Communities / Data / Transportation

One engineer has solved the New York Subway Eternal Mystery

How long should you wait for the train before finding another way to get there?

The L train is fast lol. (Courtesy image)
Eleven minutes. That’s how long you should wait before giving up.

Also, the L train is good? We dig into some of the conclusions from a fantastic bit of work by Erik Bernhardsson of Better.
Here’s the situation: You’re in a hurry, a meeting, an interview, spin class, your therapist, whatever. You’re waiting for the train to come and the minutes drag painfully on. Should I jump out and try to walk? How long would that take me, even? Should I text the interviewer I’m running late?
More minutes go by. Maybe I could take a Citi Bike? But then I’ll be all sweaty and ruffled by the time I get there. Plus it’s $10 for one ride. But then also I’d have it for 24 hours so maybe I’d use it again tomorrow and then it’ll be $5 a ride.
More minutes go by. Other people in the airless train station begin to look as nervous as you are. People check their Apple Watches. How much would an Uber cost? Would that even be faster? I’ve been standing here for at least 10 minutes, a train is bound to come soon. Plus I’d have to go up and wait a couple minutes for a car anyway. I’ll just stay put and hope a train comes.
Well, now there’s an answer. A really complicated answer that takes into account a lot of variables and preferences, but an answer nonetheless.
In his post, NY Subway Math, Bernhardsson pulled tons of data from the MTA’s open API and crunched some numbers. He found that, if you’re in a hurry, 11 minutes should be your cutoff time for waiting. Around 11 minutes in, the chances there’s a serious delay on the line begin to rise.
“The reason I started looking at this data was to understand if to what extent waiting for a subway is ‘sunk cost’ vs. an investment,” Bernhardsson wrote. “In particular, what is the optimal strategy if you’re waiting for the subway? My intuition told me that there’s a T [time] such that the expected additional time you have to wait goes down as you approach T, but then goes up afterwards. Until T, every second you wait gets you closer to the next subway. After T, there’s most likely some random issue with the subway and you should just give up.”

Waiting times under different scenarios.

Waiting times under different scenarios.

The graph above shows how long you can expect to wait for the subway, given how much time you’ve already waited. The blue line is the median, and the yellow line is the 90th percentile, the most unlucky scenario. We see that when you walk into the subway, you can expect to wait, on a normal day less than five minutes, or, if you’re unlucky, about 11 minutes.
“The interesting conclusion is that after about five minutes, the longer you wait, the longer you will have to wait,” Bernhardsson writes. “If you waited for 15 min, the median additional waiting time is another 8 minutes. But 8 minutes later if the train still hasn’t come, the median additional waiting time is now another 12 minutes.”
And that’s due likely to the fact that if the subway hasn’t come after a good time there are probably some delays or mechanical problems causing the delay.

The L train is fast

Despite the mainstream narrative that the L train is Bad, the data (limited as it is to these nine lines) shows that trains run on the L train more frequently than the other lines by a lot.
“The median waiting time is the smallest out of all the lines, and even the extreme case compares favorably,” Bernhardsson writes.
That does not, however, figure in the number of people riding on the train. The L trains are actually stuffed to the gills with people and that congestion could be the very reason why trains run so often.
Regardless, this data will be dramatically skewed come 2019 by the L’s now-confirmed upcoming 18-36 month delay.

Series: Brooklyn

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