FAQ: What is a motor vehicle? (USDOT/PHMSA definition)

The Hazardous Materials Regulations (HMR) of the Pipeline and Hazardous Materials Safety Administration within the U.S. Department of Transportation (USDOT/PHMSA) regulate the transportation of hazardous materials (HazMat) to, from, or through the U.S. by any mode. The four modes of transport identified and regulated by USDOT/PHMSA are:

Rail
Highway
Air
Water

For transportation by highway there is only one type of vehicle: the motor vehicle. Motor vehicle is defined at 49 CFR 171.8:

Motor vehicle includes a vehicle, machine, tractor, trailer, or semitrailer, or any combination thereof, propelled or drawn by mechanical power and used upon the highways in the transportation of passengers or property. It does not include a vehicle, locomotive, or car operated exclusively on a rail or rails, or a trolley bus operated by electric power derived from a fixed overhead wire, furnishing local passenger transportation similar to street-railway service.

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Let’s take a closer look.

A motor vehicle includes – but is not limited to – any of the following:

Vehicle
Machine
Tractor
Trailer
Semitrailer
Or any combination of any of the above.

A motor vehicle must be propelled or drawn by mechanical power.

: This is not a motor vehicle

: What parks here is not a motor vehicle

And…

Used upon the highways. Don’t be misled by the term “highway” to think a motor vehicle are only those traveling on I80 or some other interstate. Unfortunately, the HMR does not define a highway and I can find no letter of interpretation for it. Since USDOT/PHMSA’s regulatory scope includes all transportation to, from, or through the U.S., when the HMR reads “highway” it means the broad definition I found in Wikipedia:

A highway is any public or private road or other public way on land. It is used for major roads, but also includes other public roads and public tracks…

Or, consider the functions identified as not subject to the HMR at §171.1(d); it includes motor vehicle movements exclusively within a contiguous facility boundary where public assess is restricted. Unless the movement is on or crosses a public road. Here the term “public road” is used instead of “highway” but is meant in the same way.

: This is a highway. Photo by John Lockwood on Unsplash

: These are highways. Photo by Pelle Martin on Unsplash

: And this is a highway. Photo by Pelle Martin on Unsplash

A motor vehicle is not any of the following:

Vehicle, locomotive, or car operated exclusively on rail or rails.
A trolley bus operated by electric power derived from an overhead wire when providing local passenger transportation similar to street-railway service.

: This is not a motor vehicle. Photo by Casey Horner on Unsplash

: This is not a motor vehicle. Photo by Raychel Sanner on Unsplash

You may be confused – as I was – by the use of the term transport vehicle in the HMR (also defined at §171.8) and how it relates to the motor vehicle. Put simply, the transport vehicle is the cargo-carrying body of the motor vehicle. In some instances the transport vehicle may be the motor vehicle, e.g., a truck with an attached bed that can carry cargo. In others, the transport vehicle will be one part of the motor vehicle, e.g., a tractor-trailer combination or semitrailer where the trailer(s) is the transport vehicle and the tractor and trailer together are the motor vehicle.