• 02.25.14

A Twitter Data Scientist Hacks San Francisco’s Subway Fares

Why pay the full price to your destination on BART, when swapping tickets with a stranger mid-ride would save you both money? Perhaps because it sort of violates the social contract?

A Twitter Data Scientist Hacks San Francisco’s Subway Fares
[Image: BART via Flickr user ykanazawa1999]

When New Yorkers move to the Bay Area, they’re often accused of personality crimes. Being haughty, cagey, and ragey-for-no-reason are just a few. I know this because I was one of them, and when I lived in Berkeley, there was one experience that drew out all of the stereotypes I had in me: Riding on Bay Area Rapid Transit, or BART.


Twitter data scientist Asif Haque has had his BART frustrations, too. Thus, he decided to take a data-driven approach to see if its fares were “fair” or not. In the process, he also devised a system to help riders artificially lower the cost of riding on public transportation by switching cards with fellow passengers in mid-ride.

For those unfamiliar, BART’s swiping and pricing system works like this: A passenger puts money on a paper ticket or plastic Clipper card, swipes through a turnstile at the origin stop, then swipes through another turnstile at the destination. How much you’re charged depends on where you eventually exit, and not necessarily how many stops you travel. (It’s a mileage-based formula, plus certain taxes here and there.) Unlike New York City’s subway system, BART does not charge a flat rate ($2.50) no matter where, or how far, you’re going. It also doesn’t offer weekly or monthly discounts for people who rely on it to get to work.

There’s a lot of math involved, but Haque, a game theorist and computer scientist by training, figured out that some people who switch their tickets or Clipper cards with each other mid-route could cheat BART’s fare calculator. In fact, a public ride-sharing scheme could work for some 13% of BART route pairs. For example, one rider traveling from Millbrae, in south San Francisco, to Embarcadero, in the heart of the city, pays $4.50 for the trip. Someone coming from the opposite same direction, Glen Park, and traveling to Berkeley, pays $4.20. If they switch passes mid-route, Traveler A ends up paying $5.10 (Millbrae to Berkeley) and Traveler B pays $1.20 (Glen Park to Embarcadero), together saving $1.70 1.75.

Trip A, by no coincidence at all, is Haque’s commute.

Out of 60,334 of these route pairs, Haque says that switching mid-route for 4,666 of them could save at least $1 together. Further, he suggests that companies like Uber and Lyft might one day play the app middlemen and allow riders to swap routes by smartphone if future tickets go digital. This, he writes, might “force” monopolistic public transit systems to become more efficient by eliminating the possibility of route swapping–like by charging a flat rate per trip, as New York City’s Metropolitan Transit Authority does.

That’s one theoretical conclusion. The other outcome is deeply troubling. In 2013, after fares and parking fees, a little more than 38% of BART’s budget was funded by taxes. If the fare slice of the revenue pie decreases, taxes might end up making up the difference. That’s not decreasing the price of a ride, but simply shifting the cost onto the rest of the tax-paying public. To suggest that private companies jump in and make a profit off of potentially starving a public transportation system is a nightmare scenario–one that could create a massive gulf between functional private systems and crumbling public ones.

But Haque’s paper doesn’t really look at worst case scenarios. Instead, it’s purely focused on mathematical price efficiency. He says that he could apply this same analysis to any city’s public transportation, where efficiency is measured not by how expensive a ride is, or how profitable the transit authority might be, but whether pricing is set up in a way that makes it preferable to cheat. “For systems in which nothing is gained or lost by switching, those are efficient,” he says, citing Caltrain as one such example.


Haque suggests that if this inefficiency is brought to the attention of transit authorities, the less opportunity there would be to exploit it. He tweeted his research at BART to see how the transportation system might respond to the notion of changing its fare structure, but has yet to receive a response.

In the meantime, the likelihood of having private companies scale up Haque’s idea is nearly impossible. Crowds relying on paper and plastic ticket swapping is surely more physical trouble than it’s worth.

About the author

Sydney Brownstone is a Seattle-based former staff writer at Co.Exist. She lives in a Brooklyn apartment with windows that don’t quite open, and covers environment, health, and data.