How to hack the subway using fare arbitrage

Could you save swapping tickets with another commuter during your journey so that the total you both pay is less? This kind of riskless profit-taking, or arbitrage, is common in capital markets where traders aggressively seek out and exploit these inefficiencies in the market. Could commuters also benefit?

Today we get an answer thanks to the work of Asif Haque, a data scientist at Twitter, who has analysed the possibility of fare arbitrage on the San Francisco metro system, known as BART (Bay Area Rapid Transit). Haque says that not only are opportunities for fare arbitrage possible on BART, they occur on more than 13 per cent of all pair-wise combinations of journeys offering considerable potential for savings.

Spotting fare-arbitrage opportunities is relatively straightforward in principle. Armed with an up-to-date fare guide, it’s simple to find out whether a particular pair of trips allows for arbitrage.

People what are you waiting for?  This sounds almost as good as arbitrage using the Forever Stamp:

Haque says that 60,334 of these pairs or 13.5 per cent, have an arbitrage opportunity of at least 5 cents. And 4,666 of these pairs of trips could save commuters at least $1. Haque has generously posted the full list of these 4,666 fares here.

There is further discussion, with examples, here.  For the pointer I thank Tom Fowler.