Monitoring travel times in an urban network using video, GPS and Bluetooth

AbstractThe travel time is an important measure for the quality of traffic. This paper discusses a few methods to measure or estimate the travel time in urban road networks. First of all, it is important to know that urban travel times display a large variation, so that the measurement of a single (average) travel time is not so meaningful. The travel time distribution is more relevant than the single value of the average. This distribution can be obtained from observations of travel times of individual vehicles, for instance by tracing probe vehicles with GPS. The distribution of travel time can also be measured by Bluetooth scanners that can recognize Bluetooth devices in a car. Travel time over a link can be estimated by comparing passing times at its beginning and end. Automated Number Plate Recognition cameras have a similar possibility to follow individual vehicles from point to point. In the study of travel time measured in urban areas, the quality of data from Bluetooth scanners appeared to be disappointing. The most important reason is that outliers cannot easily be eliminated. This is especially a problem in urban areas. Another reason is the uncertainty about the Bluetooth devices’ carriers. It is difficult to identify whether the Bluetooth device belongs to a car or bus passenger, a cyclist or a pedestrian. Probe vehicles with GPS are very well appropriate for the measurements of travel times in urban areas