Mr. Mike Laws
Vice President/General Manager
Interstate Trailers, Inc.
1102 Interstate 20 West
Arlington, TX 76017

Dear Mr. Laws:

This responds to your letter requesting an interpretation on whether the tilt bed trailers your company manufactures would be excluded from the National Highway Traffic Safety Administration's (NHTSA) rear impact protection (underride guard) regulations. The answer is no, therefore a guard is required.

As shown in the drawings you enclosed with your letter, your trailers are essentially of a flatbed design, equipped with a bed that hydraulically tilts to a 13 degree angle so that construction equipment may be loaded. At the back of the bed is a long triangular full width "approach plate" that allows construction equipment to transition from the ground up onto the bed without encountering the "bump" of the edge of the bed. When the bed is lowered into the horizontal position, for transit, the approach plate is hydraulically lowered to droop down slightly, to a position in which the lower edge of the plate is 19 inches off the ground. You state that installing an underride guard would make this trailer useless and you ask if a guard is required.

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 low chassis vehicles and special purpose vehicles.

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 approach plate itself, so the question becomes whether the approach plate 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 approach plate, the agency concludes that it is not part of the chassis. First, the approach plate does not meet the "load supporting" aspect of the chassis definition because it approach ramp does not contribute to supporting cargo load. Further, the approach plate is not frame structure. It does not define the shape of the trailer. Instead, it hangs down from the rear end of the trailer, forming a protrusion from the outline of the trailer bed. The approach plate is not locked into another frame structural member in any manner. Neither the approach plate nor the steel plate arms attaching the approach plate to the sides of the trailer bed are of a similar size or strength to the other frame components. In consideration of these factors, we conclude that the approach plate is not part of the chassis, and the trailer is not a low chassis vehicle.

We turn now to the question of whether your trailer is excluded as a special purpose vehicle. A special purpose vehicle is defined in S4 of FMVSS No. 224 as "a trailer or semitrailer having work-performing equipment that, while the vehicle is in transit, resides in or moves through the area that could be occupied by the horizontal member of the rear underride guard, as defined by S5.1.1 through S5.1.3."(1) Again, the approach plate is the only part of your trailer that, while the vehicle is in transit, resides in the area that could be occupied be the rear underride guard. Therefore, the approach plate would have to be considered work-performing equipment for the trailer to be excluded.

There is no definition in the standard for "work-performing equipment." In determining the meaning of regulatory language, the first place the agency looks is the plain meaning of the words. In the context which is relevant to this safety standard, "work" is defined as "the transfer of energy from one physical system to another; especially, the transfer of energy to a body by the application of force . . ." "Perform" is defined as "to begin and carry through to completion; do." American Heritage Dictionary of the English Language, 1971. Taken together, NHTSA interprets the words "work-performing" to mean that the equipment must actively perform its function, and that the function must involve exerting force or moving something else. Approach plates do not perform work in this sense because they merely form a ramp between the ground and the vehicle driving onto the tilt bed.(2) Therefore, the approach plate is not work-performing equipment, and the vehicle does not meet the definition of a special purpose vehicle.

Since your trailer does not meet the definition of an excluded category, it would have to be equipped with an underride guard meeting our standards. We cannot provide specific guidance on how your trailer might be redesigned to accommodate a guard. We note, however, that other manufacturers of tilt bed trailers have told us that they have found engineering solutions that would meet the requirements of the standard without compromising the function of their vehicles. Some of them are using guard designs that deploy when in the flatbed configuration and automatically retract when in the tilted configuration.

Another option to consider is whether your approach plate could "be" the guard. The approach plate already appears to meet the configurational requirements for an underride guard. If it does not currently meet the strength and energy absorption requirements, you might be able to reinforce or otherwise modify the approach plate sufficiently so that it would pass these requirements. If you can do this, the approach plate itself could be labeled and certified as a guard under Standard No. 223, Rear impact guards. Perhaps some of these solutions would work for you. We emphasize that you, as the manufacturer of the vehicle, are responsible for the vehicle's compliance.

The agency would consider a petition for temporary exemption from Standard No. 224. Under one of our regulations (49 CFR Part 555), vehicle manufacturers may apply for a temporary exemption from the Federal motor vehicle safety standards. Under Sec. 555.6(a), a manufacturer whose yearly production is not more than 10,000 units may ask for an exemption of up to three years on the basis that compliance would cause it substantial economic hardship and that it has attempted in good faith to comply with the standard from which it has asked to be excused. We have enclosed a copy of Part 555 for your information. We have also enclosed a copy of our regulations relating to the protection of confidential business information. Most of the trailer manufacturers submitting petitions for temporary exemption have requested that their financial information remain confidential.

Please note Part 555 requires the agency to publish a notice in the Federal Register seeking public comment on each exemption petition before a decision can be made on such a request, and then publish a second notice either granting or denying the petition. This process normally takes three to four months from the date of submittal.

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.

John Womack
Acting Chief Counsel
Enclosures: Parts 555, 512

1. Note that this definition, as quoted, reflects an amendment made in response to petitions for reconsideration of the final rule. An unnecessary reference to pipe equipment containing hazardous materials was eliminated. See 63 F.R. 3654 (January 26, 1998).

2. To the extent that this interpretation is inconsistent with interpretation letters to Mr. Thomas M. Joyce and Mr. R. H. Anderson of Landoll Corporation, interpreting the frame rails of tilt bed trailers as work-performing equipment, those prior interpretations are superceded. The basic answer in those letters did not depend on this point, and the analysis in this letter is more thorough.