Natural Resources Defense Council, Inc. v. U. S. Environmental Protection Agency, Douglas M. Costle, Administrator, Mercedes-Benz of North America, Inc., General Motors Corporation, Volkswagen of America, Inc., Intervenors. General Motors Corporation v. Douglas M. Costle, Administrator, United States Environmental Protection Agency, Volkswagen of America, Inc., Natural Resources Defense Council, Inc., Mercedes-Benz of North America, Inc., Intervenors. Mercedes-Benz of North America, Inc. v. Douglas M. Costle, Administrator, United States Environmental Protection Agency, Natural Resources Defense Council, Inc., Intervenor. Natural Resources Defense Council, Inc. v. Douglas M. Costle, Administrator, United States Environmental Protection Agency, Automobiles Peugeot, Volkswagen of America, Inc., Intervenors

These consolidated cases present a variety of challenges to actions of the Environmental Protection Agency (EPA) in setting standards to govern emissions of particulate matter and oxides of nitrogen from diesel vehicles. The Natural Resources Defense Council (NRDC) argues that the agency's actions do not adequately protect the public health; General Motors Corporation (GM) and Intervenors Mercedes-Benz of North America, Inc., and Volkswagen of America, Inc., assert that the EPA did not give adequate consideration to safety factors, and that, in a variety of ways, the standards are too strict. Finding that the agency has stated adequate reasons for its decisions, and that its actions are consistent with statute, we uphold the challenged regulations in their entirety.

The EPA is authorized by the Clean Air Act (Act)1 to regulate emissions of harmful pollutants from motor vehicles. The Act itself specifies the quantity of acceptable emissions from light-duty vehicles for three classes of pollutants: carbon monoxide, hydrocarbons, and oxides of nitrogen. Act § 202(b)(1). Section 202(a)(1) of the Act confers on the EPA Administrator the general power to prescribe by regulation "standards applicable to the emission of any air pollutant from any class or classes of new motor vehicles or new motor vehicle engines, which in his judgment cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare." These provisions are supplemented and qualified by various specific provisions relating to particular classes of vehicles or pollutants. E.g., Act §§ 202(a)(3)(A)(i), 202(a)(3)(F), 202(b)(6)(A).

The statutory standard for hydrocarbon emissions from light-duty vehicles is an absolute one. For models manufactured from 1977 to 1979, hydrocarbon emissions may not exceed 1.5 grams per vehicle mile; for those manufactured from 1980 on, the standards must require a reduction of at least ninety percent from the emission standards applying in 1970. Act § 202(b)(1)(A). The statutory standards for carbon monoxide and oxides of nitrogen are also absolute, but they are subject to a variety of waivers for certain manufacturers who lack the technological capacity to comply. See Act §§ 202(b) (1)(B), 202(b)(5), 202(b)(6).

The emission standards set by the EPA under its general regulatory power, in contrast, are "technology-based" the levels chosen must be premised on a finding of technological feasibility. Section 202(a)(2) of the Act provides that standards promulgated under section 202(a)(1) shall not take effect until "after such period as the Administrator finds necessary to permit the development and application of the requisite technology."

The requirement that emission standards be technologically achievable highlights the need for the EPA's power to divide the broad spectrum of motor vehicles into classes or categories. See Act §§ 202(a)(1), 202(a)(3)(A)(iv). Manufacturers produce a wide variety of motor vehicles of different sizes, some using different engine technologies resulting in unusual emission characteristics. In particular, diesel engines use a different fuel, emit exhaust at a lower temperature, and produce a different distribution of pollutants than traditional gasoline engines. For example, diesel carbon monoxide levels are typically lower than those from gasoline vehicles, see 45 Fed.Reg. 5480, 5493 n.192 (1980), but diesel vehicles produce particulate emissions at thirty to seventy times the rate of gasoline vehicles, see 45 Fed.Reg. 14,496 (1980), and also produce higher levels of the unregulated pollutants sulfur dioxide and benzo(a)pyrene, see 45 Fed.Reg. 5480, 5489 (1980).

