as also suggested in dicta that the market value standard may be set aside when its application "'would result in manifest injustice to owner or public" (Duncanville Landfill, 469 U.S. at 29, quoting United States V. Commodities Trading Corp., 339 U.S. at 123). The Court has never provided much guidance as to when this exception might arise, and has rejected every attempt to invoke it. See, e.g., Commodities Trading Corp., 339 U.S. at 30-36; Lutheran Synod, 441 U.S. at 514-17. The language of these opinions and the Court's failure to apply this exception strongly suggest that it is extremely narrow, at best, and possibly even empty. Constitutional Limits on the Pricing of Access to Networks conventional rate regulation sets prices that utilities can charge for final outputs, any attempt to base regulated rates on final prices is hopelessly circular. Access reg- ulation, in contrast, alleviates this problem by allowing market-based competition to determine the prices utilities charge for final goods. It is true that the access reg- ulation approach is somewhat circular as well. For example, regulatory authorities still must establish rates to govern the terms under which incumbent firms must provide access to competitors, and the rates they set will have some influence on the prices charged for final goods. Network access nonetheless remains only one of several inputs required to produce the final good. Circularity is not a problem with respect to nonbottleneck inputs. The emergence of direct, facilities-based network competition also is of con- siderable constitutional importance. Indeed, the emergence of direct competition undercuts the justifications for imposing access regulation as a matter of princi- ple. But even setting aside the question whether access represents good policy, the emergence of substitute network technologies has profound implications for the implementation of any access regime. By facilitating the emergence of alternative networks capable of providing market-based indicia of competitive pr