BAZELON, Chief Judge:
This appeal injects us back into the midst of a long and sometimes acrimonious imbroglio over the proposed construction of a bridge across the Potomac River from Virginia into the District of Columbia. In an earlier appeal we held that the so-called Three Sisters Bridge could not be built except in compliance with the hearing, environmental protection, safety, and other provisions of federal law applicable to the construction of federally-assisted highway projects. That question, accordingly, is no longer open. We must now decide whether the Department of Transportation did, in fact and in law, heed the applicable federal statutes when it decided that the bridge should be built. On the basis of an extended factual inquiry, the District Court concluded that the Department had failed to comply with some of the provisions. We affirm that part of the District Court’s judgment. As to the provisions with which the District Court found compliance, however, we have concluded that the statutory requirements were not satisfied, and the case will therefore be remanded to afford the Secretary an opportunity to make appropriate determinations as required by the statute.
The factual background of this dispute has been described in detail in our earlier opinion and in the opinion of the District Court. Briefly stated, the controversy concerns a projected bridge between the Georgetown waterfront in the District of Columbia and Spout Run in Virginia. The bridge, which would be part of the Interstate Highway System and would be built largely with federal funds, would traverse the Three Sisters Islands, would “affect the Georgetown Historic District,” and would use some parkland. The precise amount of harm to parkland and historic sites has not yet been determined, however, since the planning of the bridge —including the approaches and access roads — is not yet finalized. A source of continuous controversy since its conception, the proposed bridge was deleted from the Interstate Highway System in January, 1969, when the National Capital Planning Commission, the official planning body for the District, adopted “a comprehensive transportation plan which did not include the Three Sisters Bridge.” The bridge was redesignated part of the Interstate System six months later after Representative Natcher, Chairman of the Subcommittee on the District of Columbia of the House Appropriations Committee, indicated unmistakably that money for construction of the District’s subway system would be withheld if the bridge plan were not revived. To satisfy the Chairman, it was necessary, first, for the Distinct of Columbia City Council to reverse its earlier position, and vote to approve the project. On August 9, 1969, the District government so voted, with the swing members loudly protesting that they would not have changed their votes but for the pressures exerted by Representative Natcher. The second prerequisite of redesignation was a decision by Transportation Secretary Volpe that the project should go ahead as part of the Interstate System. He announced that decision on August 12, 1969, and the project sprang full-blown back to life on the following day.
On April 6, 1970, we held that the hearing and planning requirements of title 23 of the United States Code were fully applicable to this project notwithstanding a 1968 Act directing that construction of the bridge begin not later than thirty days after the Act’s passage. We remanded the case to the trial court for an evidentiary hearing to determine whether the Secretary had complied with the pertinent provisions in concluding that the project should be revived. The case is before us on appeal and cross-appeal from the trial court’s decision.
I.
Given our earlier decision, the Secretary’s approval of the bridge must be predicated on compliance with a number of statutory provisions. Plaintiffs challenged with two lines of argument the District Court’s finding of compliance. First, they maintain that the Secretary’s determinations under the statute were tainted by his consideration of extraneous factors unrelated to the merits of the questions presented. They allege — and argue, moreover, that the District Court specifically found — that pressures exerted by Representative Natcher contributed to the decision to approve the bridge. Second, they argue that quite apart from the allegations of pressure, the record and applicable legal principles do not support a finding of compliance. The two strands of argument are plainly related, in plaintiffs’ view, since the alleged shortcomings under each statutory provision illustrate and lend substance to the argument that the rational, impartial evaluation of the project envisioned by the statute was impermissibly distorted by extraneous pressures. We consider first plaintiffs’ argument that the determinations could not stand even if there were no issue of extraneous pressure.
A. Requirements of § IS8
If a proposed federally-assisted highway project would encroach on parkland or historic sites, the Secretary of Transportation must determine before construction can begin that there is “no feasible and prudent alternative to the use of such land,” and, assuming such a finding, that the “program includes all possible planning to minimize harm to such park * * * or historic site.” The District Court concluded that Secretary Volpe had complied with each of these requirements.
In defending the Secretary’s action, the government can hardly maintain that there was no “feasible” alternative to construction of the Three Sisters Bridge. This exemption applies, as the Supreme Court indicated in Citizens to Preserve Overton Park, Inc. v. Volpe, only if the Secretary finds that “as a matter of sound engineering it would not be feasible to build the highway along any other route.” It could still be argued, however, that the Secretary rejected each of the feasible alternatives because none of them was “prudent.” In construing this second exemption, the Supreme Court pointed out that
the very existence of the statute indicates that protection of parkland was to be given paramount importance. The few green havens that are public parks were not to be lost unless there were truly unusual factors present in' a particular case or the cost or community disruption resulting from alternative routes reached extraordinary magnitudes. If the statutes are to have any meaning, the Secretary cannot approve the destruction of parkland unless he finds that alternative routes present unique problems.
Our review of the Secretary’s determination is hindered not only by the lack of any formal findings, but also by the absence of a “meaningful administrative record within the Department of Transportation evidencing the fact that proper consideration has been given to the requirements of this section.” However regrettable, the failure to provide explicit findings indicating why all possible alternatives to the bridge would be unfeasible or imprudent does not, in itself, invalidate the Secretary’s action. But the complete non-existence of any contemporaneous administrative record is more serious. Absent a record, judicial review of the Secretary’s action can be little more than a formality unless the District Court takes the disfavored step of requiring the Secretary to testify as to the basis of his decision. And even the Secretary’s “post hoe rationalizations,” filtered through a factfinder’s understandable reluctance to disbelieve the testimony of a Cabinet officer, will rarely provide an effective basis for review. Furthermore, it is hard to see how, without the aid of any record, the Secretary could satisfactorily make the determinations required by statute. The absence of a record, in other words, simultaneously obfuscates the process of review and signals sharply the need for careful scrutiny.
