Prairie Band Pottawatomie v. Federal Highway Administration , 684 F.3d 1002 ( 2012 )


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  •                                                                     FILED
    United States Court of Appeals
    Tenth Circuit
    July 10, 2012
    PUBLISH                 Elisabeth A. Shumaker
    Clerk of Court
    UNITED STATES COURT OF APPEALS
    TENTH CIRCUIT
    PRAIRIE BAND POTTAWATOMIE
    NATION, SIERRA CLUB,
    WETLANDS PRESERVATION
    ORGANIZATION, JAYHAWK
    AUDUBON SOCIETY, SAVE THE
    WAKARUSA WETLANDS, INC.,
    KANSAS UNIVERSITY ENVIRONS,
    and ECOJUSTICE,
    Plaintiffs - Appellants,
    v.                                             No. 11-3000
    FEDERAL HIGHWAY
    ADMINISTRATION, J. MICHAEL
    BOWER, in his official capacity as
    Division Administrator, Federal
    Highway Administration; KANSAS
    DEPARTMENT OF
    TRANSPORTATION,
    Defendants - Appellees.
    APPEAL FROM THE UNITED STATES DISTRICT COURT
    FOR THE DISTRICT OF KANSAS
    (D.C. NO.08-CV-02534-KHV-DJW)
    David Prager III (Robert V. Eye with him on the briefs) Kauffman & Eye,
    Topeka, Kansas, for Appellants.
    Eldon Shields, Gates, Shields & Ferguson, P.A., Overland Park, Kansas, for
    Appellee Kansas Department of Transportation.
    Ellen J. Durkee, Environmental & Natural Resources Division (Ignacia S.
    Moreno, Assistant Attorney General, and Maureen Rudolph, Attorney,
    Environmental & Natural Resources Division, and Barry R. Grisson, United
    States Attorney, and Jackie A. Rapstine, Assistant United States Attorney, District
    of Kansas) United States Department of Justice, Washington, DC, for Appellees J.
    Michael Bower and Federal Highway Administration.
    Before LUCERO, SEYMOUR, and TYMKOVICH, Circuit Judges.
    TYMKOVICH, Circuit Judge.
    The Plaintiffs-Appellants challenge the Federal Highway Administration’s
    selection of a route for the South Lawrence Trafficway, a proposed highway
    project in the city of Lawrence, Kansas. Appellants claim two aspects of the
    Highway Administration’s decision render it arbitrary and capricious under the
    Administrative Procedure Act. First, Appellants claim the environmental impact
    statement supporting the decision runs afoul of the National Environmental Policy
    Act and Department of Transportation noise analysis regulations. Second,
    Appellants claim the Highway Administration’s analysis under the section of the
    Department of Transportation Act that protects historic sites, including property
    associated with Haskell Indian Nations University, improperly concluded there
    was no “feasible and prudent alternative” to the selected route.
    Finding no fatal flaws in the environmental impact statement or the
    prudence analysis, we AFFIRM the judgment of the district court.
    -2-
    I. Background
    For over two decades, the citizens of Lawrence, Kansas and other interested
    parties have debated the merits of the South Lawrence Trafficway (SLT), a
    highway project designed to link state highway K-10 and Interstate 70 around the
    southern periphery of Lawrence. The SLT would allow traffic to bypass surface
    streets running through busy south Lawrence, thereby relieving traffic congestion
    and improving motorist safety. A western segment of the SLT was built many
    years ago, but the remaining portion has been stalled.
    The Appellants are a diverse collection of interested entities including the
    Prairie Band Pottawatomie Nation, the Sierra Club, the Wetlands Preservation
    Organization, the Jayhawk Audubon Society, Save the Wakarusa Wetlands, Inc.,
    the Kansas University Environs, and Ecojustice. They seek to prevent injury to
    environmental, cultural, and historical values that may be affected by the SLT.
    The Defendants-Appellees include the Federal Highway Administration
    (FHWA), the Kansas Department of Transportation (KDOT), and the official
    heads of those agencies. Another government entity, the United States Army
    Corps of Engineers, was involved in several aspects of the approval but was not a
    named defendant. Because the specific identities of these government bodies are
    not significant for the purposes of the legal challenges brought here, we will refer
    to them collectively as “the government.”
    -3-
    The route of the SLT is near several historical and environmental features.
    The Wakarusa River floodplain lies directly south of Lawrence. One potential
    route for the highway skirts the northern edge of the floodplain. This route would
    pass directly through the Haskell Agricultural Farm Property, a historic site
    eligible for listing on the National Register of Historic Places. The Haskell Farm
    was historically used for agricultural-education purposes by the Haskell Indian
    Nations University. The northern portion of the Haskell Farm, called the Upper
    Fields, contains several historic and cultural features, while the southern portion,
    called the Baker Wetlands, is an environmentally-sensitive area within the
    floodplain supporting various plant and animal life. The Upper Fields and Baker
    Wetlands are currently separated by a surface street, 31st Street.
    A less direct route for the SLT along the southern edge of the Wakarusa
    floodplain, further away from Lawrence, would avoid directly affecting the
    Haskell Farm. It would, however, cost more to build due to increased length and
    the need to bridge the floodplain and river. It would also require motorists to
    drive a more circuitous route.
    In selecting a route for the SLT, the government engaged in a multi-step
    evaluation process. Starting with an initial list of 27 identified options, the
    government selected 12 for detailed analysis. The government considered several
    factors, including encroachment on wetlands, increased noise on the Haskell
    -4-
    Farm, cost, and the extent to which each alternative achieved the project’s goals
    of traffic congestion relief and increased safety.
    After additional analysis, the government selected two finalists—the 32nd
    Street Alignment B Alternative (32B), and the 42nd Street Alignment A
    Alternative (42A)—plus a required “no action” alternative as a point of
    comparison. Alternative 32B took a direct route through the Haskell Farm, but
    incorporated mitigation measures to lessen the impact on the Farm, which
    included sound barriers and the relocation of 31st Street and other nearby surface
    roads. Alternative 42A took a longer route south of the floodplain, avoiding the
    Farm.
    The government ultimately selected alternative 32B, and issued its
    preliminary decision in a draft environmental impact statement (EIS). After a
    public notice-and-comment period, the government issued a final EIS and record
    of decision formally adopting Alternative 32B. The government determined that
    42A was not a prudent alternative due to several factors that cumulatively
    amounted to a problem of extraordinary magnitude.
    After the government issued its final decision, Appellants proposed an
    additional alternative, which they dubbed “42C.” Alternative 42C resembled a
    route along the 42nd Street alignment that the government had eliminated at a
    relatively early stage in the evaluation process. Appellants presented their own
    analysis showing that 42C would achieve a significant cost benefit over 42A, and
    -5-
    urged the government to reconsider its decision. Despite having already issued a
    final EIS, the government considered and rejected 42C, explaining that sharp
    curves in the route rendered it unacceptable from a safety standpoint.
