widening gap in many parts of the country between highway spending needs and available revenues. In the absence of significant fuels tax increases in the coming years this gap is likely to widen further, a trend that may accelerate in coming years with the gradual introduction of alternative-fuel vehicles that pay less, or even no, motor fuels taxes.

In response to these challenges, the Transportation Research Board convened a special Committee for the Study of the Long-Term Viability of Fuel Taxes for Transportation Finance. One of the many charges to the committee was to investigate the potential for a system of distance-based user fees [using recently developed electronic tolling technologies such as on-board computers, Global Positioning Systems (GPS), digital jurisdiction and road network maps, and wireless communications] to eventually replace fuels taxes. To inform their deliberations, the committee commissioned the authors of this report to perform an extensive review of innovative electronic tolling applications around the world. This review included projects already in operation as well as those that have been proposed or are in the advanced stages of planning; each was evaluated in terms of policy, technology, and political acceptance issues. This report summarizes the results of this research.

SCOPE AND METHODOLOGY

In selecting case studies to review for this research, we focused on applications that involve networkwide road use metering and tolling, as we judged these to be the most relevant to the concept of distance-based user fees. As a secondary focus, we reviewed facility congestion toll projects and cordon toll projects that might be relevant from a political or technical perspective. We did not examine standard (time-invariant) toll projects that incorporate simple electronic tolling devices (such as in-vehicle transponders), given that such projects would likely offer little technical or political guidance in the design of a comprehensive distance-based user fee system.

Within the context of the study, the goal was to address three principal questions. First, where in the world have such innovative systems been proposed, planned, or developed? Second, how have these projects and proposals been structured in terms of technical design, institutional issues, and political considerations? Third, what is the current status of the projects and proposals, and what factors have aided or impeded their implementation?

In terms of methodology, possible case studies were identified and investigated for inclusion. The scan was based on a review of the literature, a comprehensive search for documents on the World Wide Web, and several phone interviews with experts in the field. The next step was to compile a set of detailed case studies for



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