Mr. Donald T. Hoy
Senior Marketing Manager
Clean Air Partners
17301 Rimrock Drive
Golden, CO 80401

Dear Mr. Hoy:

This responds to your letter addressing this agency's regulations about converting school buses to run on a blended fuel combining diesel and compressed natural gas (CNG) or liquefied natural gas (LNG). You stated that your company manufactures a conversion system that bolts on the original equipment manufacturer's diesel engine. While the diesel engine system remains intact and operates as designed during the dual fuel cycle, your conversion system serves to reduce the flow of diesel fuel to the engine and substitutes natural gas in its place. You further state that the system automatically reverts back to 100% diesel with no interruption in driveability if the supply of CNG is depleted.

You asked two questions about converting diesel powered school buses to dual fuel school buses that run on both conventional diesel fuel and alternative fuels such as CNG or LNG. You first ask whether there are any Federal regulations preventing the conversion of a school bus from diesel to a dual fuel school bus. You then ask if there is any significance as to when the conversion system is installed on a school bus with regard to vehicle certification.

Before answering your specific questions, let me provide you with background information about the National Highway Traffic Safety Administration (NHTSA) and our regulations. NHTSA is authorized by Congress to issue Federal motor vehicle safety standards (FMVSSs) that set performance requirements for new motor vehicles and items of equipment. NHTSA has used this authority to issue FMVSSs to ensure the fuel system integrity of vehicles powered by diesel fuels and those powered by CNG. Specifically, FMVSS No. 301 regulates the fuel system integrity of gasoline and diesel powered light vehicles with a gross vehicle weight rating (GVWR) under 10,000 pounds and all gasoline and diesel powered school buses regardless of GVWR. In addition, FMVSS No. 303 regulates the fuel system integrity of CNG light vehicles and all school buses. Finally, FMVSS No. 304 regulates the integrity of CNG fuel containers. While FMVSS No. 301 has been in effect since the 1970s, the final rule establishing FMVSS No. 304 becomes effective on September 1, 1995 and the final rule establishing FMVSS No. 303 becomes effective on March 27, 1995. The agency has not issued any FMVSS applicable to vehicles powered by LNG.

In response to your first question, no FMVSS or other NHTSA regulation prohibits the conversion of a diesel school bus to a dual fuel school bus. Nevertheless, FMVSS No. 301 requires each vehicle subject to the FMVSS, including each school bus, to have a limited amount of fuel leakage from the fuel system after being subjected to crash testing. Similarly, FMVSS No. 303 requires each vehicle subject to the FMVSS, including each school bus, to have a limited amount of pressure drop in the fuel system after being subjected to crash testing. Each school bus with a GVWR under 10,000 pounds is subjected to frontal, rear, and lateral barrier crash tests and each school bus with a GVWR of 10,000 pounds or more is subjected to a moving contoured barrier crash test. With respect to a dual fuel vehicle, NHTSA explained in the final rule that "NHTSA has decided to require only one test on dual-fuel and bi-fuel vehicles that permits the amount of gaseous leakage specified in the CNG standard plus the amount of liquid leakage specified in Standard No. 301." (59 FR 19648, April 25, 1994.) In other words, after being subjected to the specified test crash or crashes, a dual fuel school bus may not leak more than the amount of fuel leakage permitted in FMVSS No. 301 plus the amount permitted in FMVSS No. 303.

In response to your second question, vehicle fuel system conversions are addressed in certain NHTSA provisions, whose application depends on when the work is done and who does the conversion. Under the statute and NHTSA's regulations, the first consumer purchase is the critical event by which certain responsibilities are specified. If your conversion system were installed as original equipment on a new vehicle, the vehicle manufacturer would be required by our certification regulations to certify that the entire vehicle (with your product installed) satisfies the requirements of all applicable FMVSS's, including the CNG fuel system standard once that FMVSS takes effect. If your conversion system were added to a new, previously-certified vehicle (e.g., a new completed school bus), the person who adds the system would be required to certify that, as altered, the vehicle continues to comply with all of the safety standards affected by the alteration. This means that if you convert a school bus prior to the first consumer purchase, then you would be responsible for certifying that the school bus as manufactured conforms to all applicable FMVSS, including FMVSS No. 301 and, once FMVSS No. 303 and 304 take effect, those standards as well.

If you convert a bus after the first consumer purchase, you would not have any certification responsibilities under NHTSA's regulations. However, an installer that is a vehicle manufacturer, distributor, dealer or repair business would have to ensure that it did not knowingly make inoperative, in whole or in part, the compliance of the vehicle with any applicable safety standard. Since all school buses are currently required to comply with FMVSS No. 301, any aspect of the conversion to a dual fuel school bus must not make the diesel school bus more vulnerable to diesel fuel leakage or otherwise impair the school bus' fuel system integrity. After the September 1, 1995 effective date for FMVSS No. 303, any aspect of your conversion to a CNG/diesel school bus to a dual fuel school bus must not make the school bus more vulnerable to fuel leakage.

The "make inoperative" provision does not apply to individual vehicle owners who alter their own vehicles. Thus, under our requirements, individual owners may install any item of motor vehicle equipment regardless of its effect on compliance with the FMVSS's. However, NHTSA encourages vehicle owners not to degrade the safety of their vehicles.

In addition, manufacturers of motor vehicles and items of motor vehicle equipment are subject to the statutory requirements concerning the recall and remedy of products with defects related to motor vehicle safety. In the event that NHTSA or the manufacturer of the container or vehicle determines that the product contains a safety-related defect, the manufacturer would be responsible for notifying purchasers of the defective equipment and remedying the problem free of charge.

With regard to additional requirements for vehicle conversions, you should also note that the Federal Highway Administration (FHWA) of this Department has operational and equipment requirements for commercial vehicles used in interstate commerce. For information about possible FHWA requirements affecting your conversions, you can contact that agency's Chief Counsel's office at (202) 366-0650.

I hope you find this information helpful. If you have any other questions, please contact Marvin Shaw at this address or by phone at (202) 366-2992.


Philip R. Recht Chief Counsel ref:303 d:2/27/95