Phase 2 of Metrorail to Dulles will absolutely happen, area leaders said at a conference sponsored by Bisnow at the Ritz-Carlton Tysons on Monday.

However, where the money comes from and how high the tolls on the Dulles Toll Road will rise are the variables that keep changing, said former Virginia congressman Tom Davis.

"There are three certainties about Phase 2," said Davis, a member of the Metropolitan Washington Airport Authority (MWAA) board. "It will bring higher density and higher tolls, and the county will have higher operating expenses.

"We are working to keep tolls as low as possible," he said. "No one can tell you with a straight face what the tolls may be."

The funding structure of Phase 2 is different than Phase 1, which received $900 million in federal money. Phase 1 is 50 percent complete and scheduled to run from Tysons Corner to Wiehle Avenue in Reston when it opens in late 2013.

Phase 2 is not getting federal money. About one-quarter of the price tag - which officials are trying to keep at $2.5 billion - will be paid for by Fairfax and Loudoun Counties and MWAA. The rest will come from Toll Road users, which has some people predicting tolls of $10 to $20.

Patrick Forrest, Republican candidate for state senate in Virginia's 32nd District, has said research shows that there will eventually be $17 tolls. He has made that a foundation of his campaign.

Longtime Fairfax County developer Til Hazel said at the conference figuring out who is going to pay is a paramount issue.

"It's not being addressed by the political sector," he said. "It needs to be addressed much more than than this enthusiastic 'we are going to build a train to Dulles!' Everyone says 'tolls will pay for it.' That is absolute nonsense."

Fairfax County Board of Supervisors Chair Sharon Bulova, speaking on the Bisnow panel, said there may be a federal commitment to Phase 2 in the form of Transportation Infrastructure Finance and Innovation Act (TIFIA) loans.

In any case, Phase 2 - which recently required intervention from US Transportation Secretary Ray LaHood and a reversal of a MWAA vote to build a costly underground station at Dulles International Airport - is not in danger of falling apart, agreed Davis, Bulova and Patricia Nicoson, president of the Dulles Corridor Rail Association.

"At the end of the day, I would bet my house that this will get done," said Davis.

Nicoson, a member of Reston's Master Plan Special Study Task Force, says the group is still considering scenarios about the kind of density and population increase rail will bring to Reston.

The task force said last week it will submit a scenario of George Mason University's 2030 scenario, plus 20 percent. However, Nicoson said some people want to add 50 percent to the scenario.

Nicoson said the task force should have two scenarios for the county ready in the next few weeks. The county transportation study is expected to take four months. Task force recommendations may be ready to present to the board of supervisors by late summer 2012.

"We're not afraid of density and we want to use it as a tool to improve the community," Nicoson said.

Bulova reiterated that in order for Metrorail to have an impact here and not overwhelm the roads, there has to be more transit-oriented housing. She says while there will always be a desire and need for suburban communities, Tysons Corner and Reston need to "be able to offer housing choices" that are different than we have.

Davis is not as optimistic.

"You can't just direct all new housing and say 'this is where people will live,' " he said. "People don't move to the suburbs to be near a city; they move to be away from the city. These areas are now turning into cities."