Opinion for the Court filed by Circuit Judge TATEL.
Dissenting opinion filed by Circuit Judge WILLIAMS.
TATEL, Circuit Judge:Petitioner challenges several provisions of the 1997 Final Rule issued by the Environmental Protection Agency pursuant to the 1990 amendments to the Clean Air Act. That statute prohibits a metropolitan planning organization from approving and the Department of Transportation from funding any transportation project unless it comes from a regional transportation plan and program that conform to applicable state-level air quality standards. Because the challenged “conformity” and “grandfather” regulations allow both local approval and federal funding of transportation projects that satisfy neither this requirement nor the single exception the statute permits, we hold that these regulatory provisions violate the Clean Air Act. In addition, we remand the regulations which allow conformity to be based on emissions budgets unapproved or disapproved by EPA for further proceedings to harmonize those regulations with the statute’s general conformity requirements. Finally, we hold that the regulation which allows conformity to be based on revised budgets that include “safety margin” emissions violates the statute’s requirement that conformity be evaluated against approved or applicable air quality standards.
I
The Clean Air Act establishes a joint state and federal program for regulating the nation’s air quality. The Act requires EPA to establish National Ambient Air Quality Standards (“NAAQS”) for various pollutants. See 42 U.S.C. § 7409 (1994). It also requires each state to adopt a State Implementation Plan (known as a “SIP”) that “provides for implementation, maintenance, and enforcement of [NAAQS] in each air quality control region (or portion thereof) within such State.” Id. § 7410(a)(1). SIPs must include “enforceable emission limitations and other control measures, means, or techniques ... , as well as schedules and timetables for compliance, as may be necessary or appropriate” to meet the NAAQS. Id. § 7410(a)(2)(A). “[A]fter reasonable notice and public hearings,” each state must submit a SIP with such pollution control strategies to EPA. Id. § 7410(a)(1). EPA typically approves SIPs pursuant to notiee-and-comment rulemaking.
In 1977, Congress amended the Clean Air Act to ensure that transportation planning at the local level conforms to pollution controls contained in approved SIPs. To accomplish this, the 1977 amendments prohibit federal agencies from assisting, approving, or supporting “any [transportation] activity which does not conform to [an applicable SIP].” Pub.L. No. 95-95, tit. I, sec. 129(b), § 176(c), 91 Stat. 745, 750 (1977).
Because Congress “offered little guidance” on the 1977 conformity requirement, and because federal agencies “largely ... ignored” it, Clean Air Conference Report, 136 Cong. Rec. 36,103, 36,105-06 (1990), Congress amended the Act again in 1990 to expand the content and scope of this requirement. See Pub.L. No. 101-549, tit. I, sec. 101(f), 110(4), § 176(c), 104 Stat. 2409, 2470 (1990) (codified at 42 U.S.C. § 7506(c)). The focus of this ease, the 1990 amendments do two things. First,' they establish general criteria for determining whether a transportation activity conforms to a SIP:
(1) .... Conformity to an implementation plan means—
(A) conformity to an implementation plan’s purpose of eliminating or reducing the severity and number of violations of the national ambient air quality standards and achieving expeditious attainment of such standards; and
(B) that such activities will not—
(i) cause or contribute to any new violation of any standard in any area;
(ii) increase the frequency or severity of any existing violation of any standard in any area; or
(iii) delay timely attainment of any standard or any required interim emission reductions or other milestones in any area.
42 U.S.C. § 7506(c)(1). Heads of federal agencies have “an affirmative responsibility” to assure conformity of any federally assisted or approved activity to an applicable SIP. Id.