    Appellants then challenged the government’s decision in the court below,
    bringing claims under the Administrative Procedure Act (APA), the National
    Environmental Policy Act (NEPA), and section 4(f) of the Department of
    Transportation Act. The district court rejected all of Appellants’ claims, and
    Appellants appealed.
    II. Environmental Impact Statement Challenge
    Appellants first claim the government’s adoption of the EIS did not comply
    with NEPA, and therefore was arbitrary and capricious. Appellants identify four
    flaws in the EIS: (1) the noise analysis failed to adhere to United States
    Department of Transportation regulations; (2) the government should not have
    rejected Alternative 42C; (3) the cost analysis underestimated the costs for 32B;
    and (4) the safety analysis used incorrect safety criteria.
    Our review of the statutory and administrative claims is de novo:
    We review NEPA claims under the APA independently, giving no
    particular deference to the district court’s review of an agency
    action. As with other challenges arising under the APA, we review
    an agency’s NEPA compliance to see whether it is arbitrary,
    capricious, an abuse of discretion, or otherwise not in accordance
    with law. In the context of a NEPA challenge, an agency’s decision
    is arbitrary and capricious if the agency (1) entirely failed to consider
    an important aspect of the problem, (2) offered an explanation for its
    decision that runs counter to the evidence before the agency, or is so
    -6-
    implausible that it could not be ascribed to a difference in view or
    the product of agency expertise, (3) failed to base its decision on
    consideration of the relevant factors, or (4) made a clear error of
    judgment.
    Forest Guardians v. U.S. Fish & Wildlife Serv., 
    611 F.3d 692
    , 710–11 (10th Cir.
    2010).
    “Deficiencies in an EIS that are mere ‘flyspecks’ and do not defeat NEPA’s
    goals of informed decisionmaking and informed public comment will not lead to
    reversal.” New Mexico ex rel. Richardson v. BLM, 
    565 F.3d 683
    , 704 (10th Cir.
    2009). Furthermore, even if an agency violates the APA, its error does not
    require reversal unless a plaintiff demonstrates prejudice resulting from the error.
    APA § 706 (“[D]ue account shall be taken of the rule of prejudicial error.”); see
    New Mexico ex rel. Richardson, 
    565 F.3d at 708
    . Importantly, “[a] presumption
    of validity attaches to the agency action and the burden of proof rests with the
    appellants who challenge such action.” New Mexico ex rel. Richardson, 
    565 F.3d at 704
    .
    With this standard of review in mind, we turn to the four EIS deficiencies
    claimed by the Appellants.
    -7-
    A. Noise Analysis
    1. Legal Framework
    Federal law requires the Secretary of Transportation to “develop and
    promulgate standards for highway noise levels compatible with different land
    uses.” 
    23 U.S.C. § 109
    (i). This requirement is implemented by federal
    regulations establishing a three-stage noise analysis process that FHWA must
    follow for new highway projects. See 
    23 C.F.R. § 772
    .
    First, FHWA must determine whether a proposed project will result in
    “traffic noise impacts.” § 772.11(a). “Traffic noise impacts” are defined as noise
    levels that approach or exceed a defined limit listed in the regulations, or that
    create a substantial noise increase over existing noise levels. See § 772.5; tbl. 1.
    The defined limit varies depending on the land use; for example, hotels and
    offices have higher limits than residential areas. See id. To determine whether
    traffic noise impacts will occur requires FHWA to determine existing noise
    levels, predict future noise levels for each alternative under consideration, and
    compare the existing and predicted noise levels. 1 See § 772.11.
    Second, if FHWA determines that a project will create traffic noise
    impacts, “noise abatement shall be considered and evaluated for feasibility and
    1
    Specifically, the regulations state: “The highway agency shall determine
    and analyze expected traffic noise impacts. . . . For projects on existing
    alignments, predict existing and design year traffic noise impacts.” § 772.11(a).
    “The analysis of traffic noise impacts shall . . . validate predicted noise level [sic]
    through comparison between measured and predicted levels.” § 772.11(d).
    -8-
    reasonableness.” § 772.13(a). Before adopting a record of decision, FHWA must
    identify and document “(1) Noise abatement measures which are feasible and
    reasonable, and which are likely to be incorporated in the project; and (2) Noise
    impacts for which no noise abatement measures are feasible and reasonable.”
    § 772.13(g).
    Third, FHWA may not “approve project plans and specifications unless
    feasible and reasonable noise abatement measures are incorporated into the plans
    and specifications.” § 772.13(h). The final approval of plans and specifications
    is a separate decision from the adoption of a record of decision and, in this case,
    has not yet occurred.
    2. Relevant Facts
    The EIS includes the results of a noise impact analysis conducted by a
    government contractor. The contractor first measured existing noise levels at
    various points on the Haskell Farm and surrounding areas. The contractor then
    used computer modeling to forecast what noise levels would be in the year 2025
    for each alternative with and without mitigating sound barriers, using 2025
    vehicle traffic projections provided by KDOT. The results showed that
    Alternative 32B had a very significant impact on noise levels on the Haskell Farm
    without mitigation measures. But when sound barriers were included in the
    modeling, 32B had less noise impact than the “no action” and 42A alternatives,
    because those alternatives involved increased traffic on existing surface streets.
    -9-
    The parties dispute whether the EIS adequately compared future noise
    levels to existing levels. Appellants point to a sentence in the government’s
    Traffic Noise Analysis Summary that suggests a comparison was not made, and a
    direct comparison of existing and predicted noise levels does not appear in the
    body of that document, in the EIS, or in the 4(f) analysis. The government,
    however, points to some data tables in the record that it claims include the
    relevant comparison. The record is somewhat unclear as to whether these data
    constitute a full or only partial comparison of existing and predicted noise levels,
    and whether the government actually “validate[d] predicted noise level [sic]
    through comparison between measured and predicted levels” as required.
    § 772.11(d).
    3. Discussion
    Even assuming the government’s analysis did not adequately compare
    existing and predicted noise levels, any error was harmless. The effect of the first
    stage of a § 772 analysis is only to determine whether there will be noise impacts.
    If there will be noise impacts, then the government is required to proceed to stage
    two and consider noise abatement measures. Here, the government in fact found
    there would be noise impacts, and continued to stage two. At stage two, the
    government conducted the correct analysis; that is, it identified “[n]oise
    abatement measures which are feasible and reasonable, and which are likely to be
    incorporated in the project.” § 772.13(g). Because any error at stage one did not
    -10-
    actually prevent the government from proceeding to stage two, and because the
    analysis at stage two was conducted correctly, we see no possible harm.