The present challenges concern the EPA's promulgation of standards governing particulate2 emissions from light-duty diesel vehicles and light-duty diesel trucks,3 and the EPA's waiver of the statutory standard for oxides of nitrogen4 for light-duty vehicles.5 The EPA's particulate standard and NOx decisions are appropriately linked in the present proceeding because current technology creates an unfortunate trade-off between particulate control and control of oxides of nitrogen. The primary technique used today for reducing NOx emissions is exhaust gas recirculation (EGR). While lowering the NOx content of the exhaust, EGR increases the particulate content, and "the greater the EGR rate, the greater the increase in particulate emissions." Environmental Protection Agency, Regulatory Analysis (of) Light-Duty Diesel Particulate Regulations 33 (1980) (hereinafter cited as Regulatory Analysis), Joint Appendix (J.A.) 510. Thus the stringency of a technology-based particulate standard depends on the level of the NOx standard concurrently applied. We consider the EPA's actions and the NRDC and industry challenges in turn.6

The EPA announced its intention to promulgate standards for particulate emissions from light-duty diesels on February 1, 1979. See 44 Fed.Reg. 6650 (1979). The proposed standards would have limited diesel particulates to 0.60 grams per vehicle mile (gpm) in model year 1981, and to 0.20 gpm in model year 1983. The agency concluded that a single standard, governing all light-duty vehicles, was the preferable regulatory strategy, although 1979 certification data indicated that diesel particulate performance among those vehicles ranged from the 0.23 gpm achieved by the Volkswagen Rabbit to the 0.84 gpm emitted by the Oldsmobile 350. Id. at 6651. Furthermore, these restrictions would have applied equally to light-duty vehicles and light-duty trucks. Id. at 6654-55.

After analyzing the comments elicited by its notice of proposed rulemaking, the EPA promulgated as final standards a modification of the rules originally announced. See 45 Fed.Reg. 14,496 (1980). The limit of 0.60 gpm was retained, but its effective date was postponed to model year 1982, because the rulemaking process had absorbed so much time that testing and certification of 1981 models was no longer feasible. Id. at 14,497. The agency concluded that the technology necessary to make the 0.20 gpm standard feasible would probably not be developed in time for implementation in 1983 model vehicles; 1984 was a more likely goal, but the effective date was postponed to model year 1985 to give sufficient margin for error. Id. at 14,498. Finally, the EPA believed that light-duty trucks would not be able to perform as well as light-duty vehicles, and the 1985 standard for light-duty trucks was therefore adjusted to 0.26 gpm. Id. at 14,497.

The auto industry petitioners do not challenge the 1982 standard of 0.60 gpm, but they vigorously deny the likelihood that technology will be available to meet the lower standards in 1985.7 In setting the 1985 standards, the EPA predicted that a currently experimental particulate control device, known as a "trap-oxidizer," would be perfected early enough to allow its mass production and installation in 1985 model diesel vehicles. The manufacturers argue that this prediction lacked a sufficient evidentiary basis, and that the agency's action must therefore be invalidated as failing to meet the requirement of reasoned decisionmaking. They also argue that the EPA gave inadequate consideration to the safety risks involved in trap-oxidizer technology.

NRDC insists that the EPA's entire regulatory strategy is an inadequate response to the agency's statutory mandate to protect the public health. The EPA deliberately set a single standard for all light-duty diesel vehicles, predicting that even the worst performing diesel could meet it. NRDC argues that that regulatory choice is inconsistent with the EPA's statutory responsibilities; it urges a variable standard, imposing more rigorous requirements on better performing vehicles. NRDC also urges that the agency failed to consider the risks posed by diesel particulate as a carcinogen, and that in giving "appropriate consideration" to cost as a factor in standard-setting, it should have tried to discourage purchase of polluting vehicles through economic disincentives. Finally, NRDC attacks the postponement of the 0.20 gpm standard from 1984 to 1985 as unnecessary and irresponsible.

In order to evaluate these claims, we first determine the applicable statutory directives. We then turn to light-duty vehicles and, after discussing the proper standard of review in this case, assess the manufacturers' attack on the EPA's prediction of technological feasibility. Next, we examine the NRDC's claims and, finally, turn to light-duty trucks.