Second, the 1990 amendments integrate the attainment and maintenance of air quali*644ty standards with the specific transportation planning process prescribed by the Urban Mass Transportation Act. As the Clean Air Conference Report put it, “[t]he purpose of the new ‘conformity’ requirement is to ensure that the transportation systems choices made by the community and incorporated into the regional transportation plan required by [federal transportation statutes] are consistent with achieving the allowable emission targets for each pollutant assigned to mobile sources in the SIP.” 136 Cong. Rec. at 36,106 col.2. Under the Urban Mass Transportation Act, the governor of each state, in agreement with local officials, must designate a metropolitan planning organization (known as an “MPO”) for each urban area with more than 60,000 people. See 49 U.S.C.A. § 5303(e)(1). The MPO plans for the transportation needs of that area. It develops a long range transportation plan (referred to in the statute as a “plan”) which specifies the facilities, services, financing techniques, and management policies that will comprise the area’s transportation system over a 20-year period, see id. § 5303(f), as well as a short-term transportation improvement program (referred to in the statute as a “program” and in the regulations as a “TIP”) which identifies and prioritizes the specific transportation projects to be carried out over the next three years, see id. § 5304(b). The heart of the Clean Air Act’s 1990 conformity requirements consists of the following restrictions on approval and funding of transportation plans, programs, and projects:
(2) Any transportation plan or program developed pursuant to Title 23 or the Urban Mass Transportation Act shall implement the transportation provisions of any applicable implementation plan ... applicable to all or part of the area covered by such transportation plan or program. No Federal agency may approve, accept or fund any transportation plan, program or project unless such plan, program or project has been found to conform to any applicable implementation plan in effect under this chapter. In particular—
(A) no transportation plan or transportation improvement program may be adopted by a [MPO], or be found to be in conformity by a [MPO] until a final determination has been made that emissions expected from implementation of such plans and programs are consistent with estimates of emissions from motor vehicles and necessary emissions reductions contained in the applicable implementation plan ...;
(C) a transportation project may be adopted or approved by a [MPO] or any recipient of funds designated under Title 23 or the Urban Mass Transportation Act, or found in conformity by a [MPO] or approved, accepted, or funded by the Department of Transportation only if it meets either the requirements of sub-paragraph (D) or the following requirements—
(i) such a project comes from a conforming plan and program;
(D) Any project not referred to in subparagraph (C) shall be treated as conforming to the applicable implementation plan only if it is demonstrated that the projected emissions from such project, when considered together with emissions projected for the conforming transportation plans and programs within the nonattainment area, do not cause such plans and programs to exceed the emission reduction projections and schedules assigned to such plans and programs in the applicable implementation plan.
42 U.S.C. § 7506(c)(2). According to the Agency, these provisions apply only to “non-attainment” areas (i.e., areas that have not met an air quality standard for a particular pollutant) and to “maintenance” areas (i.e., former nonattainment areas that have met the appropriate standard). See 40 C.F.R. §§ 93.101, 93.102(b) (1998).
In addition to specifying general conformity criteria and imposing restrictions on regional transportation planning, the 1990 amendments establish conformity criteria that apply to transportation plans, programs, and projects prior to Agency approval of a submitted SIP. See 42 U.S.C. § 7506(c)(3). *645The amended Act also authorizes EPA to promulgate criteria and procedures for determining conformity, provided that “in no case shall [conformity] determinations for transportation plans and programs be less frequent than every three years.” Id. § 7506(e)(4)(B)(ii).
EPA first issued criteria and procedures for making conformity determinations in 1993. See 58 Fed.Reg. 62,188 (1993). It then amended those procedures in a series of rulemakings. See 60 Fed.Reg. 40,098 (1995); 60 Fed.Reg. 57,179 (1995). In recent years, this court has heard two challenges to these amended rules. See Sierra Club v. EPA, 129 F.3d 137 (D.C.Cir.1997) (invalidating one-year exemption from statutory conformity requirements for transportation activities in nonattainment areas); Environmental Defense Fund, Inc. v. EPA, 82 F.3d 451 (D.C.Cir.1996) (upholding various regulations as reasonable interpretations of the statute).