Secretary Volpe’s testimony before the District Court did little to allay the doubts generated by the lack of an administrative record. Indeed, his testimony — on occasion uncertain and inconsistent with the testimony of others —itself gives rise to at least a serious question whether he considered all possible alternatives to the plan eventually approved. It is clear, moreover, that the Department of Transportation failed to apply its own procedures generally applicable to determinations under § 138. That failure is especially disquieting since the procedures at issue were designed specifically to insure that determinations under § 138 would be made, in the Secretary’s words, only after “a great amount of real independent and genuine review [by] people who were not particularly highway oriented . ”
Furthermore, an apparent misconception about our earlier decision may itself have distorted the Secretary’s determination under § 138. The government has read our earlier opinion to mean that a bridge must be built, albeit in accordance with the provisions of title 23, somewhere in the vicinity of the proposed Three Sisters Bridge. Congress did direct, as we previously indicated, “that a bridge be built over the Potomac following the general configurations laid out in the cost estimates.” Viewed in context, however, the statement does not convey the meaning which the government suggests, for we held that “nothing in the statute indicates that Congress intended the Bridge to be built contrary to its own laws.” If the bridge cannot be built consistently with applicable law, then plainly it must not be built. It is not inconceivable, for example, that the Secretary might determine that present and foreseeable traffic needs can be handled (perhaps by expansion of existing bridges) without construction of an additional river crossing. In that case, an entirely prudent and feasible alternative to the Three Sisters Bridge might be no bridge at all, and its construction would violate § 138. Thus, the Secretary may have disregarded one possible prudent and feasible alternative to the use of parkland and historic sites on the mistaken assumption that that alternative was foreclosed by our earlier decision.
While these difficulties give rise to at least a substantial inference .that the Secretary failed to comply with § 138, that inference ripens into certainty when one turns to the second determination required by § 138. Before the project can begin, the Secretary must determine that all possible planning has been done to minimize harm to the affected parkland and historic sites. Yet the District Court found, and the Secretary apparently concedes, that final design of the ramps and interchanges is not yet complete. Thus, when Secretary Volpe purportedly complied with § 138 in August, 1969, he could at best have been “satisfied * * * that the designs which would be developed based on the preliminary plans would result in a minimum taking of parkland,” but he could not have concluded that the necessary planning had already been'done. The District Court reasoned that the expectation of future planning could satisfy § 138. But that reasoning seems inconsistent with the Supreme Court’s subsequent admonition that § 138 can be obeyed “only if there has been ‘all possible planning to minimize harm’ to the park.” Moreover, the District Court approved the § 138 determination on the basis of the Secretary’s testimony that a “minimum of parkland would be taken” for the ramps and interchanges. More is at stake, however, than the “minimum taking” of parkland. Section 138 speaks in terms of minimizing “harm” to parkland and historic sites, and the evaluation of harm requires a far more subtle calculation than merely totaling the number of acres to be asphalted. For example, the location of the affected acres in relation to the remainder of the parkland may be a more important determination, from the standpoint of harm to the park, than determining the number of affected acres. The Secretary has not yet determined which acres will be taken. In addition, a project which respects a park’s territorial integrity may still, by means of noise, air pollution and general unsightliness, dissipate its aesthetic value, crush its wildlife, defoliate its vegetation, and “take” it in every practical sense.
Absent a finalized plan for the bridge, it is hard to see how the Department could make a meaningful evaluation of “harm.” Furthermore, Secretary Volpe did not consult with other planning agencies to coordinate efforts to minimize harm to the park and historic sites. He also made no studies of potential air pollution damage to the park. His approval of the project under § 138 was, in short, entirely premature, and we hold that he must make new determinations consistent with the statutory standards.
B. Requirements of § 134
The Secretary cannot approve federally-assisted highway projects in urban areas unless he finds “that such projects are based on a continuing comprehensive transportation planning process” carried out in conformance with Congress’s objective of promoting the development of transportation systems. The Secretary reasoned, and the District Court approved his reasoning, that the bridge project was consistent with such a planning process since the bridge had been approved by, and was subject to the continuing scrutiny of, the Transportation Planning Board (TPB) of the Metropolitan Washington Council of Governments. Plaintiffs, on the other hand, emphatically deny compliance with § 134 on the grounds that the “comprehensive transportation plan promulgated by the National Capital Planning Commission (NCPC) in December 1968, specifically ‘rejects the Three Sisters Bridge . as being both unnecessary and undesirable.’ ” While plaintiffs point out that NCPC is the official planning agency for the District of Columbia and that it alone has prepared a comprehensive transportation plan, the government contends that the Council of Governments, unlike the NCPC, is a regional organization which must consider the interests of the surrounding jurisdictions.
We are unwilling to resolve this dispute by some abstract balancing of NCPC disapproval against TPB approval. That approach would, we are convinced, entirely miss the point of § 134. That section does not suggest that the Secretary has satisfied his statutory responsibility as soon as he has found a single plan which incorporates a proposed highway project. Nor can it reasonably be interpreted to mean that the project must be approved by every plan applicable to the affected region. The section speaks, after all, in terms of “planning,” not “plans,” and it is not our function to decide that one plan has merit while another does not. Rather, it is for the Secretary to determine whether a particular project will be consistent with sound transportation planning for the region.
Decisionmaking responsibility under § 134 has been delegated by Secretary Volpe to the Public Roads Division Engineer, Mr. Hall. Mr. Hall disregarded NCPC disapproval of the project because he believed that “TPB [was] the primary agency to which he should look in making his finding.” The District Court approved his finding on that same reasoning. But that reasoning cannot do service for the more sophisticated determination required by the statute. In making his “mental” finding of compliance with § 134, Mr. Hall apparently did no more than adopt TPB’s conclusion that the project was “consistent with comprehensive planning” for the region. Yet that is precisely the determination that the Department of Transportation, taking into account the recommendations of local plans, must make. The statute plainly does not permit the Department to delegate its statutory responsibility to a local planning agency. On remand, the Department must reevaluate the project in light of the purposes of § 134.
