Only two stations with side platforms, rather than a single island platform in between the tracks, have ever served as the end station of a Metro line: Dupont Circle and Ballston. Here’s how we think it worked at Ballston.

Ballston, a side-platformed (former) terminus. Photo by OR_MarLo on Flickr.

Between Ballston station’s opening in 1979 and the extension to Vienna in 1986, it was the terminus of the Orange Line. Because, like most other stations in the Rosslyn-Ballston Corridor, Ballston was designed with side platforms in order to minimize disruption to the streetscape above during the cut-and-cover construction, this presented a fairly unique challenge for managing passenger flow.

The only other side-platformed terminus in WMATA history was Dupont Circle, which operated as the western terminus of the Red Line for almost five years, from it’s opening in January 1977 until the extension to Van Ness in December 1981. That station had to be built with side platforms because the Red Line’s tracks were constructed in a single large-bore tube between Farragut North and Woodley Park, making it difficult to fit an island platform between them at Dupont.

Ballston’s platform and track layout. Graphic by the author.

As Metro expert Matt Johnson explained in a very detailed 2014 post on the logic behind Metrorail platform layouts, island platform stations function much better as terminals than side platform stations. When a terminal has an island platform and a track crossover on the inbound side, trains can stop on either track, discharge and board their passengers, and then leave on the “correct” track to head back to the city.

At a terminal where trains service both side platforms, however, a train would have to berth at one platform, move beyond the station to switch tracks, and then turn around to service the opposite platform - a very time-consuming and inefficient method. It’s possible for a side platform station to avoid this problem by only utilizing one platform for both alighting and departing, but this severely limits the capacity of the terminus.

Building island platforms at terminals also makes sense from a passenger flow standpoint. At a side platform terminal station where inbound trains might depart from either track, passengers will congregate on the “tuning fork” mezzanine to wait for a train to arrive rather than waiting down on the platform, as we saw occur at Ballston during the first Safetrack surge back in June.

When a terminal station has an island platform, the passengers feel safe waiting on the platform because they know that they can board a train no matter which track it arrives on.

“Tuning fork” mezzanine at Ballston. Photo by the author.

Although building a terminal without an island platform is not ideal, Ballston seemed to function well as a side platform terminal for over six years. Matt Johnson believes that this was accomplished by only using one platform at Ballston — a method that would have limited Ballston’s capacity as a terminus (as mentioned above), but which would have been tenable because Metro would have been running far fewer trains during its early years of operation.

Under this method of operation, what is now Ballston’s outbound or “westbound” (Vienna/Wiehle-bound) track and its corresponding platform would not be used in regular service. Instead, a train approaching Ballston from Virginia Square would cross over to the “inbound” track at the switch just east of the station, before berthing on the inbound (now the New Carrollton/Largo Town Center-bound) platform. Passengers would board and alight the train on this platform while the operator changed cabs, then the train would leave the station in the direction of downtown, leaving the platform open for the next train to service.

Conjectural terminal operations at Ballston, with the outbound track in red. Graphic by the author.

Today, the only vestige of Ballston’s time as a terminus is the “terminal supervisor’s booth,” located underneath the mezzanine on the inbound platform. The booth is made of inexpensive and easy-to-assemble materials, because Ballston was only planned to function as a terminus for a short time, although it still appears to be staffed. Permanent booths made of concrete are typically constructed at stations that are planned to function as terminals for an extended amount of time, such as this booth at the end of the platform at Silver Spring station.

Terminal supervisor’s booth at Ballston. Photo by the author.

Alex Cox is a transit analyst who currently lives and works in the Boston area. He is a longtime Greater Greater Washington reader, former intern at the Coalition for Smarter Growth, and a native of Arlington County. The views expressed here are his own.