Interpretation ID: aiam5048
OH 44036;
"Dear Mr. Hopkins: This responds to your letter of August 3, 1992 seeking an interpretation of Standard No. 124, Accelerator Control Systems (49 CFR 571.124). More specifically, your letter sought 'confirmation of (y)our position that vehicles equipped with electronic engine control systems ... which include an electronic treadle assembly are not covered by the scope and requirements of FMVSS"; "124.' As explained in detail below, your understanding is incorrect Standard No. 124 applies to all listed vehicle types, regardless of whether their engine control systems use electronic or mechanical means to control the engine. The purpose of Standard No. 124 is to reduce deaths and injuries caused by vehicles that continue to supply fuel to the engine when there is a malfunction in the accelerator control system. To ensure that drivers could bring vehicles that experience a problem with the accelerator control system to a controlled stop, instead of having the vehicle continue to speed forward, Standard No. 124 requires that the vehicle's throttle return to the idle position whenever the driver removes the actuating force from the accelerator control and that the throttle return to idle whenever there is a severance or disconnection in the accelerator control system. The safety need for these requirements is the same for all vehicles, regardless of whether their accelerator control system is electronic, mechanical, or some other type of technology. S4.1 sets forth the following definitions: Throttle means the component of the fuel metering device that connects to the driver-operated accelerator control system and that by input from the driver-operated accelerator control system controls the engine speed. Fuel metering device means the carburetor, or in the case of certain engines, the fuel injector, fuel distributor, or fuel injection pump. Driver-operated accelerator control system means all vehicle components, except the fuel metering device, that regulate engine speed in direct response to movement of the driver-operated control and that return the throttle to the idle position upon release of the actuating force. You said in your letter that the electronic treadle assembly in your company's accelerator control system 'modulates an electric signal, received from an outside source, in response to the input of the operator's foot. This signal is an input to the engine electronic controller which in turn provides electronic signals that operate the engine fuel injectors to control engine power.' You asserted that the electronic treadle assembly is not a throttle, as that term is defined in Standard No. 124. Based on the information provided in your letter, we agree. Standard No. 124 expressly provides that the throttle must be part of the fuel metering device. In the example you have given, the electronically controlled fuel injectors, together with any pumps or other metering systems connected to those injectors, appear to be the 'fuel metering device.' Based on the information provided in your letter, it appears that the electronic treadle assembly would be considered to be part of the 'driver- operated accelerator control system,' because it is a vehicle component that regulates engine speed in direct response to movement of the driver-operated control. You went on to assert that no component of an electronically controlled diesel engine would be considered a throttle, as that term is defined in Standard No. 124. We disagree. Standard No. 124 defines a throttle as 'the component of the fuel metering device that connects to the driver-operated accelerator control system and that by input from the driver-operated accelerator control system controls the engine speed.' Every engine design of which we are aware, including electric, diesel, conventional gasoline, and Wankel rotary gasoline, has a component that controls the engine speed in response to inputs from the driver. That component is the throttle. Indeed, an engine design without a throttle would not allow the driver to control the engine speed. NHTSA has already addressed the applicability of Standard No. 124 to electronic accelerator control systems. In an August 8, 1988 letter to Mr. Koji Tokunaga of Isuzu (copy enclosed), the agency explained how Standard No. 124 would apply to a proposed electronic accelerator control system. In a November 9, 1988 letter to Mr. J.E. Carr of Caterpillar (copy enclosed), the agency explained how Standard No. 124 applies to an electronically controlled diesel engine. Hence, the issue of how Standard No. 124 applies to electronic accelerator control systems has been settled at least since 1988. Given the broad language used in the standard, the agency's previous interpretations of the standard, and the compelling safety need to prevent runaway vehicles if malfunctions should occur in the accelerator control system, we must reject your suggestion that Standard No. 124 should be interpreted in such a way that it does not apply to electronically controlled diesel engines. I hope you find this information helpful. If you have any other questions or would like some additional information on this subject, please feel free to contact Mary Versailles of my staff at this address or by phone at (202) 366- 2992. Sincerely, Paul Jackson Rice Chief Counsel Enclosures";