Since the determination was not grounded on a correct understanding of the statute’s requirements, we need not now decide whether the substantive result, if reached pursuant to appropriate procedures, would itself be supportable. But to aid the Department’s redetermi-nation under § 134, we should make clear our misgivings about the result and our doubts that it could be upheld on the present record even under the constrained standard of substantive review. TPB approved the bridge project in 1967, two years before Mr. Hall made his finding under § 134. No comprehensive transportation plan had been adopted at that time, either by TPB or any other planning agency. NCPC, which did not formulate its plan until December, 1968, was on record at the time of TPB’s action in 1967 as approving- the bridge project. TPB approved the project not under § 134, but under the Demonstration Cities and Metropolitan Development Act of 1966. NCPC, on the other hand, developed a transportation plan in response to President Johnson’s call for the development of a “comprehensive plan for a D.C. highway system” which would permit the Department of Transportation to determine whether the Three Sisters Bridge and other projects would be “appropriate links” in such a plan; it then rejected the bridge proposal. And even if TPB approval were not — at least on its face — stale, inapposite, and unsupported by any underlying, comprehensive plan, we would still have difficulty accepting the Department’s finding without some explanation of how the § 134 determination could be made before plans for the bridge are finalized. Nothing in the record suggests that TPB approval— whatever its other apparent shortcomings — embraced each conceivable design that might eventually be adopted.
C. Requirements of § 109(a)
The Secretary’s approval of plans for a federally-assisted highway project is conditioned on a determination that the proposed facility will “adequately meet the existing and probable future traffic needs and conditions in a manner conducive to safety, durability, and economy of maintenance.” The District Court held that planning for the Three Sisters Bridge had not “proceeded to a sufficient degree for the responsible officials to determine that the planned facility is structurally feasible.” Accordingly, the Court enjoined construction of the bridge until the planning had advanced to a stage where structural feasibility was assured. We find the District Court’s judgment consistent with the statute' and the facts presented, and it is therefore affirmed.
Plaintiffs also argue, however, that the project was approved before the Secretary could be certain, first, that river bed conditions would support the bridge, and second, that no safety hazard would arise from the increase in air pollution attributable to traffic on the bridge. Again, we are unable to accept the District Court’s disposition. With regard to river bed conditions, the District Court noted that
[bjefore the construction of a bridge, it is necessary to make extensive investigations of subsurface conditions to determine if they are sufficient to support the foundations for the bridge piers. This is done primarily by means of borings. * * * At the time Mr. Hall approved the plans, specifications and estimates for the pier construction, these borings had not been completed, and subsequently problems developed so that the plans for the project had to be modified.
Called to testify before the District Court, Mr. Hall still could not be certain “that the present planned foundation is adequate.” Nevertheless, the District Court found compliance with § 109(a) because of Mr. Hall’s testimony “that there is no question that the piers can be built to support the bridge as presently planned.” The Department of Transportation is obviously unwilling to construct a bridge known to be unsafe, and during the course of construction the Department would surely verify the suitability of the river bed conditions. But § 109(a) requires not only that the bridge be safe, but also — and no less important — that its safety be ascertained before the Secretary approves the project. That requirement minimizes the safety hazards and at the same time insures that public funds will not be squandered on a demonstrably unsafe proposal. Where planning reveals defects in design or location, those defects can be corrected on paper rather than on steel and concrete.
The District Court’s findings are not entirely clear as to whether questions about the safety of river bed conditions could be more fully resolved before construction resumes. We hold that if such questions do exist, the Secretary must take steps to resolve them to the fullest practical extent before granting approval of the project under § 109(a).
Plaintiffs' second contention under § 109(a) concerns the dangers of air pollution. The District Court concluded that evidence of a potential air pollution hazard was insufficient to support a finding “that the defendants are required to undertake a study of such [air pollution] effects.” We can find no basis in the statute’s language or purpose for the conclusion that certain hazards are, as a matter of law, immaterial to the Secretary’s evaluation of a project’s safety. The District Court would surely agree that Congress did not intend to permit construction of a bridge in a situation, however rare, where air pollution would be a significant threat to safety. It does not follow, of course, that air pollution will be a significant hazard in all — or even any — highway projects. And the District Court apparently concluded that no extraordinary dangers are likely to arise from the Three Sisters Bridge. Still, the gathering and evaluation of evidence on potential pollution hazards is the responsibility of the Secretary of Transportation, and he undertook no study of the problem. His staff has far greater resources and expertise on this matter than the District Court, and it is possible that a study by the Department would reveal significant dangers which had escaped the attention of the District Court. Inquiry into this issue cannot be foreclosed merely because the District Court found no significant evidence of air pollution hazards. That determination must be made in the first instance by the Secretary of Transportation.
D. Requirements of § 128
Section 128 requires that public hearings be held before construction can begin. In the earlier appeal we specifically held applicable to the Three Sisters Bridge project not only § 128, but also the Department of Transportation’s implementing regulations. Those regulations require, in certain specified situations, a hearing on project location and a hearing on project design. After exhaustive consideration of the record, the District Court concluded that the Department had not complied with the design hearing requirement, but that the location hearing requirement had been satisfied.
While the government did not admit error with regard to the design hearing, it nevertheless chose to hold the necessary hearing in a commendable effort to reduce the number of issues outstanding. Since the question has now been mooted, we express no opinion on the District Court’s conclusion. As for the location hearing, the District Court reasoned that a hearing held in 1964 satisfied the requirement, even though different proposals were the subject of that hearing, since the change in plan was “so insubstantial that the public would not be affected any differently than by the original proposal which formed the basis for the first hearing . ” We have no quarrel with the District Court’s reasoning, but on the present record we are unable to accept its application to this case. Of the proposals submitted at the 1964 hearing, the one most similar to current plans for the bridge was still off by 1500 feet on the District of Columbia shore and 950 feet on the Virginia shore. Ramps and interchanges as well as the routing of traffic have also been substantially redesigned. Nevertheless, the District Court could not “conceive how many members of the public would be affected differently by the present location than by one of the three” considered in 1964. It is entirely conceivable to us that the differences in the plans would, in fact, have a substantially different impact on persons on both shores. We would be reluctant, of course, to disturb the District Court’s finding of fact on this point if it were clear that a finding had actually been made. But there is no indication in the record before us that the District Court gathered evidence on this issue, and we have nothing to support the conclusion but the conclusion itself. Moreover, in making the determinations required by this opinion, the Secretary may conclude that current plans must be abandoned in favor of a new location. Accordingly, we remand this issue to the District Court for clarification of the factual basis of its conclusion, and for reconsideration in light of any further location changes the Secretary of Transportation may order.
