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Interpretation ID: NCC-250121-001 FMVSS No 135.Parking Brake Indicator-lanetta signed 11.8.25

October 8, 2025

 

U.S. Department of Transportation 

National Highway Traffic Safety Administration 

Office of the Chief Counsel 

1200 New Jersey Avenue SE. 

Washington, DC 20590

 

Ms. Christie Iannetta 

Nelson Mullins 

101 Constitution Avenue, NW 

Suite 900

Washington, DC 20001   

 

Dear Ms. Iannetta:

I am writing in response to your letter addressed to NHTSA dated January 15, 2025, asking the agency to reconsider an interpretation issued on October 31, 2024 ("the interpretation").1 The interpretation was issued in response to a request you submitted on behalf of an anonymous client on February 26, 2024. In the request, you asked for clarification on Federal Motor Vehicle Safety Standard (FMVSS) No. 135, "Light vehicle brake systems." Specifically, you asked about paragraph S5.5.1, which sets out requirements for when certain brake indicators must be activated. In the interpretation, the agency concluded that the parking brake system described in your letter likely would not comply with FMVSS No. 135's requirements. 

Your January 15 letter requests that we reconsider the interpretation. After considering your request and evaluating the conclusion and analysis in the interpretation, we do not believe we misunderstood your original interpretation request, and we are not reconsidering the interpretation. A detailed explanation of our reasoning follows. 

Background 

By way of background, the National Highway Traffic Safety Administration (NHTSA) does not provide approvals of motor vehicles or motor vehicle equipment. Under 49 U.S.C. Chapter 301, manufacturers are required to ensure that their vehicles and equipment meet applicable requirements. The following represents our opinion based on the facts provided in your letter. 

Please also note that our answer below is based on our understanding of the specific information provided in your letter. This letter does not have the force and effect of law and is not meant to bind the public in any way. This letter is intended only to provide clarity regarding existing 

1 NHTSA Interpretation File Search, ID: NCC-230308-001, https://www.nhtsa.gov/interpretations/ncc-230308-001- nelsonmullinsparkingbrakeindicatorinterp.

requirements under the law and represents the opinion of the agency on the questions addressed in your letter at the time of signature. 

FMVSS No. 135 establishes requirements for light vehicle braking systems. Paragraph S5.5.1 therein requires indicators to be activated when the ignition (start) switch is in the "on" ("run") position and one or more of seven scenarios occur. Paragraph (c) of S5.5.1 requires an indicator to be activated upon "application of the parking brake." Therefore, if the parking brake is applied and the vehicle's ignition is in the "on" position, a parking brake indicator must be activated. 

You explain that your client's vehicle uses an Electronic Parking Brake (EPB) system where the parking brake can be applied manually by the driver or automatically by the system. The driver can engage the parking brake via the in-vehicle control at any time before shifting the vehicle into park, and when the parking brake is engaged by the driver, the parking brake indicator displays clearly in front of the driver. However, the EPB system can also apply the parking brake on its own, and it does so whenever the vehicle is shifted into park. If the EPB system engages the parking brake on its own, the parking brake indicator does not display. Finally, regardless of how the parking brake is engaged (by the driver or by the EPB system), the parking brake always disengages automatically once the vehicle is shifted out of park, or in some vehicles, when the brake pedal is depressed. 

In the interpretation we concluded that your client's system is likely not compliant with the requirements of FMVSS No. 135. Specifically, we explained that S5.5.l(c) requires that if a vehicle ignition is in the "on" position and the parking brake is applied, an indicator must activate to inform the driver of the status of the parking brake. You may reference the interpretation for our complete analysis on the issue. 

In your January 15 letter, you express your belief that we misunderstood an important fact about the manufacturer's parking brake system, and that we failed to consider relevant regulatory context. 

NHTSA's Response 

We adequately understood the functionality of your client's parking brake system, and we also considered all of the relevant regulatory background. 

