Validation of Automatic Vehicle Location Data in Public Transport Systems

Performance metrics for public transport systems can be calculated from automatic vehicle location (AVL) data but data collection subsystems can introduce errors into the data which would invalidate these calculations, giving rise to misleading conclusions. In this paper we present a range of methods for visualising and validating AVL data before performance metrics are computed. We illustrate our presentation with the specific example of the Lothian Buses Airlink bus, a frequent service connecting Edinburgh city centre and Edinburgh airport. Performance metrics for frequent services are based on headways, the separation in space and time between subsequent buses serving a route. This paper provides a practical experience report of working with genuine vehicle location data and illustrates where care and attention is needed in cleaning data before results are computed from the data which could incorrectly reflect the true level of service provided.