Development of A System to Collect Loop Detector Event (Individual Vehicle) Data

Typical freeway inductance loop detection systems, under normal operation, aggregate individual loop detector actuations sampled at 60 Hz into 20 second or 30 second average velocity, flow, and lane occupancy measurements. While such aggregations are appropriate for serving as inputs to control system algorithms, and save disk space for archiving loop data, much useful data regarding individual vehicles are lost. For single loop detectors, the lost information includes individual vehicle arrival, departure and presence times. For speed traps, the lost information also includes the calculated individual vehicle speed and length. Yet this information about individual vehicles is very desirable for transportation researchers and planners. Furthermore, the unavailability of this information makes in-depth investigation of detector errors difficult or even impossible. In this paper, a detector event data collection (DEDAC) system is proposed. This system is able to sample loop actuations with sampling rates of 60 Hz or higher and then save, process and present the collected event data in real time without interfering with the detector controller’s normal operation. The authors have developed a stand-alone Windows program for performing real-time high-frequency loop event data collection. A system reliability test and a field application indicate that the system has the capability of collecting real-time detector event data at a high sampling rate (60 Hz or higher). Additionally, this system makes real-time loop data quality evaluation, loop malfunction identification, and loop error correction feasible.