  Transit fare arbitrage is the scenario when two or more commuters agree to
swap tickets during travel in such a way that total cost is lower than
otherwise. Such arbitrage allows pricing inefficiencies to be explored and
exploited, leading to improved pricing models. In this paper we discuss the
basics of fare arbitrage through an intuitive pricing framework involving
population density. We then analyze the San Francisco Bay Area Rapid Transit
(BART) system to understand underlying inefficiencies. We also provide source
code and comprehensive list of pairs of trips with significant arbitrage gain
at github.com/asifhaque/transit-arbitrage. Finally, we point towards a uniform
payment interface for different kinds of transit systems.
