A day without Metro meant worse traffic for some but not others

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When the region’s Metrorail system shut down for a whole day on March 16, many predicted a traffic nightmare. While such a scenario unfolded for some, traffic for others wasn’t that much different than a typical Wednesday.

Metro announced the all-day closure of its rail system late in the day on March 15. Almost immediately, the media, the public, and elected officials began speculating about what would happen on area roads. On a normal weekday, Metrorail carries about 700,000 trips, 70% of which are made by commuters. How would all of those people get to and from work?

TPB traffic experts recently performed a preliminary analysis showing that congestion at the regional scale was actually slightly lower on the day of the shutdown compared to a typical Wednesday. “The regional Travel Time Index, the ratio of actual travel time to free-flow travel times, was very close to typical conditions,” the analysis said. But traffic conditions varied greatly depending on where and when you were traveling.

Where and when was the worst traffic?

The worst traffic occurred inside the Capital Beltway during the morning commute. According to the analysis, travel times on roads in the District of Columbia, Arlington, and Alexandria between 7:00 and 8:00 a.m. were an average of 12% higher on the day of the shutdown than on a typical Wednesday. Elsewhere in the region, traffic at that hour was about the same as normal.

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Freeways in the inbound direction were especially hard hit. The analysis found that travel times on key freeways heading into the downtown core were as much as three times longer than normal between 7:00 and 8:00. Northbound I-395 in Northern Virginia saw a 125%-increase in travel times, jumping from 28 minutes on a typical Wednesday to 64 on the day of the shutdown. Northbound I-295 in the District saw a 218%-increase, jumping from an 18-minute trip normally to nearly an hour on March 16.

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Outside the Beltway, though, things weren’t nearly as bad. In fact, many routes saw improved traffic on the day of the shutdown. On I-66, the trip from VA-286 to the Beltway, which on a normal Wednesday takes 22 minutes, took just 15 on the day of the shutdown.

And the evening commute was, by comparison, a cinch in all parts of the region. In the regional core, congestion was about 3% lower than usual, as it was in the rest of the region. And nearly every freeway both inside and outside the Beltway showed drops in outbound travel times.

Why the differences depending on geography and time?

It’s not totally clear why traffic was so much worse in the regional core than outside the Beltway, though the fact that Metro largely serves downtown employment centers probably had a lot to do with it. Since the majority of commuters who normally use Metro are traveling to jobs in the core, it would make sense that the major routes entering downtown saw the worst congestion. But it could also be that more commuters who live outside the Beltway already drive to work and were unaffected by the shutdown. Or that commuters living outside the Beltway, those who would have faced the longest drives into downtown, simply opted not to go into the office that day, instead taking advantage of unscheduled leave or unscheduled telework.

It’s even less clear why congestion was so much lower during the afternoon commute than the morning. It‘s possible that after experiencing congestion in the morning, drivers adjusted when they left at the end of the day or made other driving trips like school or childcare drop-offs. Another possible explanation is that people decided not to make certain discretionary trips, like shopping or going to the gym, given the unusual and uncertain travel conditions.

More analysis to come. Stay tuned!

The TPB’s traffic analysts are still looking into other pieces of the Metro shutdown story. In particular, they want to know how people adjusted their travel on the day of the shutdown, whether by changing their travel time or route, choosing a different travel mode, or avoiding traveling altogether by taking advantage of unscheduled leave or telework. That analysis is expected in the coming weeks, so stay tuned!

Read the full technical analysis of traffic impacts of the March 16 Metro shutdown

Photo: I-395 Leaving DC by Valerie on Flickr