In this case, petitioner Environmental Defense Fund argues that various provisions of EPA’s most recent Final Rule, see 62 Fed. Reg. 43,780 (1997) (codified at 40 C.F.R. §§ 93.100-93.128), violate the conformity requirements set forth in the 1990 amendments to the Clean Air Act. Specifically, petitioner contends: (1) that section 93.121(a)(1) of the regulations unlawfully permits local authorities to approve transportation projects in the absence of a currently conforming transportation plan and program; (2) that section 93.102(c)(1) suffers from the same defect with respect to federal funding of transportation projects; and (3) that sections 93.118(e)(1), 93.120(a)(2), and 93.124(b) unlawfully require or permit conformity determinations to be based on emissions budgets in SIPs that EPA has disapproved or not yet approved.
Applying Chevron’s two-step inquiry, we take up each claim in turn. We begin by asking “whether Congress has directly spoken to the precise question at issue.” Chevron U.S.A. Inc. v. Natural Resources Defense Council, Inc., 467 U.S. 837, 842, 104 S.Ct. 2778, 81 L.Ed.2d 694 (1984). If so, “that is the end of the matter; for the court, as well as the agency, must give effect to the unambiguously expressed intent of Congress.” Id. at 842-43, 104 S.Ct. 2778. However, if “the statute is silent or ambiguous with respect to the specific issue,” we must defer to the Agency’s construction of the statute as long as it is reasonable. Id. at 843, 104 S.Ct. 2778.
II
We start with EDF’s challenge to section 93.121(a)(1) of the regulations, which provides that an MPO or other recipient of federal funds may adopt or approve a regionally significant transportation project if “[t]he project was included in the first three years of the most recently conforming transportation plan and TIP (or the conformity determination’s regional emissions analyses), even if conformity status is currently lapsed.” 40 C.F.R. § 93.121(a)(1). Conformity status of a transportation plan or program lapses when more than three years pass without a new conformity determination by an MPO or the Department of Transportation. See 42 U.S.C. § 7506(e)(4); 40 C.F.R. § 93.104(b)(3), (c)(3). Under section 93.121(a)(1), local officials may approve a transportation project as long as it once appeared in a conforming plan and program, even if the plan and program no longer conform at the time of project approval. By authorizing this result, petitioner argues, section 93.121(a)(1) violates the Clean Air Act’s requirement that projects “come[ ] from a conforming plan and program.” 42 U.S.C. § 7506(c)(2)(C). We agree.
At the outset, we think it important to make clear that this dispute over the legality of section 93.121(a)(1) relates only to approval of won-federally funded projects. The Agency’s rule makes clear that local transportation projects receiving federal funds must satisfy a more stringent conformity requirement than section 93.121(a)(1). Federally funded projects may not proceed unless there exist “a currently conforming transportation plan and currently conforming TIP at the time of project approval.” 40 C.F.R. § 93.114 (emphasis added). In other words, during a plan or program conformity lapse, an MPO may not find a federally funded project to be in conformity, and therefore that project may not go forward. The ques*646tion here is whether reora-federally funded projects — defined as “projects which are funded or approved by a recipient of federal funds ... but which do not rely at all on any [federal] funding or approvals,” 62 Fed.Reg. at 43,788 — may attain conformity status in the absence of a currently conforming plan and program.
We begin with the text of the Clean Air Act. Under section 7606(c)(2)(C), an MPO may find a local transportation project to conform with an applicable SIP only if the project meets one of two requirements: Either it must “come[ ] from a conforming plan and program,” id. § 7506(c)(2)(C)(i), or its “projected emissions..., when considered together with emissions projected for the conforming transportation plans and programs within the nonattainment area, [must] not cause such plans and programs to exceed the emission reduction projections and schedules assigned to such plans and programs in the applicable [SIP],” id. § 7606(c)(2)(D). Claiming that the requirement that a project “come from a conforming plan and program” is ambiguous, EPA insists that it has reasonably construed this requirement to permit project approval during a conformity lapse, as long as the project comes from the first three years of a once-conforming plan and program. This approach, EPA argues, strikes the proper balance between protecting air quality and avoiding disruption to the transportation planning process. According to petitioner, the statutory text leaves no ambiguity: A project that “comes from a conforming plan and program” means a project that comes from a currently conforming plan and program. Therefore, EDF argues, the statute prohibits approval of any projects, federally funded or not, during a conformity lapse.
