The benefits of providing active bus priority at traffic signals through selective detection have become well established, both at isolated junctions and, more recently, in UTC. In the UK, SCOOT Version 3 contains the bus priority facilities developed in the EC project PROMPT, with capabilities for bus detection either through transponder/detector communications, as used in London or via Automatic Vehicle Location (AVL) systems. A first trial of the latter configuration has been undertaken in Southampton. A key element of system optimisation is bus journey time prediction from the point of detection to clearance of the stopline, particularly where a green time extension is implemented. Overestimation can cause unnecessary signalling disruption while underestimation can cause many buses to miss priority. With AVL accurate prediction is further complicated because the bus could be polled at any location on a link. This paper describes requirements and methods for bus journey time prediction based on a detailed database collected in Southampton and London during an EPSRC research study. Results are presented concerning factors affecting journey time variability, including detection location, site conditions and bus operating characteristics. The implications on priority strategies and signal control of journey time variability and predictive accuracy are discussed. The paper concludes with recommendations for journey time prediction within operating systems.
Abstract