Photo by the author.

Periodically, we get questions about some of the nuances of Metro’s service and operations. Some of these came up in a recent thread. While some of you know the answers, many don’t. Therefore, we decided to review some of these topics.

In December 2006, Metro began extending Yellow Line trains to Fort Totten off peak. It started as a pilot, but increasing demand for Metro in the mid-city made the extension permanent. If the project was so successful, why not have the Yellow Line run to Fort Totten all the time?

There are several technical hurdles that would need to be dealt with before Metro could run the Yellow Line to Fort Totten during rush hour:

Empty Pockets
The primary reason is that Fort Totten does not have a pocket track. A pocket track is a third track located between the two main tracks. These allow trains to leave the mainline, change ends, and then wait for clearance for the other track without disrupting through trains on either track.

There are only a few pocket tracks in the Metro system. They are located:

  • Red: North of Grosvenor
  • Red: North of Farragut North
  • Red: North of Silver Spring
  • Orange: At West Falls Church
  • Orange and Blue: East of Stadium-Armory
  • Blue and Yellow: At National Airport
  • Yellow and Green: North of Mount Vernon Sq.

Silver Spring pocket track. Photo by the author.

Currently, the pockets at Silver Spring and Grosvenor are used for the short-turning Red Line trains which don’t run all the way to the end of the line. The Mount Vernon Square pocket is used to terminate Yellow Line trains during rush periods. The other pockets don’t see as regular use, although the West Falls Church pocket is used for some trains being brought into or out of the rail yard there.

Of course, pockets aren’t the only place where trains can change tracks. Crossovers are located throughout the rail system, generally between every other station or so, though that varies based on station spacing. Since trains can crossover at any of these switches, they can be candidates for short turning. This is the case at Fort Totten, where a simple diamond crossover allows Yellow Line trains to turn back off peak.

During rush hour, the Green Line operates at a 6 minute headway. The Yellow Line also operates every 6 minutes during peak. That means that the combined segment of the Green and Yellow Lines—between L’Enfant Plaza and Mount Vernon Square—sees a train every 3 minutes. With a pocket track, this is not an issue. Three minutes between trains is plenty of time to reset the switches and keep the subway moving.

But without a pocket, the Yellow Line train would have to sit on the mainline while it changed ends and waited on clearance. At three minute headways, that would create massive delays.

The current setup at Fort Totten works because off-peak the Green and Yellow Lines each run at headways no better than 12 minutes. With 6 minutes between trains, there’s enough time. Even so, northbound Green Line trains are still often held on the platform at Fort Totten because the Yellow Line train is waiting for the southbound Green Line train to clear before crossing over.

Fleet Size Matters
The other technical hurdle to extending the Yellow Line to Fort Totten during rush hours is that there aren’t enough railcars. The longer a rail line is, the more railcars are needed to operate the line at the same headway. Fort Totten might not feel like it’s that far from Mount Vernon Square, but a peak period extension of the Yellow Line would require 30 more railcars than are currently used.

Metro doesn’t have that many extra railcars. An extension would either have to wait for extra cars to be purchased and built, or it would require the cannibalization of railcars from other lines.

Metro is currently in the process of procuring the new 7000 series railcars, but those cars won’t be enough. The initial contract is for 428 cars, although it is expandable. These cars will be enough for the Silver Line (128 cars) and to replace the 1000 series (300 cars). In 5 years or so, when they’ve been delivered, further fleet expansion might make a full-time Yellow Line extension feasible.

Money Matters
It would cost $3 million more per year to operate the Yellow Line to Fort Totten during rush hour. That’s not pocket change for WMATA’s operating budget. In fact, this year, WMATA seriously considered eliminating the off-peak Yellow Line extension to save $3 million per year.

But the capital costs are an obstacle too. In 2006, WMATA estimated that the capital costs of a full-time Yellow extension would be $150 million. That would pay for an underground pocket track, signal system improvements, new maps, and railcars.

Some of these improvements are probably good ideas regardless of what happens with the Yellow Line. A new pocket track at Fort Totten would improve redundancy in the system. New railcars would ease crowding throughout the system.

But even if Metro had the resources to get started immediately, it would be several years before the full-time extension would be feasible. The railcars wouldn’t be on site until after the Tysons and Dulles cars and the 1000-series replacements. And digging a new underground pocket track would take several years to complete and would be disruptive to Green Line riders along the way.

Of course, that doesn’t mean it won’t ever happen. While there are no plans currently, the Mid-City has been growing tremendously, and Columbia Heights has seen dramatic ridership growth over the past year or so. But ridership is still within the ability of the Green Line to provide. Within a few years, some Blue Line trains will be calling at Mid-City and northern Prince George’s stations, and that will also help to alleviate crowding. But that’s a topic for another post.

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Tagged: wmata

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.