E. Requirements of § 817
If the Secretary determines that lands owned by the United States are needed for a proposed highway project, he must
file with the Secretary of the Department supervising the administration of such lands or interests in lands a. map showing the portion of such lands or interests in land which it is desired to appropriate.
After concluding that the bridge project would use federal parklands under the jurisdiction of the Interior Department’s National Park Service, and after noting defendant's admission that a map had not been filed, the District Court still found “compliance with the spirit, if not' the letter, of § 317.” The court based its findings on the consultation between the Transportation and Interior Departments with regard to this project, and on the issuance by the latter of permits for the use of the parkland.
We agree with the District Court that the failure to supply a map should not be an absolute bar to the construction of the bridge if the purposes of § 317 have in fact been realized. That section is designed, as the District Court acknowledged, to
require the Secretary of Transportation to give notice to the Secretary of the Department having control of the land, and provide a means by which the latter may protect any governmental interest in use of the property for purposes other than highway construction.
We need not decide whether the District Court erred in finding compliance with the spirit of § 317. In view of our conclusion that the case must be remanded for new determinations, it would not appear to be a significant burden on the Department to remove all doubts under this section by filing the appropriate map.
F. Provisions Other Than Title 23
At the hearing below, the District Court barred plaintiffs from presenting evidence on ■ a number of allegations in their complaint because those allegations related to statutory provisions which the District Court found inapplicable to the Three Sisters Bridge project. Thus, the Court concluded that the project was exempted by Congress from compliance with certain provisions of the federal Code, as well as provisions of the District of Columbia Code.
In 1968 we held in D.C. Federation of Civic Associations, Inc. v. Airis that this project must comply with pertinent requirements of the D.C.Code. Later that year, Congress directed, in Section 23 of the Federal-Aid Highway Act, that
[notwithstanding any other provision of law or any court decision or administrative action to the contrary . . . construction [of the Three Sisters Bridge] shall be undertaken as soon as possible . . . and shall be carried out in accordance with all applicable provisions of Title 23 of the United States Code.
The District Court then held explicitly that the Three Sisters Bridge had been exempted from all of the pre-eonstruetion provisions of title 23, and implicitly that the bridge had been exempted from the comparable provisions of the D.C. Code. On appeal from that decision, we held that the bridge must comply with all applicable provisions of title 23. Our opinion did not indicate flatly, however, that the project must also comply with non-title 23 provisions. In view of the District Court’s conclusion that compliance with nontitle 23 provisions is not required, we must now resolve the ambiguity arguably left by our earlier opinion.
The applicability of these provisions was not squarely faced in the parties’ briefs, nor was it discussed at oral argument. While our earlier opinion did make one specific reference to the issue, the parties now draw opposite conclusions from that reference. Discussing section 23’s directive that the bridge be built “notwithstanding any * * * court decision * * * to the contrary,” we pointed out that
[presumably the “court decision” language refers to our decision in Airis [holding D.C.Code provisions applicable to the Three Sisters Bridge], but the reference is mistaken since that decision was not “to the contrary.”
Under these circumstances, we are reluctant to resolve the dispute without providing the parties an opportunity to discuss the question on the merits. Accordingly, we defer judgment on this issue to permit the parties to file, within twenty days from the date of this opinion, memoranda dealing with the question.
II
As Part I of this opinion makes clear, the Secretary’s determinations failed to comply with a significant num- • ber of title 23 provisions applicable to the Three Sisters Bridge. Taken as a whole, the defects in the Secretary’s determinations — in particular, his effort to make the determinations before plans for the bridge were complete — lend color to plaintiffs’ contention that the repeated and public threats by a few .Congressional voices did have an impact on the Secretary’s decisions. As the District Court pointed out,
[t]here is no question that the evidence indicates that strong political pressure was applied by certain members of Congress in order to secure approval of the bridge project. Congressman Natcher stated publicly and made no secret of the fact that he would do everything that he could to withhold Congressional appropriations for the District of Columbia rapid transit system, the need for which is universally recognized in the Washington metropolitan area, until the District complied with the 1968 Act.
When funds for the subway were, in fact, blocked, Representative Natcher
made his position perfectly clear, stating that “as soon as the freeway project gets under way beyond recall then we will come back to the House and recommend that construction funds for rapid transit be approved.”
The author of this opinion is convinced that the impact of this pressure is sufficient, standing alone, to invalidate the Secretary’s action. Even if the Secretary had taken every formal step required by every applicable statutory provision, reversal would be required, in my -opinion, because extraneous pressure intruded into the calculus of considerations on which the Secretary’s decision was based. Judge Fahy, on the other hand, has concluded that since critical determinations cannot stand irrespective of the allegations of pressure, he finds it unnecessary to decide the ease on this independent ground.
In my view, the District Court clearly and unambiguously found as a fact that the pressure exerted by Representative Natcher and others did have an impact on Secretary Volpe’s decision to approve the bridge. The Court pointed out that
[t]he statement issued by the Secretary at the time he directed the Federal Highway Administrator to restore the bridge to the Interstate System indicates that the pressure on the rapid transit funds was a consideration at that time.
The Court also found, on the basis of the Secretary's contemporaneous statements and his testimony before the Court, that
There is no question that the pressure regarding the rapid transit appropriations was given some consideration at the time of the approval of the project in August, 1969.
