Estimation of Freeway Traffic Density with Loop Detector and Probe Vehicle Data

Density, speed, and flow are the three critical parameters for traffic analysis. High-performance traffic management and control require the estimation–prediction of space mean speed and density for large spatial and temporal coverage. Speed, including spot mean speed and space mean speed, and flow estimation are relatively easy to measure and estimate, while less attention has been devoted to measuring and estimating density. Because IntelliDrive (previously known as vehicle infrastructure integration) is a promising technology for providing a new type of real-time traffic data, and loop detector systems have already been widely deployed, this paper proposes a method to estimate freeway traffic density with both loop detector data and IntelliDrive-based probe vehicle data. The proposed method has been validated with Berkeley Highway Laboratory loop detector data combined with field-collected probe vehicle data in the first validation study and next-generation simulation video trajectory data in the second validation test. The algorithm can be used offline and in real time.