Fairfax County officials are considering imposing $500 million in new taxes on the developers of Tysons Corner to help pay for the roads needed in what would become the county's urban downtown.

County officials have already approved some of the planned Tysons projects, including Capital One's redevelopment of its 26-acre campus near McLean, even though they need an additional $1.2 billion to pay for roads. Another dozen projects are up for approval this month.

The county's latest plan, to be taken up by the Planning Commission on Tuesday, would place a new tax on developers that would raise about $250 million. It also would create a new tax district around the redeveloped area that would generate an additional $250 million in new taxes, county officials said. It's the county's third plan to fund road construction since first approving the 40-year development project in 2010.

Those new taxes would be in addition to what the county already plans to charge developers to build streets around their businesses, expected to cost $865 million alone, and the other amenities developers have agreed to provide, like the 30,000-square-foot community center Capital One agreed to build.

The rest of the $1.2 billion needed to pay for improvements associated with Metro's new Silver Line, among other things, will fall to all county taxpayers. The county last week unveiled a long list of potential tax increases that could raise the money it needs, including a 4 percent food tax or 1 percent sales tax on services.

Supervisor Pat Herrity, R-Springfield, said he'd heard few complaints from businesses and expects development to continue "as long as they consider the move to be profitable."

But the new tax plan has raised concerns for some developers and businesses in Tysons.

Brian Gordon, the Virginia vice president of government affairs for the Apartment and Office Building Association, said he's concerned about what will happen if Tysons doesn't develop as quickly or successfully as business leaders hope.

"What if the growth we're expecting doesn't come?" he asked, noting it would likely shift the burden of financing roadways onto taxpayers living and working inside the special tax district.

Other Tysons developers, including Capital One, Cityline Partners, Science Applications International Corp., Greystar Real Estate Partners and Prudential Real Estate Investors, all declined comment.

The County Board of Supervisors voted in June 2010 to completely redevelop Tysons Corner from a midsize office park into a massive mini-city filled with high-rise offices, hotels, restaurants and shops along the Metro's new Silver Line.

The development will require an extensive road network, including the widening of Route 7 and extending Jones Branch Drive.