Opinion for the Court filed by Circuit Judge HARRY T. EDWARDS.

Concurring opinion filed by Circuit Judge STEPHEN F. WILLIAMS.

The 1990 amendments to the Clean Air Act (“CAA”) altered section 202(a)(6) to require the Environmental Protection Agency (“EPA”), after “consultation” with the Department of' Transportation (“DOT”), to promulgate standards by November 15, 1991, that would require new “light-duty” vehicles1 to be equipped with on-board refueling vapor recovery (“ORVR”) systems over a specified phase-in period. After consulting with DOT, EPA concluded that the safety risks of ORVR systems were unreasonable given the availability of alternative mechanisms for controlling refueling vapor emissions and declined to promulgate ORVR standards by the statutory deadline. This decision was Noticed as a Final Agency Action in April, 1992. 57 Fed.Reg. 13,046 (1992). In explaining its decision, EPA contended that amended section 202(a)(6) contained residual authority for EPA to exercise discretion in deciding whether to promulgate ORVR standards if the Agency determined that ORVR was unreasonably unsafe. The Natural Resources Defense Council (“NRDC”) initiated this suit, alleging that EPA lacked discretion under the statute and that its failure to promulgate ORVR standards was therefore unlawful.

Because the language of section 202(a)(6) plainly imposes a mandatory duty, we agree that EPA’s decision not to promulgate ORVR standards was beyond the pale of its statutory authority. There is nothing in the statute to substantiate EPA’s claim for residual discretionary authority, nor is there ambiguity that would warrant deference by this court to EPA’s construction. Furthermore, EPA’s findings regarding ORVR safety do not establish that all such systems present inherent and unreasonable safety risks. We are thus not faced with a situation in which a literal reading of the section produces nonsensical results. Whatever doubts EPA may have about the wisdom of choices implicit in the statute must be raised with Congress. This court is not the proper forum in which to argue the relative merits of those choices. Therefore, the Final Agency Action is set aside and EPA is ordered to promulgate ORVR standards in compliance with the CAA.

I. Background

A. The “Refueling Vapor Recovery” Problem

During the normal operation of gasoline fueled vehicles, hydrocarbon vapors build up in the fuel tank. When the fill cap is removed during refueling, most of these vapors are forced out of the tank and into the environment by the influx of liquid gasoline. This release of vapors poses significant health and environmental hazards. Of primary concern is the effect these vapors have on the production of ozone, which is formed when hydrocarbons and nitrogen oxides react in sunlight.2 Excessive ozone pollution is a persistent environmental hazard in major metropolitan areas. See Air Quality Designations and Classifications, 56 Fed.Reg. 56,694 (1991) (designating nonattainment areas for ozone pollution). In addition, escaping gasoline vapors contain known carcinogens.3 Thus, the control and containment of these vapors has been an environmental concern for many years.

*237Two basic approaches have emerged for controlling the emission of hydrocarbon vapors during refueling: “Stage II” controls4 and ORVR systems. Stage II controls— typically a rubber boot on the fuel nozzle that creates a tight seal with the fuel filler spout so that escaping vapors are recaptured and funneled to underground tanks— are relatively simple mechanisms that have been used since 1976 in many counties in California as well as certain cities in the United States. See DOT, Assessment of the Safety of Onboard Refueling Vapor Recovery Systems at 3 (July 1991) [hereinafter “DOT Assessment”]. Under the current CAA, Stage II controls are required in most nonattainment areas of moderate or worse severity. See 42 U.S.C. §§ 7511a(b)(3), (c), (d), (e) (Supp. 1990).

ORVR systems, on the other hand, are more sophisticated and have not yet been used in production vehicles. As the name implies, onboard refueling vapor recovery systems are built into the vehicle itself to contain the vapors before they reach the fuel filler spout. There are presently two types of technology that have been seriously considered for operational ORVR systems. The first is the ORVR “canister,” which collects vapors as they are forced through a regulating orifice and stores them in a charcoal-filled canister. See DOT Assessment at 1. As the engine operates, ambient air is drawn through the canister to purge the hydrocarbons from the charcoal and meter the vapors back into the engine for combustion (“purging”). See id.5 Canister systems are more fully evolved than other ORVR systems because virtually all of the necessary technology for canister systems is currently available. Indeed, most passenger cars on the road today already carry a small charcoal filled canister (so called “evaporative canisters”) to collect the relatively modest quantities of vapor that accumulate in fuel tanks during operations other than refueling. It was, in fact, modified versions of current evaporative canisters that the National Highway Transportation Safety Administration (“NHTSA”) studied in order to provide EPA with DOT’S recommendations regarding the safety of ORVR. Id. at 2.

