Vаcated and remanded by published opinion. Judge MOTZ wrote the opinion, in which Judge SHEDD and Judge AGEE joined.
OPINION
The North Carolina Department of Transportation and the Federal Highway Administration (collectively “the Agencies”) recently approved construction of a new twenty-mile toll road in North Carolina linking Mecklenburg and Union Counties — the Monroe Connector Bypass. Seeking to enjoin construction of the toll road, the North Carolina Wildlife Federation, Clean Air Carolina, and Yadkin Riverkeeper (collectively “the Conservation Groups”) filed this suit, contending that the process by which the Agencies approved the road violated the National Environmental Protection Act (“NEPA”). The district court granted summary judgment to the Agencies. The Conservation Groups now appeal. Because the Agencies failed to disclose critical assumptions-underlying their decision to build the road and instead provided the public with incorrect information, they did indeed violate NEPA. Accordingly, we must vacate the judgment of the district court and remand for further proceedings consistent with this opinion.
I.
We begin by recounting the undisputed facts and the procedural history of this case.
A.
In 2007, after a number of failed attempts, the North Carolina Department of Transportation again proposed construction of the Monroe Connector Bypass (hereinafter “the Monroe Connector”) and, under the Federal Highway Administration’s supervision, commenced the environmental assessment procеss required by NEPA.
The Agencies began by creating a Statement of Purpose and Need, which evaluated the region’s existing transportation network, including an in-depth analysis of U.S. Highway 74. That road serves as the “primary transportation connection between Union County, the fastest growing county in North Carolina, and Mecklenburg County/City of Charlotte, the economic hub of the region,” and “also serves as an important commercial corridor.” The Agencies determined that U.S. 74’s “[ajverage travel speеds range from approximately 20 to 30 miles per hour during the peak hour” with “one-third of the intersections operating at an unacceptable Level of Service.” The' Statement of Purpose and Need concluded that U.S. 74 suffers from “[cjapacity [deficiencies” and does not allow for “high-speed regional travel.”
To remedy these shortcomings, the Agencies proposed developing “a facility that allows for safe, reliable, high-speed regional travel in the U.S. 74 Corridor ... whilе maintaining access to properties along existing U.S. 74.”
*599 In evaluating possibilities that might meet these goals, the Agencies created an Environmental Impact Statement (hereinafter “Impact Statement”). The Agencies began with a draft Impact Statement, and after taking public comment, published a final Impact Statement. See 40 C.F.R. §§ 1502.9(a), 1503.1(a), 1503.4.
The draft Impact Statement analyzed a wide variety of proposals, among them the Agencies’ preferred choice — the Monroe Connector. Aftеr two initial screenings, the Agencies eliminated all but three categories of proposals: (1) improve U.S. 74, (2) construct the Monroe Connector, and (3) a hybrid — combining the Monroe Connector with improvements to U.S. 74. Within these categories, the Agencies developed twenty-five “preliminary study alternatives.” They analyzed these preliminary study alternatives to determine which ones “should be carried forward” as “detailed study alternatives” to receive greater analysis. After considering economic impacts and traffic projections, the Agencies “carried forward” sixteen “build” alternatives for detailed study. 1 These “build” alternatives consisted of nearly identical paths for constructing the Monroe Connector.
The Agencies also carried forward a “no action” alternative — a scenario “without major improvements.” The draft Impact Statement and the final Impact Statement explained that the purpose of the “no action” or “no build” alternative was “tо provide a baseline for comparison” with the “build” alternatives. For example, in the draft Impact Statement, the Agencies compared the year-2035 traffic projections for the “build” alternatives against the year-2035 traffic projections for the “no build” baseline. Similarly, in the final Impact Statement the Agencies compared the indirect and cumulative environmental effects of the “build” alternatives with the “no build” baseline. Given its widespread use the accuracy of the “no build” basеline was critically important.
