"The beast," says Ginger Evans, "is out of the cage and trotting down the road."

That would be a toll road, and the beast, for now, is leashed to Dulles International Airport. After a lot of drama and hand-wringing over whether a tunnel would be better than an elevated light rail guideway down the median of Route 7, the need for federal funding—and the opinions of some key tunnel experts versus others—prevailed.

Fairfax County Board of Supervisors approved June 18 funding for the first $2.4-billion to $2.7-billion phase of a planned 22-mile rail connection between Tysons Corner and Dulles International Airport. Despite misgivings about the impact of the initial 11.6-mile phase—which will include elevated sections but not a tunnel—the county did not want to jeopardize $900 million in eligible federal funding. Adding a half-mile tunnel segment would have added $250 million and required more time for an environmental review.

The Virginia Dept. of Rail and Public Transportation is now awaiting completion of a risk assessment by the Federal Transit Administration, which could happen by the end of August. If the risk assessment determines that the project is still eligible for the $900-million grant, design-build consortium Dulles Transit Partners, LLC, led by Bechtel Corp. and Washington Group, will begin a $2.6-million utility relocation along 1.5 miles of Route 7, which will be expanded as part of the overall $4-billion project, says VDRPTA spokesperson Marcia McAllister.

"It's a big first to have someone use a toll road and finance transit," says Evans, a senior vice president with Carter & Burgess. Primarily an aviation expert, she notes that other airports across the country are taking notice of the unique arrangement. Carter & Burgess will provide program management support services for the $4-billion program, for which a joint venture of Bechtel and Washington Group is the design-builder. Some 23 acres of land will be acquired, mostly for the stations.

Plans to route a 0.4-mile segment of a proposed extension of the Washington, D.C.-area Metro subway through a tunnel under congested Tysons Corner, Va., collapsed last September, but the idea was enticing enough that new proponents kept it alive (haven't they heard about Seattle and Sound Transit?).

A panel of engineers had suggested the tunnel option, which Spanish construction giant Dragados put forward, be "strongly considered." Although it would add $250 million to the project cost, it would have a service life of 120 years—twice that of the aerial option—and would save money on operations and maintenance as well, the panel said.

"A tunnel was considered in the EIS," counters Evans. "All the impacts and visual issues associated with aerial transit were discussed. Stakeholders agreed it was the way to go. Secondly, it is not cheaper and doesn't take less time to build a tunnel. The tunnel got the community stirred up by saying it's faster and cheaper. The report alleged they could save six months on the schedule and up to $300 million over lifecycle. What we said was "look, to make an informed decision, you have to have good information."

Both C&B's report, which utilized a team of tunneling firms like Hatch Mott MacDonald, and another report for the FTA by Hill International, says the Dragados proposal was "optimistic" about project schedule and would have the tunnel relatively shallow— less than one tunnel diameter's worth below ground.

"There was not an awareness of the risks - underground water, under a busy roadway," adds Evans.

Dragados, with its hefty resume of roadwork and tunneling work globally, begs to differ. Although Jose Antonio Muniz-Lopez, the Dragados USA spokesperson, declined to officially comment, he did show me a letter from another independent source (name eliminated) that supported the Dragados proposal. The source stated that the tunnel alignment, "located mainly inside the residual soils and decomposed rock" is suited to Earth Pressure Balanced excavation. With no direct buildings atop the tunnel alignment, notes the unnamed source, risks are reduced, although "detailed pre-survey of existing buildings and structures…and implementing a suitable monitoring system" was also recommended.

The source estimated that an 18,000-ft-long tunnel could be built within two years.

Be that as it may, it looks like rail tunnelling will be left to agencies in Seattle, Los Angeles and New York. I wonder if the perspective on risk in such projects may differ enough in Europe—where Dragados and parent company ACS are so active, than from the U.S., where agencies like the FTA adhere to a more conservative view when doling out funds—to pose an cross-cultural challenge for Dragados as it pursues U.S. work.