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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?

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.

[Image: BART via Flickr user ykanazawa1999]

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  • This experiment is very interesting...especially for metro systems that charge a fee based on distance traveled by each rider. Question: for the BART, what are the fares for "same station" trips? How about swapping tickets with a person that entered at the same station you plan to exit?

    Frequent commuters could probably pair themselves with another commuter that "gets on" where they typically "get off". The only "trick" is the coordination to meet at a station to do the physical ticket swap.

    Depending on "same station" trip fares, I can see suck a "hack" working on DC's METRO system as well. But, I'd hate for such a widespread loophole to increase taxes & fees for the masses as an eventual result of the trickery.

  • Same station is the same as a lost ticket on bart and will cost you over $5 (I can't remember if it's $5.50 or $5.25) so same station switching would be far more expensive.

  • Sean Oliver

    I'm afraid of what happens if something like this scales and starts causing the city money. I envision much higher BART fares for everyone, and the people who ultimately lose are those who choose not to cheat the system.

  • As a Swede living in Munich, Germany (highly functioning pub trans - in a RICH city - that benefits a lot of people every day) I don't really see what's so "deeply troubling" with taxes paying for it. Everyone is benefiting from (well functioning and safe) public transport; even the "I'M NOT GONNA PAY FOR OTHERS WELL BEING!" - conservative.

    • No need to drive as much car in the city
    • Less traffic jams in the streets
    • Less pollution
    • A way for the less well off to get about (finding jobs, saving money ect).
    • Softer values like "happiness". Less tangible but not less valuable.
  • In the subways (u-bahn), Trams or Buses of Munich I can sit alone with my music at 3am after attending a party, and I won't feel less secure than in my own home.

  • There's a HUGE error in your article, namely that "BART does not charge a flat rate ($2.50) no matter where, or how far, you're going." A BART ride anywhere from Balboa Park to Embarcadero Station is a FLAT $1.85 ($0.65 for youth/seniors). Your calculation in the next paragraph is also incorrect. A pays $4.50 for their trip, B's pays $4.20 for theirs, for a total $8.70. If they switch passes mid-route, you say A ends up paying $5.10 and B $1.20. This would be a saving of $8.70-$6.30, or $2.40, not $1.70. However, B's card would actually be charged $1.85 upon alighting at Embarcadero, and A's card charged $5.10 upon alighting in Berkeley, totaling $6.95, a saving of $1.75. Where you do get it right is in saying that "Crowds relying on paper and plastic ticket swapping is surely more physical trouble than it's worth."

  • There is a little error in this article. The passengers from Glen Park and Milbrae aren't going opposite directions. They both board the same Richmond-bound train which stops in Milbrae -> Glen Park -> Embarcadero -> Berkeley. So neither party has to exit the train in order to swap cards.

  • Fun facts:

    Millbrae and South San Francisco are separate cities, both from each other, and from the city of San Francisco proper. Fares in Millbrae and South SF are higher than for the rest of the system because the county they’re in, San Mateo, doesn't pay property taxes to fund system operations & maintenance like the other counties served by BART does.

    Also, Embarcadero Station is along the northeast edge of the city. "The heart of the city" is roughly along a Union Square–Financial District axis, which Embarcadero Station is in proximity to, but not directly a part of.

    Further, BART is more directly comparable to New York's commuter railroads. Embarcadero to Pittsburg/Bay Point is about a 36-mile trip, comparable to 34 miles from Stamford to Grand Central Terminal on the Metro-North railroad. The system is being extended further east to Antioch, another 9 miles or so. Should $2.50 flat fares be extended to Metro-North, LIRR, and NJT too? It's only fair.

  • Eh, I see Oakland, Berkeley, South SF, etc. as more culturally/functionally similar to the NYC boroughs. But the Staten Island Ferry is free, and you don't have to pay more to commute to Manhattan from any of the boroughs. When you're broke and commuting into SF (like I once was), saving some dollars might make a difference.

    But as I mentioned, starving public transit is a bad idea.

    And for the record, Embarcadero is solidly within the Financial District.