United Parcel Service, Inc. v. PRC , 890 F.3d 1053 ( 2018 )


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  •  United States Court of Appeals
    FOR THE DISTRICT OF COLUMBIA CIRCUIT
    Argued January 22, 2018              Decided May 22, 2018
    No. 16-1354
    UNITED PARCEL SERVICE, INC.,
    PETITIONER
    v.
    POSTAL REGULATORY COMMISSION,
    RESPONDENT
    VALPAK FRANCHISE ASSOCIATION, INC., ET AL.,
    INTERVENORS
    Consolidated with 16-1419
    On Petitions for Review of Orders
    of the Postal Regulatory Commission
    Jeffrey A. Lamken argued the cause for petitioner. With
    him on the briefs were James A. Barta, Steig D. Olson, and
    Sara E. Margolis.
    Bryan N. Tramont and Craig E. Gilmore were on the brief
    for amicus curiae J. Gregory Sidak in support of petitioner.
    Michael Shih, Attorney, U.S. Department of Justice,
    argued the cause for respondent. With him on the brief were
    2
    Michael S. Raab, Attorney, David A. Trissell, General Counsel,
    Postal Regulatory Commission, and Christopher J. Laver,
    Deputy General Counsel.
    Morgan E. Rehrig and Eric P. Koetting, Attorneys, U.S.
    Postal Service, Peter DeChiara, David M. Levy, John F.
    Cooney, and James Pierce Myers were on the brief for
    intervenors in support of respondent.
    Before: TATEL, SRINIVASAN, and PILLARD, Circuit Judges.
    Opinion for the Court filed by Circuit Judge TATEL.
    TATEL, Circuit Judge: The U.S. Postal Service holds
    congressionally authorized monopoly power over the market
    for some of its products, like first-class mail delivery, but for
    other products, like parcel post, it competes with private
    companies. To promote fair competition, Congress tasked the
    Postal Regulatory Commission with ensuring that the Postal
    Service sets competitive products’ prices high enough to cover
    all “costs attributable to [those] product[s] through reliably
    identified causal relationships.” 39 U.S.C. § 3631(b); see also
    
    id. § 3633(a)(2).
    In two 2016 orders, the Commission directed
    the Postal Service to include among the “costs attributable” to
    competitive products those costs that would disappear were the
    Postal Service to stop offering those products for sale. United
    Parcel Service, Inc., which competes with the Postal Service,
    petitions for review of both orders, arguing that the cost
    attribution methodology the Commission embraced is both
    inconsistent with the statute that gives the Commission its
    regulatory authority and arbitrary and capricious. For the
    reasons that follow, we deny the petitions.
    3
    I.
    Congress created what is now the Postal Regulatory
    Commission (the “Commission”) in 1970 to oversee the U.S.
    Postal Service’s efforts to set “reasonable and equitable rates
    of postage and fees for postal services.” Postal Reorganization
    Act, Pub. L. No. 91-375, § 3621, 84 Stat. 719, 760 (1970)
    (codified as amended at 39 U.S.C. § 404(b)); see also 
    id. § 3601,
    84 Stat. at 759 (establishing the Commission). The
    2006 Postal Accountability and Enhancement Act (the
    “Accountability Act”), Pub. L. No. 109-435, 120 Stat. 3198
    (2006), provides the framework within which the Commission
    currently exercises this oversight authority.
    Under the Accountability Act, all Postal Service products
    are either “market-dominant” or “competitive.” See 39 U.S.C.
    § 3642(b)(1). Market-dominant products are those over which
    “the Postal Service exercises sufficient market power that it can
    effectively” raise prices or decrease quality “without risk of
    losing a significant level of business to other firms offering
    similar products.” 
    Id. To prevent
    the Postal Service from
    “improperly leverag[ing]” this market power, U.S. Postal
    Service v. Postal Regulatory Comm’n, 
    785 F.3d 740
    , 744 (D.C.
    Cir. 2015), the Act requires the Commission to limit rate
    increases for market-dominant products, see 39 U.S.C.
    §§ 3622(a), (d)(1); see also 39 C.F.R. §§ 3010.1–3010.66
    (implementing this mandate).
    Different concerns attend competitive products—products
    over which “the Postal Service faces meaningful market
    competition.” U.S. Postal 
    Service, 785 F.3d at 744
    . For such
    products, Congress wished to “ensure that the Postal Service
    competes fairly,” S. Rep. No. 108-318, at 15 (2004) (“Senate
    Report”)—that is, without using revenues from market-
    dominant products subject to its monopoly power to defray
    costs competitive products would otherwise have to be priced
    4
    to cover. The Accountability Act therefore requires the
    Commission to promulgate regulations that “prohibit the
    subsidization of competitive products by market-dominant
    products,” 39 U.S.C. § 3633(a)(1); “ensure that each
    competitive product covers its costs attributable,” 
    id. § 3633(a)(2),
    defined as “the direct and indirect postal costs
    attributable to such product through reliably identified causal
    relationships,” 
    id. § 3631(b);
    and “ensure that all competitive
    products collectively cover what the Commission determines
    to be an appropriate share of the institutional costs of the Postal
    Service,” 
    id. § 3633(a)(3).
    In effect, the Accountability Act subjects each competitive
    product to a “price floor,” U.S. Postal Service v. Postal
    Regulatory Comm’n, 
    842 F.3d 1271
    , 1272 (D.C. Cir. 2016)
    (per curiam), which must be set high enough to cover both that
    product’s “costs attributable,” 39 U.S.C. § 3633(a)(2), and a
    portion of the Postal Service’s “institutional costs,” 
    id. § 3633(a)(3),
    which the Commission construes to mean
    “residual costs,” i.e., all costs that are not costs attributable, see
    Order Concerning United Parcel Service, Inc.’s Proposed
    Changes to Postal Service Costing Methodologies (UPS
    Proposals One, Two, and Three), No. RM2016-2, at 10 (Postal
    Regulatory Comm’n Sept. 9, 2016) (updated Oct. 19, 2016)
    (“Order”).
