Lars E. Gulbrandsen, Esq.

Quarles & Brady LLP

411 East Wisconsin Avenue

Milwaukee, WI 53202-4497

Dear Mr. Gulbrandsen:

This responds to your letter regarding the regulation of your clients (Eatons) product called the Hydraulic Launch Assist (HLA) system. You stated that the product is new regenerative braking system, and asked how it would be regulated under the Federal Motor Vehicle Safety Standards (FMVSSs). You stated that the HLA system is similar in purpose to the regenerative braking systems incorporated into hybrid-electric vehicles. According to your letter, the HLA system captures energy generated during braking in a large compressed gas accumulator containing nitrogen, and then releases that energy upon acceleration to produce better fuel economy. We are happy to provide answers to your questions below.

We note that in your letter, you requested that information regarding the HLA system be kept confidential. However, in a subsequent conversation with Ari Scott of my staff regarding the requirements for confidential submissions under 49 CFR 512, you agreed that it would be acceptable for the National Highway Traffic Safety Administration (NHTSA) to make your letter public in its current form, as is standard agency practice when issuing letters of interpretation.

By way of background, NHTSA is authorized to issue FMVSSs that set performance requirements for new motor vehicles and items of motor vehicle equipment (see 49 U.S.C. Chapter 301). NHTSA does not provide approvals of motor vehicles or motor vehicle equipment.  Instead, manufacturers are required to self-certify that their products conform to all applicable safety standards that are in effect on the date of manufacture. NHTSA selects a sampling of new vehicles and equipment each year to determine their compliance with applicable FMVSSs.  If our testing or examination reveals an apparent noncompliance, we may require the manufacturer to remedy the noncompliance, and may initiate an enforcement proceeding if necessary to ensure that the manufacturer takes appropriate action.

Question 1: Do the FMVSS standards applicable to Regenerative Braking Systems apply to the HLA system?


In the paragraph explaining this question, you noted that FMVSS No. 105, Hydraulic and Electric Brake Systems, defines a regenerative braking system (RBS) as an electrical energy system that is installed in an EV [electric vehicle] for recovering or dissipating kinetic energy, and which uses the propulsion motor(s) as a retarder for partial braking of the EV while returning electrical energy to the propulsion battery(s) or dissipating electrical energy. The same definition is included in FMVSS No. 135, Light Vehicle Brake Systems. You noted that the HLA does not use batteries nor is it designed to work with an electric vehicle. You stated that, accordingly, you do not read this definition to include the HLA system. We agree with this conclusion. The HLA would not be considered an RBS for purposes of these standards, and the RBS requirements specified in the standards would not apply to the HLA. We note that a vehicle subject to FMVSS No. 105 or 135 would, of course, be required to meet the other requirements of the applicable standard with the HLA as installed.


Question 2: What indicators must Eaton include on a vehicle incorporating the HLA system?


In your letter, you state that you believe Eaton is permitted to include an HLA system indicator on vehicles equipped with the HLA system under FMVSS No. 101, Controls, Telltales, and Indicators, provided this indicator does not interfere with required indicators. We note that, based on the information provided in your letter, the devices you are asking about are considered telltales under that standard, and we will refer to them as such.

According to the information you provided, the telltale will read HLA. A yellow HLA telltale would indicate that the HLA system is not functioning but that the vehicle can still be operated, while a red HLA telltale would indicate that the HLA system is not working and the vehicle should not be driven. Based on the information you provided, it is our opinion that the telltales you describe would be permitted under FMVSS No. 101.

We note that, for reasons stated above, the HLA system would not be considered an RBS under our standards. Therefore, it does not need to use the symbol RBS or ABS/RBS (the identification specified by FMVSS No. 101 for regenerative brake system malfunction telltales).

