Metrorail will reach its capacity by 2030. The Orange Line is already just about maxed out in Arlington. We can build light rail, BRT, streetcars and other modes to relieve the pressure, but Metrorail will remain the fastest and most desirable mode. The separate Blue Line would relieve some of the pressure, allowing for more trains through Rosslyn. However, a new Potomac tunnel and subway across DC would cost billions. If we can’t fund that, is there a cheaper way?

How about separating the Yellow Line instead? The Yellow Line plan Dave Murphy suggested last week, and some of your comments, suggest a possibility. If we separate the Yellow and Green lines in DC, then Metro could put many more trains over the 14th Street bridge. According to Metro planners, this option would involve building a shorter subway tunnel from the 14th Street bridge to the Convention Center along 9th Street.

While the tunnel at Rosslyn is already at its capacity, the 14th Street bridge isn’t, because all its trains must merge with Green Line trains from Branch Avenue. Metro can squeeze a few more Yellow Trains in if they reduce Blue trains, but not that many. If the trains didn’t have to compete with the Green Line, the 14th Street bridge could carry many more trains from Virginia.

The new Yellow Line could connect to Green, Blue, and Orange at L’Enfant Plaza, stopping on a new platform just west of the existing station. Metro already wants to link Metro Center and Gallery Place with a walkway; the new line could stop along there as well to connect to all other lines.

For the other two stations, walkways probably aren’t necessary. We could give them different names (Convention Center West?) However, the stations are extremely close to the existing ones, unless we put them in different spots. One advantage of lining them up and even giving them matching names is night service. When the Yellow and Green Lines are running at low frequencies, it would make more sense for Yellow trains to merge with Green, as they do today, to give each station more service (and save money by closing some entrances).

While this plan mostly benefits Virginia, it does do some good for DC and Maryland as well. The Green Line south of L’Enfant won’t be able to carry more trains, even as development picks up in the Capital Riverfront area and, hopefully, in River East and Prince George’s County one day. A separate Green Line would let all stations benefit from more frequent service. Finally, ending the Yellow Line at Convention Center always leaves open the possibility of extending it through DC and into Maryland along some route one day.

One big question mark remains. Yellow Line trains also have to compete with Blue Line trains for space between Pentagon and King Street. If we add trains over 14th Street, they have to go somewhere on the other end. How would we handle service on the Virginia side? I’ve come up with two possibilities, which I’ll show tomorrow. What can you come up with?

David Alpert is Founder and President of Greater Greater Washington and Executive Director of DC Sustainable Transportation (DCST). He worked as a Product Manager for Google for six years and has lived in the Boston, San Francisco, and New York metro areas in addition to Washington, DC. He lives with his wife and two children in Dupont Circle. Unless otherwise noted, opinions in his GGWash posts are his and not the official views of GGWash or DCST.