The § 390.5T commercial motor vehicle definition begins by setting a frame: a self-propelled or towed motor vehicle used on a highway in interstate commerce to transport passengers or property. Chapter 1 gave that frame and the headline figures inside it. What it did not give is how the four triggers within the frame actually work, and the detail is what decides real cases. They are independent — meeting any ONE of them makes the vehicle commercial, and no combination is required.

The first is weight. A gross vehicle weight rating or gross combination weight rating, or a gross vehicle weight or gross combination weight, of 4,536 kilograms — 10,001 pounds — or more, whichever is greater. Note that the rule takes rating and actual weight together and uses whichever is higher, so loading a vehicle past its rating does not keep it outside the definition. The fourth is hazardous materials: a vehicle used in transporting material found by the Secretary of Transportation to be hazardous under 49 U.S.C. 5103, transported in a quantity requiring placarding. There is no weight floor on that one; the placard is the trigger.

The middle two are the pair most often misremembered, because they differ in BOTH count and compensation. A vehicle is commercial if it is designed or used to transport more than 8 passengers, including the driver, FOR compensation — or more than 15 passengers, including the driver, when NOT for compensation. The lower threshold goes with payment and the higher one with its absence, which is the opposite of the way people tend to guess. Both counts include the driver, and both turn on what the vehicle is designed or used to do rather than on how many people happen to be aboard on a given day.