Interpretation ID: nht93-2.18

DATE: March 16, 1993

FROM: Bob Brinton -- Friction Advisory Service

TO: Office of Chief Council -- U.S. Department of Transportation, NHTSA

TITLE: Subject: Interpretation of Parking

ATTACHMT: Attached to letter dated 5-6-93 from John Womack to Bob Brinton (A41; Std. 121); Also attached to letter dated 12-9-76 from Frank A. Berndt to Leon W. Steenbock (Std. 121)

TEXT: According to FMVSS 121 a mechanical locking device must be in place within 3 seconds of actuating the parking brake control. In the case of some vehicles, especially refuse type trucks with right hand side drive, there are several systems that use either an I.C.C. flip switch valve or a push pull valve to park the vehicle on air only when the driver leaves the vehicle to pick up trash. The air park is used so that spring brakes are not applied avoiding extreme wear cycles on the spring. Is this type of parking considered legal or should all vehicles when they are parked and the driver leaves the cab have a mechanically held parking brake function? It is my understanding that new O.E.M. certified vehicles are being built with this air park work brake and many right hand drive conversion companies are also installing this type of air park configuration.

As an accident investigator I need to know if NHTSA considers this air park illegal or non-certifiable to meet the intentions of FMVSS 121 Sec. 5.6.3. Your prompt attention to this request is appreciated.