Field testing for automatic identification of turning movements at signalized intersections

Obtaining turning movement counts at signalized intersections is a routine task in traffic engineering and can be tedious and time consuming. Previous research in automating turning movement count has focused on estimating the turning movements from approach and departure volumes and developing detection systems for exclusive turning lanes. The accuracy of an alternative method, called the Time and Place System (TAPS), is examined in this research through a field study of five signalized intersections in Columbia, Missouri. TAPS uses both the locations and times of actuations from a small number of detectors to classify movements from shared approach lanes. The five intersections represent a range of geometries and signal timings. At four intersections a standard video camera was placed about 30 feet high, as close to the departure lanes as possible, to provide a reasonable view. Additional cameras showed current signal indications into the departure leg. At the fifth location a single elevated camera captured both vehicle movements and signal indications. The videotape data was used to compare TAPS results to actual flows. The errors in detections were apparently due to the sensitivity of detection system, camera angles, intersection geometries, traffic parameters and other factors. The ability of TAPS to identify turning movements at signalized intersections was supported by the study results. The information from TAPS could be used for advanced signal management, dynamic traffic assignment and traffic demand estimation.