Since a telltale indicating a malfunction in a supplemental hydraulic/pneumatic braking system is not otherwise covered by Standard No. 101 or any other standard, its identification is at the option of the manufacturer. We also note that you are using a red color to indicate a severe failure, and a yellow color to indicate a less severe failure. This scheme uses those colors in a manner similar to how they are used for other telltales in FMVSS No. 101. Therefore, we consider this consistent with the requirements of S5.4.2, which states that [a]ny indicator or telltale not listed in Table 1 and identification of that indicator or telltale must not be a color that masks the drivers ability to recognize any telltale, control, or indicator listed in Table 1.


Question 3: Should the brake lights come on when the HLA system is retarding the speed of the vehicle?


In your letter, you asked if active slowing of the vehicle by the HLA system alone necessitates the activation of the brake lights. FMVSS No. 108, Lamps, Reflective Devices, and Associated Equipment, S5.5.4, states that [t]he stop lamps on each vehicle shall be activated upon application of the service brakes. Because the HLA system is a supplemental brake system (i.e., not the service brakes), the standard does not require the stop lamps to be activated upon activation of the HLA system.

We note, consistent with past interpretations, that FMVSS No. 108 does not prohibit the activation of the stop lamps when the HLA system is retarding the speed of the vehicle after the accelerator has been released. The SAE Recommended Practices on stop lamps that are incorporated by reference into Standard No. 108, SAE J586 (May 1984) and SAE J1398 (May 1985), define stop lamps as [l]amps which indicate the intention of the operator of a vehicle to stop or diminish speed by braking. If the vehicle is designed so that release of the accelerator results in braking action from the HLA, we believe this condition can be viewed as an intention by the operator to diminish speed by braking. However, if the HLA system is deactivated, then FMVSS No. 108 would prohibit the brake lights from being activated when the accelerator is released.[1]

Question 4: Does the HLA system implicate FMVSS No. 105 [121]?


In your letter, you ask if the HLA system implicates paragraph S5.3.4.1 of FMVSS No. 105. We presume this is actually a reference to paragraph S5.3.4.1 of FMVSS No. 121, Air Brake Systems, and that you are asking about a situation where the HLA system may be installed on air-braked vehicles. That paragraph establishes certain requirements for service brake release times. The definition of service brake is given in 49 CFR 571.3, and states that [s]ervice brake means the primary mechanism designed to stop a motor vehicle. Despite the fact that the HLA system is a brake system and does change the braking torque to the wheels, it is not the primary mechanism designed to stop the motor vehicle, and therefore not a service brake. Therefore, the HLA system is not subject to this requirement. However, we note that an air-braked vehicle would have to meet all of the requirements of FMVSS No. 121 with the HLA system installed.


Question 5: As a manufacturer of the HLA system, must Eaton register under 49 CFR 566?

You ask whether Eaton is required to register with NHTSA under 49 CFR 566. The answer is it is likely Eaton is not required to register by virtue of manufacturing the HLA system, although it depends on what, specifically, has been incorporated into the HLA system.

49 CFR 566.4, Application, states, [t]his part applies to all manufacturers of motor vehicles, and to manufacturers of motor vehicle equipment to which a motor vehicle safety standard applies. As you stated in your letter, Eaton plans to manufacture and sell the HLA system to vehicle manufacturers, which will install the HLA systems themselves. Therefore, under 49 CFR 566.4, Eaton is not subject to the requirements of Part 566 with regard to those standards that apply only to motor vehicles, because Eaton is not the manufacturer of the motor vehicle that the HLA system will ultimately become a part of. We note that Standards No. 101, 105, 121, and 135 are only applicable to vehicles.[2]

However, certain FMVSSs apply not only to motor vehicles, but also to items of motor vehicle equipment. If the HLA system encompasses some item of motor vehicle equipment to which an FMVSS directly applies, then Eaton would be subject to the requirements of Part 566.

If you have any further questions, please contact Ari Scott of my staff at (202) 366-2992.

Sincerely yours,

Anthony M. Cooke

Chief Counsel



[1] See enclosed April 10, 1992 letter to Mr. Lance Watt, available at

[2] To make this determination, please refer to the Application paragraph, which is located toward the beginning of each FMVSS.