(2) Model year The term model year has the meaning given such term under section 32901(a) of such title 49. (3) Motor vehicle The term motor vehicle means any vehicle which is manufactured primarily for use on public streets, roads, and highways (not including a vehicle operated exclusively on a rail or rails) and which has at least 4 wheels. (4) Reference fuel-economy rating The term reference fuel-economy rating means, with respect to any motor vehicle, the fuel economy standard for such motor vehicle, expressed in gallons per mile, calculated by applying the relevant vehicle attributes to the mathematical function published pursuant to section 32902(b)(3)(A) of title 49, United States Code. (5) Other terms The terms automobile , passenger automobile , light truck , and manufacturer have the meanings given such terms in regulations prescribed by the Administrator of the Environmental Protection Agency for purposes of the administration of title II of the Clean Air Act ( 42 U.S.C. 7521 et seq.). (e) Special rules (1) Basis reduction For purposes of this subtitle, the basis of any property for which a credit is allowable under subsection (a) shall be reduced by the amount of such credit so allowed (determined without regard to subsection (c)). (2) No double benefit No other credit shall be allowable under this chapter for a new qualified fuel-efficient motor vehicle with respect to which a credit is allowed under this section. (3) Property used by tax-exempt entity In the case of a vehicle whose use is described in paragraph (3) or (4) of section 50(b) and which is not subject to a lease, the person who sold such vehicle to the person or entity using such vehicle shall be treated as the taxpayer that placed such vehicle in service, but only if such person clearly discloses to such person or entity in a document the amount of any credit allowable under subsection (a) with respect to such vehicle (determined without regard to subsection (c)). For purposes of subsection (c), property to which this paragraph applies