NHTSA Did Not Misunderstand Your Client's EPB System 

You indicate that we purportedly failed to understand that it is impossible for your client's vehicle to be driven with the parking brake applied because the system is designed to disengage whenever the vehicle is shifted out of park. Your letter quotes the following line from the interpretation as evidence that we misunderstood this crucial fact about the EPB system: "nothing prevents the vehicle from driving during this engagement." (See interpretation p. 3, ID: NCC-230308-001). 

When we drafted the interpretation, we did so with a complete understanding that your client's vehicle is designed to make it impossible to drive with the parking brake activated. We considered this fact when analyzing your client's system under the requirements of paragraph S5.5.1(c). We concluded that even though your client's vehicle design may potentially address the safety concern of driving with the parking brake activated, manufacturers may not disregard FMVSS requirements because they feel they have resolved the safety issue the standard was designed to address. As we stated in the interpretation, "[I]f a manufacturer believes that it has developed technology that makes certain regulatory requirements unnecessary, it may petition the agency for a rulemaking to amend the relevant requirements." Until the standard is amended, manufacturers must certify in good faith to the current requirements. 

NHTSA Did Not Ignore Important Regulatory Context 

You assert that the stated purpose of paragraph S5.5.l(c) is to prevent drivers from driving with the parking brake on, and your client's EPB system addresses that safety concern. Not only did we consider this argument in the interpretation, but our response to this argument was a central component of the interpretation. As we stated in the interpretation:

Just because a manufacturer has designed a system that purports to resolve, through other means, a safety concern addressed in an FMVSS does not mean that it is not bound by the requirements of the FMVSS or that it may introduce noncompliant motor vehicles or motor vehicle equipment to the market. If a manufacturer believes that it has developed technology that makes certain regulatory requirements unnecessary, it may petition the agency for a rulemaking to amend the relevant requirements. 

We understood then that your client believes it has created an EPB system that addresses the stated safety purpose of paragraph S5.5.l(c)'s parking indicator requirement. As noted, manufacturers must certify compliance with the express terms of an FMVSS, and not just with its stated purpose. In this case, we believe that even if your client's system may address the stated safety purpose underlying paragraph S5.5.l(c), it does not comply with the paragraph's requirements. 

Nor is your argument about the test procedures set out in FMVSS No. 135 S7.12.2 persuasive. You note that the parking brake test procedure requires a vehicle to be put into neutral and the parking brake applied, after which the parking brake must hold the vehicle stationary for a specific amount of time. One of the steps in the test procedure (S7.12.2(m)) is for the test conductor to verify the operation of the parking brake application indicator. You assert that the parking brake indicator is only evaluated after the performance of the steps within the test procedure in S7.12.2, during which the parking brake is applied manually. 

However, nothing in the parking brake test procedure negates paragraph S5.5.l(c)'s parking brake indicator requirement. The requirements that the brake system warning indicators illuminate under specified conditions exists independent of any test procedure. The duration during which a brake system warning indicator must be displayed is addressed in paragraph S5.5.3, which provides that each warning indicator "shall remain activated as long as the condition exists, whenever the ignition ('start') switch is in the 'on' ('run') position, whether or not the engine is running." Nothing in the test procedures purports to alter or limit this requirement. Thus, your client must be able to certify in good faith that its vehicle's parking brake indicator appears in plain view of the driver whenever the parking brake is engaged. We do not believe your client is able to do so based on your description of its EPB system. We note also that the final inspection procedure in paragraph S7.17 requires inspection of "[t]he brake system indicators, for compliance with operation in various key positions, lens color, labeling, and location, in accordance with S5.5." We expect that noncompliance with the requirement of paragraph S5.5.l(c) would be observed during this final inspection. 

I hope this letter provides clarity on NHTSA's stance on this matter. If you have any further questions, please contact Mr. David Jasinski of my staff at interpretations.NHTSA@dot.gov.

Sincerely,

Peter Simshauser 

Chief Counsel

 

Dated: 10/8/25
Ref: FMVSS No. 135