Vehicle reidentification and travel time measurement, Part II: Uncongested freeways and the onset of congestion

From an operations standpoint, the most important task of a traffic surveillance system is determining reliably whether the facility is free flowing or congested. The second most important task is responding rapidly when the facility becomes congested. Other tasks, such as quantifying the magnitude of congestion, are desirable, but tertiary. The tasks are complicated by the fact that conventional vehicle detectors are only capable of monitoring discrete points along the roadway. The detectors are typically placed at least 0.5 km apart and conditions between the detectors must be inferred from the local measurements. To address the first two tasks, this paper presents a new approach for traffic surveillance. It uses existing dual loop detector stations to match vehicle measurements between stations and monitor the entire roadway. Rather than expending a considerable effort to detect congested conditions, the research employs a relatively simple strategy to look for free flow traffic. The work should prove beneficial for traffic management and traveler information applications, while promising to be deployable in the short term.