Interpretation ID: nht88-3.63

TYPE: INTERPRETATION-NHTSA

DATE: 10/05/88

FROM: J. W. LAWRENCE -- MANAGER COMPLIANCE VOLVO GM HEAVY TRUCK CORP

TO: ERIKA L. JONES -- CHIEF COUNSEL NATIONAL HIGHWAY TRAFFIC SAFETY ADMINISTRATION

TITLE: REQUEST FOR INTERPRETATION FMVSS-124 ACCELERATOR CONTROL SYSTEMS

ATTACHMT: ATTACHED TO LETTER DATED 02/10/89 FROM ERIKA Z. JONES -- NHTSA TO J. W. LAWRENCE, REDBOOK A33, STANDARD 124; LETTER DATED 03/17/88 FROM ERIKA Z. JONES -- NHTSA TO LEON STEENBOCK

TEXT: Dear Ms. Jones:

Volvo GM Heavy Truck Corporation, manufacturer of "WHITEGMC" and importer of "VOLVO" trucks 26,000 lbs and greater GVWR, respectfully requests you reconsider and rescind the interpretation of FMVSS-124 issued by the Administration on March 17, 1988. Spe cifically, VolvoGM believes the March 17 statement "locking hand throttle controls are expressly prohibited by Standard 123" should either be rescinded or restated in such a way as to continue to allow installation of the devices described in this reques t.

All VolvoGM trucks available in the United States are diesel powered and do not have automatic low speed limiting devices such as automatic chokes used on gasoline engines. Like most, if not all heavy truck manufacturers, we install a hand throttle to a llow the driver to increase the low speed idle at will for a multitude of reasons. The most common uses of these hand throttle are for engine warmup, extended idle periods (some times in cold weather diesel trucks will not be shutdown for days) and voca tional applications such as pumping, ready mix delivery, compacting, etc. The vocational applications usually occur when the vehicle is stationary, however, there is no lockout device restricting their use to the non "drive" transmission positions. All hand throttles we install are "locking hand throttle controls" in that once set they hold engine idle at a driver selected level until such time as the driver selects a new idle speed or disengaged the throttle.

FMVSS-124 @ 4 Definitions addresses hand throttles.

"Idle position" means the position of the throttle at which it first comes in contact with an engine idle speed control appropriate for existing conditions according to the manufacturers recommendations. These conditions include, but are not limited to, engine speed adjustments for cold engine, air conditioning, and emission control, and the use of throttle setting devices." (emphasis added)

Source: 37FR pg. 20035 September 23, 1972

The throttle setting or hand throttle control provisions of the Standard are in direct response to a Mack Truck petition addressing hand throttles for heavy duty diesel truck. The FR37, No. 186 preamble discussion on page 20033 dated September 23, 19 72 expresses the Administration's intent at the time the Standard was promulgated.

"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 t he 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."

The standard has been in effect for 15 years during which time hundreds of thousands of heavy duty diesel trucks have been equipped with these devices apparently with no safety problems. We trust this discussion clears the technical issues and if we may be of assistance are most willing.

Sincerely,

ENCLOSURE