USDOT/FHWA- Code of Federal Regulations.
http://frwebgate.access.gpo.gov/cgi-bin/...0&TYPE=TEXT
Commercial motor vehicle means any self-propelled or towed motor
vehicle used on a highway in interstate commerce to transport passengers
or property when the vehicle--
(1) Has a gross vehicle weight rating or gross combination weight , or gross vehicle weight or gross combination weight, of 4,536 kg
(10,001 pounds) or more, whichever is greater; or
(2) Is designed or used to transport more than 8 passengers
(including the driver) for compensation; or
(3) Is designed or used to transport more than 15 passengers,
including the driver, and is not used to transport passengers for
compensation; or
(4) Is used in transporting material found by the Secretary of
Transportation to be hazardous under 49 U.S.C. 5103 and transported in a
quantity requiring placarding under regulations prescribed by the
Secretary under 49 CFR, subtitle B, chapter I, subchapter C.

In Maryland DOT has been pulling over landscaping company pickup trucks with trailers behind them and busting them for not having DOT# or USDOT# and medical cards when they are over 10,000 GCVW. The biggest thing is having the medical card.

It will be interesting now that we are expected to be managed by the DOT as commercial enterprises and then the IRS wants to declare racing for most of us as a "Hobby".

The way I feel the gov't can't have it both ways.