Giving these words their ordinary meaning, we interpret the phrase “comes from a conforming plan and program” — a phrase entirely in the present tense — to refer to projects that come from a currently conforming plan and program. But even were it possible to read the phrase, as EPA and our dissenting colleague do, to refer to projects that come from a previously conforming plan and program, we think this interpretation is foreclosed by Congress’s use of the terms “conforming plan and program” in section 7506(c)(2)(D), by the general conformity criteria of section 7506(c)(1), and by the legislative history of the conformity requirements.
Section 7506(c)(2)(D) states that a project' not included in a conforming plan and program may be found to conform only if its projected emissions “when considered together with emissions projected for the conforming transportation plans and programs within the nonattainment area,” do not exceed the SIP emissions budget. 42 U.S.C. § 7506(c)(2)(D). This provision enables a project to attain conformity status “only if the regional plans and programs are in conformity at the time the project is reviewed.” Clean Air Conference Report, 136 Cong. Rec. at 36,108 col.l. Indeed, in its 1996 notice of proposed rulemaking, which led to the Final Rule challenged here, EPA acknowledged that
[t]he option provided in section [7506](c)(2)(D) for new projects that were not previously included in a transportation plan/TIP or supporting regional emissions analysis to demonstrate conformity cannot apply during a transportation plan/TIP conformity lapse, because it requires a demonstration that “conforming transportation plans and TIPs” would still conform when the emissions of the new project are considered. Without a conforming transportation plan and TIP in place, this cannot be demonstrated.
61 Fed.Reg. 36,112, 36,120 col.2 (1996). We thus have no doubt that the word “conforming” in section 7506(e)(2)(D) means presently conforming. Since section 7506(c)(2)(D) provides an alternative means of demonstrating project conformity when a project does not “come from a conforming plan and program,” it would be quite odd to read the word “conforming” in section 7506(c)(2)(C) to mean something different from what it means in section 7506(c)(2)(D).
Moreover, were we to read the word “conforming” the way EPA suggests, there would be no assurance that projects approved under section 7506(c)(2)(C) would help eliminate, reduce, or prevent violations of national ambient air quality standards, as required by *647section 7506(c)(1). According to that provision, a “conforming” transportation project is one that will contribute to “eliminating or reducing the severity and number of violations of the [NAAQS] and achieving expeditious attainment of such standards,” 42 U.S.C. § 7506(e)(1)(A), and that “will not — (i) cause or contribute to any new violation of any standard in any area; (ii) increase the frequency or severity of any existing violation of any standard in any area; or (iii) delay timely attainment of any standard or any required interim emission reductions or other milestones in any area,” id. § 7506(c)(1)(B). Though doubting the applicability of section 7506(e)(1) to projects approved under section 7506(c)(2), the dissent nevertheless concedes that section 7506(c)(2)(A) expressly incorporates the requirements of section 7506(c)(1)(B) and makes them applicable to projects approved under section 7506(c)(2). See Dissenting Opinion (“Dissenting Op.”) at 654-655. Absent a currently conforming plan and program, there is no certainty, that a regionally significant transportation project will satisfy any of the section 7506(c)(1)(B) conformity criteria. EPA’s interpretation of section 7506(c)(2)(C) thus eviscerates the requirements of section 7506(c)(1)(B) and therefore also the requirements of section 7506(c)(2)(A), creating an untenable inconsistency not only between section 7506(c)(1) and section 7506(c)(2), but also within section 7506(c)(2) itself.
