Section 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(b) The heavy-duty vehicle classification does not include vehicles excluded as specified in 49 CFR 535.3 .76 FR 57491, 9/15/2011; 81 FR 74237, 12/27/2016