main unanswered policy and technical questions about mileage charging mechanisms that an R&D program could address. The final section outlines the key elements of such an R&D program, what it might cost, and management principles that would produce the most effective results.

BACKGROUND

Fuel taxes (gasoline and diesel) provide about two-thirds of the total user fees and about half of all the revenue collected by all levels of government and used to fund highway and transit infrastructure (TRB 2006). Thus, fuel taxes are central to the more than $160 billion invested annually by government agencies in roads and transit. The long-term viability of fuel taxes as a principal source of funding is threatened by political resistance to raising these taxes periodically to adjust for inflation and increased fuel efficiency of the motor vehicle fleet, which is causing less revenue to be collected per vehicle mile traveled. Inflation alone has eroded the buying power of federal fuel tax revenues by 33 percent since the federal gasoline tax was last increased in 1993 (National Surface Transportation Infrastructure Financing Commission 2009, 2). Even as buying power has eroded since 1993, national vehicle miles of travel (VMT) have increased 27 percent.

The committee that prepared The Fuel Tax and Alternatives for Transportation Funding (TRB 2006) recognized the threats to the fuel tax as a revenue-raising approach but concluded that fuel taxes could continue to be an important source of funding for transportation programs for another 15 years; it also concluded that “travelers and the public would benefit greatly from a transition to a fee structure that more directly charged vehicle operators for their actual use of roads” (TRB 2006, 3). The committee concluded that mileage charging appeared to be “the most promising technique for directly assessing road users for the costs of individual trips.”

In federal surface transportation reauthorization legislation of 2005, Congress created the National Surface Transportation Infrastructure Financing Commission to provide guidance on the future of the motor fuels tax, among other things. The 2009 commission report concludes



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