A Northern Virginia Republican lawmaker joined a group of Democrats lobbying Gov. Bob McDonnell to provide more state funding for a new Metrorail line to Washington Dulles International Airport.

Sen. Dick Black, R-Leesburg, was among the Republican legislators who earlier this year defeated a Democratic proposal to increase state funding for the Silver Line. But he is now asking McDonnell for $200 million to ease pressure on Dulles Toll Road drivers, who are expected to provide most of the $6 billion rail line's funding.

"I'm concerned that the current financing plan will load commuters with such exorbitant tolls that it will force traffic from the Dulles Toll Road, resulting in increased congestion on all surrounding roads," Black wrote to McDonnell.

The change of heart for Black, whose district includes the toll road, is encouraging for Democrats, who plan to renew the fight for rail funding in 2013.

"If now Republicans are seeing that what we were fighting so hard to get for Northern Virginia really does need to materialize, I'm hopeful it will have some influence on Gov. McDonnell and House Republicans," said Sen. Mark Herring, D-Leesburg. Herring introduced a bill earlier this year that would have provided $500 million in state funding for the project.

The dispute over state funding for the $6 billion rail project has grown so intense in Richmond that it threatened to bring the state government to a halt earlier this year. Senate Democrats held the state budget hostage, demanding that McDonnell and House Republicans provide an additional $300 million for the Silver Line. The money would have helped keep down the cost of tolls, which are scheduled to skyrocket in coming years to bankroll the second phase of the project.

Democrats finally lost when one of their own, Sen. Chuck Colgan, D-Manassas, broke ranks and voted with Republicans to pass the budget without the Silver Line money.

House Republicans, who control the chamber, remain opposed to providing any new money for Dulles Rail.

"They say, 'The state's got to do their part.' They overlook that we gave [the Metropolitan Washington Airports Authority] the tolls for the Dulles Toll Road," House Speaker Bill Howell said. "That's money generating cash in the future."

McDonnell's office did not respond to questions about Black's email.

Black told The Washington Examiner that rail riders, not toll-road drivers, should bear the cost of the expansion, even if it meant $10 Metro fares to Dulles.

Herring said funding should be balanced.

"You can't just put it all on the toll roads or rail users," Herring said. "There needs to be a mix of funding in part that will be paid for through fares, and in part through the tolls, and in part through state and federal government."