    The Appellants argue unpersuasively that we should not engage in a
    harmlessness analysis where the claim of error is procedural. Appellants are
    correct that, in some instances, a harmlessness analysis can be inappropriate. For
    example, when an agency fails “substantively to consider the environmental
    ramifications of its actions in accordance with NEPA,” Catron County Bd. of
    Comm’rs v. U.S. Fish & Wildlife Serv., 
    75 F.3d 1429
    , 1433 (10th Cir. 1996), we
    will not uphold the agency’s decision on the grounds that it might have made the
    same decision even without the error; otherwise, NEPA would be a near-toothless
    environmental safeguard.
    Here, however, we know for a certainty that additional noise analysis could
    not have altered the outcome because, despite the potential flaw, the government
    determined there would be noise impacts and correctly proceeded to identify
    likely noise abatement measures. That is all the government was required to do at
    that point in the decisionmaking process, as it had not yet approved the project’s
    final “plans and specifications” at the third stage of the § 772 analysis. Thus, the
    Appellants cannot “show they were prejudiced” as required by APA § 706. Bar
    MK Ranches v. Yuetter, 
    994 F.2d 735
    , 740 (10th Cir. 1993).
    Appellants also argue the error was material because the noise analysis was
    used not only for purposes of the § 772 analysis, but also played a role in
    -11-
    selecting 32B over the other alternatives. But, in weighing the relative merits of
    each alternative, the government did compare the predicted noise levels against
    each other. The error Appellants identify—failure to compare predicted noise
    levels to existing noise levels—would not have affected this relative comparison
    of the alternatives. Thus, any error was harmless.
    Separately, Appellants claim the noise analysis was deficient in its
    geographic scope. Appellants briefly make this argument in very general terms in
    their opening brief, but only develop it in detail in their reply brief. Even there,
    Appellants cite no specific legal authority for the proposition that the government
    was required to consider a larger geographic area than it actually did.
    “Setting the boundaries of the region to be analyzed involved technical and
    scientific judgments within the [government’s] area of expertise.” San Juan
    Citizens Alliance v. Stiles, 
    654 F.3d 1038
    , 1057 (10th Cir. 2011). The applicable
    regulations, quite apart from requiring a noise analysis along the entire length of
    the proposed project, specifically state that “a highway agency shall give primary
    consideration to exterior areas where frequent human use occurs.” 
    23 C.F.R. § 772.11
    . Additionally, the regulations specifically exempt “developed lands that
    are not sensitive to highway traffic noise,” § 772.11(c)(vi), and “undeveloped
    lands,” § 772.11(c)(vii), from noise impact analyses under most circumstances.
    Here, the noise analysis focused on the sensitive areas in and around the
    Haskell Farm. As the government points out, most of the remaining land along
    -12-
    routes 32B and 42A is undeveloped. Appellants allege for the first time in their
    reply brief that the government “failed to consider 32B’s noise impacts on the
    nearby noise-sensitive Prairie Park and Nature Center and city homes east of the
    Haskell Farm.” Aplt. Reply Br. at 8. Appellants, however, have not laid a
    sufficient factual basis on the record for us to conclude that the government’s
    decision to restrict the noise analysis to the Haskell Farm was arbitrary and
    capricious. To the contrary, as far as the record shows, that decision, made
    pursuant to public comment on the project, was entirely reasonable. To find
    otherwise would be to engage in “flyspeck[ing]” the noise analysis based on
    factual allegations outside the record. New Mexico ex rel. Richardson, 
    565 F.3d at 704
    . This we may not do.
    Accordingly, we find the government’s noise analysis did not violate the
    APA.
    B. Alternative 42C
    Next, Appellants claim the government erred by eliminating alternative 42C
    from consideration during the evaluation process and failing to reconsider this
    alternative at the Appellants’ request.
    1. Legal Standards
    Before commencing in-depth analyses of EIS alternatives, agencies engage
    in scoping—“an early and open process for determining the scope of issues to be
    addressed and for identifying the significant issues related to a proposed action.”
    -13-
    
    40 C.F.R. § 1501.7
    . An agency need not “analyze the environmental
    consequences of alternatives it has in good faith rejected as too remote,
    speculative, or . . . impractical or ineffective.” Colo. Envtl. Coal. v. Dombeck,
    
    185 F.3d 1162
    , 1174 (10th Cir. 1999) (quoting All Indian Pueblo Council v.
    United States, 
    975 F.2d 1437
    , 1444 (10th Cir. 1992)).
    In reviewing an agency’s choice of which alternatives to eliminate at the
    scoping stage, we apply “[t]he rule of reason.” Custer County Action Ass’n v.
    Garvey, 
    256 F.3d 1024
    , 1040 (10th Cir. 2001) (quoting Am. Rivers v. Fed. Energy
    Reg. Comm’n, 
    201 F.3d 1186
    , 1200 (9th Cir. 2000)). We also bear in mind that
    “an agency need not consider an alternative unless it is significantly
    distinguishable from the alternatives already considered.” New Mexico ex rel.
    Richardson, 
    565 F.3d at
    708–09.
    2. Relevant Facts
    At the earliest stage of project planning, the government developed five
    concept corridors for the SLT. One of these concept corridors was the 42nd
    Street corridor, which passed west of an S-curve in the Wakarusa River, at its
    narrowest point, and continued south of the floodplain.
    During the scoping process, the government developed 12 potential
    alignments along the five concept corridors for detailed review. Two of the 12
    remaining alignments were along the 42nd Street corridor: alternatives 42A and
    42B. Although these two alternatives mostly followed the path of the 42nd Street
    -14-
    concept corridor, they passed east of the S-curve in the Wakarusa River instead of
    west.
    The government admits that early in the scoping process it also considered
    an alternative along the 42nd Street alignment that would have passed west of the
    S-curve, but this alternative (along with several others) was eliminated due to
    safety concerns and thus was not included in the final 12. Later, the government
    narrowed the alternatives down to 32B and 42A, which were analyzed in further
    detail. Finally, the government selected 32B as its preferred alternative.
    The details about the concept corridors and the 12 alternatives were
    disclosed in the draft EIS that the government issued in September 2002.
    Appellants participated in the public comment process, but at that time did not
    propose an alternate route along the 42nd Street corridor.
    After the final EIS was released, the Appellants submitted a new alternative
    that they refer to as 42C. This alternative would cross the Wakarusa River west
    of the S-curve as envisioned by the original 42nd Street concept corridor.
    Appellants allege 42C would result in $17 million in savings relative to 42A
    because it would use multiple short bridges instead of a single long bridge to
    cross the floodplain.
    The government determined that the 42C alignment, as proposed by
    Appellants, encroached upon Lawrence park and public school properties, failed
    to provide a safe approach to bridges, and failed to properly align with the
    -15-
    proposed K-10 interchange. Nonetheless, the government developed a modified
    version of alternative 42C that remedied these problems.