Our dissenting colleague accuses us of “embracing] an argument” raised by petitioner “in two sentences of its ‘Summary of Argument,’ but not at all thereafter.” Dissenting Op. at 653. With all due respect, we think the dissent unfairly characterizes petitioner’s brief. It is true that petitioner first sets forth this argument in the “Summary of Argument”:
The rule ... undermines Congress’ decision to ensure that long-term investment of resources in regional transportation systems contribute to “eliminating or reducing the severity and number of [NAAQS violations]” (required by § 176(e)(1)(A)) by requiring re-assessment of the conformity of the planned regional transportation system every three-years [sic]. 42 U.S.C. § 7506(c)(4)(B)(ii). By allowing projects from a plan that no longer meets regional emission budgets to be approved, the rule allows elements of the non-conforming plan to be implemented which can interfere with progress toward attaining the NAAQS.
EDF Br. at 13 (alteration in original). But far from failing to mention this argument later in its brief, petitioner devotes three pages of its “Argument” section to developing the claim. See id. at 23-25. EDF opens this discussion by citing section 7506(c)(4)(B)(ii) for the proposition that “conformity determinations for a plan and/or program expire at least every three years by operation of law.” Id. at 23. It then argues that “[t]he three-year limit on transportation plans and TIPs plays an important role by assuring that plans and TIPs continue to reflect the latest emission targets for a region,” specifically mentioning emission reduction targets related to statutorily prescribed ozone and carbon monoxide attainment goals. Id. at 24. “Without the obligation to renew conformity findings every 3 years,” EDF concludes, “regions could continue implementing transportation systems designed to meet older emission targets no longer adequate to attain the NAAQS.” Id. In addition to paraphrasing the claim first stated in the “Summary of Argument,” which explicitly invokes section 7506(c)(1), this last sentence plainly manifests petitioner’s belief that EPA’s rule fails to ensure that transportation plans, programs, and projects will help “achieve expeditious attainment of [NAAQS]” and will not “delay timely attainment of any [NAAQS],” as section 7506(c)(1) requires. 42 U.S.C. § 7506(c)(1)(A), (c)(l)(B)(iii). We think that petitioner has adequately challenged EPA’s regulation under section 7506(c)(1).
The legislative history of the 1990 conformity requirements provides one final reason why we think the phrase “conforming plan and program” refers to currently conforming plans and programs. Congress imposed new conformity requirements in order to integrate transportation planning at the local level with attainment and maintenance of air quality standards at the state level. See Clean Air Conference Report, 136 Cong. *648Rec. at 13,106 col.l (noting that the statute “will require transportation planning agencies to view their task as the development of a transportation system that meets ... both mobility needs and air quality objectives”). By requiring plans and programs to conform to applicable SIPs at the time of project approval, Congress sought to ensure that “transportation plans and programs [would] serve as part of the pollution control strategy for the metropolitan area.” Id. To be sure, plans and programs could also serve this pollution control function, as EPA explains, by “accounting] for and offset[ting] if necessary the emissions of any non-federal projects that are implemented during a conformity lapse.” 62 Fed.Reg. at 43,790 col.l. But that approach would invite local decision-makers to approve transportation projects while deferring development of pollution control strategies during conformity lapses, thereby subverting Congress’s intent that the two processes — transportation planning and pollution control — occur simultaneously. See 136 Cong. Rec. at 36,107 col.2 (regional planning process should identify “the comprehensive transportation system for a metropolitan area” in the context of a “comprehensive consideration of alternatives ... and careful analysis of options that can contribute toward achieving the air quality objectives of the Clean Air Act”).
The Conference Report also describes section 7506(c)(2)(D) as an “exception” — indeed, it is the only exception — to the general rule of section 7506(c)(2)(C). Id. at 36,108 col.l. Under section 7506(e)(2)(D), an excluded project may go forward only if its expected emissions, together with the expected emissions from currently conforming plans and programs, do not exceed the emissions ceilings in the applicable SIP. As we indicated earlier, both Congress and EPA interpret the word “conforming” in this provision to mean currently conforming. See supra at 646. Section 7506(c)(2)(D) thus shows that Congress wanted no transportation projects to proceed without assurance that they would not undermine attainment or maintenance of current air quality standards. Directly contravening this mandate, the Agency’s rule allows local officials to approve transportation projects included in plans and programs that previously conformed but presently do not. See 40 C.F.R. § 93.121(a)(1). Because the conformity status of such projects bears no relation to current air quality attainment or maintenance goals, their approval carries no guarantee that their emissions will neither violate current standards nor contribute to existing violations. Indeed, in the preamble to the 1997 Final Rule, EPA admits — without qualification and contrary to its position in this case — that “projects cannot be approved if the plan and TIP have lapsed.” 62 Fed. Reg. at 43,797 cols.1-2.
