Metro Considers Tysons Options

Project officials said they have not determined how -- or whether -- those neighborhoods would be affected because they are focusing now on the cost, not the exact route. James Haggins, Metro's director of construction, said the neighborhood path was presented to project managers as one option that could reduce the length and expense of the tunnel.

Such a large boring machine would require excavating at 100 feet in some places, deeper than most points in the existing 106-mile Metro system. However it is built, the line would create two tracks large enough for two trains. Additional space would be used for station platforms or service or equipment areas, Haggins said.

One concern is that a shift in course could delay the start of construction. Preliminary engineering for the rail line is almost finished, and the project is awaiting federal funding this fall. But tunneling would call for a new design and possibly a new environmental review, both complicated and lengthy undertakings.

Connolly estimated that rising construction costs could add $50 million to the project each year it is delayed.

Paul Griffo, a spokesman for the Federal Transit Administration, said he could not assess whether "something that's not even in the pipeline with us right now" would face new regulatory hurdles.

Picard said his team considered a three-mile tunnel last year between the Capital Beltway and the Dulles Airport Access Road but concluded that construction would cost 50 percent more than the aboveground alignment. Haggins said he asked Dulles Transit Partners whether they had met with engineers who have used the new technology in Europe. "They said they had evaluated it only internally," Haggins said. "We were able to convince them to discuss it with Dragados," the firm working in Spain.

Most of those involved with the Dulles project agree that labor costs, soil conditions and materials are different in Northern Virginia and Spain.

Beyond a comparison of construction costs is another environmental factor that sets Tysons apart: The cost of street closures would be far higher if the line is built aboveground. Each time the state closes a road to traffic to allow crews to build the Springfield Interchange, it costs money to inform the public, direct drivers to alternative routes and hire workers to block roads.

Consider what would happen in Tysons, where redirecting traffic is anathema to retailers. "Our challenge here is that the Tysons businesses don't want us to tell their customers to go to Potomac Mills instead," said Sam Carnaggio, the state's project director for the Dulles rail project. "And people have to get to their jobs. That's a major, major difference."