An alternative to ORVR canisters is the flexible fuel bladder, which contracts as gasoline is burned, retarding- the evaporation of liquid fuel and thus the accumulation of hydrocarbon vapors. Because of potential safety benefits from such a system, aside from the environmental protection it would provide, the possibility of using flexible fuel bladders has been explored for many years. See, e.g., Memorandum from Jean Schwendeman, EPA Mechanical Engineer, to Public Docket No. A-87-11 (Mar. 1, 1988) (memorializing a meeting with a manufacturer that had been testing fuel bladders since “the early 1970’s”) [hereinafter “Schwendeman Memo”], reprinted in J.A. at 524. Nonetheless, no bladder prototypes were available at the time NHTSA conducted its study. See DOT, Review of Comments Submitted to EPA on NHTSA’s Report “An Assessment of the Safety of Onboard Refueling Vapor Recovery Systems” at 4 (Nov. 27, 1991) [hereinafter “DOT Review”], reprinted in J.A. at 163.

B. Legislative and Regulatory Responses to the “Refueling Vapor Recovery” Problem

Under the 1977 amendments to the CAA, EPA was. required to promulgate ORVR regulations if it found ORVR to be a feasible and desirable means of controlling vapor emissions during refueling. Pub.L. *238No. 95-95, § 216, 91 Stat. 760-61 (1977).6 Upon review of the information available to it in the late 1970’s, EPA initially concluded that ORVR was “technically feasible.” See 52 Fed.Reg. at 31,163 (describing conclusions reached in 1980). However, in order to avoid placing additional regulatory burdens on the ailing American automotive industry, EPA decided not to require ORVR systems at that time. See 46 Fed. Reg. 21,628, 21,629 (1981).

In 1984, EPA again took up the ORVR issue in a draft study entitled “Evaluation of Air Pollution Strategies for Gasoline Marketing Industry,” EPA-450/3-84-012a (July 1984). See 49 Fed.Reg. 31,706, 31,707 (1984) (announcing the public availability of the study). After thorough reconsideration, EPA concluded that ORVR was the preferred control technology and proceeded to detail proposed regulations for the implementation of mandatory ORVR. 52 Fed. Reg. at 31,162. In that same Federal Register Notice, EPA addressed the technical difficulties associated with a practical ORVR system. EPA concluded that ORVR was generally safe and that approximately two years of lead time would be sufficient for manufacturers to install ORVR in new models since most of the technology was already available. 52 Fed. Reg. at 31,202-03.

Researchers at NHTSA had a somewhat different view of the situation, for they had continuing concerns that ORVR would lead to an increase in crash and non-crash vehicle fires.7 See 57 Fed.Reg. 13,220 (1992). Thus, before promulgating a final rule, EPA initiated further dialogue with NHTSA in order to address these issues.

NHTSA’s concerns stemmed primarily from its view that ORVR would increase the complexity of fuel systems and concomitantly the risk of fire. EPA specifically responded to this concern in its 1988 draft report on the safety of ORVR. First, EPA challenged NHTSA’s underlying assumption that there is a positive correlation between increased complexity and increased risk. EPA noted that the increasing design complexity of automobiles without significant safety degradation “strongly suggests that onboard systems of various design complexities could also be implemented safely.” EPA Draft “Summary & Analysis of Comments Regarding Potential Safety Implications of Onboard Vapor Recovery Systems” at 3-35 (Aug. 1988) [hereinafter “EPA Draft”], reprinted in J.A. at 78. Second, even assuming that added complexity means added safety risk, EPA determined that ORVR systems need not be overly complex. According to the draft report, ORVR canister systems could be devised that would be simple extensions of present evaporative systems. See id. at 3-40. Thus, EPA found that “straightforward, reliable, and relatively inexpensive *239engineering solutions exist for each of the potential problems identified.” Id.

In order to test this conclusion, EPA constructed a simple ORVR canister system and installed it in a test vehicle. Id. at 5-6. This vehicle adequately performed under limited testing conditions, leading EPA to summarize the experiment as follows:

Onboard systems can be simple extensions or modifications of present evaporative systems. Further, modifications that are necessary can even simplify certain aspects of the current design. With the proper design, no risk need be added, and in fact, refueling controls can offer several safety benefits.

Id. at 5-7. To further assess the safety of proposed ORVR systems, EPA contracted with an outside firm to complete an independent study. In September, 1988, after reviewing the risk of vehicle fire for ten different fuel system designs, the Battelle Institute’s Transportation Safety Group concluded that the risk of fire was remote in all cases and that it would not be significantly impacted by the installation of ORVR. See EPA, Refueling Emission Controls: A Briefing for the National Highway Transportation Safety Administration at 25 (Apr. 21, 1989) [hereinafter “EPA Briefing”], reprinted in J.A. at 132.

