Critics of the gas tax say it will further diminish as a revenue source as technology improves mileage. They also note that it does not precisely reflect which roads a motorist uses. For instance, a Pennsylvania resident could regularly purchase gasoline in that state while doing most of his or her driving to a job in Baltimore.
Chief among those critics has been Peters, who opposes raising gas taxes to fill a looming shortfall in the federal transportation trust fund. She issued a report this year calling for a transition to fees based on road usage.
Under such a system, each user of the nation's roads could expect to receive a bill each month reflecting how many miles were driven - as well as when and where. The report argues that with the gas tax embedded in the cost of fuel, motorists tend to see the use of the road system as "free" - encouraging them to drive at times of peak demand and promoting congestion.
"One of the things politicians like about the gas tax is that it's invisible," Kuhl said. He said he envisions a system under which road charges are "taken out of the hands of Congress" and entrusted to a commission. The typical American now pays about $250 a year in federal and state gas taxes, he said.
Transportation advocates are hardly unanimous in accepting the idea of road use fees. The National Surface Transportation Policy and Revenue Study Commission issued a report last year calling for a gradual increase in fuel taxes of 5 to 8 cents a year over five years - with future increases indexed to inflation.
"While there is a growing consensus that alternatives to the fuel tax may be necessary in about 20 years, the fuel tax should remain an important component of surface transportation finance until viable alternatives are found," the commission said.
Peters, a member of the panel, dissented.
The Iowa study will test one of the systems that has been suggested as an eventual replacement for paying at the pump.
Kevin Leibel, a spokesman for the center, said Baltimore is one of six sites around the country where the system will be tested. Starting today, the center will run ads seeking volunteers from Baltimore and Anne Arundel, Baltimore, Carroll, Harford, Howard and Kent counties to take part in the program.
Participants will agree to have what Leibel called "a noninvasive little computer device" mounted under their car seats.
