ntertwined with others' use. Because these encum- brances effectively prevent the owner from using the property for other purposes, compensation for such a taking must reflect the property's going-concern value. It is no doubt tempting for regulatory authorities and courts to resolve takings challenges to network regulations according to the same principles applied in conventional rate regulation cases. Those principles are based on balancing tests that regard as constitutionally unproblematic those regulations backed by strong public policy justifications and having minimal economic impact. In addition, adherence to preexisting approaches allows regulators to continue employing the cost-based methodologies with which they are familiar. Rate-making authorities can thus maximize the leverage they have gained from regulatory tools developed in previous rate-making efforts. Constitutional Limits on the Pricing of Access to Networks Blind application of existing principles, however, ignores the constitutional import of the shift from rate regulation to access regulation. As noted earlier, access regulation typically requires network owners to permit permanent physical occupations of their property. Unlike rate regulation, access regulation effects a physical taking for which the government must pay compensation without regard to the magnitude of the invasion, its impact on investment-backed expectations, or the importance of the policy interests furthered by the regulation. The Court has made clear that the regulatory takings and confiscatory rate-making precedents upon which regulatory authorities have previously relied in rejecting takings challenges do not apply to cases involving physical takings. The Court's takings jurisprudence also makes clear that the best measure of just compensation is market value, which is best determined through actual market transactions. Although at one point the absence of external, market-determined benchmarks may have justified reliance on cost-based valuation methodologies, the em