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.

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.

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.

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.

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.

Each trailer is a separate transport vehicle. All together it is a motor vehicle.

FAQ: What is a transport vehicle?

The transport of a hazardous material can be accomplished by four modes (rail, highway, air, or water) and by even more forms of a transport vehicle.  If the mode of transport is highway, the transport vehicle used must be a motor vehicle.  But just what is a 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.

So, let’s break it down:

A motor vehicle includes, but is not limited to, the following or any combination of them:

• Vehicle
• Machine
• Tractor
• Trailer
• Semitrailer

Now, you might be thinking, “Hold on, how can a trailer or semitrailer be a motor vehicle?”  Well, we’re not done.  A motor vehicle must be, “propelled or drawn by a mechanical power”.  So, a trailer just sitting there is not a motor vehicle.  Combined with a vehicle, machine, tractor, or some other mechanical power, and it becomes a motor vehicle.

Where you can go with a motor vehicle is limited solely to highways.  This doesn’t mean just the interstate, it means any road with public access.

And, for the purposes of the USDOT/PHMSA Hazardous Materials Regulations, a motor vehicle must be used for the transportation of passengers or property.

That’s about it.  The rest of the definition is spent explaining what a motor vehicle is not: a vehicle, locomotive, or car operated on rails or a passenger trolley.

Frequently asked questions:

Q:  Is this a motor vehicle? (see images below)

A:  No.  Since it is not, “…propelled or drawn by mechanical power…” it can’t be a motor vehicle.

Q: But what if I use one of the above to transport a hazardous material by highway? Would it be subject to the HMR?

A: No, again.  Since it is not a motor vehicle, it does not fall with USDOT/PHMSA’s regulatory scope of transportation functions at 171.1(c) which includes “…movement of a hazardous material by rail car, aircraft, motor vehicle, or vessel…” (emphasis mine).  So, no mechanical power, no motor vehicle.  No motor vehicle, no applicable Hazardous Materials Regulations.

Q: Well, is this a motor vehicle? (see images below).

A: Yes.  Each of these is a motor vehicle.

Q:  How do a motor vehicle and a transport vehicle (also defined in §171.8) differ?

A:  Though they sound similar, a motor vehicle and a transport vehicle are defined separately and have distinct requirements under the HMR.  Refer to this article for a full explanation of a transport vehicle.  In brief, the cargo carrying components of a motor vehicle, e.g. the trailer or trailers of a semitrailer, are considered separate transport vehicles (Q1/A1 of LOI 12-0220).