Mr. Michael L. Ulsh
Mechanical Engineer
Summit Trailer Sales, Inc.
One Summit Plaza
Summit Station, PA 17979

Dear Mr. Ulsh:

This responds to your letter requesting an interpretation of whether the vehicles that your company manufactures are excluded from the National Highway Traffic Safety Administration's (NHTSA's) rear impact protection (underride guard) regulations. As explained below, your vehicles are not excluded from the regulation.

You ask about Federal Motor Vehicle Safety Standard (FMVSS) No. 224, Rear impact protection, which in January 1998 will require most trailers and semitrailers weighing over 10,000 pounds to be fitted at the rear with an underride guard. Certain trailers are excluded from these requirements. You provided drawings and descriptions of four types of vehicles your company manufactures. In each case, you are concerned with the requirement in S5.1.3 which states that "the rearmost surface of the horizontal member of the guard shall be located as close as practical to a transverse vertical plane tangent to the rear extremity of the vehicle, but no more than 305 mm [about 12 inches] forward of that plane." S4 defines the rearmost extremity, in pertinent part, as

the rearmost point on a vehicle that is . . . below a horizontal plane located 1,900 mm above the ground . . . when the vehicle's cargo doors, tailgate, and other permanent structures are positioned as they normally are when the vehicle is in motion. Nonstructural protrusions such as taillights, rubber bumpers, hinges and latches are excluded from the determination of the rearmost point.

I will discuss the vehicle types in the order that your letter did.

Frame-type dump trailer

This vehicle has a deflector plate at the rear that extends rearward 12 inches from the end of the chassis. It deflects the load away from the trailer when it is dumping. You state that the plate is not a "structural member" because it is bolted or welded to the rear of the body. You also express some concerns that the trailer rear end might have to be modified by either moving the rear tires forward or extending the frame to prevent the guard from contacting the tires when the vehicle is dumping.

Is the rear extremity measured from the end of the deflector plate?

Yes. The definition of "rear extremity" states "nonstructural protrusions such as taillights, rubber bumpers, hinges and latches are excluded from the determination of the rearmost point." Merely because the deflector plate is attached to the body does not mean that an object is nonstructural. The definition of rear extremity refers to the "rearmost point on the vehicle," (emphasis added) not the rearmost point of the chassis. The attributes that the excluded objects have in common is that they are relatively small and localized and would not have a major impact on a colliding passenger vehicle. A 0.19 inch thick aluminum (or 7 gauge steel) plate extending across the entire width of the trailer is part of the vehicle, and is not a "nonstructural protrusion."

If so, where should the guard be located so that it lies no more than 12" (305mm) from the vertical plane tangent to the rear extremity . . . What are our alternatives for mounting this guard in a feasible manner and still comply with the new regulations?"

This is an engineering question that your engineers are in a better position to answer than we are. European governments use "type approval," which means that they approve particular designs as complying with their safety standards. In the United States, we write performance standards, and the vehicle manufacturers are responsible for devising engineering solutions to meet those standards. Therefore, NHTSA is not required to suggest, and will not approve, particular designs. In some cases, trailer rear end redesign might be necessary in order to comply with our underride guard standards.

However, you might want to consider two alternatives for meeting the standards that do not involve major redesign. One would be cantilevering the horizontal member of the rear impact guard slightly rearward from the rear of the chassis so that it is within 12 inches of the rear of the deflector plate. Another, possibly simpler alternative would be attaching the deflector plate in such a way that it would pivot at its upper edge and automatically swing downward (for example, when the tailgate is closed). The determination of rear extremity will be made "when the vehicle's cargo doors, tailgate, and other permanent structures are positioned as they normally are when the vehicle is in motion." If the plate were designed to have the "dropped" configuration whenever the vehicle is in motion, then NHTSA would not consider the plate to be the rear extremity of the vehicle. In fact, your particular vehicle would then meet the definition of an excluded "wheels back" trailer, because the rearmost surface of the rear tires would be within 12 inches of the rear extremity.