    This case concerns the Commission’s rules for
    apportioning postal costs between “attributable” and
    “institutional” costs. 39 U.S.C. §§ 3633(a)(2), (a)(3). Treating
    the latter category as “residual” of the former, Order at 10,
    Commission regulations focus on identifying which costs are
    “attributable to [a specific] product through reliably identified
    causal relationships,” 39 U.S.C. § 3631(b). In doing so, the
    Commission distinguishes (albeit necessarily imperfectly)
    between “fixed costs,” such as executive salaries, which remain
    5
    constant regardless of overall product volume, and “variable
    costs,” such as wage labor or raw materials, which vary with
    the Service’s production levels. Order at 6; see also Responses
    of the United States Postal Service to Questions 1–4 of
    Chairman’s Information Request No. 2, No. RM2016-2, at 11
    n.9 (Postal Regulatory Comm’n Dec. 10, 2015) (“Postal
    Service Responses”) (acknowledging that “fixed costs can be
    difficult to identify in practice”). Except for certain product-
    specific costs not at issue, fixed costs are not attributed to
    particular products and so are considered institutional. See
    Order at 9 & n.12 (attributing only those fixed costs “that are
    uniquely associated with an individual product,” 
    id. at 9,
    such
    as product-specific advertising costs). The issue here is what
    portion of the Postal Service’s variable costs can be reliably
    attributed.
    Broadly speaking, the Postal Service, in implementing
    Commission regulations, attributes variable costs on an
    activity-by-activity basis. After drawing up a list of the discrete
    production activities, such as highway transportation, that
    collectively account for its total variable costs, the Postal
    Service calculates what share of each activity’s costs can be
    attributed to each product. See Order App’x A at 13–14 (laying
    out this process); Postal Regulatory Comm’n, FY16 Public
    Cost Segments and Components Report (2016),
    https://go.usa.gov/x54x2 (listing production activities). To
    perform this calculation, it first identifies an activity’s “cost
    driver,” defined as the unit of measurement that best captures
    the activity’s “essen[ce].” Order App’x A at 14. For example,
    highway transportation is measured in cubic-foot-miles, such
    that one “unit” of cost driver in this context represents one
    cubic foot of mail being transported one mile. See 
    id. Then, the
    Postal Service determines the share of each activity’s cost-
    driver units that each product is responsible for generating,
    typically by conducting worksite observations in order to
    6
    produce a “distribution key” that, like a pie chart, illustrates an
    activity’s product-by-product breakdown. See 
    id. at 9;
    see also
    Order at 9 n.14; Office of Inspector General, U.S. Postal
    Service, A Primer on Postal Costing Issues 17–18 (Mar. 20,
    2012), https://go.usa.gov/x54Dd (explaining the role of
    distribution keys).
    The present dispute stems from the uncertainty inherent in
    translating this product-by-product breakdown of activity
    quantity into a similar breakdown of activity costs, given the
    cost savings that accrue as total production volume increases.
    If every cost-driver unit were equally costly, the distribution
    keys could be used to apportion all an activity’s costs to
    specific products: a product responsible for 5% of the cubic-
    foot-miles accrued in highway transportation, for example,
    could be linked to 5% of that activity’s costs. But not all cost-
    driver units are created equal. Under the principle of
    diminishing marginal costs, the cost of adding each new unit—
    in economic parlance, that unit’s “marginal cost”—decreases
    as production quantity increases, due to the efficiency gains
    that result from scaling up operations. See Order at 35 (“As a
    result of economies of scale and scope, the marginal cost of
    individual units of volume . . . decreases with volume.”); see
    also Order App’x A at 2 (defining marginal cost). To transport
    one cubic foot of mail, for instance, the Postal Service must
    make an initial outlay to hire a driver and maintain a truck. But
    throwing a second cubic foot of mail onto the truck carries
    fewer additional costs, and a third cubic foot carries fewer still.
    Given this variability, introducing a new product line that
    increases the Postal Service’s total cubic-foot-mileage by 5%
    may well increase highway transportation costs by something
    less than 5%. Due to diminishing marginal costs, therefore, the
    share of cost-driver units a particular product generates might
    not determine the share of costs that can be reliably linked to
    that product.
    7
    Historically, the Commission dealt with this uncertainty
    by directing the Postal Service to attribute to specific products
    only that portion of an activity’s costs that would result if every
    cost-driver unit cost only as much as the unit with the lowest
    marginal cost. Put into agency lingo, the Commission had the
    Postal Service attribute only an activity’s “volume-variable
    cost[s],” defined as the marginal cost of the “last,” i.e.,
    cheapest, cost-driver unit, multiplied by the total number of
    units accrued. Order at 36 n.56; see also 
    id. at 9.
    A Commission
    graph, reproduced below as Figure 1, illustrates volume-
    variable costs. The downward-sloping curve shows a
    hypothetical activity’s diminishing marginal cost (marked on
    the vertical axis) as production quantity (marked on the
    horizontal axis, and measured in cost-driver units) increases.
    The shaded rectangle represents this activity’s volume-variable
    costs—the $1 marginal cost of the twentieth cost-driver unit,
    applied to all twenty units.
    Figure 1
    Order App’x A at 15 fig. A-7.
    Given that every cost-driver unit contributes an identical
    dollar amount to an activity’s volume-variable costs, the Postal
    Service, in attributing only these costs, could securely rely on
    8
    its distribution keys and assign each product a share of volume-
    variable costs equivalent to that product’s contribution to cost-
    driver quantity. For example, consider a truck carrying six
    cubic feet of mail—two cubic feet each of letters, postcards,
    and parcels—for one mile. Imagine too that the marginal cost
    of the first cubic-foot-mile is $60, the marginal cost of the
    second is $50, the marginal cost of the third is $40, and so forth.
    The activity’s volume-variable costs are $60, or the marginal
    cost of the “final” cubic-foot-mile ($10) multiplied by the total
    number of cubic-foot-miles (six). Because letters, postcards,
    and parcels each account for one-third of the cost-driver units,
    volume-variable costs can be apportioned among them in like
    manner, with one-third of those costs ($20) attributed to each
    product.
    As this example shows, the Commission’s historic
    approach left some variable costs unattributed to any one
    product. Although the volume-variable costs in this example
    amount to only $60, total highway transportation costs are $210
    ($60 plus $50 plus $40 plus $30 plus $20 plus $10). The
    remaining $150 left unattributed represents “variable costs that
    are not volume-variable costs.” Order at 35. The Commission
    calls these “inframarginal costs.” 
    Id. These costs
    can be
    visualized as the white space in Figure 1 that lies between the
    downward-sloping marginal cost curve and the shaded
    rectangle that represents volume-variable costs. Historically,
    the Commission classified all inframarginal costs as
    institutional costs, only a limited share of which competitive
    products are obliged to cover. See 
    id. at 10;
    39 C.F.R.
    § 3015.7(c) (setting competitive products’ minimum collective
    share of the Postal Service’s institutional costs at 5.5%).
    Dissatisfied with this approach, United Parcel Service, Inc.
