Vehicle Reidentification and Travel Time Measurement on Freeways Using Single Loop Detectors—From Free Flow through 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. These tasks are complicated by the fact that conventional vehicle detectors only monitor 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. It can take several minutes before an incident between detectors is observable in the point measurements and even longer to differentiate between noise and a true incident. To address such issues, this paper uses existing detector stations to match vehicle measurements between stations and monitor the entire roadway. Earlier work has already demonstrated the methodology using effective vehicle lengths measured with dual loop detectors. This paper extends the work by presenting a method to estimate vehicle lengths from single loop detectors and then applies the vehicle reidentification methodology to these common detectors with good results. The work should prove beneficial for traffic management and traveler information applications, while promising to be deployable in the short term.