    The government then considered and rejected the modified route. In a
    letter to Appellants, the government explained that 42C “would increase traffic
    accident risks due to increased curvature of the road” and due to ramping up and
    down between the multiple bridges. App. at 1014. In addition, the government
    determined that the cost savings from 42C would be only about $5 million, not
    the $17 million Appellants claimed. Thus, alternative 42C would still be
    significantly more expensive than alternative 32B.
    Appellants protested that the government’s modifications to alternative 42C
    were deliberately designed to sabotage the proposal. The government responded
    that it was “satisfied that the [modified] alignment . . . is reasonable and that it
    reflects appropriate roadway design.” App. at 976.
    3. Discussion
    The government did not act arbitrarily and capriciously in failing to include
    alternative 42C, or a similar route passing west of the S-curve, in the group of 12
    alternatives selected for detailed consideration. At the start of a highway project
    like the SLT, there are numerous possible routes. By necessity, an agency must
    select a certain number of routes for serious study and eliminate the rest without
    detailed analysis. Thus, absent a showing of bad faith, we review an agency’s
    -16-
    selection of alternatives only for reasonableness. See Custer County Action
    Ass’n, 
    256 F.3d at 1040
    .
    Here, the government did not act unreasonably or in bad faith in its
    selection of alternatives. The government selected alternatives 42A and 42B after
    conducting an “early and open” scoping process in conformity with NEPA-
    implementing regulations. 
    40 C.F.R. § 1501.7
    . Although alternatives 42A and
    42B differed somewhat from the 42nd Street concept corridor, the very notion of
    a “concept” implies that some changes will be made as plans progress.
    Alternatives 42A and 42B did not differ significantly from the concept corridor in
    terms of basic function; all three went south around the floodplain, avoiding the
    Haskell Farm but requiring a longer route. Although the concept corridor may
    have been marginally less expensive, it was also more dangerous due to the road
    curvature required. Most significantly for NEPA purposes, there is no evidence
    that the concept corridor would have been significantly different than 42A and
    42B in its environmental impact.
    To the extent Appellants argue the government erred in not giving
    sufficient consideration to their 42C proposal, we note that Appellants did not
    propose alternative 42C until after the government issued its final EIS.
    Appellants do not explain why they did not propose this route during the scoping
    process or during the public comment period for the draft EIS. Despite
    Appellants’ late proposal, the government considered their proposal and offered a
    -17-
    reasoned explanation of why it was inferior to the chosen alternative. Appellants
    argue that the government’s safety analysis for alternative 42C was inadequate,
    but given the timing of their proposal, the government arguably went above and
    beyond what was required.
    The government’s decision was not arbitrary and capricious. If Appellants
    intended a more robust review of alternative 42C’s safety, they could have
    proposed that route before the EIS was finalized.
    C. Alternative 32B Cost Analysis
    Appellants next argue that the government significantly underestimated
    construction costs for alternative 32B.
    This argument, based on a single footnote in the EIS, warrants only a brief
    discussion. The footnote in question relates to Table 2-18 of the EIS, which
    shows estimated construction, operation, and maintenance costs for the 32B, 42A,
    and no-action alternatives. One of the cost items listed is “mitigation.” For
    alternative 32B, mitigation costs are listed at $18.6 million, with a footnote call
    appended. The footnote reads: “Mitigation cost for [alternative 32B] includes
    relocation of 31st Street, Haskell Avenue and Louisiana Street, as well as noise
    walls and additional landscaping.” App. at 551 n.11. Appellants interpret this
    footnote to mean that the $18.6 million figure only includes the costs listed in the
    footnote, erroneously excluding an additional $10 million in wetlands mitigation
    costs.
    -18-
    Although Appellants’ interpretation is perhaps plausible when the footnote
    is read in isolation, it is obviously incorrect when read in conjunction with other
    sections of the EIS. Specifically, the portion of the EIS entitled Environmental
    Consequences has a subsection specifically addressing wetland mitigation for the
    32nd Street corridor. There, a table totaling the costs for 32B includes wetland
    mitigation measures as well as other measures and lists the total cost as $18.6
    million. See App. at 665.
    Thus, we are unconvinced that the government erroneously omitted
    wetlands mitigation costs from its consideration of alternative 32B. 2
    D. Safety Criteria
    Finally, Appellants complain briefly that the EIS used the wrong vehicle
    accident rate metric to calculate the relative safety of each alternative. The EIS’s
    purpose and need statement used accidents per million vehicle miles driven, but
    the EIS’s safety analysis used accidents per year. The substantive difference
    between the two metrics is that accidents per million vehicle miles driven cancels
    out accident increases created solely by increased highway length, while accidents
    per year does not. Appellants claim the use of the latter metric in the safety
    analysis was erroneous given that the former metric was used to define the
    project’s purpose and need.
    2
    Although we find the government did not omit these costs from its NEPA
    analysis, the government admits that it did erroneously omit some costs from its
    section 4(f) analysis. We address this issue separately below.
    -19-
    We find the EIS’s use of accidents per year instead of accidents per million
    vehicle miles was not arbitrary and capricious. We “are not in a position to
    decide the propriety of competing methodologies in the transportation analysis
    context, but instead, should determine simply whether the challenged method had
    a rational basis and took into consideration the relevant factors.” Comm. to Pres.
    Boomer Lake Park v. Dep’t of Transp., 
    4 F.3d 1543
    , 1553 (10th Cir. 1993).
    Appellants do not explain why accidents per year lacks a rational basis for NEPA
    purposes. To us, the total number of accidents that will be caused (or avoided)
    each year appears a reasonable safety metric, and Appellants do not attempt to
    convince us otherwise.
    We note that there is no inherent inconsistency in using accidents per year
    to evaluate safety, while also using accidents per million vehicle miles as a
    minimum standard under the purpose and need of the project. The two analyses
    actually served somewhat different purposes; the safety analysis accounted for
    accidents avoided due to decreased use of more-dangerous surface streets in
    Lawrence, while the purpose and need standard considered only the safety of the
    highway itself, which had to meet or exceed the state average for highways in
    Kansas. Significantly, Appellants do not claim that alternative 32B would
    actually fail to meet the purpose and need statement’s minimum standard.
    Thus, we reject Appellants’ claim that the government failed to rigorously
    and objectively evaluate road safety.
    -20-
    *    *     *
    In sum, the Appellants have failed to demonstrate that the EIS rendered the
    government’s selection of Alternative 32B arbitrary and capricious.
    III. Section 4(f) Challenge
    Section 4(f) of the Department of Transportation Act prevents highway
    construction on or near historic properties unless the government determines that
    there is no feasible and prudent alternative. Appellants claim the government’s
    determination that alternative 42A was not a prudent alternative was arbitrary and
    capricious.
    A. Legal Framework
    We review an agency’s section 4(f) analysis de novo under the APA.
