Dijkstra’s algorithm on-line: An empirical case study from public railroad transport

Abstract

Trac information systems are among the most prominent real{world applications of Dijkstras algorithm for shortest paths. We consider the scenario of a central information server in the realm of public railroad transport on wide{area networks. Such a system has to processa large number of on{line queries in real time. In practice, this problem is usually solved by heuristical variations of Dijkstras algorithm, which do not guarantee optimality. We report results from a pilot study, in which we focused on the travel time as the only optimization criterion. In this study, various optimality{preserving speed{up techniques for Dijkstra's algorithm were analyzed empirically. This analysis was based on the timetable data of all German trains and on a "snapshot" of half a million customer queries.