RALEIGH, N.C. — Wake County's 12 mayors on Wednesday unanimously agreed to have the North Carolina Turnpike Authority move forward with studying a plan to place tolls on Interstate 540.

The proposed tolls would be on the Western Wake Freeway, a section of I-540 between N.C. Highways 54 and 55 that is currently under construction.

Lawmakers have said the state has a $30 billion road construction shortfall. In a meeting Wednesday morning, many mayors said that toll roads would speed up construction by 2011, 15 years ahead of schedule.

Others, however, said that drivers would essentially be taxed twice by paying for the road and then to pay the toll.

"Frankly, there are so many uncertainties," said Apex Mayor Keith Weatherly. "My list of questions far exceed the answers I've been given."

The mayors said they want to make sure the proposed toll money would finance only the Western Wake Freeway and also want assurances that the tolls would be removed from the roadway once construction is finished and paid off.

A vote on whether to approve the tolls will not come until the studies are complete.