opinion offered a laundry list of considerations to guide the rate-making determination. Replacement cost did not become clearly established until the next year in San Diego Land & Town Co. V. City of National City, 174 U.S. 739, 757 (1899). See generally Siegel (1984). Pricing of Access to Networks long as the input remains only one component of the overall good, the income capitalization approach is not tautological. The degree of circularity will be limited to the percentage of the total cost of the final good represented by the regulated input. Equally important is the manner in which technological change has allowed competition among different network platforms to develop. The availability of substitute networks employing alternative means of transmission has in turn created external markets that now make it possible for regulatory authorities to base rates on prices charged in actual market transactions. In addition, the advent of facilities- based competition in turn can lead to deregulation of the rates charged for the final good, which will eliminate the circularity inherent in the income capitalization approach. In short, two fundamental changes are transforming the basic approach to regulating network industries: the development of platform competition and the shift to access regulation. These changes undercut the rationale underlying rate- making authorities' decisions both to base rates on some measure of direct costs and to exclude from their calculus components designed to reflect earning potential. Together, the development of platform competition and the shift to access regulation have rendered continued adherence to that approach untenable and mandate, as a matter of economic policy, that regulatory authorities begin to base access rates on market prices. 2. Excess Capacity and Zero Opportunity Costs Courts that have recognized the importance of ensuring that access rates contain some measure of opportunity cost have begun to employ a different gambit to justify basing access rates solely on dir