How would Metro's loop work with an Arlington express line?
While Metro's plans are still in the early stages, at the moment, they seem to be focusing on a new line that would follow I-66 between East Falls Church and Rosslyn, bypassing the crowded Rosslyn-Ballston corridor.
Metro's 2040 projections indicate the need for a new line in Northern Virginia. They estimate that by 2040, there will be significant crowding aboard inbound Silver Line trains before they even get to Tysons, but sharing track with the Orange Line constrains its capacity. They also estimate that by 2040, passengers in the Rosslyn-Ballston Corridor will find it difficult to board trains, with crowding conditions beyond what is considered acceptable today.
The new express corridor would run alongside the Orange Line in the median of I-66 from the junction with the Dulles Airport Access Road until the Orange Line splits off to follow Fairfax Drive. The new line would stay in the median of I-66 to bypass the Rosslyn-Ballston corridor.
The new line would allow up to 26 trains per hour (TPH) to run on the Silver Line as well as on the Orange Line, for a total of 52 TPH passing through East Falls Church. It would feed the proposed downtown Metro loop, along with the Blue and Yellow Lines.
The map above shows one way the new line could operate. Under this scenario, the Silver Line would have a companion, which I'm dubbing the Gold Line for the purposes of this discussion.
The downtown loop would have a capacity of 26 TPH in each direction. The Blue and Yellow lines would use 13 TPH of that capacity in each direction, leaving 13 TPH available on the inner loop and 13 TPH available on the outer loop. For this reason, half of the trains on what I'm calling the North Arlington Express line would need to run counterclockwise and half would need to run clockwise, at least to use the loop to its full capacity.
To avoid confusion, it is likely that Metro would use two different colors for the express line. In the scenario outlined in the map above, half of the trains coming from Dulles would be colored Silver, while the other half would be Gold. Each would alternate, going around the loop in the opposite direction.
Of course, it would also be possible to "transform" the lines as I described with regard to the Blue and Yellow lines on the loop in the last post. That way, riders would be used to taking the same color in the morning as the evening. But I did not illustrate that in a map, because with four lines on the loop, it becomes increasingly complex to show the transforms.
Running trains from the North Arlington Express onto the loop would maximize the capacity of the Dulles/Tysons line, the Orange Line, and the loop line at 26 TPH each.
Metro is not wedded to running the line down I-66. As planning continues, WMATA will do studies to determine the best location for the new line. It could be along I-66, or it could follow another corridor, but the concept is the same. By separating the Silver and Orange lines, WMATA can increase capacity to match the expected demand in northern Virginia.
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