Interpretation ID: aiam1685
Supervising Inspector
Commander
Enforcement Services Division
Department of California Highway Patrol
P.O. Box 898
Sacramento
CA 95804;
Dear Mr. Gibson: This is in response to your letter of October 21, 1974, inquiring as t the effect of Federal Motor Vehicle Safety Standard No. 121 on State laws relating to air brake performance. You ask whether California can impose requirements pertaining to parking brake release (on trucks and buses) and trailer emergency braking capability which differ from provisions contained in the Federal standard.; Section 103(d) of the National Traffic and Motor Vehicle Safety Act o 1966 (15 U.S.C. 1392(d)) provides that no State or political subdivision of a State may promulgate or continue in effect standards applicable to an aspect of motor vehicle or motor vehicle equipment performance which is covered by a Federal motor vehicle safety standard, unless the standards are identical.; Standard 121 includes provisions relating to truck and bus parkin brake performance and specifies requirements for an emergency braking capability on trailers. Promulgation by a State of a more restrictive parking brake requirement providing for the installation of a release not specified in the Federal standard is prohibited by S 103(d) since the Federal standard is intended to cover all aspects of parking brake performance. A State requirement specifying application of trailer service brakes on breakaway would also be preempted by Standard 121 since Section S5.8 of the Federal standard addresses the subject of emergency trailer braking capability.; The Federal requirements must be regarded as conclusive with regard t parking brake performance and emergency braking capability in order to maintain the uniformity necessary in a Federal regulatory scheme. If States were permitted to impose additional requirements in an area regulated by a Federal safety standard manufacturers would be confronted with an impossible task of compliance. This reasoning formed the basis of a recent decision rendered in a case brought by the Motorcycle Industry Council, Inc. against the State of California in the United States District Court for the Eastern District of California concerning the preemption of a California State requirement that motorcycle headlamps be wired to operate when the engine is running. The Court held that the California requirement is preempted by the Federal Motor Vehicle Safety Standard No. 108 since the NHTSA intended to cover all aspects of performance directly involving motorcycle headlamps.; Therefore, requirements such as those described in your letter would b preempted by Standard 121 since the aspects of performance that would be affected are covered by the Federal standard.; You also ask if your interpretation of Standard No. 121 t International Harvester is correct. In answer, I would like to set out a comprehensive explanation of the standard's requirements for parking brakes (S5.6) in relation to the requirements for emergency braking capability (S5.7, S5.8). I have separated the requirements for trailers from those for trucks, and further separated the truck requirements into the 'automatically-applied parking brake' systems (S5.7.1) and the 'modulated' systems (S5.7.2).; *Trailer brake requirements (other than trailer converter dollies)*. I addition to the requirement for a trailer service brake system (S5.3, S5.4), Standard No. 121 specifies that each air-braked trailer be equipped with an emergency capability (S5.8) and a parking brake (S5.6). The emergency braking capability calls for an automatic application of the parking brake system in the event the air pressure in the supply line is lost. This requirement ensures a back-up braking system in cases of service brake failure and brakes on the trailer in the event of a trailer break away.; The parking brake requirements for trailers specify that the brakes b applied by an energy source that is not affected by loss of air pressure in the service brake system and that, once applied, the parking brakes be held in the applied position solely by mechanical means. The common method to meet this requirement is, of course, to use springs to apply and hold the friction elements of the service brake system. The requirements are intended to ensure that a parked vehicle will not lose its brakes if air is lost from the system by leakage.; The NHTSA recognizes that automatic application of the 'spring brakes (as an emergency capability) could cause a safety problem if they could not be released to move the disabled vehicle from the roadway. For this reason, S5.2.1.1 specifies that each trailer be equipped with a protected reservoir that is capable of releasing the vehicle's parking brakes at least once.; Your interpretation that Standard No. 121 requires control of this tan from the driver's position after an automatic application of the parking brakes is incorrect. The parking brake requirements of S5.6 specify a system for holding stationary a vehicle (or combination) which has a totally functioning brake system. Therefore, S5.6.4 does not establish requirements for