During this period, EPA was also receiving further input from NHTSA. In October, 1988, NHTSA submitted its analysis of EPA’s draft report as well as an analysis of the public comments EPA had received as a result of its proposed ORVR regulations. First, NHTSA reiterated that increased design complexity in fuel systems tends to result in greater fire risk. See DOT, Comments on the August 1988 EPA Draft at 9 (Oct. 1988), reprinted in J.A. at 505. In addition, NHTSA discounted the value of the tests done with the EPA prototype ORVR canister system since EPA neglected to account for certain problems that would arise under actual operating conditions, such as fuel leakage and lack of “drivability” (e.g., engine stalls and hesitation during acceleration). See id. at 10. Thus, NHTSA contended that ORVR would add complexity to the system and increase, by an unquantified amount, safety hazards. Id. at 9. After reviewing NHTSA’s assessment, and in view of imminent amendments to the CAA, EPA declined to issue final rules requiring ORVR systems. See 57 Fed.Reg. at 13,220.

In 1990, Congress again amended the CAA, this time establishing a comprehensive framework for controlling refueling emissions. • Under sections 182(b)(3), (c), (d), and (e), Stage II controls are required in moderate, serious, severe, and extreme nonattainment areas. 42 U.S.C. § 7511a (Supp. 1990). Amended section 202(a)(6) of the CAA now mandates that EPA, after consultation with DOT regarding safety, shall promulgate standards for ORVR by November 15,1991.8 Pursuant to this stat*240utory mandate, EPA reinitiated consultation with DOT, through NHTSA. NHTSA then embarked upon a further review of ORVR canister safety. Since actual ORVR systems were proprietary and not available for independent testing, NHTSA used components of, and data pertaining to, current evaporative systems to reach its conclusions. DOT Assessment at 11. NHTSA acknowledged that, because of availability problems, it did not consider or evaluate ORVR systems other than canisters. See DOT Review at 4.

NHTSA’s final report was submitted to EPA in July, 1991. The report identified potential failure points of an ORVR canister system during operation. DOT Assessment at 7-8. However, this analysis was premised on four critical and unproven assumptions about ORVR canister systems. First, since ORVR systems will store more vapors than existing evaporative canisters, NHTSA hypothesized that the fire hazard posed by larger ORVR canisters would be greater than that of existing canisters. Id. at 3. Second, NHTSA speculated that the quantity of vapors being moved through the system during refueling will be large compared to that which passes through current evaporative systems. Id. at 9. Third, NHTSA assumed that the complexity of the ORVR canister system will be greater than present systems, thus increasing the possibility of component failure. Id. Finally, NHTSA contended that the increased quantity of fuel vapor being carried in the vehicle at any given time will lead to a greater chance of fire in the event of a crash in which canister integrity is lost and the contents of the canister are exposed to an ignition source. Id. Based on these assumptions, NHTSA concluded that:

Under certain conditions representative of the motor vehicle crash and operating environment, ORVR refueling vapor recovery systems would result in a substantial increase in fire potential. These occurrences result in an increased safety risk and hence would have a negative impact on safety.

Id. at 10. Although NHTSA maintained that the testing conditions it used simulated real world environments, it recognized that the occurrence of these conditions would be unlikely. Id. at 11.

After publication of the study, EPA requested public comment on NHTSA’s findings and conclusions. See 56 Fed.Reg. 43,-682-83 (1991). In late September, a public hearing on the matter was held in which both EPA and NHTSA officials participated. See 57 Fed.Reg. at 13,221. EPA then asked NHTSA to review the presentations made at the hearing and to respond to public comments. NHTSA’s technical evaluation, which followed on November 27, concluded:

On this issue, the record is clear and unambiguous. Implementation of ORVR, regardless of prototype development and technological evolution, will increase safety risks. ORVR systems will require additional components and must manage, store, and transport larger quantities of flammable fuel vapor____ Thus, further technology development and operational successes or failures of prototype vehicles will not eliminate the fundamental safety issues associated with ORVR systems.

NHTSA considers these risks to be inherent. We [NHTSA] believe that no amount of product development or engineering and quality control measures would fully alleviate these risks, regardless of lead time.

DOT Review at 4-5.

While this evaluation process was being completed, the November 15, 1991 deadline for the promulgation of ORVR standards passed without EPA action. Alleging that EPA had failed to abide by the statutory *241mandate in section 202(a)(6), NRDC filed suit in the Eastern District of Virginia under section 304(a) of the CAA. See Natural Resources Defense Council v. Reilly, 788 F.Supp. 268 (E.D.Va. 1992). Before the case could be concluded, however, EPA issued a Notice of Final Agency Action in which it determined that the safety risks of onboard systems outweighed the environmental benefits of such devices and that it would not, therefore, promulgate standards pursuant to section 202(a)(6). See 57 Fed. Reg. at 13,220-31. Noting that section 307(b)(1) of the CAA confers exclusive jurisdiction on the United States Court of Appeals for the District of Columbia Circuit to review Final Agency Action, the district court dismissed the case without prejudice. NRDC v. Reilly, 788 F.Supp. at 273-74. That decision has been appealed to the Fourth Circuit, which is holding the case in abeyance pending the outcome in this case. NRDC v. Reilly, No. 92-1534 (4th Cir. 1992).

