Well, that’s what the American Society of Engineers said to Metro ^[1]. A tunnel to Dulles may add a quarter billion dollars to the cost, but take up significantly less above-ground real estate. The 4-mile tunnel would take something like $4 Billion to make, and likely wouldn’t be completed in any of our readers’ lifetimes, but it would extend the Orange Line out to Dulles Airport by way of Tysons’ Corner. The whole run out to Dulles is roughly 23 miles and would parallel the Dulles Toll Road for the run to the Airport.