RICHMOND, VA (AP) Experts commissioned to study the proposed 23-mi. Metrorail extension to Dulles International Airport said an underground tunnel through Tysons Corner is a “feasible and cost effective” option, according to a report released July 31.

The panel from the American Society of Civil Engineers (ASCE) was enlisted by Virginia Transportation Secretary Pierce R. Homer to weigh the options of using a tunnel or an elevated track for the 4-mi. stretch through Tysons Corner as part of the project’s first phase.

The two-month study said the tunnel plan would cost approximately $2.5 billion, compared to approximately $2.25 billion for the elevated track. The total cost of the project is estimated at $4 billion.

The panel also noted numerous benefits to the tunnel plan, including less impacts on traffic through the area, longer project life span and reduced costs for maintenance.

The tunnel, the report said, would have a 120-year life span — more than double the alternative — and would allow for $5 million in annual operation and maintenance savings.

While the elevated track could be completed faster and cheaper, the study said, the tunnel option could promote plans to turn Tysons Corner into a walkable urban center.

The report said it’s “reasonable to assume that the tunnel option would provide greater positive long-term economic and business impacts.”

The panel, however, noted that tunnel construction could be delayed by approximately a year to complete preliminary engineering and to obtain proper state and federal approval.

Approximately $900 million in federal money could be invested in the proposed project, controlled by the Metropolitan Washington Airports Authority. More than half of the authority’s share of the project will be paid for with revenue from the Dulles Toll Road.

Deputy Secretary of Transportation Scott Kasprowicz said that Gov. Timothy M. Kaine and transportation officials expect to make a decision by the end of August.

The expansion of Metro’s Orange Line from West Falls Church to Tysons Corner is expected to be completed by 2011, and beyond Dulles International Airport into Loudoun County by 2015.

If Virginia recommends building a tunnel, landowners in the Tysons Corner commercial district could be asked to pay a higher tax, possibly accomplished by revising the existing tax district so that all businesses are paying at a higher rate.

The landowners — including owners of shopping malls and office buildings — already are contributing $400 million to the project through a special tax district. They agreed to the tax partly because zoning rules will allow many of them to build more densely once the rail line is in place.

U.S. Reps. Frank Wolf, R-10th, and Thomas M. Davis, R-11th, have warned officials about supporting a tunnel plan, saying the project could be delayed to conduct environmental studies, which could jeopardize federal funding.

In June, the inspector general of the U.S. Department of Transportation (DOT) ordered an audit of the proposed extension. The inspector general could determine whether underground or elevated tracks are used.

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