Beyond those general principles, our review is guided by Chevron analysis. Under Chevron step one, if Congress has clearly spoken on the issue, then “that intention is the law and must be given effect.” Chevron, 467 U.S. at 843 n. 9, 104 S.Ct. at 2781 n. 9. If the statute is “silent or ambiguous with respect to the specific issue,” we proceed to Chevron step two analysis, and if “the agency’s answer is a permissible construction of the statute,” we must defer. Chevron, 467 U.S. at 843, 104 S.Ct. at 2782.
C. Ascertaining Congressional Intent
Under Chevron step one analysis, we use traditional tools of statutory construction to determine whether Congress had “an intention on the precise question at issue.” Chevron, 467 U.S. at 843 n. 9, 104 S.Ct. at 2781 n. 9. To ascertain congressional intent, we look to the “particular statutory language at issue, as well as the language and design of the statute as a whole,” K Mart Corp. v. Cartier, Inc., 486 U.S. 281, 108 S.Ct. 1811, 1817, 100 L.Ed.2d 313 (1988), and, where appropriate, its legislative history. Ohio v. United States Department of the Interior, 880 F.2d 432, 441 (D.C.Cir.1989).
The precise question at issue here is whether Congress intended to bar NHTSA from requiring that amendments to reduce the CAFE standard be made prior to the beginning of the model year. After examining the text, statutory structure, and legislative history, we find that Congress has not clearly spoken on that question.
We begin with the statutory text. EPCA’s CAFE amendment provisions are silent with respect to whether an amendment making a CAFE standard less stringent must be issued before the model year begins, or by any precise point in time. See 15 U.S.C. §§ 2002(a)(4) and (f)(1). Looking to the statutory scheme as a whole, we find that the statute does contain an explicit deadline for any amendment that has the effect of making an average fuel economy standard more stringent. Such an amendment must be promulgated “at least 18 months prior to the beginning of the model year to which such amendment will apply.” 15 U.S.C. § 2002(f)(2). And, the statute contains explicit deadlines for purposes other than amending the CAFE standards. See, e.g., 15 U.S.C. §§ 2002(a)(3) and (b) (deadlines for establishing passenger car standards for MYs 1981-1984 and light truck standards); 15 U.S.C. § 2003(d)(3) (deadline for promulgating testing and calculation procedures).
Petitioners argue that the presence of these explicit deadlines in the statute and the absence of any express deadline for reductions of CAFE levels makes clear that Congress did not intend there to be a deadline for CAFE reduction amendments. See generally Russello v. United States, 464 U.S. 16, 23, 104 S.Ct. 296, 300, 78 L.Ed.2d 17 (1983) (it is generally presumed that Congress acts intentionally and purposely in the disparate inclusion or exclusion of statutory provisions) (citations omitted).
We are unable to perceive any such congressional intent. The existence of deadlines for amendments that have prospective effect only is not necessarily evidence from which to infer a clear congressional intent to allow retroactive actions without regard to any deadlines.7 The failure to prescribe an express deadline for CAFE reductions could mean either that no deadline was contemplated by Congress, or that Congress left the choice to NHTSA whether or not to impose a deadline in the interests of smooth operation of the CAFE law.
The latter interpretation is consistent with the bill’s legislative history. In the original Senate bill, all amendments to CAFE standards were required to be promulgated “at least 18 months prior to the beginning of the model year.” S. 1883, § 504(a)(6). See S.Rep. No. 94-179, 94th Cong., 1st Sess. 21, 39 (1975). As enacted,
7
While we do not rely on the Bowen case to control the outcome here, we do point out that its caution as to the need for clear authorization for retroactive rulemaking has an analogue in our own analysis: we will not lightly infer the existence of retroactive amending power unless Congress signals its presence.