    Courts hearing a section 4(f) challenge generally engage in a three-step inquiry:
    First, the reviewing court is required to decide whether the Secretary
    acted within the scope of his authority under § 4(f). In this initial
    inquiry, we must be able to find that the Secretary could have
    reasonably believed that in this case there are no feasible alternatives
    or that alternatives do involve unique problems.
    * * *
    Second, the court must decide whether the Secretary’s ultimate
    decision was arbitrary, capricious, an abuse of discretion or
    otherwise not in accordance with law. This inquiry involves
    determining whether the [Secretary’s] decision was based on a
    consideration of the relevant factors and whether there has been a
    clear error of judgment.
    * * *
    Finally, the Supreme Court instructs reviewing courts to determine
    whether the Secretary’s action followed the necessary procedural
    requirements.
    -21-
    Boomer Lake Park, 
    4 F.3d at 1549
     (quoting Citizens to Pres. Overton Park, Inc.
    v. Volpe, 
    401 U.S. 402
     (1971)).
    Here, however, Appellants do not attack the government’s 4(f) analysis
    along all three fronts. Instead, Appellants argue that the government’s evaluation
    of several factors under section 4(f), and its ultimate conclusion that those factors
    in combination rendered alternative 42A imprudent, were arbitrary. 3
    Section 4(f) of the Department of Transportation Act enacts “the policy of
    the United States Government that special effort should be made to preserve the
    natural beauty of the countryside and public park and recreation lands, wildlife
    and waterfowl refuges, and historic sites.” 
    49 U.S.C. § 303
    (a). In furtherance of
    this policy, section 4(f) allows the Secretary of Transportation to approve a
    transportation project that requires the “use” of historic sites “only if . . . there is
    no prudent and feasible alternative to using that land; and . . . the program or
    project includes all possible planning to minimize harm to the . . . historic site
    resulting from the use.” § 303(c).
    Section 4(f)’s implementing regulations translate this broad directive into
    specific agency guidance. The regulations define the term “use” to include both
    3
    Appellants do not argue that the government considered the wrong
    factors in reaching its decision (with the exception of one factor, the “net benefit”
    32B provides to the Haskell Farm). Thus, we will assume any factors the
    government considered that are not explicitly listed in the relevant regulations are
    nonetheless appropriate under the catch-all category of “other unique problems or
    unusual factors.” 
    23 C.F.R. § 774.17
    .
    -22-
    physical disturbance and “constructive use.” 
    23 C.F.R. § 774.17
    . A constructive
    use can encompass significant noise level increases. See § 774.15(e)(1). Here,
    the parties agree that alternative 32B would result in a direct “use” of the Haskell
    Farm, while alternative 42A would not.
    The regulations describe a “prudent avoidance alternative” as one that
    “avoids using Section 4(f) property and does not cause other severe problems of a
    magnitude that substantially outweighs the importance of protecting the Section
    4(f) property.” § 774.17. The regulations also specify:
    (3) An alternative is not prudent if:
    (i) It compromises the project to a degree that it is
    unreasonable to proceed with the project in light of its stated
    purpose and need;
    (ii) It results in unacceptable safety or operational problems;
    (iii) After reasonable mitigation, it still causes:
    (A) Severe social, economic, or environmental impacts;
    (B) Severe disruption to established communities;
    (C) Severe disproportionate impacts to minority or low
    income populations; or
    (D) Severe impacts to environmental resources protected
    under other Federal statutes;
    (iv) It results in additional construction, maintenance, or
    operational costs of an extraordinary magnitude;
    (v) It causes other unique problems or unusual factors; or
    -23-
    (vi) It involves multiple factors in paragraphs (3)(i) through
    (3)(v) of this definition, that while individually minor,
    cumulatively cause unique problems or impacts of
    extraordinary magnitude.
    Id. (emphasis added). Here, the government relied on the cumulative impact of
    several different factors in finding that alternative 42A was imprudent.
    The first major case examining section 4(f) was the landmark Supreme
    Court case Citizens to Preserve Overton Park, Inc. v. Volpe, 
    401 U.S. 402
     (1971).
    While requiring a rigorous review of agency decisions, the Supreme Court
    recognized that such decisions are “entitled to a presumption of regularity,” 
    id. at 415
    , and that reviewing courts are “not empowered to substitute [their] judgment
    for that of the agency,” 
    id. at 417
    .
    More recently, our circuit and others following Overton Park have
    emphasized the discretion agencies exercise in conducting 4(f) analyses,
    particularly in determining the prudence of alternatives. Our leading case is
    Committee to Preserve Boomer Lake Park v. Department of Transportation, 
    4 F.3d 1543
     (10th Cir. 1993), in which we evaluated the application of the 4(f)
    factors to a highway proposal through a state park. In that case, the city of
    Stillwater, Oklahoma desired to build a new road to replace a one-lane bridge
    across Boomer Lake that previously had been demolished for safety reasons. See
    
    id. at 1547
    . The city’s preferred alternative was a four-lane causeway passing in
    a straight line over a southern portion of the lake. The avoidance alternative was
    -24-
    a four-lane surface road routed around the southern end of the lake, avoiding the
    use of parkland. See 
    id. at 1548
    . FHWA found the avoidance alternative was
    imprudent based on the cumulative effect of several problems, including
    construction costs, user costs, increased traffic congestion, unsafe curves, a
    longer route, disruption to existing intersections, and increased residential and
    commercial relocations. See 
    id. at 1550
    . FHWA also rejected the “no-action”
    alternative, finding it failed to meet the purpose and need of the project. As a
    result, FHWA approved the city’s preferred alternative.
    In affirming FHWA’s 4(f) analysis, we recognized, “the Secretary acted
    within the scope of his authority and could reasonably have believed the
    alternatives involved unique problems which rendered them imprudent.” 
    Id.
    Importantly, we recognized the legitimacy of imprudence determinations based on
    multiple factors. We found that “[a]lthough none of the[] factors alone is clearly
    sufficient justification to reject the alternatives in this case, their cumulative
    weight is sufficient to support the Secretary’s decision.” Id.; see also Concerned
    Citizens Alliance, Inc. v. Slater, 
    176 F.3d 686
    , 703 (3d Cir. 1999) (“[A]n
    accumulation of smaller problems that, standing alone, would not individually
    constitute unique problems may together comprise sufficient reason for rejecting
    an alternative as imprudent.”).
    We also rejected the appellant’s argument that the Secretary erred in failing
    to evaluate a two-lane causeway alternative, noting that “the Secretary’s
    -25-
    obligation under § 4(f) is to examine enough alternatives ‘to permit a sound
    judgment that the study of additional [alternative routes] is not worthwhile,’”
    Boomer Lake Park, 
    4 F.3d at 1551
     (alteration in original) (quoting Eagle Found.,
    Inc. v. Dole, 
    813 F.2d 798
    , 807 (7th Cir. 1987)), and that the Secretary’s
    “decision concerning which alternatives to consider is necessarily bound by a rule
    of reason and practicality,” 
    id.
