Development of an Advanced Loop Event Data Analyzer (ALEDA) System for Dual-Loop Detector Malfunction Detection and Investigation

Dual-loop detector systems are widely deployed in Washington State freeway networks to collect traffic data. The Traffic Systems Management Center (TSMC) aggregates traffic volume, occupancy, speed, and length data from dual-loop detectors into 20-second intervals and stores them to save storage space of archived data and preserve the data format compatible with the control system algorithms of Washington State Department of Transportation (WSDOT). Because of the data aggregation, valuable information of individual vehicle is missing. This makes the detection and in-depth investigation of causes of dual-loop errors complicated or impossible. Since high-resolution event data preserves individual vehicle information, they are an excellent data source for such analyses. For example, our study using event data has found that the main cause of dual-loop malfunction in Washington State is the loop sensitivity discrepancy. Since event data is typically not available from TSMC, a data collection system is desired for collecting loop event data. This paper describes such a system called Advanced Loop Event Data Analyzer (ALEDA). ALEDA is a portable event data collection and real-time analysis system which can be installed on a laptop computer. Besides its capability to collect and record event data at 60 Hz or higher without interfering the operation of controllers, ALEDA analyzes the event data at dual-loop station, displays individual vehicle information, and points out sensitivity problems with solutions based on passing vehicle statistics. Consequently, ALEDA facilitates the on-site real-time identification and correction of loop sensitivity problems to improve data quality.