University of California Institute of Transportation Studies

In this project, a novel approach has been developed to estimate the traffic states on arterial road links controlled by signalized intersections using both loop detector data and signal phasing information. We derived a trapezoidal fundamental diagram that includes two occupancy thresholds to categorize the traffic states into three different regimes: uncongested, congested, and downstream queue spillback. The parameters used to compute these two thresholds are closely related to road geometry, detector layout, signal settings, and vehicle dynamics, which can be obtained from the field data.  A case study was performed using field data from three intersections along Huntington Drive in the City of Arcadia in the I-210 Connected Corridors pilot. Flow-occupancy relations were obtained for both advance and stopline detectors at the intersection approaches, and it was found that advance detector information is more reliable because it is less impacted by the traffic signal.  The proposed trapezoidal fundamental diagram was validated using a dataset with six months of detector data.