Algorithm for Finding Optimal Paths in a Public Transit Network with Real-Time Data

Abstract

Recently, transit agencies have begun opening their route configuration and schedule data to the public, as well as providing online application programming interfaces to real-time bus positions and arrival estimates. On the basis of this infrastructure for providing transit data over the Internet, the authors developed an algorithm to calculate the travel times of K shortest paths in a public transportation network where all wait and travel times were known only in real time. Although there was a large body of work on routing algorithms in transit networks, the authors took cues from an algorithm to find the shortest paths in road networks, called transit node routing. This approach was based on observation of intuitive behavior by humans: when taking transit, travelers looked for a particular set of transfer points that connected transit routes that led from the origin and destination. A lookup table was precomputed of feasible paths between the origin stop of every bus route to the terminus of every other bus route by using the transfer points. This precomputation of paths significantly reduced the computation time and number of real-time arrival requests to transit agency servers, the bottleneck in computing this problem. The computational complexity of the algorithm is linear in real time, and implementation results show that queries from a web server are returned in 3 s in the worst case.