The Agencies created the “no build” baseline using information from a local planning organization. They relied on the Mecklenburg-Union Metropolitan Planning Organization (“MUMPO”) to develop socioeconomic data based on its Regional Travel Demand Model. This model projects “population, household, and employment figures” for the region using a two-step process. First, a “top-down” analysis of “census and employment projection data ... at the county [level]” calculated “the maximum number of households, population and employment.” Appellees’ Br. at 15-16. Second, a “bottom-up” process allocated the top-down projected growth throughout the Monroe Connector’s future land use study area. Id.
The bottom-up process divided the area into 571 “traffic analysis zones.” MUM-PO’s model then calculated projected growth for each of these zones using a number of “land development factors”: developable and redevelopable residential land, population change, water availability, sewer availability, expert predicted growth, municipal growth policy, and travel time to employment. A zone’s “travel time to employment” depended on MUM-PO’s anticipated roadway network for the region. This anticipated roadway network included the proposed Monroe Connector. Thus, although the Agencies used MUM- *600 PO’s projections as the “no build” baseline, part of MUMPO’s data actuаlly assumed construction of the Monroe Connector. By using MUMPO’s data, therefore, the Agencies incorporated “build” assumptions into the “no build” baseline.
Throughout the NEPA process, public commentators repeatedly asked the Agencies whether the “no build” baseline in fact assumed construction of the Monroe Connector. In responding to these comments, the Agencies either failed to address the underlying issue or incorrectly stated that the Monroe Connector was not factored into the “no build” baseline.
For example, when the Agenсies published their estimate that the 2035 “build” traffic volume would be less than the 2035 “no build” baseline traffic volume, the Conservation Groups queried whether this “implausible]” conclusion might be the result of the “no build” data actually “assuming] that the Monroe Connector” would be built. Without responding to the Conservation Groups’ underlying concerns regarding the accuracy of the “no build” baseline, the Agencies simply issued an errata table lowering the 2035 “no build” traffic projection baseline to below the “build” levels. The Agencies offered no explanation as to the source of the error and instead summarily stated that “the 2035 No-Build Alternative [traffic] forecast was inadvertently overestimated,” and assured the public that “all other conclusions and discussions remain valid.”
Similarly, when the Agencies concluded that the indirect and cumulative environmental effects of the Monroe Connector were minimal compared to the “no build” baseline, the United States Fish and Wildlife Service requested “further clarification regarding the basis for the No-build scenario.” “Specifically,” the Fish and Wildlife Service asked “if MUMPO’s [projections] are the basis for the no-build scenario and [if] they contain the [Monroe Connector], how is this a true characterization of no-build?” The Agencies responded with a memorandum drafted by their consultant, Baker Engineering, concluding that “the methodology for determining the No-Build scenario ... is appropriate and defensible.” Baker expressly stated, however, that “the MUMPO ... projections do not account for the Monroe Connector!].” (emphasis added).
Unsatisfied with this rеsponse, the Fish and Wildlife Service asked whether the Agencies were “doubly sure about th[eir] assumption.” The Agencies subsequently asked Baker to contact MUMPO and local officials to ask whether they “would agree with [its] assumption that the[ ] [“no build” baseline] forecasts represent a future scenario without the Monroe Connector.” After receiving generally confirming responses, Baker assured the Fish and Wildlife Service. In light of this assurance, although the Fish and Wildlife Service “continued to be conсerned about the level of impacts,” it issued its Endangered Species Act concurrence, thereby removing a major impediment to the Monroe Connector.
On August 27, 2010, the Agencies issued their Record of Decision — the final component of the NEPA process. See 40 C.F.R. § 1505.2. The Conservation Groups again asked whether the underlying data represented a true “no build” scenario. The Record of Decision responded with additional denials, stating that the “socioeconomic forecasts for thе No Build Scenario did not include the Monroe Connector.” (emphasis added). The Record of Decision ultimately selected a site for construction of the Monroe Connector at an approximate cost of $800 million.
B.
On November 2, 2010, the Conservation Groups filed this action seeking to enjoin *601 construction of the Monroe Connector. After the district court denied the Conservation Groups’ motions for a preliminary injunction and to complete and supplement the record, the parties filed cross-motions for summary judgment.
