest implementation of a parking brake arrangement that would keep the spring brakes off longer or provide an isolated source of air pressure to permit their release when they do lock up.; Analysis of your test reports leads me to agree that some specificatio to limit the early application of spring brakes would be in order. Of course, as you are well aware, notice to interested persons of any change in the standard is required, along with an opportunity for comment. I believe that such rulemaking could be joined with the earlier rulemaking undertaken in response to a California Highway Patrol (CHP) petition (Docket 75-16, Notice 04).; Your final point is that, as long as early application of the parkin brake is permissible, an isolated tank of air should be available to permit release of the parking brake from the driver's position. With regard to an isolated tank, the NHTSA continues to maintain its view set forth in our November 29, 1974, letter to Donald Gibson of the CHP that the second side of the split system provides more capability than the old systems (with an isolated tank) to avoid a lockup following a service brake failure. However, you have clearly demonstrated that the capability can be essentially negated by early application of the parking brake. I believe that limitations on early application of the parking brake would be a superior correction to the problem than the addition of more components (and complexity) to the existing systems.; Because school buses are involved in the problems you cite, you are n doubt aware that S 103(d) of the National Traffic and Motor Vehicle Safety Act, while preemptive of State regulations or laws of general applicability that are not identical to Federal standards on the same aspect of performance, does not prevent a State or political subdivision from specifying a higher level of brake performance in vehicles 'procured for its own use.' Thus, the State of California may wish to order school buses with the additional isolated reservoir that you have recommended. The addition of a third tank to a system that complies with the standard's requirements would not be prevented by S 103(d).; I appreciate the constructive approach being pursued by the State o California in enforcement of Standard No. 121. Our Office of Standards Enforcement will keep you advised of the results of its investigation.; Sincerely, Robert L. Carter, Associate Administrator, Motor Vehicl Programs; |
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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.