In American Trucking Assns., Inc. v. Scheiner, 483 U.S. 266 (1987), the US Supreme Court struck down, as violative of the Commerce Clause, two Pennsylvania statutes which imposed lump-sum, annual taxes on commercial users of Pennsylvania's highways. Specifically, the Court addressed the constitutionality of two flat taxes: (1) an annual $25 fee for an identification marker imposed only on out-of-state trucks; (2) an annual fee of $36 per vehicle axle imposed on in-state and out-of-state vehicles. The Court found that the challenged fees failed the " 'internal consistency' test," which requires that a state tax be of a kind that, " 'if applied by every jurisdiction, there would be no impermissible interference with free trade' " (American Trucking Assns., Inc. v. Scheiner, 483 US at 284.) The Court concluded that the marker fee taxes were plainly discriminatory because they had the practical effect of "imposing a cost per mile on out-of-state trucks that is approximately five times as heavy as the cost per mile borne by local trucks" (American Trucking Assns., Inc. v. Scheiner, 483 US at 286). The Court continued, stating that "a state tax that favors in-state business over out-of-state business for no other reason than the location of its business is prohibited by the Commerce Clause" (id.). The Court found the axle tax similarly flawed, in that it had "a forbidden impact on interstate commerce because it exerted an inexorable hydraulic pressure on interstate businesses to ply their trade within the State that enacted the measure rather than 'among the several States' " (id. at 286-287, quoting US Const, art I, 8 3). The Court affirmed that "the Commerce Clause does not require the States to avoid flat taxes when they are the only practicable means of collecting revenues from users and the use of a more finely gradated user-fee schedule would pose genuine administrative burdens" but found that such justification was unavailable in the case at bar (id. at 296).