The Conservation Groups asserted that the Agencies violated NEPA by: “(1) failing to analyze the environmental impacts of the Monroe Connector[ ]; (2) conducting a flawed analysis of alternatives; and (3) presenting materially false and misleading information to other agencies and to the public.”
N.C. Wildlife Fed’n v. N.C. Dep't of Transp.,
The Conservation Groups timely noted this appeal.
II.
NEPA claims are subject to judicial review under the Administrative Procedure Act, which permits a reviewing court to set aside an agency action if the action was “arbitrary, capricious, an abuse of discretion, or otherwise not in accordance with law.” 5 U.S.C. § 706(2)(A);
see Dep’t of Transp. v. Pub. Citizen,
The NEPA process includes a range of “ ‘action-forcing’ procedures that require ... agencies [to] take a ‘hard look’ at environmental consequences [of a proposed action] and [to] provide for broad dissemination of relevant environmental information.”
Robertson v. Methow Valley Citizens Council,
“At the heart of NEPA is a requirement” that for every “major Federal action[] significantly affecting the quality of the human environment,” the agency involved must prepare “a detailed” environmental impact statement.
Pub. Citizen,
An agency’s assessment of alternatives to the proposed action “sharply definfes] the issues and provides] a clear basis for choice among options by the decisionmaker and the public.” 40
C.F.R.
§ 1502.14. Agencies must “Vigorously explore and objectively evaluate all reasonable alternatives.”
Id. §
1502.14(a). Although agencies have discretion to identify the range of “reasonable” alternatives, they
must
“include the alternative of no action.”
Id.
§ 1502.14(c)-(d);
see also Theodore Roosevelt Conserv. P’ship v. Salazar,
An agency’s assessment of environmental impacts, in turn, is the “scientific and analytic basis for the eomparison[ ]” of alternatives. 40 C.F.R. § 1502.16. As part of this analysis, agencies
must
measure the indirect and cumulative environmental effects of proposed actions.
See id.
§ 1502.16(a)-(b). Conclusory statements that the indirect and cumulative effects will be minimal or that such effects are inevitable are insufficient under NEPA.
See Ctr. for Biological Diversity v. U.S. Dep’t of Interiоr,
III.
In this case, there is no dispute that the Monroe Connector constitutes a “major Federal action” under NEPA, which requires an environmental impact statement. The Conservation Groups argue that the Agencies failed to assess alternatives or measure the indirect and cumulative effects of the Monroe Connector because of a fundamental inaccuracy in the “no build” baseline. Specifically, the Conservation Groups maintain that, in calculating the “no-build” baseline, thе Agencies relied on data that assumed that the Monroe Connector existed. By doing so, the Agencies assertedly conflated the “no build” and “build” scenarios, making it impossible to accurately isolate and assess the environmental impacts of the Monroe Connector. Moreover, the Conservation Groups claim that the Agencies compounded this error by refusing to acknowledge it to the public, and instead, maintaining throughout the administrative process that the “no build” data did not assume the existence of the Monroe Connector.
The Agencies concede much of the Conservation Groups’ argument. At the district court, the Agencies acknowledged that MUMPO’s data assumed the existence of the Monroe Connector.
See N.C. Wildlife Fed’n,
What the Agencies would have us ignore is that NEPA procedures emphasize clarity and transparency of process over particular substantive outcomes.
See Pub. Citizen,
The very purpose of public issuance of an environmental impact statement is to “provid[e] a springboard for public comment.”
Pub. Citizen,
This mischaracterization related to a critical aspect of the NEPA process — the accuracy of the “no build” baseline. NEPA requires that an agency’s alternatives analysis include a “no build” alternative. 40 C.F.R. § 1502.14(d). “Without [accurate baseline] data, an agency cannot carefully consider information about significant environment impacts ... resulting in an arbitrary and capricious decision.”
