Mr. Craig Heider
Manager
Jet Co.
1303 North 13th Street
Humboldt, IA 50548

Dear Mr. Heider:

This responds to your letter requesting an interpretation of whether three different trailers your company manufactures would be excluded from the National Highway Traffic Safety Administration's (NHTSA's) rear impact protection (underride guard) regulations. You ask if a grain trailer with fixed rear axles and a rearmost surface of the rearmost tires within 305 mm of the rear extremity of the trailer is excluded as a wheels back vehicle. You also ask if a flatbed/dropdeck trailer with a beavertail and a composite dropdeck trailer are excluded as a low chassis vehicle. On the basis of the information you supplied and certain assumptions discussed below, it appears that all three of these vehicles are excluded.

Federal Motor Vehicle Safety Standard No. 224, Rear impact protection, requires most trailers and semitrailers weighing over 10,000 pounds to be fitted at the rear with a rear impact (underride) guard meeting the requirements of Standard No. 223, Rear impact guards (49 CFR 571.223 and 571.224, published on January 24, 1996 at 61 FR 2004). However, certain kinds of vehicles are excluded. The only excluded categories that are relevant for the purposes of this letter are wheels back vehicles and low chassis vehicles.

Wheels-back vehicles, excluded by S3 of FMVSS No. 224, are defined in S4 as a "trailer or semitrailer whose rearmost axle is permanently fixed and is located such that the rearmost surface of [the tire] on that axle is not more than 305 mm forward of the transverse vertical plane tangent to the rear extremity of the vehicle."

You state in your letter that the rear axles of your grain trailer meet both of these criteria. The copy of a photograph you enclosed of the trailer appears consistent with your description, although no dimensions are given. Accepting your assertion that the rear surface of the tires on the fixed axle are within 305 mm of the rear extremity, NHTSA concludes that the vehicle is excluded.

Your flatbed/dropdeck trailer, labeled "53' X 102" Steel Dropdeck" in the literature you enclosed with the letter, is essentially a flatbed design, with a five foot dropdeck (also called a "beavertail") extension angling downward from the rear of the flat portion of the bed. There are two loading ramps that bridge the distance from the lower rear of the beavertail to the ground during loading, allowing vehicles to be driven onto the flatbed. During transit, the loading ramps, which are located on the left and right sides of the beavertail section, pivot on a hinge at the rear of the beavertail and flip over and lie on top of the beavertail section. The literature you enclosed states "ramps make the beavertail flat for more loading area." By this, we assume you mean that the bottom surface of the loading ramps, when sitting on top of the beavertail, forms an extension of the flat portion of the trailer during transit, and that the extension can support cargo load. In a conversation with Mr. Paul Atelsek of my staff, you clarified that the rear surface of the beavertail extends from one side of the trailer to the other and its lower surface is less than 22 inches above the ground.

Low chassis vehicles are 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." In other words, the chassis itself must satisfy the configuration requirements applicable to a guard when the vehicle is outfitted for transit. The only part of your vehicle that may meet these configuration requirements is the rear edge of the beavertail itself, so the question becomes whether the beavertail is 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. Moveable components may "lock" into the frame structure sufficiently that they are integral with other frame members-in this situation NHTSA may consider the combined components to be one frame unit. However, 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 beavertail, the agency concludes that it is part of the chassis. The beavertail helps to define the shape of the trailer. It is of a similar size and strength to the other frame components. Your beavertail is attached to the rest of your chassis sufficiently that it is considered integral with it, as one unit, a part of the frame structure. In addition, the beavertail meets the "load supporting" aspect of the chassis definition because it can support cargo load. Therefore, the beavertail is part of the chassis, and the trailer is a low chassis vehicle, excluded from the underride guard requirements..

Your third trailer type, labeled "53' X 102" Composite Dropdeck" is a straight flatbed trailer with the frame rails in the rear of the trailer extending 10 feet behind the rear wheels. The vertical face of the chassis at the rear is 13 inches from top to bottom, and although it is not apparent from your line drawing, we assume that this depth dimension is constant across the back of the trailer. The distance from the ground to the bottom of the chassis is 21 inches when the trailer is unloaded. Because the rear face is at least 4 inches high, extends outward to within 4 inches of the trailer side extremities, and is no more than 22 inches from the ground when the trailer is unloaded, it meets the configurational requirements of S5.1.1 to S5.1.3. The rear face of the trailer connecting to the frame rails is considered to be frame structure. Assuming that the rear of the bed can support load, this structure is part of the chassis. Since this structure meets the configurational requirements of the rule, this vehicle is an excluded low chassis vehicle.

You also asked about the labeling requirements if a vehicle falls in an excluded category. There are no requirements for excluded vehicles in our regulations. If you have any further questions, please feel free to contact Paul Atelsek of my staff at this address or by telephone at (202) 366-2992.

Sincerely,
John Womack
Acting Chief Counsel
ref:224
d.5/22/98