Search Interpretations


Dean L. Sicking, P.E., Ph.D.


Safety Trailers, Inc.

2620 Woodleigh Lane

Lincoln, NE 68502

Dear Dr. Sicking:

This responds to your request for an interpretation of whether your product, the Trailer Truck Mounted Attenuator (Trailer TMA) is a motor vehicle or motor vehicle equipment as defined at 49 U.S.C. 30102. Based on the information you provided, and also consideration of materials included on your companys website ( it is our opinion that the product is a motor vehicle, and, more specifically, a trailer.

By way of background, the National Highway Traffic Safety Administration (NHTSA) is authorized under 49 U.S.C. Chapter 301 to issue and enforce safety standards applicable to new motor vehicles and items of motor vehicle equipment. Manufacturers are required to certify that their vehicles and equipment meet applicable standards. NHTSA does not approve motor vehicles or motor vehicle equipment, nor do we endorse any commercial products.

In your letter, you state that the Trailer TMA looks somewhat like a trailer. You argue, however, that the new device does not serve any of the functions of a trailer. According to your letter, the product is designed to replace attenuators that are mounted to the rear of work zone trucks. You state that when attached to a construction vehicle, the TMA can safely accommodate full-size passenger cars, SUVs, and light trucks impacting the back of a work vehicle at closing speeds up to 100 km/h (62 mph).

You state that the Trailer TMA works by utilizing a

bursting tube energy dissipation system to slow impacting vehicles. When struck, the rear impact face is pushed forward and mandrels attached to the back of the impact face are pushed into the square tubes that form the side frames of the Trailer TMA. Tapered walls on the mandrels force the sides of the tube apart and cause all four corners to burst The bursting of the side walls of tubular rail elements safety decelerates impacting vehicles to a stop.

In arguing that the Trailer TMA does not serve any functions similar to a trailer, you state that it cannot be used to carry or transport any materials or equipment. You state that the Trailer TMA consists only of a tubular frame, an impact plate, an axle to support the energy absorbing frame rail elements and a mechanism for attaching the device to a work truck.

Based on our review of the information you provided, as well as materials included on your companys website, it is our opinion that the Trailer TMA is a motor vehicle, and, more specifically, a trailer.

The statutory definition of motor vehicle at 49 U.S.C. 30102(a)(6) is a vehicle driven or drawn by mechanical power and manufactured primarily for use on public streets, roads, and highways, but does not include a vehicle operated only on a rail line.

The Trailer TMA is a vehicle drawn by mechanical power, and is designed to be used on the public highways. As such, it is a motor vehicle.

The term trailer is defined at 49 CFR Part 571.3 as: a motor vehicle with or without motive power, designed for carrying persons or property and for being drawn by another motor vehicle.

It is our view that the Trailer TMA comes within this definition. We would consider the attenuator itself to be the property being transported. In addition, information provided on your companys website[1] indicates that the Trailer TMA is designed to accommodate light weight flashing arrow boards or other optional equipment. Thus, the Trailer TMA is similar in relevant respects to a product of Solar Technology, Inc., to which we addressed a January 4, 2006 interpretation letter (copy enclosed) stating that wheeled, portable solar-powered LED displays that are intended to convey messages are trailers.

I hope this information is helpful. I am also enclosing a fact sheet entitled Information for New Manufacturers of Motor Vehicles and Motor Vehicle Equipment. If you have any further questions, please feel free to contact Ms. Dorothy Nakama at this address or by telephone at (202) 366-2992.

Sincerely yours,

Anthony M. Cooke

Chief Counsel




[1] TTMA-100 Trailer TMA General Specifications, Section VII.