"Many people are concerned that the government is somehow going to track them," he said. "We don't want to show that you stopped at Joe's Grill."
This year, 1,500 new participants are being selected in Miami; Chicago; Albuquerque, N.M.; Portland, Maine; Wichita, Kan.; and Billings, Mont.
A commission created by Congress to study transportation financing released a report in February offering recommendations on how to pay for highways, other than the gas tax. A mileage-based fee was one of the top solutions.
"The most viable approach to efficiently fund federal investment in surface transportation in the medium to long run will be a user charge system based more directly on miles driven (and potentially on factors such as time of day, type of road, and vehicle weight and fuel economy) rather than indirectly on fuel consumed," the report said.
U.S. Transportation Secretary Ray LaHood floated the idea around the same time as one of several ways that the government could pay for highway building and maintenance.
"We all ought to be thinking outside the box about how we're going to fund roads, bridges, infrastructure beyond the stimulus," LaHood told reporters in February.
The White House couldn't back away from the comment fast enough.
"It is not and will not be the policy of the Obama administration," press secretary Robert Gibbs said, adding, "It's a no-go."
Still, the federal transportation trust fund, which pays for road, bridges and transit projects, is expected to run $8 billion short by August. Congress must put more money into the fund or raise the gas tax. Back in September 2008, the government chose to pump $8 billion into the fund.
The gas tax is now 18.4 cents a gallon and hasn't changed since 1993.
So now, more and more cash-strapped states are at least putting the option out there for discussion as they embark on their long-term transit planning.
At least 10 states have mentioned a vehicle-mile-traveled, or VMT, tax in planning documents, according to Jim Reed, transportation program director for the National Conference of State Legislatures. Another six have discussed it in some way or another, Reed said.
"It's still a pretty new idea," Reed said. "It's catching on nationally because we do have this shortage of funding in the gas tax."
The issue is likely to hit center stage this summer when the 6-year-old legislation dealing with the highway fund and the 18.4-cent a gallon gasoline tax comes up for reauthorization. (States charge about 20 cents extra for each gallon of gas purchased.)
Robert Puentes, a senior fellow studying transportation at the Brookings Institute, said Americans are driving less and using more fuel-efficient cars, and that gasoline taxes haven't been raised fast enough. At the same time, the demand for additional highway spending has never been higher.
"So it's a real perfect storm when it comes to transportation funding," Puentes said.
The country is heavily dependent on the fuel tax, Puentes said, and a vehicle-mile-traveled fee "is exactly the type of solution we should be talking about."
"Gasoline being consumed is less. That on the surface is not a bad thing. We've been talking about energy dependence for years and years and years and here we're finally starting to make inroads." he said. "But it has this dramatic impact on transportation funding."