    (UPS), which runs a parcel delivery service that competes with
    the Postal Service’s, petitioned the Commission in 2015 “to
    9
    initiate rulemaking proceedings to change how the United
    States Postal Service accounts for the costs of competitive
    products.” Petition of United Parcel Service, Inc. for the
    Initiation of Proceedings to Make Changes to Postal Service
    Costing Methodologies, No. RM2016-2, at 1 (Postal
    Regulatory Comm’n Oct. 8, 2015); see also 39 C.F.R.
    § 3050.11(a) (authorizing “any interested person” to submit
    such a petition). By classifying inframarginal costs as
    institutional costs, UPS argued, the Postal Service had been
    shifting “nearly all of the cost savings of [its] economies of
    scale and scope” to competitive products, see Proposal One—
    A Proposal to Attribute All Variable Costs Caused by
    Competitive Products to Competitive Products Using Existing
    Distribution Methods, No. RM2016-2, at 15 (Postal Regulatory
    Comm’n Oct. 8, 2015), enabling it to “compete unfairly”
    against private companies, like UPS, that are unable to offset
    their competitive products’ inframarginal costs by wielding
    monopoly pricing power elsewhere, 
    id. at 14.
    Seeking to spur
    the Postal Service to increase its competitive products’ prices,
    UPS urged the Commission to require that all inframarginal
    costs be attributed to specific products. See 
    id. at 1.
    UPS proposed a two-step process for performing this
    attribution. The Postal Service would first calculate each
    production activity’s inframarginal costs, and then apportion
    those inframarginal costs among products according to the
    distribution keys that show what proportion of cost-driver units
    each product generates. See 
    id. at 19–21.
    By way of example,
    recall our mail truck that carries two cubic feet each of letters,
    postcards, and parcels, and that incurs $60 in volume-variable
    costs and $150 in inframarginal costs. Because the three
    products account for equal quantities of cost driver, UPS’s
    proposal would attribute inframarginal costs, like volume-
    variable costs, equally among them. In this scenario, the
    highway transportation costs attributable to each product
    10
    would be $70—one-third of the $60 in volume-variable costs
    ($20) plus one-third of the $150 in inframarginal costs ($50)—
    with no remaining variable costs left to be classified as
    institutional. With inframarginal costs thus attributed, the
    Postal Service would need to raise competitive products’ rates
    to comply with its duty to “ensure that each competitive
    product covers its costs attributable,” 39 U.S.C. § 3633(a)(2),
    leaving UPS in a stronger market position.
    The Commission rejected UPS’s proposal in a September
    2016 order, finding that it relied on “unverifiable assumptions”
    for both “the calculation and allocation of inframarginal costs.”
    Order at 55–56. As to calculation, the Commission explained
    that a central assumption underlying UPS’s model for
    estimating a production activity’s total inframarginal costs
    “lack[ed] an empirical basis.” 
    Id. at 39.
    As to allocation, the
    Commission faulted the proposal’s use of distribution keys to
    determine any given product’s share of an activity’s
    inframarginal costs, believing that such an approach relied on
    the unsupported assumption “that the proportion of
    inframarginal costs incurred by that product is identical to the
    proportion of the cost driver [generated by] that product.” 
    Id. at 51.
    Accordingly, the Commission concluded, UPS’s
    proposal was inconsistent with the Accountability Act’s
    directive to attribute only those costs that can be linked to a
    particular product “through reliably identified causal
    relationships.” 39 U.S.C. § 3631(b); see also Order at 56
    (“[UPS’s proposal] fails to reliably identify a causal
    relationship . . . between all of the inframarginal costs it seeks
    to attribute and products.”).
    Having rejected UPS’s request that all inframarginal costs
    be attributed to individual products, the Commission then
    considered whether some such costs could nonetheless be
    reliably attributed. In particular, the Commission observed that
    11
    in the course of fulfilling its separate statutory obligation to
    “prohibit the subsidization of competitive products by market-
    dominant products,” 39 U.S.C. § 3633(a)(1), it had earlier
    approved a method that could be used to calculate a
    competitive product’s “incremental cost,” defined as “the
    difference between the [Postal Service’s] total costs . . . and the
    total costs without [that] product,” Order at 58; see also 
    id. at 12–14
    (describing the development of the incremental-cost
    methodology). Because a product’s incremental cost is the
    amount by which total costs would decrease had the cost-driver
    units associated with that product never been accrued, it
    encompasses not only that product’s share of volume-variable
    costs, but also the “inframarginal costs that would be removed”
    if the product “were not to be provided.” Order App’x A at 19.
    In effect, the incremental-cost methodology attributes to a
    product responsible for 5% of an activity’s cost-driver units the
    total cost—both volume-variable and inframarginal—of the
    “last,” i.e., cheapest 5% of those units.
    To illustrate, consider one last time the truck that carries
    six cubic feet of assorted mail and incurs $60 and $150 of,
    respectively, volume-variable and inframarginal costs. What
    happens if the driver removes the two cubic feet of parcels
    before the truck sets off? In that case, the truck would carry
    only four cubic feet of mail, for a total cost of $180—$60 plus
    $50 plus $40 plus $30. The incremental cost of parcels is $30,
    or the difference between the $210 in total costs incurred when
    parcels are included and the $180 incurred when they are not.
    This $30 includes parcels’ one-third share of highway
    transportation’s volume-variable costs, or $20, as well as the
    $10 in inframarginal costs that would not have been incurred
    but for the fifth and sixth cubic feet of mail.
    Here, the Commission concluded that because “the portion
    of inframarginal costs” included within a product’s incremental
    12
    cost has “a causal relationship” with that product, Order at 55,
    the Accountability Act “require[s] the Postal Service to
    attribute” it, 
    id. at 61.
    In December 2016, the Commission
    adopted final rules formalizing this requirement. See Changes
    to Attributable Costing, 81 Fed. Reg. 88,120, 88,123 (Postal
    Regulatory Comm’n Dec. 7, 2016). Those rules define a
    competitive product’s “attributable costs” as “the sum of its
    volume-variable costs, product-specific costs, and those
    inframarginal costs calculated as part of [its] incremental
    costs.” 
    Id. (codified at
    39 C.F.R. § 3015.7(b)). All other costs,
    including all remaining inframarginal costs, remain classified
    as institutional.
    Figure 2
    Petitioner’s Br. 37 (adapting Order App’x A at 18 fig. A-9).