II. Discussion

The principal dispute in this case involves EPA’s interpretation of section 202(a)(6) of the CAA. NRDC contends that the section contains an unambiguous requirement that EPA promulgate standards for ORVR systems. EPA, on the other hand, sees the “consultation” requirement contained in section 202(a)(6) as the last vestige of discretion permitted the Agency. In particular, the Agency argues that Congress did not intend that EPA promulgate ORVR standards if it found the systems to be inherently and unreasonably unsafe.

Since EPA is charged with administering the CAA, NRDC’s challenge to its construction of this provision must be reviewed using the analysis provided by the Supreme Court in Chevron USA, Inc. v. Natural Resources Defense Council, Inc., 467 U.S. 837, 104 S.Ct. 2778, 81 L.Ed.2d 694 (1984).

If, under the first prong of [the] Chevron analysis, we can determine congressional intent by using “traditional tools of statutory construction,” then that interpretation must be given effect. [NLRB v.] United Food & Commercial Workers, 484 U.S. [112] at 123 [108 S.Ct. 413 at 420, 98 L.Ed.2d 429] (1987). If, on the other hand, “the statute is silent or ambiguous with respect to the specific issue,” then we will defer to a “permissible” agency construction of the statute. Chevron, 467 U.S. at 843, 104 S.Ct. at 2782.

* * * * # *

[I]t is only legislative intent to delegate such authority that entitles an agency to advance its own statutory construction for review under the deferential second prong of Chevron. See Chevron, 467 U.S. at 843-44, 104 S.Ct. at 2781-82. “If Congress has explicitly left a gap for the agency to fill, there is an express delegation of authority____ Sometimes the legislative delegation to an agency on a particular question is implicit rather than explicit. In such a case, a court may not substitute its own construction of a statutory provision for a reasonable interpretation made by the administrator of an agency.” Id.

Kansas City v. Department of Housing & Urban Dev., 923 F.2d 188, 191-92 (D.C.Cir. 1991).

Given the plain and unmistakable language of section 202(a)(6), we need not proceed beyond the first step of the Chevron analysis. Section 202(a)(6) mandates that “within one year after November 15, 1990, the Administrator shall ... promulgate standards under this section requiring that new light duty vehicles ... shall be equipped with [ORVR] systems.” 42 U.S.C. § 7521(a)(6) (Supp. 1990) (emphasis added). In this case, the language of the relevant section most manifestly obligates EPA to promulgate standards for ORVR systems. See Hewitt v. Helms, 459 U.S. 460, 471, 103 S.Ct. 864, 871,* 74 L.Ed.2d 675 (1983) (“shall” is “language of an unmistakably mandatory character”); Her Majesty the Queen v. USEPA, 912 F.2d 1525, 1533 (D.C.Cir. 1990) (“shall” signals mandatory action).

Where the authors of the CAA intended to create a conditional duty, they used the familiar words of condition. See, e.g., CAA *242§ 112(d)(9)9 (“No standard for radionuclide emissions ... is required ... under this section if the Administrator determines, by rule, and after consultation with the Nuclear Regulatory Commission, that the regulatory program established by the Nuclear Regulatory Commission ... provides an ample margin of safety to protect the public health.”) (emphasis added); CAA § 110(c)(1)10 (“The Administrator shall promulgate a Federal implementation plan at any time within the 2 years after the Administrator ... disapproves a State implementation plan submission in whole or in part, unless the State corrects the deficiency, and the Administrator approves the plan or revision, before the Administrator promulgates such Federal implementation plan.”) (emphasis added). No such words of condition are found in the consultation requirement of section 202(a)(6) that derogate from EPA’s duty to promulgate ORVR standards. Therefore, EPA exceeded its statutory authority by declining to issue the standards.

Recognizing that its only hope of prevailing in this case is to reach the deferential second step of Chevron, EPA posits two facets of the legislation as evidence of ambiguity. However, neither argument undermines the congressional intention plainly evinced by the “shall promulgate” mandate of section 202(a)(6).

A. The Consultation Requirement

First, EPA argues that although section 202(a)(6) imposes a mandatory duty, the scope of that duty is circumscribed by the requirement that EPA consult with DOT regarding ORVR safety. EPA argues that the section does not specify how the consultation requirement “meshes” with the duty to promulgate standards, thus making the section at least ambiguous. We reject this argument because it is premised on a reading of “consultation” that would effectively result in DOT having a “veto” over any EPA action in compliance with the statutory duty to promulgate ORVR standards. This is a specious construction of the statute.

To begin with, the statute expressly provides that EPA “shall” promulgate standards “after” consultation with DOT, not “subject to” or “conditioned upon” that consultation.11 Thus, no substantive result of the consultation is comprehended within the text that might vitiate EPA’s mandatory duty to promulgate standards: no determination is required, no minimal standard for safety is articulated, and no particular measure or purpose of the consultation is specified. This does not mean that ORVR safety concerns will never be addressed. Sections 206(a)(3)(A) and 202(a)(4) of the Act provide for a later certification process to ensure that no system will be installed in an automobile for sale to the public unless it is safe. 42 U.S.C. §§ 7525(a)(3)(A), 7521(a)(4) (Supp. 1990); see also 40 C.F.R. Part 86 (regulatory certification process and standards). However, this safety evaluation comes at a later stage in the implementation of emission control systems. It does not affect the duty to promulgate standards in the first instance.

