WASHINGTON — Mileage-based systems could yield revenues between three and eight times higher than the gas taxes currently used to maintain the public road system and back bonds, the Congressional Budget Office found.

The results, which the CBO compiled from a lengthy 2011 report that compares gasoline taxes and vehicle mileage fees, was requested by the Senate Budget Committee and presented to the U.S. Chamber of Commerce this week.

The report evaluates gas taxes against vehicle mileage-based taxes (VMTs) on the basis of three factors: efficiency, equity, and privacy.

Compared to gas taxes, a long-utilized flat tax levied at both the federal and state level on each gallon of gas, VMTs are more efficient and at least as equitable, but raise major questions when it comes to individual privacy, according to report author Perry Beider.

VMTs would charge drivers for the miles they drive instead of just the gas they burn, using a global positioning system or an odometer reader.

Under the most efficient scenario, in which VMTs are added to augment per-gallon gas taxes and imposed throughout the nation, revenues could reach about $500 billion: triple the current cost of maintaining the roadway system, the CBO claims.

Gas taxes alone are no longer up to that task.

The most recent transportation funding bill requires transfers from the U.S. general fund to keep the national highway trust fund solvent until 2015. In addition, grant anticipation revenue, or Garvee, bonds have been downgraded because of the uncertainty surrounding future revenue collections of gas taxes. Garvees are backed by highway trust fund revenues.

Some forms of VMT would shift the financial burden disproportionately onto urban drivers, since many VMT ideas include some sort of “congestion pricing” for high traffic conditions, but traditional gas taxes would effect more rural drivers who have to drive further.

Any VMT system would have to limit the type of information collected about a driver’s habits, to alleviate concerns about violations of privacy, the CBO explains in its presentation.

With these ideas on the table, it concludes, it is now up to policymakers to hash out exactly what system should be adopted and whether the federal government, state governments, or the private sector should lead the implementation.

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