Before turning to the merits of the EPA's rulemaking activities, we must consider a threshold question that has attracted attention sporadically throughout the course of the proceedings. Although none of the parties contests the EPA's authority to regulate diesel particulate emissions, there is some disagreement as to the precise statutory provision conferring that authority. GM insists that the EPA's particulate rulemaking for non-heavy-duty vehicles8 may be viewed only as an exercise of its broad general power to prescribe motor vehicle emission standards under section 202(a)(1) of the Act;9 the EPA argues that an explicit provision of the Act specifically directs it to promulgate particulate standards.

In proposing the challenged regulations, the EPA cited as its statutory basis section 202(a)(3)(A)(iii) of the Act, added by the 1977 Clean Air Act Amendments, Pub.L.No.95-95, § 224, 91 Stat. 685. That provision, set out more fully in the margin,10 requires that "(t)he Administrator shall prescribe regulations under (section 202(a)(1)) applicable to emissions of particulate matter from classes or categories of vehicles manufactured during and after model year 1981 (or during any earlier model year, if practicable)." GM maintains that this provision empowers the agency only to set standards for heavy-duty vehicles, while the EPA reads it as applying to any "classes or categories of vehicles," including all light-duty diesels. The apparent meaning of the language of section 202(a)(3)(A)(iii), read in isolation, comports with the EPA's view, but we conclude that that language should not be read in isolation, see, e. g., Brown v. Duchesne, 60 U.S. (19 How.) 183, 194, 15 L.Ed. 595 (1857). The structure of section 202 casts doubt on the validity of a literal reading, and after a closer examination of the section's legislative history, we conclude that GM's position is correct.

The EPA's power under section 202(a)(1) antedates the 1977 amendments such authorization, to the agency and its predecessors, has been present in varying forms since the Clean Air Act Amendments of 1965, Pub.L.No.89-272, § 101, 79 Stat. 992. The legislative history of the 1970 amendments11 demonstrates that Congress "expected that section 202(a) authority would be used for regulation of particulate emissions." S.Rep.No.1196, 91st Cong., 2d Sess. 24 (1970), reprinted in 1 Legislative History of the Clean Air Act Amendments 424 (1974) (hereinafter cited as Legislative History). Congress did not write in a statutory particulate standard at that time, as it did for vehicular emissions of carbon monoxide, hydrocarbons, and oxides of nitrogen,12 because of technological obstacles:

No present measurement techniques exist to evaluate or establish standards for such particulate emissions. Such standards cannot be established on the basis of 1970 vehicles as required by subsection (b) because measurement techniques will not exist until 1972. At such time as measurement methods are developed the Secretary would be expected to establish standards for particulate emissions under 202(a) authority.

Id.

By 1977, however, Congress had become impatient with the EPA's failure to promulgate a particulate standard.

The need for a standard for the pollutant particulate matter for motor vehicles was identified in the Senate report in 1970. None has yet been proposed, except for a smoke standard for heavy duty diesels.

EPA should promulgate a standard requiring best available control technology for smoke from heavy duty diesels and other particulate emissions from heavy duty vehicles and motorcycles by model year 1978, if possible, or by model year 1979.

S.Rep.No.127, 95th Cong., 1st Sess. 67 (1977), reprinted in 3 Legislative History 1441. Congress therefore adopted the mandatory language of section 202(a)(3)(A)(iii).

The 1977 Senate report illustrates that congressional concern over vehicular particulate emissions focused on heavy-duty vehicles. They are the major source of the problem; as the EPA observed in the present rulemaking, light-duty "gasoline-powered vehicles with three-way catalysts emit very low levels of particulate." Regulatory Analysis at 31, J.A. 510. Not surprisingly, then, the origin of section 202(a)(3)(A)(iii) can be traced to a provision in the 1977 Senate bill "applicable to emissions of carbon monoxide, hydrocarbons, particulates, and oxides of nitrogen from heavy duty trucks, buses, and motorcycles and engines thereof," S. 252, 95th Cong., 1st Sess. § 19 (1977), see S.Rep.No.127, 95th Cong., 1st Sess. 193 (1977), reprinted in 3 Legislative History 1567.13

