Interpretation ID: gehman

Mr. Roland P. Gehman, P.E.
President
MGS, Inc.
178 Muddy Creek Church Road
Denver, PA 17517-9386

Dear Mr. Gehman:

This responds to your letter and telephone call requesting an interpretation of whether two flatbed trailers your company manufactures would be excluded from the National Highway Traffic Safety Administration's (NHTSA's) rear impact protection (underride guard) regulations. I regret the delay in responding.

Specifically, you ask whether the TM500 and TM600 trailer designs, which each have full width cross-members above the chassis frame rails at a height of 26 inches above the ground, would be excluded from the standard. Our answer is yes, for reasons relating to the gross vehicle weight ratings (GVWR) of the trailers. Federal Motor Vehicle Safety Standard No. 224, Rear impact protection, applies to trailers and semitrailers with a GVWR of 4,536 kilograms or more (10,000 pounds (lb) or more). The literature you enclosed with your letter states that "[t]he MGS TM 600 can carry loads up to 10,000 lbs., and the MGS TM500 up to 7,000 lbs." Standard No. 224 does not apply to vehicles with a GVWR of less than 10,000 lb.

I understand that in a June 17, 1999, telephone conversation with my staff, you had asked about the application of the standard to your trailers and also clarified drawings you had enclosed. (Mr. Atelsek, with whom you had spoken, has since left our office.) We assume that you ask about MGS trailers with GVWRs of 10,000 lb or more.

You explained that the TM500 and TM600 trailers have identical configurations at the rear. The drawing shows frame rails, constructed of longitudinal I-beams, whose lower surface is 18 inches above the ground. There is nothing between the frame rails. Above the frame rail at the rear is a full-width cross member at the back of the rear deck whose bottom is 26 inches above the ground. You asked Mr. Atelsek if these trailers are considered "low chassis vehicles" under Standard No. 224.

The answer is no. A "low chassis vehicle" is defined in S4 of Standard No. 224 as "a trailer or semitrailer having a chassis that extends behind the rearmost point of the rearmost tires and a lower rear surface that meets the configuration requirements of S5.1.1 through 5.1.3 of this section." S5.1.2 states that "[t]he vertical distance between the bottom edge of the horizontal member of the guard and the ground shall not exceed 560 mm at any point across the full width of the member."

In its current configuration, neither of your trailers meet the definition of a low chassis vehicle. The trailers have no horizontal cross member at the rear lower than 26 inches. Thus, they do not meet the 22 inch maximum height configuration requirement in S5.1.2.

In the event that your trailers are not low chassis vehicles, you asked Mr. Atelsek whether a horizontal cross member attached to the rear of the frame rails would produce a vehicle configuration that meets the definition of a low chassis vehicle. An 18-inch high horizontal member would meet the 22-inch maximum height configuration requirement in S5.1.2. However, the definition also specifies that the chassis itself must satisfy the configuration requirements applicable to a guard when the vehicle is outfitted for transit. So the question becomes whether the cross member would be considered to be part of the chassis of the vehicle.

"Chassis" is defined in S4 as "the load supporting frame structure of a motor vehicle." There are two elements to this definition that must be satisfied: "load supporting" and "frame structure." To be considered "load supporting," the frame structure has to support load when the trailer is performing its function. Generally, this means that the structure would have to contribute to supporting the cargo load when the trailer is in transit. To be considered part of the frame structure, a structural member must be either an integral part of the overall frame structure, or be connected with other frame structural members in a way that is necessary to the structural integrity of the trailer.

One factor the agency considers in deciding whether a structural member is part of the frame is its size and strength. Frame structural components often are the major structures defining the shape of the trailer. Although frame structure is not limited to the largest frame components (i.e., the frame rails for most trailers), generally frame components are substantial and have strength similar to other frame components. The agency also looks at the purpose and function of the structural member in supporting the trailer and its load.

Applying these principles to your contemplated cross member, we conclude that it would be part of the chassis. This conclusion is based on the assumption that the extension of the cross member to the bottom of the frame rails would be of the same material, thickness, etc., of the existing cross member. If this assumption is correct, we would consider such a cross member to be an integral part of the frame structure that contributes to supporting load. Therefore, the modified cross member, with its lower edge located 18 inches above the ground, would be considered part of the chassis. Since a part of the chassis would meet all the configurational requirements of S5.1.1 through S5.1.3, the trailer would then meet the definition of a low chassis vehicle, and would be excluded from Standard No. 224.

If you have any further questions, please contact us at (202) 366-2992.

Sincerely,
Frank Seales, Jr.
Chief Counsel
ref:224
d.9/27/99