EPA offers two additional justifications for its interpretation of section 7506(c)(2)(C). Neither survives scrutiny. First, the Agency points out that under a regulation effective since 1995, a certain category of transportation projects called transportation control measures (“TCMs”) may proceed even in the absence of a currently conforming plan and program. See 40 C.F.R. § 93.114(b). According to the Agency, this exemption shows that section 7506(c)(2)(C) of the statute requires no currently conforming plan and program at the time of project approval. But we see no reason to extend the exemption for TCMs to ordinary transportation projects, since the former reduce pollution, see id. § 93.101, while the latter add to it. TCMs are “specifically identified and committed to in the applicable implementation plan,” id., and exempted from the requirements of section 7506(c)(2)(C) because, as the Agency explained in the preamble to the 1995 rule, “[b]y definition, a TCM in an approved SIP conforms to the SIP because it is contained in the SIP.” 60 Fed.Reg. at 57,180 col.2. This rationale has no applicability to non-TCM projects because such projects never appear in SIPs. See id. at 57,180 col.3.
Second, the Agency argues that although the statute requires plan and program conformity determinations at least once every three years, see 42 U.S.C. 7506(e)(4)(B)(ii), the statute contains no such requirement for project conformity determinations. Inferring from this that Congress intended project conformity to be determined not more than once, EPA maintains that a project included in a previously conforming plan and program retains its conformity sta*649tus, even if conformity of that plan and program eventually lapses. We disagree. Although the statute suggests that Congress did not intend project conformity determinations to occur every three years, it does not follow that Congress intended project conformity determinations to occur only once. Based on our analysis above, we read the statute to require non-federally funded projects to follow the three-year conformity determination schedule applicable to transportation plans and programs up to the point of MPO approval. After MPO approval, non-federally funded projects need undergo no further conformity determinations.
In sum, the language and history of the statute’s conformity requirements show that Congress intended transportation planning and air quality management to proceed in lock step. By allowing local approval of transportation projects in the absence of currently conforming plans and programs, the Agency’s regulation undermines section 7506(c)(2)(C)’s criteria for demonstrating conformity of regionally significant transportation projects to state-level air quality standards. Finding clear congressional intent and thus no need to proceed to Chevron’s second step, we hold that section 93.121(a)(1) of the regulations violates the Clean Air Act.
Ill
Next, petitioner challenges section 93.102(c)(1) of the regulations, which provides that
[pjrojects subject to this subpart for which the NEPA process and a conformity determination have been completed by DOT may proceed toward implementation without further conformity determinations unless more than three years have elapsed since the most recent major step (NEPA process completion; start of final design; acquisition of a significant portion of the right-of-way; or approval of the plans, specifications and estimates) occurred.
40 C.F.R. § 93.102(c)(1). Known as the “grandfather” rule, this section reflects the Agency’s view that “there should only be one point in the transportation planning process at which a project-level conformity determination is necessary.” 62 Fed.Reg. at 43,783 col.2. According to petitioner, this regulation, like the one discussed above, violates section 7506(e)(2)(C) of the statute because it allows transportation projects to receive federal funding in the absence of a currently conforming plan and program. Again, we agree.