The Secretary’s testimony indicated, as the court below pointed out, that “his decision was based on the merits of the project and not solely on the extraneous political pressures.”
Notwithstanding these findings of fact, the Court determined as a matter of law that since the Secretary was not acting in a judicial or quasi-judicial capacity, his decision would be invalid only if based -solely on these extraneous considerations. I cannot accept that formulation of the applicable legal principle. While Judge Fahy is not entirely convinced that the District Court ultimately found as a fact that the extraneous pressure had influenced the Secretary’s decision — a point which is for me clear- — he has authorized me to note his concurrence in my discussion of the controlling principle of law: namely, that the decision would be invalid if based in whole or in part on the pressures emanating from Representative Natcher. Judge Fahy agrees, and we therefore hold, that on remand the Secretary must make new determinations based strictly on the merits and completely without regard to any considerations not made relevant by Congress in the applicable statutes.
The District Court was surely correct in concluding that the Secretary’s action was not judicial or quasi-judicial, and for that reason we agree that much of the doctrine cited by plaintiffs is inap-posite. If he had been acting in such a capacity, plaintiffs could have forcefully argued that the decision was invalid because of the decisionmaker’s bias, or because he had received ex parte communications. Well-established principles could have been invoked to support these arguments, and plaintiffs might have prevailed even without showing that the pressure had actually influenced the Secretary’s decision. With regard to judicial de-cisionmaking, whether by court or agency, the appearance of bias or pressure may be no less objectionable than the reality. But since the Secretary’s action was not judicial, that rationale has no application here.
If, on the other hand, the Secretary’s action had been purely legislative, we might have agreed with the District Court that his decision could stand in spite of a finding that he had considered extraneous pressures. Beginning with Fletcher v. Peck, the Supreme Court has maintained that a statute cannot be invalidated merely because the legislature’s action was motivated by impermissible considerations (except, perhaps, in special circumstances not applicable here). Indeed, that very principle requires us to reject plaintiffs’ argument that the approval of the bridge by the District of Columbia City Council was in some sense invalid. We do not sit in judgment of the motives of the District’s legislative body, nor do we have authority to review its decisions. The City Council’s action constituted, in our view, the approval of the project required by statute.
Thus, the underlying problem cannot be illuminated by a simplistic effort to force the Secretary’s action into a purely judicial or purely legislative mold. His decision was not “judicial” in that he was not required to base it solely on a formal record established at a public hearing. At the same time, it was not purely “legislative” since Congress had already established the boundaries within which his discretion could operate. But even though his action fell between these two conceptual extremes, it is still governed by principles that we had thought elementary and beyond dispute. If, in the course of reaching his decision, Secretary Volpe took into account “considerations that Congress could not have intended to make relevant,” his action proceeded from an erroneous premise and his decision cannot stand. The error would be more flagrant, of course, if the Secretary had based his decision solely on the pressures generated by Representative Natcher. But it should be clear that his action would not be immunized merely because he also considered some relevant factors.
It is plainly not our function to establish the parameters of relevance. Congress has carried out that task in its delegation of authority to the Secretary of Transportation. Nor are we charged with the power to decide where or when bridges should be built. That responsibility has been entrusted by Congress to, among others, the Secretary, who has the expertise and information to make a decision pursuant to the statutory standards. So long as the Secretary applies his expertise to considerations Congress intended to make relevant, he acts within his discretion and our role as a reviewing court is constrained. We do not hold, in other words that the bridge can never be built. Nor do we know or mean to suggest that the information now available to the Secretary is necessarily insufficient to justify construction of the bridge. We hold only that the Secretary must reach his decision strictly on the merits and in the manner prescribed by statute, without reference to irrelevant or extraneous considerations.
For the purposes of the foregoing discussion, we have assumed that pressures exerted by Congressional advocates of the bridge are irrelevant to the merits of the questions presented to Secretary Volpe. It does not seem possible to make even a colorable argument of relevance except with regard to § 138. But it might be argued that the potential loss of the subway was the type of “unique problem” and cost of “extraordinary magnitude” that the Secretary could properly consider in deciding, pursuant to § 138, that there were no prudent alternatives to the use of parkland for the bridge. The Secretary plainly understood that the price of abandoning, modifying, or even delaying construction of the bridge was the loss of appropriations for the District’s subway. He undoubtedly viewed the prospect of that loss with understandable alarm, and may have concluded that the destruction of parkland was inescapable and appropriate in the face of Representative Natcher’s clear and enforceable threat. We cannot agree, however, that a determination grounded on that reasoning would satisfy the requirements of § 138.
Neither the section’s legislative history nor the Supreme Court’s decision in Overton Park indicates clearly whether or not this sort of consideration should be deemed relevant. We are persuaded, however, that holding these pressures relevant would effectively emasculate the statutory scheme. The purpose of § 138, in our view, was to preserve parkland by directing the Secretary to reject its use except in the most unusual situation where no alternative would be available. The “unusual situation” posited here is entirely the product of the action of a small group of men with strongly-held views on the desirability of the bridge, who, it may be assumed, are acting with the interests of the public at heart. They may well be correct in concluding that a new bridge is needed and that no alternative location is available. But no matter how sound their reasoning nor how lofty their motives, they cannot usurp the function vested by Act of Congress in the Secretary of Transportation. Until the statute is amended or repealed by another Act of Congress, the Secretary must himself decide, bearing in mind the statute’s mandate for the preservation of parkland, whether a prudent alternative is available. Congress could not have contemplated that an alternative would be “imprudent” merely because persons who are convinced that parkland should be used have the power to decree that all alternatives to the use of that parkland shall henceforth be agonizing. Our interpretation of § 138 is essential if the Secretary is to be insulated from extraneous pressures that have no relevance to his assigned statutory task.
