49 C.F.R. § 523.2 provides the following definition for work trucks: “Work truck means a vehicle that is rated at more than 8,500 and less than or equal to 10,000 pounds gross vehicle weight, and is not a medium-duty passenger vehicle as defined in 40 CFR 86.1803-01 effective as of December 20, 2007.” (Emphasis added). (the definition of a medium-duty passenger vehicle is provided below). A medium-duty passenger vehicle (“MDPV”), according to 40 C.F.R. § 86.1803-01, “means any heavy-duty vehicle (as defined in this subpart) with a gross vehicle weight rating (GVWR) of less than 10,000 pounds that is designed primarily for the transportation of persons.