The Senate provision was compromised in conference with a less stringent House provision, and the contents of the Senate's bulky paragraph were distributed among subparagraphs of paragraph 202(a)(3)(A) under circumstances suggesting that the omission of the words "heavy duty" from subparagraph 202(a)(3)(A) (iii) was inadvertent. The section of the act that emerged from conference bore the title, "Emission Standards for Heavy Duty Vehicles or Engines and Certain Other Vehicles or Engines," Pub.L.No.95-95, § 224, 91 Stat. 685; the substance of that section indicates that the "certain other vehicles" are motorcycles. Subparagraphs 202(a)(3)(A)(i) and 202(a)(3)(A)(ii) still retain the limitation to heavy-duty vehicles. Subparagraph 202(a)(3)(A)(iv), which empowers the Administrator to establish "classes or categories of vehicles or engines for purposes of regulations under this paragraph," is not so restricted, but the conference report is written as if it were: "The Administrator is specifically authorized to subdivide heavy duty vehicles into classes or categories for purposes of this section." H.R.Rep.No.564, 95th Cong., 1st Sess. 164 (1977), reprinted in (1977) U.S.Code Cong. & Ad.News 1502, 1544, 3 Legislative History 544.

This accumulation of detail convinces us that Congress did not intend, in adding section 202(a)(3)(A)(iii), to mandate adoption of particulate standards for light-duty vehicles. Rather, Congress directed the EPA to give priority to establishing particulate emission standards for heavy-duty vehicles, and left the agency free to exercise its power under section 202(a)(1) to regulate light-duty automobiles, whether diesel-powered or otherwise.14

Our conclusion that the EPA cited the wrong section of the statute15 as authority for its rulemaking does not necessitate a remand, even though paragraph 202(a)(1) requires, as subparagraph 202(a)(3)(A)(iii) does not, a threshold finding that the regulated pollutant "may be anticipated to endanger public health or welfare." Particulates have long been recognized as one of the major targets of the Clean Air Act. See, e. g., U.S. Dep't of Health, Education, and Welfare, Air Quality Criteria for Particulate Matter (National Air Pollution Control Administration Publication No. AP-49) (1969). And the EPA, in issuing the present regulations, made specific findings on the environmental impact of diesel particulates:

Section 202(a)(3)(A)(iii) directs EPA to control particulate emissions; it does not require that the Agency first conduct an environmental impact assessment. Nevertheless, EPA has carefully examined the environmental impact of this rulemaking.

....

... Small particles, which are much more likely to be deposited in the alveolar region and which require much longer periods of time to be cleared from the respiratory tract, have a greater potential to affect human health than larger particles. Thus, control of diesel particulate, of which 100 percent is less than 15 micrometers in diameter and approximately 97 percent of which is less than 2.5 micrometers in diameter, is especially important with respect to human health.

45 Fed.Reg. 14,496, 14,498-99 (1980). Indeed, GM expressly concedes in its brief that "the Administrator considered and discussed the health risks of particulate emissions during rulemaking (and that his) determination that particulate emissions require priority control to protect human health would entitle him to prescribe particulate standards under § 202(a)(1) for light-duty vehicles." Reply Brief for Petitioner General Motors Corp. at 6 (hereinafter GM Brief).16

The EPA's choice of the 0.20 gpm standard for light-duty diesels in 1985 was the result of adjusting current diesel particulate emission data by the percentage of reduction expected from certain technological improvements, most notably the trap-oxidizer. The manufacturers' attack on the standard focuses on the EPA's prediction concerning the probable pace of development of trap-oxidizer technology. Before examining the details of the agency's reasoning and the industry challenges, however, we find it useful to discuss the legal standard that governs our inquiry.