Read in context, the central purpose of section 202(a)(6) is to impose regulatory standards for ORVR systems over a given and detailed time frame. Inserted parenthetically in this structure is a requirement that EPA consult with DOT regarding safety issues. Contrary to EPA’s contention, the fact that the DOT consultation is merely advisory does not make it meaningless. At least two reasons for the requirement *243are apparent: first, the process might have been meant to provide EPA with a better awareness of various systems so that ORVR standards might accurately conform to imminently available technology; conversely, the process might allow EPA to structure standards that will promote the design and development of safer systems. In any event, as a matter of statutory construction, such a general consultation clause will not normally render nugatory other substantive requirements in a statute. See, e.g., Natural Resources Defense Council v. Train, 510 F.2d 692, 704 (D.C.Cir. 1974) (consultation requirement in Federal Water Pollution Control Act did not undermine a mandatory duty). So here, too, we find that it does not call into question the express command of the section.

Further, the structure of current section 202(a)(6) stands in stark contrast with that of its predecessor, which required EPA to determine the feasibility and desirability of ORVR prior to promulgating ORVR standards. In the former section, it was necessary for EPA to determine that such systems were safe as a condition precedent to the promulgation of ORVR standards. Thus, it was implicit in that statutory scheme that EPA exercise discretion in deciding whether or not to implement regulations for ORVR systems. By deleting the determination requirement in the new section, Congress sent an unmistakable message that the consultation requirement is not to be used by EPA to avoid its obligation to promulgate standards for ORVR systems.

It is important to note that this is not a case in which EPA has made an irrefutable finding that no ORVR system could be developed in the foreseeable future that would be safe. Both EPA and NHTSA restricted their analysis of ORVR to charcoal canister systems similar to those used in present evaporative systems. 57 Fed. Reg. at 13,230. Both agencies rationalized this limitation by pointing out the embryonic nature of other ORVR technologies. See DOT Review at 4 (other technologies not available for evaluation); 57 Fed.Reg. at 13,230 (EPA did not consider “undeveloped technologies]”). Yet, this narrow review is not defensible on the facts of this case.

First, the statute clearly calls for EPA to evaluate ORVR “systems.” The use of the plural defeats any implication that Congress intended EPA to consider only ORVR canister technology. Cf. Association of American Railroads v. Costle, 562 F.2d 1310, 1315 (D.C.Cir. 1977) (reference to “equipment and facilities” in Noise Control Act of 1972 encompasses “all such equipment and facilities”) (emphasis in original); Natural Resources Defense Council v. USEPA, 915 F.2d 1314, 1320 (9th Cir. 1990) (use of plural in Clean Water Act foreclosed EPA from restricting the scope of its duties).

We have previously noted a distinction between provisions in the CAA that are “technology-based” and those that are “absolute.” See Natural Resources Defense Council v. USEPA, 655 F.2d 318, 322 & 332 n. 25 (D.C.Cir. 1981). Technology-based provisions require EPA to promulgate standards only after finding that the requisite technology exists or may be feasibly developed. Id. at 322. Absolute standards, on the other hand, require compliance with statutorily prescribed standards and time tables, irrespective of present technologies. Id. Absolute standards presume that industry can be driven to develop the requisite technologies.12 In this case, the use of the word “systems” in section 202(a)(6), in combination with the statutorily fixed time table, indicates that this provision falls into the “absolute” category and, hence, is technology-forcing. There is nothing in the *244section warranting EPA’s decision to limit its consideration of ORVR to a single existing technology. Moreover, this statutory command was not, EPA’s protestations to the contrary notwithstanding, unrealistic. While it is true that alternative control methods are not production-ready, several are beyond the conceptualization stage and should have been amenable to engineering evaluation.

For instance, vapor condensers and vapor combusters have been considered as alternatives to canister containment systems, and both were sufficiently developed to be the subject of investigation by auto manufacturers in 1988. EPA Draft at 3-3. Perhaps the most promising alternative to canisters are the previously mentioned flexible fuel bladders. The record indicates that this option has been extensively researched and that EPA had information in its possession four years ago tending to show that bladder systems could be production-ready within one or two years.13 There is simply no basis for us to believe that Congress was not aware that flexible bladders represented a plausible alternative to charcoal canisters or that Congress did not intend for EPA to consider them in promulgating ORVR standards. See S.Rep. No. 228, 101st Cong., 2d Sess. 94 (1990), U.S.Code Cong. & Admin.News 1990, 3385, 3479 (specifically noting flexible fuel bladder alternative); see also 52 Fed. Reg. at 31,175 (bladders recognized as an alternative in 1987); id. at 31,202 (bladders may improve fuel system safety). In addition, at least two other systems have been hypothesized which might eliminate or reduce many of the safety hazards that EPA perceived as attendant to ORVR canister systems. See U.S. Patent No. 4,880,135 (Nov. 14, 1989) (bellow tank); Memorandum from Karen Lostoski, Mechanical Engineer, EPA, to Public Docket No. A-87-11 (Sept. 9, 1988) (carbon cloth as a substitute for granulated activated carbon in ORVR canisters), reprinted in J.A. at 527.14 Thus, in restricting its safety analysis to a single type of ORVR system, EPA disregarded its responsibility under the Act.

