An automobile is any 4-wheeled vehicle that is propelled by fuel, or by alternative fuel, manufactured primarily for use on public streets, roads, and highways and rated at less than 10,000 pounds gross vehicle weight, except:
49 C.F.R. §523.3
Sec. 9, Pub. L. 89-670, 80 Stat. 981 ( 49 U.S.C. 1657 ); sec. 301, Pub. L. 94-163, 89 Stat. 901 ( 15 U.S.C. 2002 ); delegation of authority at 41 FR 25015, June 22, 1976