Interpretation ID: 18165.135

Mr. Peter Böhm
Manager Regulations
ITT Automotive Europe GmbH
Postfach 90 01 20
60441 Frankfurt am Main
Hausadresse: Guerickstraße 7
60488 Frankfurt am Main, Germany

Dear Mr. Böhm:

Please pardon the delay in responding to your letter to this office in which you asked whether parking brake systems your company is developing comply with the requirements of paragraph S5.2 of Federal Motor Vehicle Safety Standard (Standard) No. 135, Light vehicle brake systems.

You stated that ITT is developing parking brake systems that are activated electrically. One version consists of an electrically-activated disc brake. You stated that when the vehicle is locked in a parking position by a friction-type brake, an interlock device is actuated to lock the wheels or the gearbox. Then, when the interlock has reached its locking position, the friction brake is released. You stated, therefore, that the parking brake is of a friction type and the vehicle is held with solely mechanical means. You also stated that it is the interlock device and not the friction brake that holds the vehicle stationary. You further stated that unlike ECE R-13 and 72/320 EEC, Standard No. 135 has only static requirements for the parking brake. You commented, however, that the requirement to use a friction brake as a parking brake might be something like a dynamic requirement because it makes activation of the parking brake possible while the vehicle is still moving. Also, you stated that if this was the intention to require a friction brake for the parking brake, the interlock device should be allowed to hold the vehicle stationary provided that dynamic application is ensured by other means. You then asked whether such a system meets the requirements of S5.2, Standard No. 135. The answer is no.

As you probably know, Standard No. 135 is a new standard. Compliance will become mandatory for passenger cars manufactured on and after September 1, 2000, and for multipurpose passenger vehicles, trucks, and buses with gross vehicle weight ratings of 3,500 kilograms (7,716 pounds) or less manufactured on and after September 1, 2002. Until those dates, vehicle manufacturers have the option of complying either with Standard No. 135 or Standard No. 105, Hydraulic brake systems.

Paragraph S5.2 of Standard No. 135 was patterned after paragraph S5.2 of Standard No. 105 and provides that "Each vehicle shall be equipped with a parking brake system of a friction type with solely mechanical means to retain engagement." The term "parking brake" is defined in 49 Code of Federal Regulations 571.3 as "a mechanism designed to prevent the movement of a stationary motor vehicle." Thus, with respect to paragraph S5.2 of Standard No. 135, the parking brake must prevent the movement of a stationary motor vehicle by means of friction. Your design, however, would prevent movement of a stationary vehicle by means of the interlock device rather than by friction. I also note that, under S5.2, the parking brake system must have a "solely mechanical means to retain engagement," meaning that although the parking brake may be applied and released by non-mechanical means, it must be held by solely mechanical means. It cannot be held by non-mechanical means such as fluid, air, or electricity.

With respect to your comment that the requirement for a friction brake resembles a dynamic requirement because it makes activation possible while the vehicle is still moving, NHTSA has addressed that issue. In our Notice of Proposed Rulemaking of May 10, 1985 (50 Federal Register (FR) 19744), and again in our Supplemental Notice of Proposed Rulemaking of January 14, 1987 (52 FR 1474), the agency proposed a dynamic test intended to ensure that a driver could use the parking brake to stop a moving vehicle in emergency situations. Several commenters opposed that proposal, arguing that the purpose of parking brakes is to statically hold a vehicle in place, not to decelerate a moving vehicle. They stated that it could be dangerous for drivers to apply parking brakes in dynamic situations because of the difficulty of modulating the application force, which could lead to uncontrollable rear wheel lockup and loss of vehicle control. NHTSA was persuaded by those comments and in the final rule of February 2, 1995 (60 FR 6411), withdrew the proposal to require a parking brake dynamic test.

You stated that your system uses a friction-type brake until the interlock device has reached its locking position, after which the friction brake is released. Whether or not the interlock device is a mechanical means, Standard No. 135 requires the parking brake to be of a friction type. Therefore, if the interlock device disengages the friction brake, the system does not comply with Standard No. 135.

I hope this information is helpful to you. Should you have any further questions or need additional information, feel free to contact Walter Myers of my staff at this address or by telephone at (202) 366-2992, or fax at (202) 366-3820.

Sincerely,
Frank Seales, Jr.
Chief Counsel
ref:105#135
d.12/22/98