     See also Safeguarding the Historic Hanscom
    Area’s Irreplaceable Resources, Inc. v. F.A.A., 
    651 F.3d 202
    , 210–11 (1st Cir.
    2011) (“This was a judgment call—and one that fell within the purview of the
    [agency’s] expertise.”). We recognized that “[w]e are instructed to conduct a
    careful and searching inquiry into the facts, but once we are satisfied the
    Secretary took a ‘hard look’ at the relevant factors, we are not to substitute our
    judgment for that of the agency.” Boomer Lake Park, 
    4 F.3d at 1551
    .
    B. Discussion
    The government found alternative 42A was imprudent based on the
    cumulative impact of the following seven factors: (1) 42A does not meet the
    purpose and need for the project as well as 32B; (2) 42A costs significantly more
    than 32B; (3) 42A has greater environmental and development-related impacts on
    the Wakarusa floodplain; (4) 42A would accelerate urban development south of
    the Wakarusa River; (5) 42A would have a greater overall impact on the Haskell
    Farm than 32B, due to the indirect impact of increased traffic near the Farm; (6)
    42A has other negative environmental impacts; and (7) 32B, unlike 42A, results
    -26-
    in a “net benefit” to the Haskell Farm, due to the rerouting of a road that currently
    runs through the Farm and the installation of sound barriers.
    Appellants argue the government’s analysis of each of these factors was
    arbitrary. Appellants also argue that the seventh factor—the “net benefit” to the
    Haskell Farm—was an impermissible factor for the government to consider under
    section 4(f).
    1. Purpose and Need of the Project
    The government determined that alternative 42A would not meet the
    project’s purpose and need as well as alternative 32B for two reasons. First, it
    would divert less traffic from Lawrence city streets due to its more circuitous
    route, and, second, it would result in more car accidents. Appellants dispute the
    government’s conclusion, citing their own calculation, based on data in the EIS,
    that 42A would relieve more total traffic than 32B. The government, however,
    explains that the relevant congestion relief measure is not total traffic reduction in
    Lawrence, but rather relief of east-west congestion along 23rd Street. On this
    measure, 32B better relieves congestion.
    The government’s conclusion in this regard is reasonable and is entitled to
    deference. “Courts are not in a position to decide the propriety of competing
    methodologies in the transportation analysis context, but instead, should
    determine simply whether the challenged method had a rational basis and took
    into consideration the relevant factors.” Boomer Lake Park, 
    4 F.3d at 1553
    . The
    -27-
    government’s method here did so. The record shows that east-west traffic
    through Lawrence is the primary congestion problem the SLT is meant to remedy,
    and that 23rd Street is currently the primary east-west route. Thus, it was
    reasonable for the government to use 23rd Street traffic levels to determine that
    32B would meet the project’s traffic-reduction goals better than 42A.
    The government’s conclusion that 42A would be more dangerous than 32B
    appears somewhat simplistic, but not fatally so. In calculating the accident levels
    for 32B and 42A, the government assumed an accident rate along both routes that
    conformed to the state average for four-lane highways. Thus, the higher number
    of total accidents projected for 42A is solely a result of its longer length relative
    to 32B. The government, however, argues that an increase in accidents caused
    solely by increased length is a legitimate factor to consider.
    While we might quarrel with the methodology, we recognize that section
    4(f) does not require every factor to be calculated with absolute precision. For
    example, in Boomer Lake Park, we approved FHWA’s use of an “unsubstantiated
    dollar figure” for road-user costs because it was based on reasonable assumptions.
    See Boomer Lake Park, 
    4 F.3d at 1553
    . Despite the fact that “we f[ou]nd no
    substantiation” for the specific dollar figure calculated—a user cost increase of
    $730,000 over the preferred alternative—we approved of the more general
    conclusion that the costs of the avoidance alternative “would be higher due to
    increases in the distance and time travelled, more curves and interchanges, and a
    -28-
    higher accident rate.” 
    Id.
     Although this analysis was “not a model of clarity,” we
    found it “sufficiently adequate” in the context of an imprudence finding based on
    several cumulative factors. 
    Id.
    Similar to the user-cost analysis in Boomer Lake Park, the safety analysis
    here is based on the common-sense assumption that increases in time and distance
    traveled lead to more accidents. While the analysis here differs in that it did not
    incorporate additional common-sense factors such as curves, it has the significant
    compensating advantage that the accident increase is not “unsubstantiated,” but
    rather is grounded in specific calculations based on road length and state highway
    statistics. And while Appellants criticize the government’s analysis, they do not
    show that the calculations used were irrational or irrelevant; nor do they identify
    any significant differences between 32B and 42A, apart from length, that the
    government reasonably should have considered in its safety analysis.
    Accordingly, on the current record, we will not disturb the government’s
    conclusion that 32B would fulfil the project’s safety-related goals better than
    42A.
    2. Cost
    The government calculated that 42A would cost approximately $19 million
    more than 32B. Cost is a proper consideration under section 4(f). See 
    42 C.F.R. § 774.17
    . Appellants allege, and the government admits, that the cost
    calculations for 32B erroneously omitted approximately $8.5 million in wetlands
    -29-
    mitigation costs. The government, however, claims that this error was offset by
    another error which double-counted $8 million in bridge costs for 32B, thereby
    creating a net error of only about $500,000.
    When “an agency relies on a number of findings, one or more of which are
    erroneous, we must reverse and remand only when there is a significant chance
    that but for the errors the agency might have reached a different result.” Nat’l
    Parks & Conservation Ass’n v. F.A.A., 
    998 F.2d 1523
    , 1533 (10th Cir. 1993).
    Here, the errors resulted in a $500,000 understatement of 32B’s costs. While a
    half million dollars is not a de minimis amount, it is highly unlikely that this
    amount would have changed the government’s decision in light of the $19
    million gap between 42A and 32B. Accordingly, we need not reject the cost
    analysis, despite its offsetting errors.
    Appellants also argue the government erroneously eliminated 42C in its
    consideration of costs. As discussed earlier, however, the government did not err
    in rejecting 42C, and it was not an alternative the government was required to
    consider under section 4(f). Even if 42C had been considered as part of the 4(f)
    analysis, it still would have been approximately $14 million more expensive than
    32B.
    3. Floodplain Impacts
    Executive Order 11988 and its implementing regulations discourage
    highway construction and other development upon floodplains. The government
    -30-
    determined that 42A would have a greater impact upon the Wakarusa floodplain
    than would 32B. Appellants, however, claim that the government did not explain
    how 42A would actually impact the floodplain.