To avoid any misconceptions about the nature of our holding, we emphasize that we have not found — nor, for that matter, have we sought — any suggestion of impropriety or illegality in the actions of Representative Natcher and others who strongly advocate the bridge. They are surely entitled to their own views on the need for the Three Sisters Bridge, and we indicate no opinion on their authority to exert pressure on Secretary Volpe. Nor do we mean to suggest that Secretary Volpe acted in bad faith or in deliberate disregard of his statutory responsibilities. He was placed, through the action of others,. in an extremely treacherous position. Our holding is designed, if not to extricate him from that position, at least to enhance his ability to obey the statutory command notwithstanding the difficult position in which he was placed.
III.
We conclude that the case should be remanded to the District Court with directions that it return the case to the Secretary for him to perform his statutory function in accordance with this opinion. It seems clear that even though formal administrative findings are not required by statute, the Secretary could best serve the interests of the parties as well as the reviewing court by establishing a full-scale administrative record which might dispel any doubts about the true basis of his action. Accordingly, the District Court is directed to enjoin construction of the bridge until the defendants have complied with the applicable statutory provisions as set forth in our opinion. Reversed and remanded.
. D.C. Federation of Civic Ass’ns, Inc. v. Volpe, 140 U.S.App.D.C. 162, 434 F.2d 436 (1970), holding that “both the planning and building of the Three Sisters Bridge [must] comply with all applicable provisions of Title 23.” Id., at 447. In their complaint before the District Court on remand plaintiffs alleged that the Secretary had not complied with the following provisions: 23 U.S.C. §§ 102, 103, 128(a), 134, 138, and 317 (1970), and the regulations implementing § 128 (a), 23 C.F.R. Part 1, App. A (1970). Apart from alleged violations of title 23, plaintiffs also complained of violations of various sections of title 7 of the District of Columbia Code, and of 16 U.S.C. §§ 1, 470; 33 U.S.C. §§ 401, 403, 525; and 49 U.S.C. § 1655 (1970). At the commencement of trial, the District Court granted plaintiffs’ motion to amend their complaint to allege also a violation of 23 U.S.C. § 109(a) (1970). The Court granted plaintiffs a hearing on each complaint under title 23, but not under any of the other statutory provisions. See pp. 1244, 1245, infra-, D.C. Federation of Civic Ass’ns, Inc. v. Volpe, 316 F.Supp. 754, 761 & nn. 13-14 (D.D.C.1970).
. 316 F.Supp. 754 (D.D.C.1970).
. 140 U.S.App.D.C. 162, 434 F.2d 436 (1970).
. 316 F.Supp. 754 (D.D.C.1970).
. Id. at 769.
. Id. at 774.
. Id. at 759.
. Id.
. On Jan. 17, 1969, the District’s City Council had voted to approve the NCPC transportation plan which rejected the Three Sisters Bridge as unnecessary and undesirable. Id.
. Id. at 764, 767.
. Pub.L.No.90-495, 82 Stat. 827 (1968) ; cf. pp. 1244-1245 infra.
. For purposes of this opinion we refer to the D.O. Federation of Civic Associations, appellants (and cross-appellees) in this Court, as “plaintiffs,” and to Secretary Volpe, the District of Columbia, and the other appellees (and cross-appellants) as “defendants.”
. 23 U.S.C. § 138 (1970).
. 401 U.S. 402, 411, 91 S.Ct. 814, 821, 28 L.Ed.2d 136 (1971) (emphasis added).
. Id. at 412-413, 91 S.Ct. at 821.
. 316 F.Supp. at 769.
. Citizens to Preserve Overton Park, Inc. v. Volpe, 401 U.S. 402, 409, 91 S.Ct. 814, 28 L.Ed.2d 136 (1971). But see note 88 infra.
. Citizens to Preserve Overton Park, Inc. v. Volpe, 401 U.S. 402, 420, 91 S.Ct. 814, 825 (“review [of the Secretary’s decision) is to be based on the full administrative record that was before the Secretary at the time he made his decision”). Bee also Environmental Defense Fund, Inc. v. Ruckelshaus, 142 U.S.App.D.C. 74, 88 439 F.2d 584, 598 (1971).
. Citizens to Preserve Overton Park, Inc. v. Volpe, 401 U.S. 402, 420, 91 S.Ct. 814, 28 L.Ed.2d 136 (1971) ; United States v. Morgan, 313 U.S. 409, 422, 61 S.Ct. 999, 85 L.Ed. 1429 (1941).
. Cf. Citizens to Preserve Overton Park, Inc. v. Volpe, 401 U.S. 402, 420, 91 S.Ct. 814, 826, 28 L.Ed.2d 136 (1971) (“Such an explanation will, to some extent, be a ‘post hoc rationalization’ and thus must be viewed critically.”).
. Secretary Volpe testified, for example, that he “believed that he had consulted with Mr. Braman’s office with respect to the Bridge project,” (Transcript at 808-809), but Mr. Braman pointed out that his office was “not involved in the Three Sisters matter at any time.” (Tr. at 1005.) The Secretary also testified that the Federal Highway Administrator, Mr. Turner, had discussed with him the § 138 problem, and that the Administrator had made an oral recommendation. (Tr. at 722.) Nevertheless, Mr. Turner indicated in his testimony that he did not believe he had made any recommendation to the Secretary or had even discussed with him the specific question of the determination under § 138. (Tr. at 977.) See generally Brief for Appellants at 34-35. Asked about his consideration of a number of alternatives to the Three Sisters Bridge, Secretary Volpe testified that he could not recall having considered the possibility of a tunnel at “any location other than the Three Sisters Islands,” (Tr. at 780), upgrading the Jefferson Davis Highway to Interstate standards (Tr. at 779), or a number of other potential alternatives. See Brief for Appellants at 36-38.
. 316 F.Supp. at 769-770. The procedures in question involved the Department’s Office of Environmental and Urban Systems, headed by Mr. James Braman.
. Tr. at 644 (testimony of Secretary Volpe).
. 140 U.S.App.D.C. at 172, 434 F.2d at 446.
. Id. at 447.
. Cf. Environmental Defense Fund, Inc. v. Corps of Engineers, 325 F.Supp. 749, 761 (E.D.Ark.1971).
