FMCSR definitions:

[Teddy Lancaster <Teddy@runningbear.com>]

Commercial motor vehicle means any self-propelled
or towed vehicle used on public highways
in interstate commerce to transport passengers or
property when:

(a) The vehicle has a gross vehicle weight rating
or gross combination weight rating of 4,537 or
more kilograms (10,001 or more pounds); or

(b) The vehicle is designed to transport more than
15 passengers, including the driver; or

(c) The vehicle is used in the transportation of
hazardous materials in a quantity requiring
placarding under regulations issued by the
Secretary under the Hazardous Materials
Transportation Act (49 U.S.C. 5101 et seq.).

Teddy (more to come as I find them)