J.W. Lawrence, Manager, Compliance
Volvo GM Heavy Truck Corporation
7825 National Service Road
Airpark West, P.O. Box 26115
Greensboro, NC 27402-6115

Dear Mr. Lawrence:

This is a response to your letter of October 5, 1988, asking this agency to "reconsider and rescind" an interpretation of Standard 124, Accelerator Control Systems (49 CFR /571.124). The interpretation which was the subject of your request was addressed to Mr. Leon Steenbock and dated March 17, 1988. Mr. Steenbock asked whether it is permissible under Standard 124 to install a locking hand throttle control in a new motor vehicle. In our response to Mr. Steenbock, we stated that while nothing in the Standard prohibits installing a hand-throttle control in a new vehicle, "'locking hand throttle controls' are expressly prohibited by Standard 124."

In your letter, you stated that most (and perhaps all) heavy truck manufacturers install hand throttles for engine warm-up, extended idle periods; and for vocational applications such as pumping, compacting, and mixing. You also stated that your company installs only locking hand throttle controls and that these locking hand throttle controls hold the driver-selected engine idle speed until such time as the driver selects a new idle speed, or disengages the throttle.

In support of your position that the letter to Mr. Steenbock was incorrect, you referred to the agency's response to petitions for reconsideration of Standard 124. NHTSA's response to requests that special provisions be made for hand throttles was as follows:

Mack and Alfa Romeo petitioned that "hand-throttles" and throttle positioners be specifically excluded from the definition of "idle position." Petitioners stated that in the event such a device is used a return to the preset throttle position occurs upon release of the driver-operated accelerator control system. This request is granted. If a driver choose to raise the lowest engine speed threshold by the use of a throttle positioning device, the throttle should return to that new position within the same time requirements specified in section S5.3. Accordingly, the NHTSA is amending the definition of "idle position" to provide for the use of throttle positioners. (37 FR 20033, September 23, 1972.)

In accordance with this stated intent, the definition of "idle position" in S4.1 of Standard 124 was amended to read:

(T)he position of the throttle that will provide the lowest engine speed for existing conditions according to the manufacturers' recommendations. These conditions include, but are not limited to, engine speed adjustments for cold engine, air conditioning equipment, and emission control equipment, and the use of throttle setting devices.

Because of this language, we agree with your position that Standard 124 permits the installation of hand throttles, including locking hand throttle controls, provided that the vehicle's engine returns to the lowest engine speed threshold as adjusted by use of the hand throttle within the time and under the conditions set forth in S5 of Standard 124. To the extent that our March 17, 1988 letter is inconsistent with this interpretation, it is incorrect.

I hope you find this information helpful. If you have further questions, please call Joan F. Tilghman of my staff at (202) 366-2992.


Erika Z. Jones Chief Counsel

cc: Mr. Leon Steenbock Administrative Manager, Engineering FWD Corporation Clintonville, WI 54929-1590

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