Interpretation ID: nht94-1.93

TYPE: Interpretation-NHTSA

DATE: March 23, 1994

FROM: John Womack -- Acting Chief Counsel, NHTSA

TO: Richard A. Zander -- AlliedSignal Automotive Proving Grounds (New Carlisle, IN)

TITLE: None

ATTACHMT: Attached to letter dated 5/19/93 from Richard A. Zander to NHTSA Office of Chief Council

TEXT:

This responds to your letter asking about the fade and recovery requirements of Federal Motor Vehicle Safety Standard No. 105, Hydraulic Brake Systems. I apologize for the delay in our response. You noted that the standard requires vehicles with a GVWR of 10,000 pounds or less to be capable of making a specified number of fade stops "at a deceleration not lower than 15 fpsps for each stop." You stated that you are aware of a number of different understandings within the industry of the quoted phrase, and requested an interpretation as to whether vehicles must be capable of maintaining an average deceleration of at least 15 fpsps or a minimum deceleration of at least 15 fpsps. As discussed below, vehicles must be capable of maintaining a minimum dec eleration of at least 15 fpsps.

By way of background information, the National Traffic and Motor Vehicle Safety Act (15 U.S.C. S 1381, et seq.) authorizes the National Highway Safety Administration (NHTSA) to issue safety standards applicable to new motor vehicles and items of motor ve hicle equipment. NHTSA does not, however, approve motor vehicles or motor vehicle equipment. Instead, the Safety Act establishes a "self-certification" process under which each manufacturer is responsible for certifying that its products meet all appli cable safety standards.

Manufacturers must have some independent basis for their certification that a product complies with all applicable safety standards. This does not necessarily mean that a manufacturer must conduct the specific tests set forth in an applicable standard. Certifications may be based on, among other things, engineering analyses, actual testing, and computer simulations. Whatever the basis for certification, however, the manufacturer must certify that the product complies with a standard as it is written, i.e., that the vehicle will pass all applicable requirements if it is tested exactly according to the standard's test conditions and other specifications.

Standard No. 105's fade and recovery test requirements are set forth in S5.1.4. These requirements must be met under the conditions prescribed in S6, when tested according to the procedures set forth in S7. See S5.1. The purpose of the fade and recover y test requirements is to help ensure that brakes retain adequate stopping capacity during and after exposure to conditions caused by prolonged or severe use, such as long, downhill driving.

The standard specifies two fade and recovery tests for vehicles with a GVWR of 10,000 pounds or less. Each of the fade and recovery tests consists of three parts: (1) baseline check stops, (2) fade stops, and (3) recovery stops. The requirements for t he fade stops are set forth in S5.1.4.2(a), which states that:

Each vehicle with a GVWR of 10,000 lbs or less shall be capable of making 5 fade stops (10 fade stops on the second test) from 60 mph at a deceleration not lower than 15 fpsps for each stop, followed by 5 fade stops at the maximum dec eleration attainable from 5 to 15 fpsps."

As noted, S5.1.4.2(a) must be read in conjunction with S7.11.2.1, which sets forth the procedure for conducting the fade stops. It reads, in relevant part, as follows:

Make 5 stops from 60 mph at 15 fpsps followed by 5 stops at the maximum attainable deceleration between 5 and 15 fpsps for each stop. ... Attain the REQUIRED DECELERATION within 1 second and, AS A MINIMUM, MAINTAIN IT for the remaind er of the stopping time. Control force readings may be terminated when the vehicle speed falls to 5 mph. (Emphasis added.)

The words "required deceleration" in S7.11.2.1 refer to 15 fpsps. (That value is set forth both in S5.1.4.2(a) and the first sentence of S7.11.2.1.) Thus, in conducting fade stops, within one second of beginning a stop, a deceleration of 15 fpsps must be attained. S7.11.2.1 then specifies that, "as a minimum," the required deceleration (15 fpsps) must be maintained for the remainder of the stopping time. (The word "it" in the highlighted sentence refers back to the phrase "required deceleration.") Thus, after a deceleration of 15 fpsps is attained (within one second of beginning the stop), the deceleration cannot drop below 15 fpsps even momentarily.