    The parties have produced a helpful graphic depiction of
    the Commission’s new incremental-cost approach, reproduced
    above as Figure 2. The shaded area represents the incremental
    cost of a product that is responsible for a share of a hypothetical
    activity’s cost-driver units. This area includes not only a
    corresponding share of the activity’s volume-variable costs—
    the only costs that would have been attributed to the product
    13
    under the Commission’s prior approach—but also the
    inframarginal costs associated with the “final,” lowest-priced
    share of cost-driver units, which are included among the
    product’s costs attributable under the new approach.
    The approach the Commission adopted under the 2016
    orders is responsive to UPS’s complaint that the historic
    approach, by attributing no inframarginal costs, left
    unattributed some costs that could be reliably linked to specific
    products. It differs from UPS’s proposed approach, however,
    in that it attributes to a product responsible for x% of a given
    activity’s cost-driver units only those inframarginal costs
    associated with the lowest-priced x% of units, rather than, as
    UPS would prefer, x% of that activity’s total inframarginal
    costs.
    Unhappy with its partial victory, UPS petitioned this court
    for review of the 2016 orders, arguing that the Commission’s
    decision not to require the Postal Service to attribute all
    inframarginal costs to specific products was both inconsistent
    with the Accountability Act and arbitrary and capricious. See
    39 U.S.C. § 3663 (establishing that Commission orders are
    reviewed under 5 U.S.C. § 706, which directs courts to set
    aside agency action that is “arbitrary, capricious, an abuse of
    discretion, or otherwise not in accordance with law,” 
    id. § 706(2)(A)).
    Economist J. Gregory Sidak has filed an amicus
    brief supporting UPS, and a quartet of intervenors—Amazon
    Fulfillment Services, Inc.; National Association of Letter
    Carriers, AFL-CIO; Parcel Shippers Association; and the U.S.
    Postal Service—has filed a brief supporting the Commission.
    In Part II, we consider whether the challenged orders are,
    as UPS claims, contrary to the Accountability Act. In Part III,
    we consider UPS’s argument that the orders reflect arbitrary
    and capricious decision-making. We are grateful to counsel for
    14
    both sides for their excellent briefs and fine oral argument,
    which have helped us considerably.
    II.
    UPS presses two statutory arguments as to why, in its
    view, the challenged orders conflict with the Accountability
    Act. We reject both.
    A.
    UPS first argues that the Commission’s classification of
    all inframarginal costs not included in a product’s incremental
    cost as “institutional costs,” 39 U.S.C. § 3633(a)(3), is
    inconsistent with that term’s unambiguous meaning, see
    Chevron, U.S.A., Inc. v. Natural Resources Defense Council,
    
    467 U.S. 837
    , 842–43 (1984) (“If the intent of Congress is
    clear, that is the end of the matter; for the court, as well as the
    agency, must give effect to the unambiguously expressed intent
    of Congress.”). According to UPS, “institutional costs”
    unambiguously refers to “costs, such as overhead and
    executive compensation, associated with operating the Postal
    Service as an establishment, independent of production,”
    Petitioner’s Br. 35, and so excludes all variable costs, including
    inframarginal costs.
    Even though the Accountability Act nowhere defines
    “institutional costs,” it does define the complementary category
    of “costs attributable.” 39 U.S.C. § 3631(b). Because UPS
    never disputes the Commission’s view that “[a]ll Postal Service
    costs are . . . either attributable or institutional,” Order at 9, it
    must believe that all variable costs—in its view,
    unambiguously excluded from “institutional costs”—are
    “attributable” under the statute. But UPS offers no basis for
    believing that the Accountability Act unambiguously compels
    the Commission to treat each variable cost as a “cost[]
    attributable” without first considering whether it possesses the
    15
    statutorily requisite “reliably identified casual relationship[]”
    with any one product. 39 U.S.C. § 3631(b).
    Instead, UPS hinges its argument on three pieces of
    evidence that, it says, establish unambiguously that
    “institutional costs” exclude variable costs. First, it cites a
    dictionary that defines “institutional” to mean “of, relating to,
    involving, or constituting an institution.” Petitioner’s Br. 34–
    35 (quoting Webster’s Third New International Dictionary
    1171 (2002)). This definition, however, is fully consistent with
    classifying some variable costs as institutional. Variable postal
    costs, such as the hourly wages of employees who deliver the
    mail, “relate to” the Postal Service no less than do fixed postal
    costs, such as the Postmaster General’s annual salary. UPS next
    cites its own amicus’s statement in a law review article that
    “[i]nstitutional costs are fixed overhead and capital costs that
    are not volume-sensitive.” 
    Id. at 36
    (emphasis omitted)
    (quoting J. Gregory Sidak & Daniel F. Spulber, Monopoly and
    the Mandate of Canada Post, 14 Yale J. on Reg. 1, 56 (1997)).
    But this lone characterization—which itself cites no
    authority—falls far short of demonstrating that UPS’s
    definition of “institutional costs” is so universally accepted that
    Congress must have adopted it. Finally, UPS cites the Act’s
    Senate Report, which refers to “salaries for management and
    other overhead costs” as examples of “institutional costs.” 
    Id. at 35
    (quoting Senate Report at 9). That Congress intended the
    term to include some fixed costs, however, hardly compels the
    conclusion that it intended the term to exclude all variable
    costs.
    With no indication that the statute requires UPS’s reading,
    we are left to ask whether the Commission’s own interpretation
    is “permissible,” deferring to the agency under Chevron,
    U.S.A., Inc. v. Natural Resources Defense Council, 
    467 U.S. 837
    (1984), if it is. U.S. Postal 
    Service, 785 F.3d at 750
                                    16
    (quoting 
    Chevron, 467 U.S. at 843
    ). As we have explained, the
    Commission understands the undefined category of
    “institutional costs” to consist of all “residual” Postal Service
    costs, fixed or variable, that fall outside the statutory definition
    of “attributable” costs. Order at 9–10. In addition to its
    consistency with statutory structure, this reading gains support
    from the established meaning “institutional costs” held in the
    postal ratemaking context long prior to the Act’s 2006
    enactment. As early as 1975, the Commission observed that
    “the Postal Service considers certain costs . . . to be
    attributable” and that “[a]ll other costs are classified as
    institutional.” Opinion and Recommended Decision, No. R74-
    1, at 99 (Postal Rate Comm’n Aug. 28, 1975). And since then,
    the Commission has continued to conceive of “the institutional
    cost pool” as “[t]he remaining portion” of total costs after
    attributable costs are subtracted. See United Parcel Service,
    Inc. v. U.S. Postal Service, 
    184 F.3d 827
    , 842 (D.C. Cir. 1999)
    (per curiam) (alteration in original) (internal quotation marks
    omitted) (quoting Opinion and Recommended Decision, No.
