The Problem with Rosslyn

Every sector of our economy that uses energy will have to change if we are going to respond to the climate crisis. Right now, the largest overall contributor to greenhouse gas emissions is transportation. Vehicles, planes, and ships collectively account for 29 percent of the problem. Since we are a car-focused culture, the major thrust has been to make electric cars and trucks more widely adopted though tax credits and planned investment in charging infrastructure. So long as the electricity is produced from renewable sources, we would have a self-sustaining infrastructure after the transition that solves the problem. That would, of course, be easier if we had to build fewer electric cars in the first place.

Public transit is the most efficient method of quickly reducing transportation emissions. Every person taking a bus or subway when going about their business is one less car on the road that needs to be replaced, allowing the transition to progress that much faster. At least once (or if) we get past the pandemic. At its height, the DC subway system was moving over 600,000 people per day. Whether light rail, subways, trams, or anything else, making infrastructure investments in our cities can have a major impact. That is, if they actually work properly.

The DC Metro system is, shall we say, having a difficult go of it lately. As if COVID-related issues weren’t enough, they’ve had to take the majority of the fleet out of service due to issues with the wheels staying on the tracks, something I’m told is very important. We’re back to using the old cars, the ones that have a tendency to start fires. You can’t say you’ve experienced the District until you’ve had your first evacuation from Metro Center, clambering up the escalators as medics tend to people suffering from smoke inhalation.

These problems are acutely visible, but far from the only ones plaguing what should be a great system for getting people off the road and reducing emissions. My biggest consternation upon moving to DC was trying to figure out when to leave for in the morning. In a rational world, leaving home at the same time every day would result in the same commute. Not so with the Metro. Every morning feels like a gamble as soon as you set foot in the station: you may get there on time, a bit late, or so late you might as well go home.

That was unacceptable.

As a scientist, I could not sit idly-by and let entropy dictate my schedule. There must be a rational order, a way to calculate just how long it will take me to get somewhere, which will let me, finally, have some measure of agency over my morning. But before I could control the system, I had to understand it, so I spent a month collecting data and running statistics on the trains where I spent five percent of my pre-pandemic life.

The daily commute was quantified by tracking three classes of variable: time waiting for a train to arrive, time spent on the train, and where and for how long the train stopped for no apparent reason. This methodology doesn’t take into account the time I spend walking to the station or between platforms when changing lines as those stretches were under my personal control, and it wouldn’t be fair to Metro to include them. The study lasted for a month, yielding at least 18 data points for each variable. I did not record times on the weekend to ensure applicability to the work commute, and because only a fool tries to ride the Metro on weekends on any kind of schedule.

The first barrier to a quality day is waiting for the train to arrive at the platform. At the time, I was embarking at Ballston between 7:45 and 8:00 am, and usually only had to wait one to three minutes for a silver (S) or orange (O) line train (figures below). However, instead of a nice normal distribution, there were significant outliers 10-15 percent of the time. The same is true once you’re on the train as well: half the time you’ll get from Ballston to Rosslyn in eight minutes, the other half is a guessing game, even up to 19 minutes at worst.

At least with the orange and silver lines there is a clear median time you could base your day around, but not so once you reach Rosslyn. There is no way to predict whether you’ll be boarding a blue (B) line train in one minute or seven, or maybe it’s a really bad day and you’ll be there for a quarter hour. There’s just no way to know!

In a somewhat beautiful symmetry, the afternoon distributions mirror the morning. Waiting for the blue line at the Pentagon station around 5:00 pm is, again, uncontrollable, but the silver and orange at Rosslyn are fairly repeatable. The total transit times are also reversed, with the Pentagon to Rosslyn leg dragging on some days, while the silver and orange are mostly right on time. Overall, both morning and afternoon commutes similar amounts of time (21 and 19 minutes), but the variance in the morning is 50% larger than afternoon (9 and 6 min).

The third variable I collected sheds some light on the situation. In a perfect world, the train would have the same probability of randomly stopping at any point along the route due to some unforeseen issue. However, the world is not perfect, and all of these delays are focused on the trains going into Rosslyn station (figure below). This makes sense when considering the layout of the metro there: the blue line is merging in with silver and orange on the same platform (DC direction). Once you get away from the station, you’re back on time, with both legs going into Virginia having their own track to work with.

(Circle area is proportional to the delay duration)

These problems around the Rosslyn bottleneck were occurring when Metro was running normally before the pandemic. With trains running much less frequently, it is surely an even greater chore to use. This highlights an inevitable issue with decarbonizing our transportation infrastructure. It is not enough to simply build public transit systems, they must be reliable and able to meet people’s needs, otherwise it is so much wasted resources. This concept extends to other planned investments, like favoring cheaper but slower EV charging stations. If the system sucks, people won’t use it. But keeping things working takes an additional resource commitment over the entire length of the system’s existence. We need to be prepared for that, as any long-term solution to climate change needs to account for the maintenance of what we build, whether that’s our power lines or metro lines.