You stated that you are aware of the following three understandings within the industry concerning the meaning of this requirement:

1. The average deceleration for the stop must be greater than 15 fpsps. The average deceleration is calculated one second after the stop begins to a vehicle speed of 5 mph.

2. After 1 second the deceleration can not drop below 15 fpsps even for an instant. If the deceleration drops below 15 fpsps at any time it is considered a failure even if the average deceleration is greater than 15 fpsps.

3. The average deceleration for the stop must be greater than 15 fpsps and the deceleration must be greater than 15 fpsps for at least 75% of the stop excluding the first second of the stop.

Of the three understandings, the first and third are inconsistent with the plain wording of S7.11.2.1 which specifies that, after the required 15 fpsps deceleration is attained (within one second of beginning the stop), it must, as a MINIMUM, be maintain ed for the remainder of the stopping time. The first and third understandings would, among other things, replace S7.11.2.1's specification that the 15 fpsps deceleration be maintained as a "minimum" with one that it be maintained as an "average."

The second understanding is largely correct. It is correct to state that, in conducting a fade stop, after a 15 fpsps deceleration is attained (within one second of beginning the stop), the deceleration cannot drop below 15 fpsps even

for an instant. However, if the deceleration did drop below 15 fpsps, that would not necessarily indicate a "failure" but might simply be an invalid test. As you note in your letter, a deceleration might fall below 15 fpsps because the driver did not co mpensate for in-stop fade. However, if a vehicle was unable to pass Standard No. 105's fade stop test requirements at the specified deceleration rates, it would not comply with the standard, notwithstanding the fact that it might be able to pass the req uirements at slightly lower deceleration rates.

You stated in your letter that the second understanding appears to not consider the intent of the fade procedure, the intent being that a vehicle must be capable of making multiple high deceleration stops in a short period of time without drastic changes in effectiveness. As discussed above, the purpose of the fade and recovery test requirements is to help ensure that brakes retain adequate stopping capacity during and after exposure to conditions caused by prolonged or severe use, such as long, downhi ll driving. If a vehicle was unable to pass Standard No. 105's fade stop test requirements at the specified deceleration rates, it would indicate inadequate stopping capability during conditions caused by prolonged or severe use, such as long, downhill driving.

You also stated that in the Laboratory Test Procedure for Standard No. 105, published by NHTSA's Office of Vehicle Safety Compliance (OVSC), the data sheet for the fade stops requests the following information for the deceleration: "Average Sust Decel." You stated that it therefore appears that NHTSA's interpretation of the phrase "at a deceleration not lower than 15 fpsps for each stop" is "the average sustained deceleration."

It is incorrect to interpret the OVSC Laboratory Test Procedures as limiting the requirements of the Federal motor vehicle safety standards. I call your attention to the following note which is set forth at the beginning of the Laboratory Test Procedure :

The OVSC Laboratory Test Procedures, prepared for use by independent laboratories under contract to conduct compliance tests for the OVSC, are not intended to limit the requirements of the applicable FMVSS(s). In some cases, the OVSC Laboratory Test Procedures do not include all of the various FMVSS minimum performance requirements. Sometimes, recognizing applicable test tolerances, the Test Procedures specify test conditions which are les s severe than the minimum requirements of the standards themselves. Therefore, compliance of a vehicle or item of motor vehicle equipment is not necessarily guaranteed if the manufacturer limits certification tests to those described in t he OVSC Laboratory Test Procedures.

I am enclosing a copy of the most recent version of the Laboratory Test Procedure for Standard No. 105, in response to your request. I hope this information is helpful. If you have any further questions, please feel free to contact David Elias of my st aff at this address or by telephone at (202) 366- 2992.