    R97-1, at 220 (Postal Rate Comm’n May 11, 1998)).
    The Commission’s interpretation of the Accountability
    Act in line with this longstanding usage is perfectly reasonable
    under Chevron. We typically presume that Congress is “aware
    of established practices and authoritative interpretations of the
    coordinate branches,” United States v. Wilson, 
    290 F.3d 347
    ,
    357 (D.C. Cir. 2002), and here the Act’s legislative history
    confirms that the enacting Congress knew the Commission
    took “institutional costs” to mean those costs that “cannot be
    attributed to any specific product,” Senate Report at 9. One
    could reasonably infer that, in employing a known term of art
    in the statute, “Congress intended it to have its established
    meaning.” McDermott International, Inc. v. Wilander, 
    498 U.S. 337
    , 342 (1991).
    17
    UPS challenges the idea that the meaning the Commission
    now assigns to “institutional costs” has such a consistent
    pedigree in the postal ratemaking context that the agency could
    reasonably construe the Accountability Act to accommodate it.
    UPS’s evidence of inconsistency is underwhelming. It first
    points to a Postal Service publication stating that institutional
    costs “can be considered common costs or overhead costs
    needed for overall operations,” but that same publication,
    consistent with longstanding practice, defines institutional
    costs as those “[p]ostal costs that cannot be directly or
    indirectly assigned to any mail class or product,” and then
    expressly contrasts such costs with “attributable cost[s].” U.S.
    Postal Service, Glossary of Postal Terms 104 (2013),
    https://about.usps.com/publications/pub32.pdf. Next, UPS
    pulls a sentence from a 2012 Commission order saying that
    “institutional costs do not vary with volume.” Order Reviewing
    Competitive Products’ Appropriate Share Contribution to
    Institutional Costs, No. RM2012-3, at 23 (Postal Regulatory
    Comm’n Aug. 23, 2012) (“2012 Order”). But this remark,
    which appeared well after the Accountability Act’s passage
    and so could not have informed Congress’s meaning, was made
    in passing in connection with an issue that had “not [been]
    raised by the parties” to that agency proceeding. 
    Id. Even if
    UPS is correct that this stray sentence in a single agency order
    conflicts with the meaning the Commission has long and
    repeatedly assigned “institutional costs,” it hardly follows that
    it was unreasonable for the Commission to interpret the
    Accountability Act to be consistent with that longstanding
    meaning.
    Finally, UPS emphasizes that the Commission’s approach
    leaves nearly half the Postal Service’s costs in the “institutional
    costs” category. True enough, but UPS has failed to show why
    reading “institutional costs” to permit this outcome is
    unreasonable under the statute. Indeed, in passing the
    18
    Accountability Act, Congress found “no reason for changing”
    existing attribution standards, Senate Report at 10, under
    which, it recognized, institutional costs made up “40 percent of
    the Postal Service’s costs,” 
    id. at 9;
    see also Newsweek, Inc. v.
    U.S. Postal Service, 
    663 F.2d 1186
    , 1200 (2d Cir. 1981)
    (“There is nothing in the legislative history [of the
    Accountability Act’s predecessor statute] to suggest that
    attribution of fifty percent of postal costs is inadequate.”).
    Given our conclusion that the Commission’s reading of
    “institutional costs” is reasonable and so merits our deference,
    we need not consider the Commission’s argument that, under
    Chevron, its reading is not only permissible, but also
    unambiguously correct.
    B.
    UPS next argues that the Commission’s orders give no
    effect to the word “indirect” in the Accountability Act’s
    requirement that a product’s “costs attributable” include the
    “direct and indirect postal costs attributable to such product
    through reliably identified causal relationships.” 39 U.S.C.
    § 3631(b). Contending that “[i]ndirect costs are costs that are
    jointly caused by multiple products,” Petitioner’s Br. 39, UPS
    argues that because the Commission’s methodology attributes
    only those costs that are “caused by providing a specific
    product,” Order at 52, that methodology will attribute no
    “indirect” costs and so is “not in accordance” with the Act, 5
    U.S.C. § 706(2)(A). In addressing this argument, we assume
    without deciding that, as UPS contends, the statute’s reference
    to “direct and indirect” costs means that the Commission may
    lawfully adopt an attribution formula only if the formula
    assigns at least some “indirect” costs to specific products.
    Even if UPS has correctly interpreted “indirect postal
    costs” to mean joint costs, the Commission has reasonably
    19
    concluded that its approach in fact attributes some such costs.
    See U.S. Postal 
    Service, 785 F.3d at 750
    (where statute’s
    meaning is not at issue, court asks whether “the Commission’s
    exercise of its authority [was] ‘reasonable and reasonably
    explained’” (quoting Manufacturers Railway Co. v. Surface
    Transportation Board, 
    676 F.3d 1094
    , 1096 (D.C. Cir. 2012))).
    Observing that both volume-variable and inframarginal costs
    “contain common costs,” Order at 50, defined as “costs that are
    shared by multiple products but do not directly vary with any
    of those individual products,” 
    id. at 7,
    the Commission
    explained that its new cost-attribution methodology “do[es] not
    exclude all common costs, but only those without a reliably
    identified causal relationship to [a specific] product,” 
    id. at 52.
    For example, the cost of fueling a truck that delivers letters
    and parcels may, we think, be viewed as a common cost. It is
    “shared by” the two products that contribute to it, but it “do[es]
    not directly vary” with either product: the amount by which it
    rises (or falls) when mail is added to (or taken from) the truck
    is unaffected by whether that mail consists of letters, parcels,
    or some combination. 
    Id. at 7.
    The mere fact that the
    Commission is capable of calculating how much the truck’s
    fuel costs would decrease in the absence of parcels (or,
    importantly, in the absence of an identical volume of letters)
    does not change the characteristics that make those fuel costs
    “common.” The orders, therefore, lay out an attribution
    methodology that the Commission reasonably understands to
    be consistent with even UPS’s own view of the statute.
    In any event, the Commission does not agree that “indirect
    postal costs,” 39 U.S.C. § 3631(b), refers only to joint costs. In
    rejecting UPS’s “perceived definition of indirect costs,” Order
    at 32, the Commission contemplated that indirect costs can
    include the costs of those single-product production activities
    “that contain support activities,” 
    id. at 103,
    and that—in
    20
    consequence—are only “indirectly linked to the volume of the
    product that cost was incurred to produce,” Respondent’s Br.