The standard of review in this case is the traditional one for judicial scrutiny of agency rulemaking: we are to set aside any action found to be "arbitrary, capricious, an abuse of discretion, or otherwise not in accordance with law." Act § 307(d)(9)(A). As nonscientists, we must recall that "(o)ur 'expertise' is not in setting standards for emission control but in determining if the standards as set are the result of reasoned decisionmaking." Essex Chemical Corp. v. Ruckelshaus, 486 F.2d 427, 434 (D.C.Cir.1973), cert. denied, 416 U.S. 969, 94 S.Ct. 1991, 40 L.Ed.2d 558 (1974). Despite this limited role, our examination of the record must be searching, for

the necessity to review agency decisions, if it is to be more than a meaningless exercise, requires enough steeping in technical matters to determine whether the agency "has exercised a reasoned discretion." ... We cannot substitute our own judgment for that of the agency, but it is our duty to consider whether "the decision was based on a consideration of the relevant factors and whether there has been a clear error of judgment."

Portland Cement Ass'n v. Ruckelshaus, 486 F.2d 375, 402 (D.C.Cir.1973), cert. denied, 417 U.S. 921, 94 S.Ct. 2628, 41 L.Ed.2d 226 (1974).

In the present case, GM attacks the EPA's estimation of the period of time "necessary to permit the development and application of the requisite technology" to achieve compliance with the 1985 particulate standards, see Act § 202(a)(2). The agency has determined that the technology will be available in time, and now seeks to defend its conclusion as a product of reasoned decisionmaking. Such predictions inherently involve a greater degree of uncertainty than estimations of the effectiveness of current technology. If we judge the EPA's action by the standard of certainty appropriate to current technology, the agency will be unable to set pollutant levels until the necessary technology is already available.

The legislative history of both the 1970 and the 1977 amendments demonstrates that Congress intended the agency to project future advances in pollution control capability. It was "expected to press for the development and application of improved technology rather than be limited by that which exists today." S.Rep.No.1196, 91st Cong., 2d Sess. 24 (1970), reprinted in 1 Legislative History 424; H.R.Rep.No.294, 95th Cong., 1st Sess. 273 (1977), reprinted in (1977) U.S.Code Cong. & Ad.News 1077, 1352, 4 Legislative History 2740. In designing the particulate standard, the EPA recognized the uncertainty necessarily accompanying its duty to predict:

When projecting a near-term standard when little time exists for technological advances, it is relatively simple for a regulatory agency to predict what the best available control technology will be, and to set a standard based on its application. It is more difficult to regulate on this basis in the long-term because of the uncertainty that inevitably surrounds expected technological improvements. Nevertheless, ... EPA has concluded that it is absolutely necessary to issue standards which motivate the private sector to maximize its efforts in reducing particulate emissions from light-duty vehicles.

Regulatory Analysis at 32, J.A. 511.

This court has upheld the agency's power to make such projections, while recognizing that it is "subject to the restraints of reasonableness, and does not open the door to ' "crystal ball" inquiry.' " International Harvester Co. v. Ruckelshaus, 478 F.2d 615, 629 (D.C.Cir.1973). The Clean Air Act requires the EPA to look to the future in setting standards, but the agency must also provide a reasoned explanation of its basis for believing that its projection is reliable. This includes a defense of its methodology for arriving at numerical estimates. Id.

The thoroughness and persuasiveness of the explanation we can expect from the agency will, of course, vary with the nature of the prediction undertaken. "Where existing methodology or research in a new area of regulation is deficient, the agency necessarily enjoys broad discretion to attempt to formulate a solution to the best of its ability on the basis of available information." Industrial Union Dep't v. Hodgson, 499 F.2d 467, 474 n.18 (D.C.Cir.1974). At one extreme, this court has recognized that the EPA's decision to regulate potentially harmful pollutants involves a large element of policy choice that cannot be demonstrably "correct," although it must have a genuine scientific basis.

The Administrator may apply his expertise to draw conclusions from suspected, not completely substantiated, relationships between facts, from trends among facts, from theoretical projections from imperfect data, from probative preliminary data not yet certifiable as "fact," and the like. We believe that a conclusion so drawn a risk assessment may, if rational, form the basis for health-related regulations under the "will endanger" language of Section 211.

