Posts about Graphs

NOTE: the station traffic, total entries and exits, is indicated by the diameter of each circle, not the area. If you're interested in seeing the raw data, it is available here.

As one might expect, traffic is centralized around several major nightlife centers and drops as you move farther out of the city center. In many respects, the picture underscores all that much more the importance of late night service, while in other respects it raises interesting questions.

First, some assumptions. An entry between 12 am and 4 am most likely represents the location a person was spending their evening. An exit between 12 am and 4 am, with slightly less but still relative certainty, likely represents the final destination of a rider, i.e. home. Thus a station more weighted toward entries should be a nightlife hub, while a station weighted toward exits is likely a residential area.

On the entries side, this seems to hold true in the aggregate, though the stations with the three highest entry to exit ratios aren't exactly the epitome of nightlife. Farragut West had the highest, followed closely by Federal Triangle and Archives. Their entry to exit ratios are 7.3, 6, and 5.4 to 1, respectively.

What's telling about those is that they are near some nightlife destinations, but not ones that would be considered late-night attractions, and are also generally devoid of residences.

The biggest circles, on the other hand, are places with diverse nightlife activities, as well as more (or growing in the case of Gallery Place) residential areas. Of the four busiest stations, Dupont Circle and Woodley Park are the least red, with respective entry to exit ratios of 3.6 and 3.1 to 1. These are also the two with the most residential density nearby.

As a result, you might expect a truly livable, "balanced" neighborhood to have relatively even entries and exits. This holds true in many cases: Columbia Heights and Eastern Market are relatively busy but have ratios between 0.8 and 1.3 to 1.

More suburban activity centers are also relatively busy but tend to lean more toward exits than their center city counterparts. Silver Spring, the busiest station outside the District, has nearly 2 exits for every entry.

Bethesda and Ballston, too, have more exits than entries. Of major activity centers outside of DC, only Clarendon and King Street have more entries than exits, and King Street only by 4%.

Meanwhile, suburban stations, where there is little development around and the stations boast large park-and-ride lots, are generally bright, bright blue.

Several end-of-the-line stations are even quite busy and are also the most heavily exit-oriented station. Vienna was actually the 14th busiest station on this particular Saturday night and had nearly 14 exits for every entry.

What's more interesting are the anomalies. Eisenhower Avenue, one stop from the end of the line, and within walking distance of practically nothing, actually has more entries than exits, though just barely. Suitland, home to a sprawling federal campus and several small, low density neighborhoods has nearly 2 entries for every exit!

Largo Town Center, at the end of the Blue line, actually ties with King Street, in walkable, Old Town Alexandria, for the most balanced station, with only 4% more exits than entries. Interestingly, the more distant stations in Prince George's County are noticeably more purple than those in Montgomery or Virginia.

What could explain these outliers? I can't say for sure. Perhaps with the comparatively poorer populations served by the eastern stations, more people enter late at night to travel across the city to a night-shift job, but that is difficult to tell. What do you think explains the anomalies?

The primary point is this: DC's evening travel patterns are complex. Far more complex than they used to be, too, as Ben pointed out. Late night service serves a variety of people coming from and going to a variety of places for a likely variety of reasons.

These patterns make late night Metro service extremely difficult to replace with night buses and shuttle services. And they make cutting that service even more detrimental to way of life our region has fostered over the last few decades.