Interpretation ID: nht80-3.1

DATE: 06/11/80

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: Kelsey-Hayes Company

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your December 7, 1979, letter to Docket No. 79-03; Notice 2 on Heavy Duty Vehicle Brake Systems. That letter was in part a comment to the docket and in part a request for an interpretation of Standard No. 121, Air Brake Systems. The points raised in your comment to the docket will be considered in our final rule on the issues proposed in Notice 2. This letter responds to your interpretive question whether your trailer emergency valve is permitted in accordance with the requirements of section 5.2.1.1 of the standard. The answer to your question is no.

Section 5.2.1.1 of the standard requires that vehicles be equipped with a reservoir that is capable of releasing the parking brakes when the air in the service brake system fails. The valve that you suggest would not provide such a reservoir but would merely reroute air from the trailer air supply system which would be used to release the parking brakes. The agency does not believe that this complies with the requirement that a reservoir be provided.

Recently, the Berg Manufacturing Company has petitioned the agency to amend the standard in a manner that would permit the type of system that you suggest. The agency is now evaluating that petition and will issue a notice in the near future addressing this issue. We suggest that you closely follow this rulemaking action.