See N. Plains Res. Council, Inc. v. Surface Transp. Bd.,
*604
In an attempt to avoid this outcome, the Agencies contend that although they provided the Fish and Wildlife Service, the Conservation Groups, and the public incorrect information regarding the “no build” data, their subsequent admissions during this litigation cured these missteps. They cite no support for this proposition, and we have found none. To accept the Agencies’ argument would amount to acceptance of “post hoc ratiоnalizations for agency action,”
State Farm,
This we cannot do. For “[i]t is well-established that an agency’s action must be upheld, if at all, on the basis articulated by the agency itself.”
State Farm,
The Agencies now admit that the administrative record mischaracterizes the “no build” data. Such an acknowledgment made during litigation does not change the fact that the NEPA process itself relied on those mischaraсterizations. For example, the Record of Decision — the “final agency action,”
Natural Desert,
When relevant information “is not available during the [impact statement] process and is not available to the public for comment[,] ... the [impact statement] process cannot serve its larger informational role,
*605
and the public is deprived of [its] opportunity to play a role in the decision-making process.”
N. Plains,
In sum, although we need not and do not decide whether NEPA permits the Agencies to use MUMPO’s data in this case, we do hold that by doing so without disclosing the data’s underlying assumptions and by falsely responding to public concerns, the Agencies failed to take the required “ ‘hard look’ at environmental consequences.”
Shenandoah Valley,
IV.
For the reasons discussed above, we vacate the judgment of the district court and remand for further proceedings consistent with this opinion.
VACATED AND REMANDED
Notes
. The Agencies eliminated the hybrid category after determining that the necessary improvements "would have a significant adverse impact on businesses and the economy of Union County.” They eliminated the "improve U.S. 74” category after projecting that by 2035, daily traffic volume on an improved U.S. 74 would far exceed traffic volume on U.S. 74 and the Monroe Connector combined.
.
Laguna Greenbelt v. U.S. Department of Transportation,
. The Agencies have steadfastly opposed the Conservation Groups' attempts to supplement the administrative record with contemporaneous emails between agency officials, assertedly evidencing that the Agencies acted in bad faith. In doing so, the Agencies have repeatedly argued that the certified administrative record provides the complete basis for judicial review. See Appellees’ Br. at 55. Though we need not decide whether the district court abused its discretion in denying the Conservation Groups' motion to supplement the administrative record with these emails, we do note the incongruity of the Agencies' position: the Agencies contend that the Conservation Groups should not be permitted to add to the administrative record emails sent before the record closed, while at the same time urging us to give controlling weight to their litigation concessions, not made until well after the administrative record closed.
. The Agencies briefly raise two other arguments. First, they contend that through Baker they adequately rеsponded to concerns about the propriety of the “no build” data. But in response to queries from public and private groups as to the propriety of the "no build” data, Baker undertook two patently inadequate steps. One concluded that the Monroe Connector was not in the “no build” baseline, the other did not focus at all on the potential error.
Second, the Agencies maintain that the Conservation Groups "overstate” the importance of the error involved in including thе Monroe Connector in the "no build” baseline. The Agencies acknowledge that the error affected one of the factors in MUMPO’s model — travel time to employment. In general, areas with reduced travel time to employment tend to experience greater population growth and development, which can substantially impact the local environment. But by including the Monroe Connector in the "no build” baseline’s travel time to employment, the Agencies
assumed
that the new road
would not
decrease travel time to employment, and thus would not cause development with attendant environmental impacts. To minimize this mistake, the Agencies argue that the model incorporated other, untainted factors. In doing so, the Agencies ignore their own record evidence of the importance of travel time to employment. Not only did this factor receive disproportionate weight in the model, but the Agencies repeatedly noted that decreased travel time to employment often spurs development. Accordingly, the administrative record does not demonstrate the irrelevance of travel time to employment. To assume this fact would overstep our limited scope of review.
See Chenery,
. The Conservation Groups point to a number of other instances where the Agencies assertedly failed to comply with NEPA’s requirements. See, e.g., 40 C.F.R. § 1502.24. We need not address these contentions because on remand, when the Agencies reevaluate the Impact Statement, they will have an opportunity to provide full public'*disclosure and all necessary explanations of their process.
