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Identification and Correction of Dual-Loop Sensitivity Problems

Freeway traffic speed and bin volumes for different vehicle categories are typically collected by dual-loop detectors. Good quality dual-loop detector data are crucial for effective real-time traffic management systems and traveler information systems. However, loop detectors are subject to various malfunctions that can result in erroneous measurements. Previous studies indicated that loop sensitivity-level discrepancies between two single loops forming a dual-loop detector and unsuitable sensitivity levels of the single loops are two major causes of quality degradation in dual-loop data. This paper presents an algorithm and its implementation for identifying and correcting such loop sensitivity problems. The algorithm identifies dual-loop sensitivity problems using individual vehicle data extracted from loop event data and corrects dual-loop sensitivities through a two-step procedure: (a) remove the sensitivity discrepancy between the two single loops and (b) adjust their sensitivities to the appropriate level. Elimination of dual-loop sensitivity problems significantly enhances the reliability of dual-loop detectors and improves the quality of traffic speed and bin volume data.