Photo by tracktwentynine on Flickr.

Yesterday, we discussed how Metro could grow its core capacity if it chooses to build a Rosslyn wye in the short run. Today we’ll look at how a terminal for the Blue Line could fit into the picture.

Today, Rosslyn is the biggest bottleneck in the system, which will only get worse when the Silver Line opens. Three lines vie for space in one tunnel from Rosslyn eastward, which limits trains on the Blue, Orange, and Silver Lines.

Metro could relieve the pressure for now by either building a new terminal for the Blue Line at Rosslyn, or a “wye” to let some trains from Tysons go to Arlington Cemetery and farther south in Virginia. But in the long run, Metro needs more capacity over the Potomac River.

Post-2025 solutions with a Rosslyn terminal

The Rosslyn terminal would enable Blue Line trains to terminate at Rosslyn without interfering with the Orange or Silver Lines. This would allow more Orange and Silver trains from Tysons and the Rosslyn-Ballston corridor. But it also means that all Blue Line riders going to DC would need to transfer at Rosslyn or Pentagon.

That solution might work for a few years, but if Metro ridership continues to grow, the Rosslyn terminal would need to become the first phase of a new Potomac crossing.

A separated Blue Line: Metro could easily expand a Rosslyn Terminal into a new line to DC. A likely path would take the line under the river to Georgetown and then east into the downtown core.

In addition to the 26 trains per hour (TPH) running between Rosslyn and Downtown on the Orange/Silver subway, an a separated Blue Line to Georgetown and into downtown would allow 12-16 additional trains to cross the Potomac at Rosslyn.


This would increase the number of trains running between Virginia and DC per hour during the peak from 40 to 52.

However, because the Blue Line shares with the Yellow Line, the new subway across downtown Washington would only be able to operate at roughly half of its maximum capacity. That’s probably fine in terms of ridership for a while (and off-peak for much longer), but in order to get the full potential out of the new line, it would need to be separated from the Yellow Line.

A separated Blue Line could also allow for more service on the Green Line through the Waterfront or Capitol Riverfront areas, which are quickly adding jobs. Metro could get some additional Green capacity by shifting some Huntington trains to the new Blue subway via Rosslyn (a sort of reverse Rush Plus).


Shifting some Huntington trains to run through Rosslyn would not increase the number of trains crossing the Potomac beyond what could cross under the first separated Blue Line scenario, but it would enable more service on the Green Line.

Two new subways?

What about both a separated Blue Line and a separated Yellow Line? Two new subways in the core would be very expensive. But if Metro wants to maximize the capacity on its system, it has to separate each line in the core.

One way to do this is to build a new terminal for the Blue Line at Pentagon. The Blue Line could have its own platforms, and trains from Franconia-Springfield (now all colored Yellow, or perhaps a new color) and Huntington would all cross the 14th Street bridge.


This would also have the advantage of reducing the amount of interlining in the system. With the lines no longer sharing with each other, delays wouldn’t cascade across multiple lines if a train were to break down or some other mishap were to occur.

But the real issue is being able to have the flexibility to balance trains across the different lines. Right now, the Blue and Orange must be balanced based on ridership demand, as do the Green and Yellow. The problem is that Metro is bumping up against the absolute capacity of both subways.

With just a separated Blue, there would still be demand for a direct trip across the 14th Street Bridge. And once that demand outstrips Metro’s ability to provide supply, Metro won’t be able to do anything (because the Yellow shares with the Green). With just a separated Yellow, service between Pentagon and the western side of downtown is constrained by demand for the Orange/Silver.

At some point in the future, if Metro keeps growing, it may become necessary to build the other separated line. With both a separated Blue and a separated Yellow, the number of trains crossing the Potomac would increase to a maximum of 78.

Other improvements would probably be necessary to enable a full 26 trains per hour to run on the Green Line. It’s not clear if the terminals at the end of each line could handle turning 26 trains each hour. Metro would probably need places for trains to turn around short of the terminals, like the pocket tracks at Silver Spring and Grosvenor on the Red Line. Alternatively, Metro could look into rebuilding the terminals, Branch Avenue and Greenbelt, with more capacity.

It’s hard enough to say if we can get one new subway by 2040, given the funding picture today. But a second new subway might be in the cards farther down the line, and now is the time to start planning for it.

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Matt Johnson has lived in the Washington area since 2007. He has a Master’s in Planning from the University of Maryland and a BS in Public Policy from Georgia Tech. He lives in Greenbelt. He’s a member of the American Institute of Certified Planners. He is a contract employee of the Montgomery County Department of Transportation. His views are his own and do not represent those of his employer.