Frameless dump trailer

This type of trailer has a subframe that rolls forward when the trailer is dumping so that the front wheels leave the ground. You state that an underride guard attached to the subframe would rotate downward with the subfame and contact the ground slightly (according to your illustration) before the trailer reaches its maximum dump angle of 54 degrees.

Where should the guard be placed to comply with FMVSS No. 224, yet not interfere with the normal operation of the trailer? Are there any exclusions for this particular design?

There are no exclusions for dump trailers. As stated above, NHTSA cannot help to design your trailers. The previously mentioned possibility of a drop down deflector plate would probably also work for the frameless dump trailer. We would like to note that there is no requirement to mount the underride guard to the subframe. You could mount the guard to the axle or any other structural member that would provide adequate support.

Dual Arm trailer

This trailer has a steel bucket attached to two hydraulic arms which extend rearward on the sides of the trailer. During transit, the bucket is transported behind the trailer, with its lower rear corner at a distance of 36 inches behind the rear of the chassis and 70 inches from the ground.

Does this trailer qualify for the "special purpose vehicle" exclusion? If not, where should the guard be placed to comply with FMVSS No. 224?

Your dual arm trailer does not meet the definition of 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 . . . ." (Emphasis added.) According to your drawing, the bucket does not pass through the area where the horizontal member of the underride guard would be located while the vehicle is in transit, but instead resides about 70 inches off the ground. Therefore, your trailers are not excluded from the standard as special purpose vehicles.

As to locating the guard, your difficulty is the same as with the frame-type dump trailer. A piece of the trailer extends into the zone of consideration for determining the vehicle's "rear extremity," thereby creating a rear extremity (and therefore a required guard location) that is significantly behind the end of the trailer chassis. The bucket stows while in transit at a height that is not quite high enough to be excluded from consideration as the vehicle "rear extremity." Rear extremity is defined as the rearmost point "below a horizontal plane located 1,900 mm (about 75 inches) above the ground . . . ."

Although we do not know how feasible it would be, your drawing indicates that if the bucket were stowed only a few inches higher, above the upper limit of the zone of consideration for rear extremity, the rear extremity would then be considered to be the end of the chassis (or the end of the "bucket holder side plate," depending on where that is moved to). That would produce a fairly standard situation for attaching the guard to the end of the chassis.

Walking floor trailer

This trailer has steel chassis beams that extend 6 inches beyond the end of the trailer body to form a "pusher bumper." The bumper is 42 inches wide and approximately 39 inches from the ground.

Is the rear extremity measured from the end of the pusher bumper?

Yes. As indicated in the discussion of your dual arm trailer, the rearmost point of the trailer below approximately 75 inches from the ground will be considered the rear extremity. The pusher bumper is 39 inches off the ground, and is certainly too massive to be considered in the excluded category of "rubber bumpers." Therefore, it would be considered the rear extremity.

The guard would have to be mounted no more than 12 inches forward of the pusher bumper. However, S5.1.3 states that "the rearmost surface of the horizontal member of the guard shall be located as close as practical [to the vehicle's rear extremity](emphasis added). Therefore, unless there is some reason that it would not be practical, you are required to mount the guard so that the rearmost face of the guard's horizontal member aligns with the rear face of the pusher bumper.

This letter merely applies the existing regulatory language to the questions you posed, and does not constitute a judgment that your trailers could operate with a conventional underride guard in place. We have made a few observations that may suggest some engineering solutions that would meet the requirements of the standard without compromising the function of your vehicles. However, we reiterate that NHTSA is not responsible for vehicle design.

If there are solutions that you would not be able to implement before the January 26, 1998 effective date of the rule, you can apply for a temporary exemption. 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. I have enclosed a copy of Part 555 for your information. Please note that it takes three to four months from the date of submittal before a decision can be made on such an application because it has to be submitted for public comment.

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
Enclosures: 49 CFR Part 555
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d.10/20/97