49 CFR § 523.6 - Heavy-duty vehicle.
(a) A heavy-duty vehicle is any commercial medium or heavy-duty on-highway vehicle or a work truck, as defined in 49 U.S.C. 32901(a)(7) and (19). For the purpose of this section, heavy-duty vehicles are divided into four regulatory categories as follows:
(1) Heavy-duty pickup trucks and vans;
(2) Heavy-duty vocational vehicles;
(3) Truck tractors with a GVWR above 26,000 pounds; and
(4) Heavy-duty trailers.