Interpretation ID: nht74-4.3

DATE: 06/07/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Engineer/Transit Technology

TITLE: TITLE: FMVSS INTERPRETATION

TEXT: This responds to your April 2, 1974, request for a ruling on whether trolley and motor buses equipped with air brake systems and dynamic electric or hydraulic devices are required to be equipped with antilock equipment.

Standard No. 121, Air brake systems, requires stopping distance performance which must be met by any bus equipped with air brakes, whether or not it is equipped with supplementary dynamic braking means, and the stops must be made with only controlled wheel lockup over 10 mph. Although the standard does not require antilock devices, many manufacturers have indicated they will use antilock devices to meet this requirement.

In evaluating a vehicle's compliance with the stopping distance performance requirements of S5.3 and S5.7.2.3, auxiliary braking devices may be utilized in making the stops provided such devices are engaged by means of the same service brake pedal or parking brake control that operates the air brakes. It should be noted, however, that these stops must be made with the transmission selector control in neutral or the clutch disengaged (S6.1.3).

It can be foreseen that at least one difficulty may arise in testing with supplementary brake systems. S6.3 requires that the transmission be in neutral or the clutch be disengaged during deceleration, which might eliminate the torque from your dynamic brake.

Please write again if this or other difficulties arise in the certification of your buses.

Sincerely,

April 2, 1974

National Highway Traffic Administrator

Dear Sir:

The Municipality of Metropolitan Seattle has recently written a specification for the purchase of more than 600 motor and trolley buses. The first draft of this specification is presently in circulation to potential bidders, transit properties, governmental agencies, consultants and other interested individuals for their comments. These comments must be received by the Municipality by April 30, 1974, for evaluation and possible implementation into the final specification which is scheduled for release about the middle of June, 1974.

In a telephone conversation with Assistant Chief Counsel Richard Dyson on March 26, 1974, I brought up a question related to bus brakes and FMVSS 121. The Municipality has a specification requirement for dynamic brakes on our new trolley buses in addition to the standard air brakes. We also have a specification requirement for an electric or hydraulic retarder on two of our new larger types of motor buses in addition to the standard air brakes. The question, as asked of the Municipality by an interested foreign manufacturer, is whether it is still necessary to provide anti-skid equipment or brake equalization with dynamic braking on the trolley bus, and whether it is necessary to provide anti-skid equipment or brake equalization with an electric or hydraulic retarder on the motor buses. The electric retarder operates off the gear box, drive shaft or differential and the hydraulic retarder operates off the transmission.

Mr. Dyson advised me to put the question with supplementary background in written form and address it to you for an interpretation and ruling. I have enclosed a copy of the letter regarding the brake question, a copy of the bus specification of the buses for the Municipality of Metropolitan Seattle, a copy of the information on the electrical retarder and a copy of the information on the hydraulic retarder.

We shall look forward to your reply so that we can advise potential bidders of this decision.

Very truly yours,

Alden G. Olson

Engineer/Transit Technology

Enclosures

TRANSPORTATION EQUIPMENT DEVELOPMENT CO.

MARCH 14, 1974

John Aurelius Mgr., Transit Technology SEATTLE METRO 410 West Harrison Street Seattle, WA 98119

SUBJECT: FMVSS QUESTIONS

Arne Lindqvist and I finally caught up with each other in New York so we had an opportunity to discuss our mutual problems as they relate to bus production for the U.S. market.

As he told you, meeting the Federal Motor Vehicle Safety Standards is a bit of a thorn for European producers inasmuch as there is a somewhat different approach to safety in Europe.

There is one important point which, to our knowledge, has not yet been clarified. This is the question of brake equalization in a trolley coach. With dynamic braking, is it still necessary to provide anti-skid equipment or brake equalization? Is it possible to obtain an exception?

This same line of thinking would lead us to similar questions relating to motor coaches. All new motor coaches in Switzerland are equipped with dynamic braking as are a high percentage of the new commercial vehicles in other countries. The Telma retarder would be recommended for the second and third axlesof the HESS articulated motor coach.

Can you secure a ruling on these points? Perhaps you have already explored this subject and can advise us.

Very truly yours,

H.T. HAWKES---President