Photo by Phil King on Flickr.

Despite popular belief, having more tracks isn’t necessary for proper maintenance of the Metro system. It also turns out that express tracks wouldn’t provide much benefit to everyday riders, and it might even do more harm than good.

This may seem a bit surprising to people familiar with express trains on the New York subway, where express tracks can cut a rider’s trip by a third, or even a half. But New York’s stops are spaced much more closely— an average of two to three per mile throughout the system— than Metro’s. This means that a local train in New York spends much more of its time in stations than a Metro train, so there’s a lot more time to be saved by skipping stops.

Here’s how I simulated a system with express tracks:

With Metro, each mile travelled adds about 1.2 minutes to the trip, while each intermediate station adds about 1.1 minutes. I determined this by comparing the scheduled time to the distance between stations for each of the 93 pairs of adjacent stations in the system. From this data, I was able to model the travel time between all of the system’s stations.

Along with a model for trip time, analyzing the possible benefits of express tracks requires a proposed set of local-only and express stations. To demonstrate the maximum benefit that could be achieved with express tracks, I considered a system with minimal express stops.

Along with transfer stations and the ends of lines, I chose nine of Metro’s other high-ridership stations for expresses: Bethesda, Dupont Circle, Farragut North, Union Station, and Silver Spring on the Red Line; Foggy Bottom, Farragut West, and McPherson Square on the Orange, Blue, and Silver lines; Pentagon City on the Yellow and Blue lines, and Columbia Heights on the Green and Yellow lines.

Map from WMATA, with alterations to show potential express stations by the author.

Express tracks aren’t that useful if you aren’t coming from the edges of the system

To determine how much time could be saved, I compared the current travel time between pairs of stations to the travel times my model predicted for express trains. Since doing this analysis for each of the 8148 possible station pairs, I analyzed the 30 station pairs with the highest AM rush hour ridership, based on October 2014 data. These station pairs represent ten percent of the total AM rush hour ridership, and include trips from the six most heavily used end-of-line stations to the downtown stations where the most AM rush hour trips terminate, particularly Farragut North and West.

If Metro were to have express trains, the maximum time savings for trips to Farragut Square would be from Shady Grove and New Carrollton. In each case, an express train would save riders eleven minutes, about one-third of their current trips. From Glenmont, Vienna, and Wiehle, the time savings would be about eight minutes—one quarter of the current trips—is saved; and from Franconia-Springfield, the savings would be six minutes—less than a fifth of the current trip.

The time savings would be much less for riders traveling from closer in: riders between the thirty station pairs I considered would save an average of four-and-a-half minutes. Riders traveling to or from less-used stations would likely save no time, since their stations would be local-only and waiting to transfer to an express would consume their time savings.

In comparison, riders on the New York subway can save much more time by taking express trains. In Manhattan, the IRT Broadway-Seventh Avenue Line has 12 local-only and six express stops in the six miles from 96th Street to Chambers Street, while the IRT Lexington Avenue Line has 14 local-only and six express stops in the seven miles from 125th Street to Brooklyn Bridge-City Hall.

Because of the close stop spacing, a local train on either line takes 30 minutes, for an average speed of 12 to 14 miles per hour, less than half of Metro’s 30-mile-per-hour average speed. Express trains cut these trips by one-third to one-half, but they still only manage average speeds of around twenty miles per hour.

Having express tracks is one thing. Paying to run trains on them is another.

Even without express tracks, Metro’s greater stop spacing allows Metro trains to maintain higher average speeds than New York subway express trains can manage in Manhattan. However, if the system had been built with express tracks throughout, it would still save riders some time, right?

Not necessarily. The usual explanation for why Metro couldn’t have been built with express tracks is that doing so would have substantially increased construction costs, and significant amounts of the current system would have had to been cut to make up for this.

However, capital costs aren’t the only issue: operating costs would need to be considered as well.

Maintaining current service frequency at local-only stops would mean that any express trains operated would have to be in addition to the service that operates today. During off-peak times, Metro’s frequency—particularly on branches, where most local-only stops would be—is already minimal for a rapid-transit system.

Either the express tracks would be unused except during rush hour, or Metro would need a sizable increase in its operating budget, simply to operate the additional trains needed, without considering the additional rail car and track maintenance required. Given Metro’s current struggles to obtain enough funding to operate the system we have, a system with express tracks would probably see significantly reduced frequencies at many stations.

The upside of the fact that running expresses often leads to a decreased frequency of locals is that a line with a pair of express tracks has twice the maximum capacity of a line with only local tracks. This is one reason that express tracks are beneficial on the New York subway, which has an annual ridership per mile of revenue track about three times that of Metro, even though most of its core lines, and many of its branch lines, have express tracks.

The fact that much of the system’s ridership consists of north-south traffic on Manhattan, a narrow island with a limited number of possible north-south routes makes the New York subway a near-optimal situation for using express tracks to increase capacity. The London Underground, which has a similar total ridership and ridership and ridership per track mile to New York, but which operates in a more symmetric and much less geographically constrained city, achieves a high core capacity by having many double-tracked lines crisscrossing the urban core instead of a lower number of four-tracked lines with express tracks.

If we were to have more tracks, downtown would be the place for them

One section of the Metro system where express tracks could help solve capacity issues is the shared segment of the Orange, Silver, and Blue lines between Rosslyn and Stadium-Armory. The large number of commuters from Virginia who enter DC via the Rosslyn tunnel and the frequency reductions on branches needed in order to share one track-pair between three lines lead to severe congestion in this section of the system.

Express tracks here would eliminate the capacity issues that WMATA currently hopes to solve by building a separate Blue Line tunnel under M Street downtown. They would also shorten commute times for riders traveling to downtown from New Carrollton and Largo Town Center (though not from Virginia).

A four-track line between Rosslyn and Stadium-Armory—or elsewhere in the system—would also provide the benefit of providing a work-around when tracks have to be closed for maintenance or due to accidents. However, any argument for express tracks on Metro needs to depend on these benefits and increased capacity, rather than hopes of significantly faster service.