Moreover, with respect to ORVR canisters, it is not clear that either EPA or NHTSA concluded that these systems are incapable of being made reasonably safe.15 Rather, it appears from the record that both EPA and NHTSA balanced the risks and benefits of ORVR against the risks and benefits of Stage II controls. See DOT Assessment at 3 (NHTSA weighed availability of Stage II controls in its ORVR safety assessment); 57 Fed.Reg. at 13,223 (EPA considers the availability of Stage II controls integral to decision); see also id. at 13,221 (NHTSA concluded that “some risk” was inherent in ORVR canisters that was not present in Stage II controls); Letter from Jerry Ralph Curry, NHTSA, to William G. Rosenberg, Assistant Administrator for Air and Radiation, EPA (Oct. 31, 1991) (“after weighing the alternatives,” NHTSA would find ORVR an unreasonable safety risk), reprinted in J.A. at 464; EPA Briefing at 9a (relative effectiveness of *245ORVR and Stage II controls); cf. 57 Fed. Reg. at 13,223 (canister systems “potentially subject to additional failure modes”) (emphasis added). This reading is borne out by EPA’s explanation of its final action that the decision not to promulgate ORVR standards was heavily dependent upon the ready availability of Stage II controls. See id. at 13,230.

Although EPA finally concluded that canister based systems present safety problems which are not “entirely capable of resolution,” id., much of the data in the record directly contravenes this assertion. For instance, NHTSA assumed that ORVR canisters would add complexity to current fuel systems.16 Yet, the EPA simple prototype proved that it was at least possible to build a simple ORVR canister system.17 Moreover, the analytical approach used by NHTSA contains a logical flaw. NHTSA’s tests seem to show that ORVR may increase risk under certain conditions. However, NHTSA presented no data on the likelihood of those conditions existing in the real world. Therefore, it is impossible to move directly from NHTSA’s data to EPA’s conclusion that ORVR canisters pose an unreasonable risk.

In addition, many of the benefits of ORVR that were recognized by EPA in its 1988 draft report were largely ignored in its final determination that ORVR is unreasonably unsafe. For instance, the number of service station fires18 will almost certainly be reduced by ORVR. EPA Draft at 4-1. Second, repeated or prolonged dermal contact with liquid gasoline due to spillage can be reduced by ORVR, thus relieving the resultant skin irritation and dermatitis. See id. at 4-12. Perhaps most significantly, ORVR may help lower fuel tank pressures.19 Greater fuel tank pressure leads to, among other things, fuel dispersion in tank rupture accidents. ORVR canister systems would require an increase in the size of the fuel tank venting orifices and thus decrease fuel tank pressures. Id. at 4-14. Finally, under operating conditions, vehicles sometimes create vapors that exceed the capacity of current evaporative canisters leading to so called “breakthrough” and the seepage of vapors into the engine compartment. Larger canisters *246in ORVR systems would capture and contain these vapors.

In short, the record as a whole does not substantiate a finding that ORVR systems present inherent and unreasonable safety risks. What is clear is that EPA has decided that ORVR canister systems are not worth the risk given that Stage II controls are a viable alternative. However, even were we to accept that Congress left some small amount of discretion in the statute for EPA to decline to require ORVR if it found such systems unreasonably hazardous, that discretion would be constrained to a measurement of the safety considerations of ORVR alone, weighed against the incremental environmental protection that ORVR systems would provide.20 Thus, EPA’s balancing of ORVR canisters against Stage II controls would still be an inappropriate basis upon which to decline to promulgate ORVR standards.21

B. The Lapse of Stage II Requirements

EPA also argues that section 202(a)(6)’s provision for the lapse of Stage II requirements when EPA promulgates ORVR standards creates an ambiguity that warrants deference to the Agency’s interpretation of the statute under the second step of Chevron. Specifically, section 202(a)(6) reads in pertinent part:

The requirements of section 7511a(b)(3) of this title (relating to stage II gasoline vapor recovery) for areas classified under section 7511 of this title as moderate for ozone shall not apply after promulgation of such standards and the administrator may, by rule, revise or waive the application of the requirements of section 7511a(b)(3) of this title for areas classified under section 7511 of this title as Serious, Severe, or Extreme for ozone, as appropriate, after such time as the Administrator determines that onboard emissions control systems required under this paragraph are in widespread use throughout the motor vehicle fleet.