To understand how the “grandfather” rule works, consider the following hypothetical: In 1993, an MPO approves and adopts a regional highway project — for example, an urban beltway. At the time, the beltway is included in both a conforming plan and a conforming program. Three years later, in 1996, the conformity status of the plan and program lapses. In 1997, the MPO acquires a significant portion of the right-of-way for the beltway. Today, ready to start building, the MPO seeks funding from the Department of Transportation. EPA’s “grandfather” rule would allow DOT to fund the beltway, since a “major step” — acquisition of right-of-way— occurred within the past three years. But section 7506(e)(2)(C)’s conformity requirement expressly prohibits DOT from “ap-prov[ing], accepting], or fund[ing]” the beltway unless it “comes from a conforming plan and program.” This means that no transportation project may receive federal funds in the absence of a currently conforming plan and program. See supra Part II. Therefore, to the extent that section 93.102(a)(1) of the regulations allows projects to receive federal funds during plan and program conformity lapses, it violates the Clean Air Act.
Defending its “grandfather” rule, EPA cites Environmental Defense Fund, Inc. v. EPA, supra. But that case sustained the “grandfather” rule only as a transition measure “to avoid immediate ‘retroactive’ implementation of the new [1990] conformity requirement which would impose a substantial and unforeseen burden on federal projects that had already satisfied existing federal requirements [i.e., NEPA review].” 82 F.3d at 456. Nothing in that decision supports what the Agency has done here — forever exempting a project' from further conformity determinations where the project’s most recent conformity determination occurred more than three years ago and where a “major step” occurred within the past three years.
*650While invalidating section 93.102(a)(1) with respect to federally funded projects, we note that the statute does not preclude the “grandfather” clause from applying to non-federally funded projects. Although section 7506(c)(2)(C) of the statute prohibits MPO or DOT approval of non-federally funded projects during a plan and program conformity lapse, it nowhere prohibits implementation of such projects as long as their approval occurred prior to the conformity lapse.
IV
We turn finally to petitioner’s challenge to those sections of the regulations that permit or require plan, program, and project conformity to be based on motor vehicle emissions budgets in SIP revisions that a state has submitted to EPA, but that EPA has not yet approved or has disapproved. See 40 C.F.R. §§ 93.118(e)(1), 93.120(a)(2), 93.124(b). Under these regulations, if EPA disapproves a submitted SIP revision without a “protective finding” — i.e., a determination that the submission “contains adopted control measures or written commitments to adopt enforceable control measures that fully satisfy the [relevant statutory] emissions reductions requirements,” id. § 93.101 — then “[d]uring the first 120 days following [such] disapproval..., transportation plan, TIP, and project conformity determinations shall be made using the motor vehicle emissions budgets) in the disapproved control strategy implementation plan.” Id. § 93.120(a)(2). Emissions budgets contained in a submitted SIP revision also guide conformity determinations when EPA makes no finding within 45 days of submission regarding the adequacy of the budgets. See id. § 93.118(e)(1); see also id. § 93.124(b) (allowing conformity to be based on submitted but not-yet-approved SIP revisions). Submitted budgets, however, do not supersede emissions budgets in an approved SIP for the years covered by the SIP. See id. § 93.118(e)(1).