Ethyl Corp. v. EPA, 541 F.2d 1, 28 (D.C.Cir.1976) cert. denied, 426 U.S. 941, 96 S.Ct. 2663, 49 L.Ed.2d 394 (1976) (footnote omitted); see Environmental Defense Fund v. EPA, 598 F.2d 62, 83-85 (D.C.Cir.1978). We have also acknowledged the necessarily speculative nature of agency predictions in the social sciences, including judgments of the competitive impact of regulatory decisions. United States v. FCC, 652 F.2d 72, 100 (D.C.Cir.1980); National Small Shipments Traffic Conference v. CAB, 618 F.2d 819, 829-30 (D.C.Cir.1980). At the other extreme, this court's inquiry into agency methodology in the physical sciences has been far more exacting "where the facts pertinent to (a) standard's feasibility are available and easily discoverable by conventional technical means." National Lime Ass'n v. EPA, 627 F.2d 416, 454 (D.C.Cir.1980).

The present case lies between those two extremes. It does not involve questions at the frontier of physiological knowledge, but it does require a determination by the EPA of the likely sequence of further technological development. There is no known scientific technique for calculating when an as yet unsolved design problem will be ironed out. Thus, unlike the short-term feasibility assessments scrutinized in National Lime Association, the present determination presents the court with "the question how much deference is owed a judgment predicated on limited evidence when additional evidence cannot be adduced or adduced in the near future," id. at 454.

The time element in the EPA's prediction affects our reviewing task in three distinct ways. First, it introduces uncertainties in the agency's judgment that render that judgment vulnerable to attack. At the same time, however, the time element gives the EPA greater scope for confidence that theoretical solutions will be translated successfully into mechanical realizations, for "the question of availability is partially dependent on 'lead time', the time in which the technology will have to be available." Portland Cement Ass'n v. Ruckelshaus, 486 F.2d 375, 391 (D.C.Cir.1973), cert. denied, 417 U.S. 921, 94 S.Ct. 2628, 41 L.Ed.2d 226 (1974). Finally, the presence of substantial lead time for development before manufacturers will have to commit themselves to mass production of a chosen prototype gives the agency greater leeway to modify its standards if the actual future course of technology diverges from expectation.

The relevance of lead time, and of the ability to modify standards in light of future developments, to the degree of justification the agency must offer may be seen in this court's opinion in International Harvester Co. v. Ruckelshaus, 478 F.2d 615 (D.C.Cir.1973). That case, despite numerous dissimilarities to the present one, provides a useful point of reference, and all the parties seek to claim it as their own. In International Harvester, the court reversed the EPA's refusal to suspend for one year strict new 1975 model year emission standards that had been set by Congress in the 1970 amendments. This court, reviewing in early 1973 an EPA decision of May 1972, stressed the harm that would result from "a relaxation of standards, and promulgation of an interim standard, at a later hour after the base hour for 'lead time' has been passed, and the production sequence set in motion." Id. at 637. Too late a relaxation would penalize technologically advanced firms, like Ford, which would already have begun manufacture of vehicles that achieved better emission control at the expense of road performance. For this and other reasons,17 the hardship resulting if a suspension were mistakenly denied outweighed the risks from a suspension needlessly granted. Because of that balance of hardships, the court probed deeply into the reliability of the EPA's methodology.18 The present case is quite different; the "base hour" for commencement of production is relatively distant, and until that time the probable effect of a relaxation of the standard would be to mitigate the consequences of any excessive strictness in the initial rule, not to create new hardships.

The significance of the time factor in International Harvester was increased by the fact that the EPA was not predicting future technological advances, but rather was imposing an interpretation on current industry data. That data uniformly indicated that the standards were not being met, yet the EPA claimed that "adjustments" of the data demonstrated the likelihood of compliance. But the court concluded that the agency had failed to demonstrate the reliability of its methodology sufficiently to defend its reinterpretation of apparently adverse data.19

