Fairfax County taxpayers could be on the hook for nearly $1 billion in traffic improvements at Tysons Corner, as officials sort out ways to pay for the $3 billion project.

The transportation upgrades would be phased in over the next 40 years as the area is transformed from a commercial district to a walkable, highly developed area with far more apartment buildings and a resident-friendly vibe with the coming of Metro's Silver Line.

"Transformation in Tysons is probably a three-generation activity," said Walter Alcorn, chairman of the Fairfax County Planning Commission's Tysons Committee. "We want to make sure transportation infrastructure keeps up with that."

County planners decided taxpayers should pay for most of the public transit, road improvements that will make getting into neighborhoods easier and improvements outside the immediate area that would benefit Tysons. Those upgrades add up to at least $993 million. More exact estimates of what taxpayers would pay are due in the fall.

Taxpayers will also have to pay $734 million in bus operating costs through taxes or fares. And a special tax district for Tysons-wide upgrades could include some residential landowners in addition to commercial landowners -- meaning those who live near Tysons would have to foot even more of the bill.

Private developers and commercial landowners who benefit from the redevelopment would pay the rest of the $3 billion cost.

"The county needs to step up and make it clear how much county taxpayers are on the hook for," said Rob Jackson, former president of the McLean Citizens Association. "There are some serious concerns because we really need the county to say we're not going to put any more on the local taxpayers than 25 percent [of the total cost]."

County planners hope state and federal funds will help offset the costs to local taxpayers.

"It's not just county. It's state; it's federal," Alcorn said. "It wouldn't be borne by one particular group."

The planning commission will vote on the funding plan before sending it to the county board in October.