    The purpose of Executive Order 11988 is “to avoid to the extent possible
    the long and short term adverse impacts associated with occupancy and
    modification of floodplains and to avoid direct or indirect support of floodplain
    development wherever there is a practicable alternative.” Exec. Order No. 11988,
    
    42 Fed. Reg. 26951
     (May 24, 1977). The regulations implementing E.O. 11988
    state that “[i]t is the policy of the FHWA . . . to avoid support of incompatible
    flood-plain development.” 
    23 C.F.R. § 650.103
    . The regulations distinguish
    between an “encroachment,” which includes any “action within the limits of the
    base flood plain,” and “significant encroachment,” which is defined as:
    a highway encroachment and any direct support of likely base flood-
    plain development that would involve one or more of the following
    construction-or-flood-related impacts:
    (1) A significant potential for interruption or termination of a
    transportation facility which is needed for emergency vehicles or
    provides a community’s only evacuation route. [sic]
    (2) A significant risk, or
    (3) A significant adverse impact on natural and beneficial flood-plain
    values.
    
    23 C.F.R. § 650.105
    (q). Significant encroachments may not be approved unless
    the government finds there is no “practicable alternative.” § 650.113(a). This
    -31-
    finding must be included in the EIS and state (1) “the reasons why the proposed
    action must be located in the flood plain,” (2) “the alternatives considered and
    why they were not practicable,” and (3) “a statement indicating whether the
    action conforms to applicable State or local flood-plain protection standards.” Id.
    Here, the government analyzed two potentially significant encroachments:
    support of incompatible floodplain development, and adverse impacts on natural
    and beneficial floodplain values. The government determined that both 32B and
    42A “have some potential to stimulate floodplain development.” App. at 660.
    The government found that the 42nd Street alignment had a higher potential to
    stimulate development than 32B. The record shows that the land north of the
    floodplain is urban, while the area to the south is rural and agricultural. 42A has
    the potential to stimulate residential and commercial construction south of the
    floodplain, thereby surrounding the floodplain with urban development, which
    could degrade its natural quality. This prediction is based on Lawrence city
    planning documents and on observed development that occurred after the
    construction of the western portion of the SLT. These findings appear to be
    reasonable, and Appellants do not offer evidence to the contrary.
    The government’s finding regarding “natural and beneficial floodplain
    values,” while somewhat conclusory, appears to be reasonable. The government
    found 42A would degrade those values more than 32B because it would pass
    directly over the floodplain rather than skirting its northern edge. Appellants
    -32-
    protest that this fact is not material because 42A will feature bridges that lift the
    road above the floodplain. But the category of “natural and beneficial floodplain
    values” does not include risks directly related to flood levels; rather, it
    encompasses “fish, wildlife, plants, open space, natural beauty, scientific study,
    outdoor recreation, agriculture, aquaculture, forestry, natural moderation of
    floods, water quality maintenance, and groundwater recharge.” 
    23 C.F.R. § 650.105
    (i). The government reasonably determined that the presence of
    significant bridging directly across the floodplain, as well as the presence of
    significant activity during construction, had the potential to compromise these
    values.
    Overall, the government’s floodplain analysis—bolstered, in particular, by
    its analysis of future urban development—does reasonably show that 42A would
    have a greater negative floodplain impact than 32B. Accordingly, the floodplain
    analysis supports the government’s determination that 42A would be imprudent. 4
    4
    Appellants make much of the fact that alternative 32B would destroy 58
    acres of wetlands, while 42A would only destroy 4.45 acres, making 42A the
    better choice as far as natural and beneficial floodplain values are concerned. As
    the government points out, however, the mitigation plan for 32B includes the net
    creation of 259 acres of wetlands, while 42A would result in only a net increase
    of 76 acres. In this context, it was reasonable for the government to consider the
    net creation of wetlands in its overall evaluation of floodplain values. And, in
    any event, the balancing of competing floodplain values pursuant to E.O. 11988 is
    clearly a task warranting a significant degree of deference to the expertise of the
    agency involved. Cf. Greater Yellowstone Coal. v. Flowers, 
    359 F.3d 1257
    , 1271
    (10th Cir. 2004).
    -33-
    4. Accelerated Development South of the Wakarusa River
    The government found that 42A, due to its southerly route, would hasten
    undesirable urban development south of the Wakarusa River. This conclusion
    relies on essentially the same reasoning as the just-discussed finding regarding
    undesirable development in the floodplain area, but is broader in scope since it
    includes non-floodplain areas as well. This conclusion is also based on the
    government’s finding that accelerated development south of the river would stress
    city and county infrastructure and financial resources.
    Appellants argue that the “effects of 42A on planned development are not
    an extraordinary problem but merely a normal one.” Aplt. Br. at 47. That is true
    so far as it goes, but misses the point. The government never claimed problems
    related to accelerated development were of an extraordinary magnitude; rather, it
    claimed accelerated development as one of the “individually minor” factors that
    “cumulatively cause unique problems or impacts of extraordinary magnitude.” 
    23 C.F.R. § 774.17
    ; see Boomer Lake Park, 
    4 F.3d at 1550
     (“A cumulation of small
    problems may add up to a sufficient reason to use § 4(f) lands.” (quoting Hickory
    Neighborhood Def. League v. Skinner, 
    910 F.2d 159
    , 163 (4th Cir. 1990)). Again,
    Appellants do not argue that accelerated urban development, in general, is an
    impermissible factor for the government to consider in its 4(f) analysis.
    Appellants direct us to a 2006 letter from the Lawrence-Douglas County
    Metropolitan Planning Organization, claiming the letter undermines the
    -34-
    government’s conclusion that 42A would accelerate development south of the
    river. But that letter makes no mention whatsoever of accelerated development
    south of the river, and in fact makes no mention of 42A at all. Rather, that letter
    advocates an entirely different solution to traffic congestion in Lawrence that
    involves linking K-10 and I-70 east of the city. As the letter has nothing to say
    regarding the problem of accelerated development south of the river, it neither
    bolsters nor calls into question the government’s conclusions.
    Appellants point to no other evidence showing that the government’s
    conclusions regarding accelerated development were unreasonable. Accordingly,
    we will not remand on this ground.
    5. Indirect Impacts on the Haskell Farm
    The government calculated that 42A would have a greater negative impact
    on the affected properties than 32B when secondary and indirect impacts were
    considered. These secondary impacts included increased traffic on adjacent roads
    contributing to noise and the loss of the 32B mitigation area adjacent to the
    Haskell Farm, on which future urban development may occur if 42A were
    adopted. Appellants claim the government miscalculated these secondary
    impacts, and that the government arbitrarily failed to consider the impact 32B
    might have on the Haskell Farm’s historic register eligibility.
    With regard to noise-related secondary impacts, Appellants simply renew
    their attack on the government’s noise analysis. For the same reasons discussed
    -35-
    above with regard to the NEPA analysis, the government’s noise analysis was
    reasonable.