    50; see also Intervenors’ Br. 16 (“At least since the mid-1970s,
    the term ‘indirect postal costs’ has referred . . . [to] costs that
    vary with other costs.”). These costs would include, for
    example, the cost of hiring supervisors to oversee employees
    who sort parcels: the number of supervisors needed depends on
    the number of employees, which in turn depends on the volume
    of parcels. See, e.g., Direct Testimony of Joe Alexandrovich on
    Behalf of U.S. Postal Service, No. 97-1, at 3 (Postal Rate
    Comm’n July 10, 1997) (“Alexandrovich Testimony”); Direct
    Testimony of Howard S. Alenier on Behalf of U.S. Postal
    Service, No. R80-1, at 6 n.1 (Postal Rate Comm’n Apr. 21,
    1980) (“Alenier Testimony”). Supervisors’ wages are thus a
    product-specific cost that varies only indirectly with volume—
    the sort of cost that the Postal Service calls a “piggyback” cost.
    See Postal Regulatory Comm’n, Financial Analysis of United
    States Postal Service Financial Results and 10-K Statement 49
    (Mar.        31,        2017)       (“Financial        Analysis”),
    https://go.usa.gov/x5kWz (describing a product’s “indirect
    cost[s]” as those that are “piggybacked to the direct cost”).
    The Commission’s reading of “indirect postal costs” to
    include this sort of single-product piggyback cost is reasonable.
    Past testimony before the Commission has, after all, repeatedly
    confirmed that “indirect costs,” in the specific context of postal
    accounting, has long included costs that vary only indirectly
    with product volume due to the presence of an intermediate
    factor. See, e.g., Alexandrovich Testimony at 3 (“Direct and
    indirect variable costs are terms distinguishing whether or not
    there is at least one intervening link between cost and
    volume.”); Alenier Testimony at 6 (“The terms direct and
    indirect [cost] indicate whether or not at least one intermediate
    element links cost to volume.” (footnote omitted)).
    21
    UPS argues that the statute forecloses the Commission’s
    reading, but here too its evidence is insufficient. It first notes
    the Supreme Court’s observation that a study upon which
    Congress relied in enacting a predecessor statute defined
    indirect costs as “[t]hose elements of cost which cannot
    unequivocally be associated with a particular output or
    product.” National Ass’n of Greeting Card Publishers v. U.S
    Postal Service (“NAGCP”), 
    462 U.S. 810
    , 827 n.21 (1983)
    (alteration in original) (internal quotation marks omitted). This
    definition, however, is not necessarily inconsistent with the
    Commission’s view that indirect costs include those that are
    associated only indirectly with product volume, or “output,”
    even if they can be associated with a single “product.” 
    Id. Next, UPS
    cites a federal accounting regulation, which actually
    supports the Commission’s reading because it defines
    “[i]ndirect cost” as a cost “identified with two or more final
    cost objectives or with at least one intermediate cost
    objective,” 48 C.F.R. § 9904.418-30(a)(3) (emphasis added),
    such as the employees who report to the supervisor in the
    example above. Finally, UPS cites an accounting textbook that
    defines indirect costs as those “incurred in providing benefits
    to several different cost objects.” Petitioner’s Br. 40 (emphasis
    omitted). UPS, however, never explains why single-product
    costs that support intermediate cost objects (such as
    subordinate employees) as well as final cost objects (i.e., end
    product) fall outside this definition.
    Put simply, UPS has failed to show that the Accountability
    Act unambiguously compels a reading of “indirect postal
    costs” that includes only those costs that are shared across
    products. Under Chevron, we therefore defer to the
    Commission’s reasonable view that the term can include those
    single-product costs that vary indirectly with volume.
    22
    C.
    UPS argues that even if the Commission’s interpretations
    of “institutional costs” or “indirect postal costs” are
    permissible, Chevron deference is inappropriate because the
    Commission made “no ‘reasonable attempt to grapple’ with or
    even refer back to the statutory text.” Petitioner’s Br. 45
    (quoting BP Energy Co. v. FERC, 
    828 F.3d 959
    , 965 (D.C. Cir.
    2016)). In our view, the Commission had no need to say
    anything more. “Institutional costs” and “indirect postal costs”
    have established meanings in the postal ratemaking context,
    see supra at 14–21, and the orders are faithful to these
    meanings, see Order at 10 (describing “institutional costs” as
    “residual costs”); 
    id. at 103
    (explaining that “the piggyback
    method” applies to “cost components that contain support
    activities”). To be sure, “no amount of historical consistency
    can transmute an unreasoned statutory interpretation into a
    reasoned one.” Southeast Alabama Medical Center v. Sebelius,
    
    572 F.3d 912
    , 920 (D.C. Cir. 2009). Here, however, the
    longstanding definitions upon which the Commission relied
    create no anomalies and flow sensibly from text, history, and
    statutory structure. Cf. 
    id. at 919–20
    (requiring agency to
    explain its historical view that a hospital’s “wage-related costs”
    include postage costs where, even in litigation, the agency
    offered but “one somewhat opaque rationale” that was itself
    apparently inconsistent with the agency’s treatment of certain
    other costs). The Commission therefore had no duty to
    expressly justify its decision to continue embracing them. See
    Hall v. McLaughlin, 
    864 F.2d 868
    , 872 (D.C. Cir. 1989)
    (“Where the reviewing court can ascertain that the agency has
    not in fact diverged from past decisions, the need for a
    comprehensive and explicit statement of its current rationale is
    less pressing.”).
    UPS believes that this rationale cannot save the orders’
    treatment of either “institutional costs” or “indirect postal
    23
    costs.” With respect to “institutional costs,” UPS argues that
    the interpretation reflected in the orders represents an
    unexplained deviation from the Commission’s prior reading of
    the term. See Encino Motorcars, LLC v. Navarro, 
    136 S. Ct. 2117
    , 2125 (2016) (agency must provide “a reasoned
    explanation” for a change in policy position). By including
    some variable costs among institutional costs, UPS argues, the
    Commission has departed from its previous statements that
    “institutional costs do not vary with volume,” 2012 Order at
    23, and that “variability with volume should be sufficient to
    establish causality” and thus attribution, Appendices to
    Opinion and Recommended Decision, App’x B, No. R80-1, at
    26 (Postal Rate Comm’n Feb. 19, 1981). Notwithstanding these
    sentences, cherry-picked and shorn of context, the Commission
    has never taken the view that all variable costs, including all
    inframarginal costs, bear an adequate causal relationship with
    specific products to be counted among costs attributable or—
    what amounts to the same thing—that no variable costs may be
    considered institutional costs. Indeed, it was the Commission’s
    previous classification of all inframarginal costs—which UPS
    accepts are variable costs, see Petitioner’s Br. 44—as
    institutional that prompted UPS to petition the Commission in
    the first place.