. Testifying before the District Court, Secretary .Volpe did indicate that he “had considered several alternatives including the bridge, no bridge, the tunnel, various types of ramp connections etc. . . . ” (Tr. at 742) (emphasis added). It is possible, however, that the Secretary might have given that alternative (and the studies which seem to support it, see Brief for Appellants at 36 n. 2) more extensive consideration if his Department had not been convinced, judging by its representations before this Court, that “no bridge” was not a viable alternative in view of Section 23 of the Federal-Aid Highway Act of 1968.
. 316 F.Supp. nt 775 (emphasis added).
. Citizens to Preserve Overton Park, Inc. v. Volpe, 401 U.S. 402, 405, 91 S.Ct. 814, 816, 28 L.Ed.2d 136 (emphasis added).
. 316 F.Supp. at 775.
. Compare Brief for Federal Appellees at 11: “The park areas underneath the bridge would, in essence, remain available for park purpose uses. ...”
. 316 F.Supp. at 794.
. 23 U.S.C. § 184 (1970).
. 316 F.Supp. at 794.
. Id.
. 316 F.Supp. at 794.
. n>. at 1109.
. 316 F.Supp. at 794.
. See Citizens to Preserve Overton Park, Inc. v. Volpe, 401 U.S. 402, 415-416, 91 S.Ct. 814, 28 I>.Ed.2d 136 (1971).
. 316 F.Supp. at 794.
. 42 U.S.C. § 3334 (1970) ; see 316 F. Supp. at 794 n. 57.
. Statement of President Johnson, August 23, 1968, 114 Cong.Ree. (Part 24) 30959 (1968).
. The Secretary is not required, of course, to resolve every conceivable ambiguity in a proposed plan before testing its compliance with the applicable statutory provisions. But where he does purport to make a determination required by statute, for example under § 134, in advance of the completion of planning, his determination must remain flexible and be subject to continuing reconsideration as the plans for the project mature.
. 23 U.S.C. § 109(a) (1970).
. 316 F.Supp. at 793.
. 316 F.Supp. at 790.
. Tr. at 604.
. 316 F.Supp. at 790.
. 316 F.Supp. at 791.
. We express no opinion at this time on the amount or type of investigation which the Secretary should undertake in evaluating the air pollution hazards. In his testimony before the District Court, Secretary Volpe indicated that his Department “consider [s] air pollution in the overall consideration of all our projects,” Tr. at 811, and it is possible that the consideration already given would satisfy the requirements of the statute. But the District Court made no findings on the Secretary’s action, and approved the project apparently because the evidence seemed insufficient, in its view, to warrant a holding that the Department must undertake a study of the problem. 316 F. Supp. at 791. Bather than returning the case to the District Court for clarification of its findings on this point, it seems • most efficient, in view of our remand to the Secretary under other provisions, to permit the Secretary to reconsider at the same time his determination under § 109 (a).
. 23 U.S.C. § 128(a) (1970).
. Policy and Procedure Memorandum 20-8, 23 C.F.R. Part I, App. A (1970).
. Naturally, we do not decide whether the design hearing held by the Department complied with the requirements of PPM 20-8 and § 128(a). That question has not been presented to us. If plaintiffs have objections to the hearing, those objections should be lodged in the District Court.
. The plan under consideration in 1964, the so-called Howard Needles report, proposed three possible locations for a central Potomac crossing. 316 F.Supp. at 778.
. Id. at 779.
. Id. at 778.
. Id. at 779.
. The District Court made an additional finding of error under § 128(a). The section requires that the “State highway department . . . certify to the Secretary that it has had public hearings. . . . ” (emphasis added). The District Court held, and we agree, that the certifying officer “should be one who knows as a fact that the actions to which he is certifying have been taken.” 316 F.Supp. at 789. The District Court found that the certifying officer had assumed that certification was appropriate “merely because the project had reached the stage where the certification is normally made.” Id. That assumption, the District Court held, was an “insufficient basis for the certification.” Id. at 790. The defendants do not contest that finding, and it is therefore affirmed.
. 23 U.S.C. § 317 (1970).
. 316 F.Supp. at 796-797.
. United States v. 10.69 Acres of Land, 425 F.2d 317, 319 (9th Cir. 1970).
. Subsequent to the District Court’s decision, the National Park Service announced in a letter (a photocopy of which is included in Brief for Appellants) that it does object to at least one aspect of the bridge plan. ’Letter from George B. Hartzog, Jr., Director, National Park Service, Department of the Interior, to Martin K. Schaller, Executive Secretary, Office of the Mayor-Commissioner, Dec. 15, 1970, reproduced in Brief for Appellants at App. A. That objection, moreover, includes an allegation that current plans for the bridge “conflict with [the Service’s] understanding of the terms of an agreement signed May 25, 1966, by the National Park Service” and the Virginia and District of Columbia highway departments. It is precisely that prior — and, perhaps, misconstrued — agreement on which the government now relies to demonstrate compliance with the “spirit” of § 317. The letter may, in other words, have undercut the factual predicate of the District Court’s reasoning. Whatever the signifiance of this attempted supplementation of the record, it is clear that any doubts will be removed by our holding that the Secretary must comply with the letter of § 317.
. At issue are 16 U.S.C. §§ 1, 470; 33 U.S.C. §§ 401, 403, and 525; 49 U.S.C. § 1655 (1970), and various sections of title 7 of the District of Columbia Code.
. 129 U.S.App.D.C. 125, 391 F.2d 478 (1968).
. Pub.L. No. 90-495, 82 Stat. 827 (1968).
. 308 F.Supp. 423 (D.D.C.1970).
. Plaintiffs clearly asked for a ruling in this Court on 16 U.S.C. § 470f (1970), and provisions of title 7 of the D.C.Code. They have not explicitly asked for a ruling on any other non-title 23 provision.
. D.C. Federation of Civic Ass’ns, Inc. v. Volpe, 140 U.S.App.D.C. 162, 173, 434 F.2d 436, 447 & n. 50 (1970).
