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That may be the result of what many transportation ... experts see as an inevitable revolution in the way Americans pay for their highways.

The flow of the gas tax pipeline that has poured cash into one of the world's premier highway systems has slowed as some people drive less and others choose more fuel-efficient vehicles. Maintaining that aging network and tackling the rush-hour congestion afflicting most cities will require billions of dollars. As gas tax revenue dwindles, federal and state lawmakers have an option created by innovative new technology: charge the nation's 201 million drivers for every mile they travel.

That prospect was raised last year by a congressional commission, a Brookings Institution report and a highly regarded nonpartisan transportation research group.

In 2008, then-U.S. Transportation Secretary Mary E. Peters warned a Senate subcommittee that the "fuel tax is unsustainable in the future."

"Virtually every economist who has studied transportation says that direct pricing of road use, similar to how people pay for other utilities, holds far more promise . . . than do traditional gas taxes," she said.

But getting the public and its elected officials to accept that idea may be a tough sell.

It is a change that could spark more debate than health-care reform, as federal and state policymakers weigh the use of pioneering technology against expected opposition from those who fear an invasion of their privacy and view paying per mile of road use as a form of taxation.

"Technology is not the limiter," said Ginger Goodin, a senior research engineer at the Texas Transportation Institute who did a major study on pricing. "The decision is in the policy arena. It's entirely up to lawmakers and their constituents."

On the road to change

The need for transformation in the way Americans pay for highways is in large measure the result of what they drive and how much.

Pennies per gallon paid at the pump have provided much of the tax revenue that states and the federal government have used to build and repair 8.5 million lane miles of roadway. Since 1993, the federal government has collected a tax of 18.4 cents per gallon, while state rates range from 8 cents in Alaska to 46.6 cents in California. When the two taxes are combined, Americans pay 46.9 cents on average.

If fuel consumption drops 20 percent by 2017, a goal set by President George W. Bush, gas tax revenue will drop as well. But it could fall far faster. President Obama mandated that new cars get even better mileage -- 35.5 miles on average per gallon -- by 2016, and he designated $2.4 billion in grants for companies developing car battery and hybrid technology.