    With respect to “indirect postal costs,” UPS argues that the
    orders failed to make clear what meaning the Commission
    assigned to the term because, as the Commission
    acknowledges, they “‘declined’ to pass on whether ‘indirect
    costs’ include joint costs.” Reply Br. 13 (quoting Respondent’s
    Br. 53). But the Commission had no need to opine on whether
    “indirect postal costs” include joint costs in addition to single-
    product costs that vary indirectly with product volume:
    recognizing that the term includes at least the latter, as the
    Commission has consistently done, was sufficient to defeat
    UPS’s argument that no indirect costs would be attributed
    24
    under the Commission’s newly adopted cost-attribution
    scheme.
    III.
    This brings us to UPS’s argument that the challenged
    orders are “arbitrary, capricious, [or] an abuse of discretion.” 5
    U.S.C. § 706(2)(A). In considering this argument, we
    emphasize our “‘reluctan[ce] to interfere with [an] agency’s
    reasoned judgments’ about technical questions within its area
    of expertise.” Alliance of Nonprofit Mailers v. Postal
    Regulatory Comm’n, 
    790 F.3d 186
    , 197 (D.C. Cir. 2015)
    (second alteration in original) (quoting NRG Power Marketing,
    LLC v. FERC, 
    718 F.3d 947
    , 953 (D.C. Cir. 2013)). As the
    Supreme Court has recognized, Congress vested postal
    ratemaking authority in the Commission out of a desire to
    harness “the educated and politically insulated discretion of
    experts.” 
    NAGCP, 462 U.S. at 823
    . Consequently, Congress
    has not “dictate[d] or exclude[d] the use of any method of
    attributing costs,” 
    id. at 820,
    leaving it to “the expert ratesetting
    agency, exercising its reasonable judgment . . . to decide which
    methods sufficiently identify the requisite causal connection
    between particular services and particular costs,” 
    id. at 827.
    In
    considering whether the orders suffer from arbitrary and
    capricious decision-making, then, we ask only whether “the
    Commission’s exercise of its authority [was] ‘reasonable and
    reasonably explained.’” U.S. Postal 
    Service, 785 F.3d at 750
    (quoting Manufacturers Railway 
    Co., 676 F.3d at 1096
    ).
    A.
    UPS first argues that the Commission failed to “reasonably
    explain[]” the adoption of its incremental-cost methodology.
    
    Id. (quoting Manufacturers
    Railway 
    Co., 676 F.3d at 1096
    ).
    Given that we have already considered and rejected UPS’s
    claim that the Commission inadequately explained its statutory
    25
    interpretation, see supra at 22–24, UPS is left with its argument
    that the Commission failed to explain how its chosen approach
    “serve[d] the [Accountability Act’s] objectives,” Northpoint
    Technology, Ltd. v. FCC, 
    412 F.3d 145
    , 151 (D.C. Cir. 2005).
    We find the Commission’s explanation perfectly adequate.
    Though recognizing that the Accountability Act was
    “intended to ensure that the Postal Service competes fairly in
    the provision of competitive products,” Order at 121 (quoting
    Senate Report at 19), the Commission rejected UPS’s
    complaint that attributing only incremental costs fails to fulfill
    this goal, see 
    id. at 57.
    In the Commission’s view, “[t]he
    purpose of the incremental cost test is not to ensure that the
    Postal Service is competing fairly,” but rather, as used here, to
    “ensure that products cover all of the costs the Postal Service
    incurs in providing them,” which in turn plays but a
    contributing role in the statute’s overall pro-competitive aims.
    
    Id. at 58.
    The Commission properly recognized that its role is to
    carry out the particulars of the scheme Congress created, not to
    engineer specific market outcomes. The Supreme Court, while
    acknowledging that “Congress’ concern about . . . cross-
    subsidies, of course, was one motive for including [a] rate
    floor” in a predecessor statute, observed that Congress also
    took care to provide that cost attribution be methodologically
    sound. 
    NAGCP, 462 U.S. at 829
    n.24. Indeed, before the
    Commission, UPS itself recognized that “[t]he relevant
    inquiry” in selecting a cost attribution approach “is whether the
    Postal Service’s . . . practices comply with [the Accountability
    Act],” Reply Comments of United Parcel Service, Inc.
    Regarding UPS Proposals One and Two, No. RM2016-2, at 33
    (Postal Regulatory Comm’n Mar. 25, 2016), not the approach’s
    effects on “market conditions,” 
    id. at 36.
    This is correct.
    “Congress,” as UPS explained, “did not direct the Commission
    26
    to consider prevailing market conditions in connection with”
    cost attribution. 
    Id. at 37.
    In any event, despite its fear that
    leaving some inframarginal costs unattributed “might allow the
    Postal Service to monopolize otherwise competitive markets,”
    Petitioner’s Br. 49, UPS offers no reason to doubt that the
    Accountability Act’s prohibition on cross-subsidization, 39
    U.S.C. § 3633(a)(1), and requirement that competitive
    products cover a share of institutional costs, 
    id. § 3633(a)(3),
    will adequately ameliorate any competitive deficit left by the
    Commission’s approach to cost attribution, cf. 
    id. § 3633(b)
    (requiring Commission to consider “the prevailing competitive
    conditions in the market” when setting competitive products’
    share of institutional costs); Competitive Postal Products, 83
    Fed. Reg. 6758, 6774 (Postal Regulatory Comm’n Feb. 14,
    2018) (proposing a new, formula-based method for
    determining competitive products’ share of institutional costs
    that will be “more responsive to changing market conditions”).
    B.
    Next, UPS argues that the Commission’s adoption of an
    incremental-cost approach to attribution was itself arbitrary
    and capricious, insisting that this approach suffers from the
    very same features that led the Commission to reject UPS’s
    proposal that all inframarginal costs be attributed. See U.S.
    Postal 
    Service, 785 F.3d at 753
    (“The agency fails to
    reasonably explain its decision if it gives ‘differential treatment
    of seemingly like cases.’” (quoting LePage’s 2000, Inc. v.
    Postal Regulatory Comm’n, 
    642 F.3d 225
    , 232 (D.C. Cir.
    2011))). In support, it offers three arguments, none persuasive.