application and release of the parking system of the towed vehicle in an emergency when, for example, a supply line to the towed vehicle has burst. The requirement of S5.7.2.2 that parking brakes remain operable is not addressed to trailers.; You pointed out in your July 11, 1973, comments to the docket that th standard should be amended to require that the trailer's protected tank be equipped with a manual valve that releases the parking brakes to permit moving a disabled trailer from the roadway. We are preparing a proposal on parking brake systems in response to an American Trucking Associations petition, which may be responsive to your suggestions.; *Truck (and bus) requirements*. In addition to the requirement for service brake system (S5.3, S5.4), Standard No. 121 specifies that each air-braked truck (and bus) be equipped with an emergency braking capability (S5.7) and a parking brake system (S5.6).; The parking brake requirements of S5.6, as noted above, specify system for holding stationary a vehicle (or combination) which as a totally functioning brake system. S5.6.4 does not therefore establish control requirements in the event of a failure in the system. Only the brake control requirements listed in S5.7 are required during and after a stop which follows a failure in the service brake system.; Section S5.7 permits the manufacturer to provide the emergency brak capability and associated controls in one of two ways: automatically-applied parking brakes (S5.7.1) or a modulated braking capability (S5.7.2). To our knowledge few if any manufacturers have chosen to build an emergency system which conforms to S5.7.1. Because the International Harvester (IH) system and those of other manufacturers conform to S5.7.2, the following discussion addresses only that option.; S5.7.2 specifies an emergency braking capability which can stop th truck or bus within a certain distance in the event of a failure of the service brake system other than a failure of a common valve, manifold, brake fluid housing, or brake chamber housing (S5.7.2.3). When a failure of this type occurs in the truck, S5.7.2.1 specifies that the towing vehicle emergency brake system control be capable of controlling service or parking brakes on any towed vehicle equipped with air brakes. This does not mean that control must be exercised over the trailer brakes if a failure occurs in the supply line or control line to the trailer.; S5.7.2.2 specifies a dynamic braking capability in the parking brak system (subject to manual application) in the event of a total failure of the service- emergency braking capability.; From a study of the brake system schematics for the IH split syste (with spring brakes), it appears that the system would comply with Standard No. 121. In your letter to IH you conclude that their system does not comply 'since the spring brake [on the truck] can not be released when the service air is lost.' You base your interpretation on language of S5.7.2.2 that 'loss of air [due to failure in both service and emergency modes] shall not cause the parking brake to be inoperable'. Your concern is that a failure of this nature would prevent a disabled vehicle from being moved from the roadway if the parking brake is not releasable.; As earlier noted, S5.7.2.2 specifies a dynamic parking brake capabilit in the event of catastrophic failure. This section is not a requirement that the parking brake operate as it would in a totally functioning and stationary vehicle. Such a requirement in S5.7.2 for release of the parking brakes to move the vehicle is impractical with some of the specified failures. Moreover, it is also unnecessary, because a modulated emergency system provides a driver with several applications and releases of the emergency brake system to move the disabled vehicle off the road after the signal from the warning system (S5.1.6) that the vehicle has lost its service brake system. These applications are the equivalent of the California requirement that the spring brake system be capable of being applied, released, and reapplied by the driver, following notice of the service brake system failure, as indicated by an automatic brake application.; You make the statement that IH must meet the requirements of S5.7.1. because its parking brakes apply automatically after both the service system fails and the emergency system is depleted. In fact IH has chosen to meet S5.7.2 and is not required to meet any of the specifications of S5.7.1.; Because these differences exist between the present Californi regulations and the soon-to-be-implemented Federal requirements, manufacturers like International Harvester will have difficulty in effecting an orderly transition to the new systems. We have encouraged manufacturers to introduce the new systems in small numbers before the effective date to gain some experience with them, and we feel that it would be unfortunate if these manufacturers were penalized by the States for their early introductions.; I invite comments from the State of California on our upcoming parkin brake system proposal.; Yours truly, Richard B. Dyson, Acting Chief Counsel