40 U.S.C. § 17509

(a) Priority in Reducing Headquarters Use .— The heads of executive agencies shall give first priority to meeting the goals established by the President under section 17507(a) of this title by reducing the costs of administrative motor vehicles used at the headquarters and regional headquarters of executive agencies, rather than by reducing the costs of motor vehicles used by line agency personnel working in agency field operations or activities. (b) Regulations, Standards, and Definitions .— The President shall require the Administrator of General Services, in cooperation with the Director of the Office of Management and Budget, to prescribe appropriate regulations, standards, and definitions to ensure that executive agencies meet the goals established under section 17507(a) of this title in the manner prescribed by subsection (a).