42 U.S.C. § 7521(a)(6) (Supp. 1990). The effective date of the Stage II requirements under section 182(b)(3) of the Act, 42 U.S.C. § 7511a(b)(3) (Supp. 1990), is November 15, 1992, one year after the date by which EPA was obligated to promulgate ORVR standards. EPA concludes from this that Congress provided for an alternative pollution control system in the event that EPA determined that ORVR is unsafe.

However, this reasoning relies on a specious reading of the statutory language. Section 202(a)(6) expressly provides for the termination of Stage II requirements after ORVR standards are promulgated, not if they are promulgated—the implication clearly being that ORVR standards will, at some future time, be promulgated and that Stage II will become unnecessary in certain nonattainment areas at that time. The Stage II requirements, then, are not so much an alternative to ORVR as they are an interim measure to provide environmental protection in the event that ORVR standards are inexplicably delayed.

This “fail-back” approach does not run afoul of any of our standard canons of interpretation. To begin with, there is no direct conflict between the two related sections of the CAA. If ORVR standards had been promulgated on time, the Stage II requirements in moderate nonattainment areas would merely have been superfluous. On the other hand, if EPA missed the statutory deadline—as it in fact has—some vapor emission control would be provided. Although perhaps not the most elegant framework, it was not unreasonable for Congress to provide for contingent environmental protection in the event that EPA missed the statutory deadline, given EPA’s *247record with regard to implementing the CAA. See NRDC v. Thomas, 805 F.2d at 416 (EPA “behind the statutory timetable” of the CAA); Sierra Club v. California, 658 F.Supp. 165, 175 (N.D.Cal. 1987) (EPA had “long-standing unwillingness to comply with” the CAA); see also 136 Cong.Rec. S2,436 (daily ed. Mar. 8,1990) (“[T]he history of the Clean Air Act demonstrates that we cannot rely on EPA to follow through on even its mandatory obligations.”) (statement of Senator Lieberman). Thus, the overlap between sections 182(b)(3) and 202(a)(6) demonstrates not an ambiguity in the statute, but congressional prudence in providing for foreseeable administrative delays.22

It was suggested at oral argument that requiring EPA to promulgate ORVR standards at this point in time, now that the deadline has passed and Stage II controls have become mandatory in moderate and worse non-attainment areas, would impose inefficient double-controls in many areas. Yet, this is not precisely correct, since overlapping Stage II and ORVR controls will not result in complete duplication. As EPA explained in its Final Action, the benefits provided by ORVR are small23 at first and increase as fleet turnover occurs. 57 Fed. Reg. at 13,225. Even by the most optimistic view, it will be well into the twenty-first century before a substantial portion of the automobile fleet will be equipped with ORVR fuel systems. See id. (at least ten years until ORVR becomes an effective control). Stage II controls will provide important environmental protection in the areas with the worst ozone accumulation while this turnover takes place. In addition, by the terms of the statute, ORVR standards will only apply to light-duty vehicles. Whatever investment has already been made in Stage II controls for moderate nonattainment areas that would have been unnecessary had EPA promulgated ORVR standards on time will benefit the environment by capturing vapor emissions from heavy trucks, motorcycles, and other vehicles not encompassed within the ORVR standards. Thus, a literal reading of the statute does not lead to patently incoherent results. In any event, to the extent that double-control will occur now that the statutory deadline has passed, that contingency was so obvious that it must have been contemplated and accepted by Congress. It is not within the province of this court to second guess such clear legislative policy choices.

The converse problem was also raised at oral argument by EPA, which noted that a period of no control could occur in some moderate nonattainment areas if the requirements for Stage II controls cease to apply after the promulgation of ORVR standards and actual ORVR systems prove to be unreasonably unsafe so that they are denied certification under section 206(a)(3)(A). Although this is a legitimate concern for the Agency, it is not one that we can resolve.24 The CAA provides that *248the requirements for Stage II controls shall not apply in moderate nonattainment areas once ORVR standards are promulgated. The possibility that ORVR systems will not reach the production fleet because of a failure to satisfy certification requirements must have been known to Congress when it passed the 1990 amendments. Thus, the scheme reflects an implicit policy decision by Congress. Whatever the wisdom of that decision, it is committed to Congress alone to make.

III. Conclusion

The text of section 202(a)(6) clearly manifests a congressional intent that EPA promulgate ORVR standards. The requirement that EPA consult with DOT prior to promulgating the standards does not derogate from that mandatory duty. In addition, the provisions in the CAA for Stage II controls provide for an interim solution to the problem of ozone accumulation until ORVR systems become commonplace. ORVR and Stage II controls are not two alternative approaches between which EPA has discretion to choose. Moreover, even if we were to allow that Congress did not intend for EPA to require ORVR systems if EPA found that ORVR presented inherent and unreasonable safety risks, the record would not support such a finding. At most, it appears that EPA performed a net weighing of the risks and benefits of ORVR canisters relative to Stage II controls. In the end, EPA concluded that it preferred Stage II controls. However, that is not the equivalent of a finding that all ORVR systems present inherent and unreasonable safety risks. Thus, EPA’s final decision must be set aside and ORVR standards promulgated in compliance with the CAA.