    It begins by challenging the Commission’s rejection of the
    assumption that any given product is just as likely to be
    responsible for “early,” more expensive cost-driver units as it
    is for “later,” less expensive units. This assumption, which the
    Commission deemed “empirically unverifiable,” Order at 46,
    27
    underlay UPS’s proposal to distribute inframarginal costs
    among products according to each product’s contribution to
    cost-driver quantity. The Commission’s rejection of this
    assumption was arbitrary, UPS argues, because the
    Commission’s own incremental-cost approach was “based on
    [the] even more unverifiable assumption” that all products use
    only the latest, lowest-priced cost-driver units and so bear the
    minimum possible inframarginal costs. Petitioner’s Br. 53.
    UPS misunderstands the Commission’s statutory task,
    namely to attribute only those costs that can be linked to a
    product “through reliably identified causal relationships.” 39
    U.S.C. § 3631(b). Contrary to UPS’s claim that the
    Commission untenably assumed that “every product comes
    last” in the production chain, Petitioner’s Br. 53, the
    Commission simply declined to assume that any given product
    incurred more than the minimum cost that could reliably be
    assigned to it. Attributing more than this amount, after all,
    necessitates guesswork, and the Commission sensibly
    concluded that such guesswork was inconsistent with its
    statutory obligation to base attribution on only “reliably
    identified causal relationships.” 39 U.S.C. § 3631(b).
    UPS’s second argument—that the Commission acted
    arbitrarily in rejecting distribution keys as a means of
    apportioning inframarginal costs—fails for the same reason. As
    the Commission saw it, attributing inframarginal costs on the
    basis of distribution keys, which measure only the share of
    cost-driver units for which a given product is responsible,
    would rely on the “unverifiable assumption that the proportion
    of inframarginal costs incurred by [a] product is identical to the
    proportion” of cost-driver units generated by that product.
    Order at 51. Here, too, the Commission reasonably declined to
    make this assumption absent supporting evidence. Nor,
    contrary to UPS’s argument, did the Commission act
    28
    inconsistently by using distribution keys as part of its
    incremental-cost approach. After all, the Commission uses
    them only for their intended purpose—to determine how many
    of any given activity’s cost-driver units derive from any one
    product. From there, the Commission calculates “the marginal
    cost of providing [each of these] specific unit[s]” without
    further recourse to the distribution keys. 
    Id. at 50.
    The third and final argument takes aim at the
    Commission’s rejection of UPS’s proposed method for
    estimating an activity’s total inframarginal costs in the first
    place, prior to any question of attribution. To arrive at an
    estimate of an activity’s total costs, the Postal Service would
    have to estimate the cost of each cost-driver unit, even the
    earliest, most costly units associated with low levels of volume.
    As the Commission explained, though, “[a] real-world multi-
    product firm does not have the information necessary” to
    estimate costs at such volume levels because “it has not
    experienced” them. 
    Id. at 8.
    UPS proposed to get around this
    problem by employing an assumption of constant elasticity—
    i.e., an assumption that each added unit of product quantity
    corresponds to an equal decrease in marginal cost—that would
    allow the Postal Service to extrapolate backwards from present,
    observed volumes. 
    Id. at 38;
    see also Order App’x A at 4–5
    (explaining constant elasticity). The Commission rejected this
    approach as untenable because “[a]pplying the constant
    elasticity assumption to levels of volume far beyond the range
    of actual experience produces results that are inadequately
    supported and unreliable.” Order at 39.
    Here, too, UPS responds that the Commission itself relies
    on a constant-elasticity assumption when extrapolating
    backward from present values to estimate a product’s
    incremental cost. The Commission, however, explained that
    the incremental-cost test “avoids the issues facing UPS’s
    29
    proposed method by restricting itself to limited amounts of
    volume” and by “estimat[ing] inframarginal costs in a very
    small range of [an activity’s] cost curve where the constant
    elasticity assumption has been empirically verified.” 
    Id. at 42.
    UPS challenges the Commission’s claim that it applies the
    assumption over only a small range of volumes. As the
    Commission points out, however, competitive products make
    up a small fraction of the Service’s total business, see Financial
    Analysis at 92, making it reasonable to believe that any one
    competitive product represents a comparatively small range of
    any given activity’s marginal cost curve. UPS further argues
    that, even within that range, the Commission’s empirical
    justification for the constant-elasticity assumption rests on a
    20-year-old article that predated “significant changes in the
    Postal Service’s competitive parcel business in the 21st
    century.” Petitioner’s Br. 61. But UPS has identified no
    substantive deficiency in the article or any way intervening
    events have undermined its conclusions. At any rate, it was
    hardly arbitrary for the Commission to find the constant-
    elasticity assumption sufficiently reliable to make a limited
    extrapolation from present conditions but insufficiently
    reliable to estimate cost at all levels of production volume.
    Alternatively, UPS suggests that the Commission could
    calculate inframarginal costs by simply subtracting one known
    quantity—an        activity’s    volume-variable     costs—from
    another—that activity’s total costs. The Commission, however,
    reasonably concluded that this method of calculation would
    “result[] in an overstatement of the inframarginal costs of that”
    activity because it disregards the fact that fixed costs—neither
    volume-variable nor inframarginal—comprise part of an
    activity’s total costs. Order at 39. UPS responds that “the Postal
    Service can subtract those fixed costs from the [activity’s] total
    costs.” Petitioner’s Br. 62. But the Postal Service informed the
    Commission that it does not currently “determine which of its
    30
    costs are fixed,” and that doing so would require it to “answer[]
    difficult counterfactual questions” about “which costs would
    remain if the Postal Service handled no volume.” Postal
    Service Responses at 11 & n.9. UPS has proposed no reliable
    means of calculating fixed costs, merely claiming without
    support that additional data from the Postal Service would, if
    made available, suggest a way forward.
    IV.
    The Accountability Act requires a competitive product to
    cover only those costs that can be attributed to the product
    “through reliably identified causal relationships.” 39 U.S.C.
    § 3631(b). In establishing this causal requirement, Congress
    expected that “the expert ratesetting agency, exercising its
    reasonable judgment” would “decide which methods
    sufficiently identify the requisite causal connection between
    particular services and particular costs.” 
    NAGCP, 462 U.S. at 827
    . Here, the Commission did exactly that, settling on a cost-
    attribution methodology that implements its statutory mandate
    and falls well within the scope of its considerable discretion.
    Because “the Commission’s exercise of its authority [was]
    ‘reasonable and reasonably explained,’” U.S. Postal 
    Service, 785 F.3d at 750
    (quoting Manufacturers Railway 
    Co., 676 F.3d at 1096
    ), we deny UPS’s petitions for review.
    So ordered.