Conceding that the Clean Air Act generally requires conformity to be evaluated against approved SIPs, the Agency argues that these regulations represent reasonable responses to statutory silence as to how conformity should be determined when no approved SIP exists or when the approved SIP contains no adequate motor vehicle emissions budget. We disagree. Although the statute nowhere explicitly dictates how conformity should be determined under the circumstances EPA describes, any attempt by the Agency to fill these gaps must satisfy section 7506(c)(l)(B)’s generally applicable conformity requirements. Where EPA disapproves a SIP revision without a protective finding, i.e., without determining that it contains adequate measures to reduce emissions to statutorily required levels, see 40 C.F.R. § 93.120(a)(2), or where EPA fails to determine the adequacy of motor vehicle emissions budgets in a SIP revision within 45 days of submission, see id. § 93.118(e)(1), there is no reason to believe that transportation plans and programs conforming to the submitted budgets “will not — (i) cause or contribute to any new violation of any standard in any area; (ii) increase the frequency or severity of any existing violation of any standard in any area; or (iii) delay timely attainment of any standard_” 42 U.S.C. § 7506(c)(1)(B). Indeed, nothing in the regulations requires MPOs to show that an area’s projected emissions would be lower if plans and programs conforming to a submitted budget were implemented than if they were not. See 62 Fed.Reg. at 43,781 col.2 (noting that submitted budgets replaced “build/no-build test” as measure of conformity under Final Rule). Even if it were true that section 93.118(e) gives states an incentive to file emissions budgets conforming to law, see Dissenting Op. at 656, the regulation would still violate the statute by allowing conformity determinations to take effect where federal agencies and MPOs have not discharged their “affirmative responsibility” to provide an “assurance of conformity.” 42 U.S.C. § 7506(c)(1). To be sure, section 93.118(e)(6) of the regulations provides that “the MPO and DOT’s conformity determinations [based on unapproved or disapproved SIPs] will be deemed to be a statement that the MPO and DOT are not aware of any information that would indicate that emissions consistent with the motor vehicle emissions budget” would violate section 7506(e)(l)(B)’s conformity criteria. But how can an MPO or DOT satisfy its “affirmative responsibility” to provide an *651“assurance of conformity” through a “deemed” statement indicating mere ignorance of non-conformity? For these reasons, we grant petitioner’s request that we remand sections 93.118(e)(1) and 93.120(a)(2) to EPA for further rulemaking to harmonize these regulations with section 7506(c)(l)’s conformity requirements.
Section 93.124(b) is also inconsistent with the Clean Air Act, but for a different reason. That provision reads:
If an applicable implementation plan submitted before November 24, 1993, demonstrates that emissions from all sources will be less than the total emissions that would be consistent with attainment and quantifies that “safety margin,” the State may submit an implementation plan revision which assigns some or all of this safety margin to highway and transit mobile sources for the purposes of conformity. Such [a SIP] revision ... may be used for the purposes of transportation conformity before it is approved by EPA.
Id. § 93.124(b). Unlike sections 93.118(e)(1) and 93.120(a)(2), which apply when there is no applicable SIP or no SIP with an applicable emissions budget, section 93.124(b) applies when there is an applicable SIP — i.e., it does not purport to fill a statutory gap. While it may be true that plans and programs conforming to a SIP revision under section 93.124(b) “will not cause, worsen, or prolong violations of air quality standards,” Dissenting Op. at 658, the statute nevertheless requires conformity determinations to be based on a SIP “approved or promulgated under section 7410 of this title” where such a SIP exists. 42 U.S.C. § 7506(e)(1); see also id. § 7506(c)(2) (requiring transportation plans, programs, and projects “to conform to any applicable implementation plan in effect under this chapter”). Indeed, EPA itself has said that it “does not believe that it is legal to allow a submitted SIP to supersede an approved SIP for years addressed by the approved SIP.” 62 Fed.Reg. at 43,783 eol.3; see also 40 C.F.R. § 93.118(e)(1). Because section 93.124(b) would allow a submitted but unapproved SIP revision to supersede an approved SIP, it violates the Clean Air Act.
V
Our dissenting colleague charges that our conclusions today frustrate EPA’s goal of allowing greater flexibility in the conformity determination process. See Dissenting Op. at 651-652. Whatever the Agency’s policy goals, our job is to interpret the statute. Here, the statute imposes an elaborate array of requirements that, according to the dissent, amount to “a congressional effort to micromanage local transportation planning.” Id. at 652. If this legislative scheme is too onerous, it is up to Congress to provide relief, not this court.
We grant EDF’s petition for review and hold that sections 93.121(a)(1) and 93.102(c)(1) of EPA’s regulations are unlawful because they depart from the criteria for demonstrating project conformity established in section 7506(c)(2)(C) of the Clean Air Act. In addition, we remand sections 93.118(e)(1) and 93.120(a)(2) of the regulations for the Agency to align these regulations with the general conformity criteria of section 7506(c)(1)(B). Finally, we hold that section 93.124(b) of the regulations violates section 7506(c)(l)-(2) of the Act by allowing a submitted SIP revision to supersede an approved or applicable SIP.
So ordered.