International Harvester has been cited frequently in cases involving presently-available-technology standards, as well as in other cases in which the agency's "central argument is that the standard is achievable because it has been achieved," National Lime Association, 627 F.2d at 432-33 (emphasis in original); Bunker Hill Co. v. EPA, 572 F.2d 1286 (9th Cir. 1977); Duquesne Light Co. v. EPA, 522 F.2d 1186 (3d Cir. 1975), vacated, 427 U.S. 902, 96 S.Ct. 3185, 49 L.Ed.2d 1196 (1976); CPC International, Inc. v. Train, 515 F.2d 1032 (8th Cir. 1975); Portland Cement Ass'n v. Ruckelshaus, 486 F.2d 375 (D.C.Cir.1973), cert. denied, 417 U.S. 921, 94 S.Ct. 2628, 41 L.Ed.2d 226 (1974). The defense of a projection methodology in such cases has required "that variables be accounted for, that the representativeness of test conditions b(e) ascertained, that the validity of tests be assured and the statistical significance of results determined." National Lime Association, 627 F.2d at 452-53 (footnotes omitted). But statistically-based techniques for reviewing the methodology of contemporary projections do not translate well into rules for reviewing predictions of future progress. If the agency is to predict more than the results of merely assembling preexisting components, it must have some leeway to deduce results that are not represented by present data.

The EPA has generally been granted "considerable latitude in extrapolating from today's technology" when it predicts future technological developments for the purposes of the Clean Water Act, 33 U.S.C. §§ 1251-1376 (1976 & Supp. II 1978). See California & Hawaiian Sugar Co. v. EPA, 553 F.2d 280, 288 (2d Cir. 1977). The courts have had numerous occasions to review EPA determinations that a given control technique constitutes the "best available technology economically achievable" in the 1980s.20 Most of the opinions, including our own American Paper Institute v. Train, 543 F.2d 328, 352-53 (D.C.Cir.1976), cert. dismissed, 429 U.S. 967, 97 S.Ct. 398, 50 L.Ed.2d 335 (1976), steer close by the shores of their factual contexts and yield little in the way of explicit doctrine. But their essential requirement is that the agency provide "a reasonable basis for belief that a new technology will be available and economically achievable."21 Hooker Chemicals & Plastics Corp. v. Train, 537 F.2d 620, 635 (2d Cir. 1976). When a technology is already in use in other industries, the court often expects more solid evidence that the technology can be transferred to the industry in question, or at least that relevant dissimilarities have been considered. American Meat Institute v. EPA, 526 F.2d 442, 465 (7th Cir. 1975).

To apply these general considerations to our task of review in the present case, we must examine the nature of the EPA's determination. The agency has predicted that the manufacturers will be able to develop a satisfactory version of the trap-oxidizer in the time remaining. This device was designed specifically for the purpose for which EPA intends it, and prototypes have achieved partial success. GM itself has characterized trap-oxidizers as "(t) he most promising particulate traps," and has admitted that "current program status (would) indicate a possibility of 1985 model year production."22 General Motors Response to EPA Notice of Proposed Rulemaking 132, 175 (1979) (hereinafter GM Response), J.A. 279, 284. The EPA's decision must be judged in terms of record evidence available in early 1980, allowing a "time frame of 2-21/2 years for completion of the design development phase (and) 2-21/2 years of production lead time."23 45 Fed.Reg. 48,133, 48,139 (1980).

Given this time frame, we feel that there is substantial room for deference to the EPA's expertise in projecting the likely course of development. The essential question in this case is the pace of that development, and absent a revolution in the study of industry, defense of such a projection can never possess the inescapable logic of a mathematical deduction. We think that the EPA will have demonstrated the reasonableness of its basis for prediction if it answers any theoretical objections to the trap-oxidizer method, identifies the major steps necessary in refinement of the device, and offers plausible reasons for believing that each of those steps can be completed in the time available. If the agency can make this showing, then we cannot say that its determination was the result of crystal ball inquiry, or that it neglected its duty of reasoned decisionmaking.

2. The Time "Necessary to Permit the Development and Application of the Requisite Technology"

Applying the standard described in the preceding section to the challenged particulate regulations, we can determine whether the EPA has presented an adequate exposition of its reasons for believing that the necessary technology will be available for 1985 model year light-duty diesels to comply with the standard. The EPA bases its prediction that the 1985 standard will be achieved on two factors: modifications decreasing the particulate output of diesel engines,24 and development of "aftertreatment" technology, that is, means by which the vehicle will remove particulate matter from its own exhaust. The larger proportion of the expected reduction in particulate emissions depends on aftertreatment, and it is the availability of that technology that provokes the major controversy in this case.

The EPA has identified a number of strategies for extracting particulates from diesel