Efficient monitoring of public transport journeys

Many things can go wrong on a journey. From minor disturbances like a track change to major problems like train cancellations, everything can happen. The broad availability of smartphones enables us to keep the traveler up-to-date with information relevant for the journey. This way, the traveler can react to changes as early as possible and make well-informed decisions. Naive approaches are too inefficient to monitor a large number of journeys in real-time. This paper presents an efficient way to monitor millions of journeys in parallel. In our approach, the selection of change notices to be communicated to a traveler may be flexibly adapted to the travelers individual needs.