. 316 F.Supp. at 762. The “1968 Act,” section 23 of the Federal-Aid Highway Act of 1968, is discussed at pp. 1244-1245 supra.
. 316 F.Supp. at 762.
. Id. at 764-765 (emphasis added).
. Id. at 766 (emphasis added).
. Id. at 765-766 (emphasis added).
. Id. at 765.
. See Citizens to Preserve Overton Park, Inc. v. Volpe, 401 U.S. 402, 414-415, 91 S.Ct. 814, 28 L.Ed.2d 136 (1971).
. See, e. g., Pillsbary Co. v. FTC, 354 F. 2d 952 (5th Cir. 1966); Jarrott v. Scrivener, 225 F.Supp. 827 (D.D.C.1964).
. See generally 2 K. Davis, Administrative Law §§ 12.01 et seq. (1958).
. Gf. Sangamon Valley Television Corp. v. United States, 106 U.S.App.D.C. 30, 269 F.2d 221 (D.C.Cir. 1959).
. See, e. g., Pillsbury Co. v. FTC, 354 F. 2d 952, 964 (5th Cir. 1966).
. 10 U.S. (6 Cranch.) 87, 129-131, 3 L. Ed. 162 (1810).
. Cf. Griffin v. County School Bd. of Prince Edward County, 377 U.S. 218, 231, 84 S.Ct. 1226, 12 L.Ed.2d 256 (1964); Gomillion v. Lightfoot, 364 U.S. 339, 347, 81 S.Ct. 125, 5 L.Ed.2d 110 (1960). But see Palmer v. Thompson, 403 U.S. 217, 224-225, 91 S.Ct. 1940, 29 L.Ed.2d 438 (1971).
. See 23 U.S.C. § 103(d) (1970).
. United States ex rel. Kaloudis v. Shaughnessy, 180 F.2d 489, 491 (2d Cir. 1950). See also United States ex rel. Accardi v. Shaughnessy, 347 U.S. 260, 74 S.Ct. 499, 98 L.Ed. 681 (1954), a case remarkably similar to the one before us. Cf. Shaughnessy v. United States ex rel. Accardi, 349 U.S. 280, 75 S.Ct. 746, 99 L.Ed. 1074 (1955).
. Cf. Perry v. Perry, 88 U.S.App.D.C. 337, 338, 190 F.2d 601, 602 (1951).
. Citizens to Preserve Overton Park, Inc. v. Volpe, 401 U.S. 402, 416, 91 S.Ct. 814, 823 (1971) (“the court must consider whether the decision was based on a consideration of the relevant factors”) (emphasis added) ; Wong Wing Hang v. I. & N. S., 360 F.2d 715, 719 (2d Cir. 1966), cited with approval in Citizens to Preserve Overton Park, Inc. v. Volpe, supra, 401 U.S. at 416, 91 S.Ct. 814, 28 L.Ed. 2d 136; L. Jaffe, Judicial Control of Administrative Action 182 (1965).
See also SEC v. Chenery Corp., 318 U.S. 80, 87-88, 92-94, 63 S.Ct. 454, 87 L.Ed. 626 (1942), where the Court pointed out, inter alia, that “[i]f an order is valid only as a determination of policy or judgment which the agency alone is authorized to make and which it has not made, a judicial judgment cannot be made to do service for an administrative judgment.” Id. at 88, 63 S.Ct. at 459. Accord, SEC v. Chenery Corp., 332 U.S. 194, 196, 67 S.Ct. 1575, 91 L.Ed. 1995 (1947) ; Sunbeam Television Corp. v. FCC, 100 U.S.App.D.C. 82, 243 F.2d 26 (1957) (Fahy, J.) ; Chae-Sik Lee v. Kennedy, 111 U.S.App.D.C. 35, 294 F.2d 231 (1961).
It might be argued that a remand would be futile here since the agency can only repeat the process it purports already to have undertaken: namely, considering the project solely on its merits. While we agree that a remand would be academic if the agency would inevitably arrive at the same result, NLRB v. Wyman-Gordon Co., 394 U.S. 759, 766-767 n. 6, 89 S.Ct. 1426, 22 L.Ed.2d 709 (1969) ; Friendly, The “Limited Office” of the Chenery Decision, 21 Ad.L.Rev. 1, 5 (1968), it seems entirely possible that the agency could reacli a different result if it could insulate itself from extraneous pressures unrelated to the merits of the question. On remand, the agency will have an opportunity to take steps to achieve the insulation required by statute and long-established principles of administrative law, perhaps by compiling a full-scale administrative record, utilizing fully intra-agency review procedures, and consulting with other agencies and planning groups.
. Cf. Sunbeam Television Corp. v. FCC, 100 U.S.App.D.C. 82, 243 F.2d 26 (1957).
. See Citizens to Preserve Overton Park, Inc. v. Volpe, 401 U.S. 402, 412-413, 91 S.Ct. 814, 28 L.Ed.2d 136 (1971).
. Cf. id. at 419 n. 33, 91 S.Ct. 814, 28 L.Ed.2d 136.
. While formal findings are not required by statute, they are compelled by one of the Department’s own internal regulations, DOT Order 5610.1, issued on October 7, 1970. See generally Citizens to Preserve Overton Park, Inc. v. Volpe, 401 U.S. 402, 417-419, 91 S.Ct. 814, 28 L.Ed.2d 136 (1971). That Order was not in effect at the time the Secretary’s determinations were made. Plaintiffs argue that the Order should be applied retrospectively, and that it should therefore constitute an independent basis for reversal. While the Supreme Court rejected a similar claim in Overton Park, supra, that decision may be distinguishable in that a full administrative record was available there to facilitate review. Id. at 419, 91 S.Ct. 814, 28 L.Ed.2d 136. While the proposed distinction would seem to have a good deal of force, we need not reach the question in view of our conclusion that the Secretary failed, irrespective of DOT Order 5610.1, to make the determinations required by statute. When the Secretary makes new determinations on remand, the Order will presumably apply.