    Appellants also attack the traffic calculations. First, Appellants claim the
    government arbitrarily omitted from its analysis traffic traveling directly on 32B.
    As the government explains, however, the impact from traffic on 32B would be
    mitigated by sound walls, which in turn would be masked by greenery. This
    reasonably accounts for both noise-related and visual effects of traffic traveling
    directly on 32B. The secondary impacts analysis quite reasonably focused on
    impacts that would not be mitigated.
    Second, the government omitted a quarter-mile segment of Haskell Avenue
    between alternative 32B and 31st Street from its traffic analysis. The government
    admits the error, but explains that the additional traffic along this segment would
    have little, if any, negative impact because the 32B alternative calls for Haskell
    Avenue to be relocated 1,000 feet further away from the Haskell Farm.
    Appellants do not refute this explanation. Although they claim the increased
    traffic along this segment will result in “possible commercial development
    pressures” along this segment, Aplt. Br. at 51, we note that the relevant area
    around Haskell Avenue, as it would be relocated under 32B, is already a
    developed area. It would seem that, if anything, the relocation of Haskell Avenue
    would steer development further away from the affected properties. Moreover,
    the traffic along this segment was not omitted from the noise analysis. We find
    -36-
    the government’s explanation reasonable in light of the record.
    Finally, Appellants argue the government erred in not considering 32B’s
    potential impact on the Haskell Farm’s eligibility for registration as a historic
    site. The EIS, however, reveals that the government did, in fact, consider this
    factor. The government determined that 32B was unlikely to compromise the
    Haskell Farm’s historic features because it did not disturb any of the particular
    historic structures that contribute to the Farm’s eligibility. Appellants point to a
    letter from a National Park Service official expressing concern that “[t]he creation
    of any road through the wetlands or upper fields would represent a great impact
    on the historic character” of the Farm. App. at 1095. That letter, however,
    explicitly declined to offer any official view about the desirability of the
    alternatives. Moreover, a road already crosses the Farm at 31st Street.
    Alternative 32B would relocate 31st Street so as to place it next to the SLT,
    thereby maintaining a single transportation corridor across the property. The
    government reasonably concluded that this relocation would minimize the impact
    on the Farm’s historic features.
    6. Other Environmental and Historical Impacts
    The EIS noted that 42A would impact 5.2 acres of riparian woodlands and
    18.2 acres of upland woods, while 32B would only impact 1.2 acres of riparian
    woodlands and 9.6 acres of upland woods. While these impacts may not be
    extraordinary—and the government does not claim they are—it was reasonable
    -37-
    for the government to take into account the potential impacts on these
    environmental resources.
    The government also noted that 42A would potentially impact two other
    sites of historic interest: Blanton’s Crossing and Meair’s Farmstead. Although
    Blanton’s Crossing is not officially listed as a historic site, it was listed in an
    official Management and Use Plan in 1999 as a “high potential site” for the
    Oregon and California National Historic Trails. App. at 1337. It was therefore
    reasonable for the government to take it into account. With regard to Meair’s
    Farmstead, the government noted 42A’s potential impact while candidly admitting
    in the EIS that with mitigation measures the impact would be de minimis. We see
    no error in the government’s approach.
    7. 32B’s “Net Benefit” to Haskell Farm
    The EIS claims 32B provides a “net benefit” to the Haskell Farm by
    creating more wetlands than it destroys, preventing property near the Farm from
    ever being developed, building educational and recreational facilities in the area,
    relocating roads, and reducing the level of traffic noise on the Haskell Farm by
    2025. Appellants acknowledge that 32B provides some benefits, but claim these
    benefits are irrelevant to the question whether 42A has unique problems of
    extraordinary magnitude.
    As a general matter, an alternative’s prudence is determined by the
    problems it creates and the extent to which it meets the project’s goals—not by
    -38-
    the “benefit” provided by a different alternative. See 
    23 C.F.R. § 774.17
    . Even
    so, the relevant regulations do provide for the consideration of beneficial
    mitigation measures in determining whether an alternative will have a “de
    minimis impact,” and thus not require consideration of avoidance alternatives.
    See § 774.3(b).
    It is less clear whether “net benefits” could be a part of an analysis of
    “other unique problems or unusual factors.” § 774.17. Appellants do not explain
    why the government erred in considering the advantages of the selected
    alternative as a factor relevant to its prudence determination. But even if this
    factor should not have been considered, the government did not err in its
    evaluation of the cumulative impacts of alternative 42A.
    8. Cumulative Causation of Impacts of Extraordinary Magnitude
    In sum, the government determined alternative 42A was imprudent based
    on “multiple factors . . . that while individually minor, cumulatively cause unique
    problems or impacts of extraordinary magnitude.” § 774.17. As discussed above,
    Appellants contested the relevance of only one of the seven factors it considered
    in reaching that decision—32B’s “net benefit” to the Haskell Farm.
    A section 4(f) analysis, like an environmental impact statement, need not be
    flawless. In Boomer Lake Park, for example, we found that FHWA’s failure to
    consider a certain alternative was a “material fact.” Boomer Lake Park, 
    4 F.3d at 1552
    . We nonetheless found that “the oversight [was] not sufficient to cause a
    -39-
    reasonable trier of fact to find the Secretary’s decision arbitrary and capricious.”
    
    Id.
     We found that the legitimate factors considered by FHWA provided sufficient
    justification to conclude that alternatives to the selected route were imprudent.
    Additionally, FHWA considered the benefits of their preferred route as part
    of their section 4(f) analysis, much as the government did here. Specifically,
    FHWA found their preferred alternative would improve fishing access, water
    quality, and bicycle and pedestrian transportation links. See 
    id. at 1550
    .
    Although the extent to which FHWA relied on those benefits in its prudence
    determination is not clear, our affirmance demonstrates at least that the
    consideration of these side benefits was not fatal, in light of the other factors
    supporting FHWA’s decision.
    Here, it is clear from the record that the government took a “hard look” at
    several relevant factors—project goals, cost, floodplain impacts, accelerated
    development, and environmental impacts—and reasonably demonstrated that 42A
    posed enough problems along these factors to render that alternative imprudent.
    We have no doubt that had the discussion of 32B’s mitigation measures been
    deleted entirely from the 4(f) analysis, the government nonetheless would have
    been justified in rejecting 42A due to its multiple problems. Cf. 
    id. at 1553
    (“Even without the road-user cost estimate, there is ample evidence to support the
    Secretary’s decision that the alternatives were imprudent.”).
    -40-
    We thus conclude the government’s section 4(f) analysis was sufficient to
    overcome Appellants’ claim it was arbitrary and capricious.
    IV. Conclusion
    After a close review of the record, we conclude the government’s NEPA
    and section 4(f) analyses were not arbitrary and capricious under the APA.
    Accordingly, we AFFIRM the judgment of the district court.
    -41-