So Ordered.

concurring:

I reluctantly agree with the court that the “shall” of § 202(a)(6) is mandatory, as most “shalls” are, subject only to a very narrow escape hatch—one that would open only if EPA’s consultation with the Department of Transportation yielded a finding that all plausible “onboard” (ORVR) sys-. terns “present inherent and unreasonable safety risks”. Maj. Op. at 273. The EPA finding does not rise to that extreme level. Maj. Op. 268-71. I write separately for two reasons. First, I wish to identify yet another snag that this congressional choice may lead to—a snag that is, however, inherent in the sort of command-and-control, technology-forcing solution that Congress adopted. Second, I wish to emphasize that the exact character of the EPA’s decision under § 202(a)(4) is not before this court, so that our judgment necessarily leaves that issue open.

I

The majority opinion addresses two risks that the statute runs under our interpretation. First, it may leave these ozone-generating vapors substantially uncontrolled either by “onboard” systems installed by motor vehicle manufacturers or by “Stage II” controls installed by gas station operators. Maj. Op. at 273. Second, it may lead to overlapping controls by both. Maj. Op. at 272-73. There is yet a third risk—that auto and gasoline buyers will bear the expense of both systems (or much of that expense) yet secure the benefits of neither. Auto makers will incur at least the R & D costs of onboard controls (and auto buyers will bear them) because of the regulation required by our decision, yet, if none ever passes the ultimate safety test of § 202(a)(4), they will not be installed. Gasoline station operators may incur many of the costs of Stage II controls because they will apply in “moderate” (and worse) areas until such time as the EPA actually issues the required onboard regulation, but they will cease to apply in moderate areas once the onboard regulation issues, because thereafter (regardless of whether the on-board system ever can be installed), the last sentence of § 202(a)(6) specifies that the Stage II controls “shall not apply” in *249moderate areas after promulgation of the onboard standards. See Maj. Op. 264-65 n. 8.

As the majority observes of the no-eontrol and the overlapping control scenarios, however, all this is implicit in the scheme. See Maj. Op. 272, 273. Congress evidently believed that a reasonably safe system of onboard controls was likely enough, and the value of securing them great enough, to justify running the various risks outlined in these opinions. The risks are, as the majority observes, perfectly obvious. Ours not to count the cost.

Is all this an inevitable cost in the quest for a clean environment? Under a system of either emissions fees or marketable permits, firms whose production or products pollute can be induced to invest in R & D for pollution-reducing devices under conditions substantially similar to those under which they invest in R & D for products whose demand is generated by consumers—investing up to the point where the marginal cost equals the marginal expected1 revenues. The difference is simply that the marginal expected revenues take the form of emissions taxes averted, emission permit expenses averted, or revenues from the sale of emissions permits. Such systems offer comparatively efficient methods for addressing pollution, similar to the ways a market economy produces other goods. With rare exceptions, however, Congress has declined to use such methods. Accordingly, consumers must bear the burdens implicit in the statute that we interpret today.

II

The majority opinion suggests at 244-45 and 246 that the safety determination made by the EPA, prefiguring the one ultimately to be made before installment under § 202(a)(4), may not take into account the comparative effectiveness of Stage II controls. Perhaps so, but I should be most reluctant to reach any such conclusion. If system A posed a safety risk of 100 lives a year, one might conclude that that was an acceptable price for a 50% reduction in ozone if it were the only way of achieving the reduction. But if the same reduction could be achieved by system B, at a safety risk of only 10 lives a year and no material alternative drawbacks, it would be odd to find system A reasonable. The interaction that Congress specified between onboard and Stage II controls (in the last sentence of § 202(a)(6)) makes clear that Congress saw them as at least partial substitutes, as they plainly are as a matter of physics and technology. Under these circumstances, a court should not leap to the view that the “reasonableness” balancing called for by § 202(a)(4), see Maj. Op. 244 n. 15, precludes any consideration of the effect of the Stage II applications that legally depend on the absence of onboard controls.

Indeed, no party here argues that the § 202(a)(4) balancing must be so narrow. EPA, as the majority notes, regarded the two alternative methods as relevant to the § 202(a)(4) assessment on onboard devices. Maj. Op. at 269-70; see also 57 Fed.Reg. 13,220, 13,230/3 (April 15, 1992). Petitioners do not object to this element of EPA’s reasoning. Rather, they make the much more limited argument that EPA was internally inconsistent in that it considered the safety benefits of Stage II controls at the gas stations where they would be installed without addressing the absence of control at the gas stations that would be uncontrolled even if Stage II controls were as broadly applicable as possible under the statute. See Reply Brief at 16-19 & n. 10. As the permissible scope of the § 202(a)(4) balance is not before us, there is no need to take any position on the subject. To the extent that the text, Maj. Op. 244-45, 246 is in tension with id. 246 n. 21, plainly the footnote should be deemed controlling.