The real villain with the W&OD situation goes back to J.P. Morgan. He formed the Southern Railway Company in the 1890s, and started absorbing rail lines (including the one that had been started in Southern Pennsylvania and eventually became the route for the PA Turnpike). Once they had taken in the Washington and Old Dominion, which at that point had gone to Bluemont, Morgan, or at least one of his staff, ensured that this would be the end of the line so they could not go to Winchester and connect with the mainline in the Shenandoah Valley. There was a viable route to do this, but they never got the chance.
As this decreased the viability of the railroad, dooming it to the status of local short line, they could never get the momentum going to be of any major importance. So, it hauled grain, milk and passengers. They tried to dump passengers around 1940, but when WWII started they had to pick them up again due to wartime shortages and transportation issues due to rationing. Just about when they could have shut down around 1959, Dwight Eisenhower, who literally was the one that chose the Loudoun County airport site over one near Burke, changed all that. The W&OD was now a primary mover for building materials to the Herndon station, about 2.5 miles from airport property. The line was important again for three years, but Route 28 north of Chantilly was rerouted to the current alignment, further negating the need for the train.
It stopped operating in 1966 and they pulled track in 1967. A stretch of it in Arlington was snapped up by the state or the feds to build 66 between East Falls Church and Spout Run. The rest obviously became the park.
To make it viable for Metro, it would have to be about three times as wide as the current path, have several over/underpasses built (the bike trail usually goes over or under now, of course), and possibly ditch some houses through eminent domain. Since the Dulles Access Road was constructed with a rail system in mind, and the W&OD skirts the northern end of the property by more than three miles, not really a contender.
I think I got most of the facts correct on this, but open to clarification or correction. And as Morgan probably set, "It's not personal. It's business.
"OK, it's also personal!"
Rails and Ragtime Rhythm
