Volume 25, Issue 2 (March 1997)
Evaluation of Overhead and In-Ground Vehicle Detector Technologies for Traffic Flow Measurement
As part of the U.S. FHWA-sponsored Detection Technology for IVHS program, ultrasonic, microwave radar, infrared laser radar, nonimaging passive infrared, video image processing with visible and infrared spectrum imagery, acoustic array, high sampling rate inductive loop, conventional inductive loop, microloop, and magnetometer detector technologies were evaluated at freeway and surface street arterial sites in Minnesota, Florida, and Arizona. These states were chosen because they exhibited a wide range of climatic conditions. The criteria for selecting the detector evaluation sites included searching for roadways with high traffic density and suitable structures for mounting the overhead detectors. Approximately 5.9 Gbytes of digital and analog vehicle detection and signature data and more than 300 video tapes of the corresponding traffic flow were recorded.
The detector outputs were time tagged and recorded on 88 Mbyte magnetic cartridges by using a data logger specifically designed and built for this project. Detectors with serial RS-232 outputs required interface software to be written for each unique data structure. Data analysis software was also written to convert the raw data into an easily accessible Paradox database format compatible with a Windows personal computer operating system. Traffic volume ground truth data, obtained by counting vehicles from the recorded video imagery, were compared with the counts from the detector outputs. Speed ground truth data, obtained by driving probe vehicles through the field of view of the detectors and noting their speed as measured by the vehicle's speedometer, were compared with the speed measurement from the detectors. Several types of detectors were found to satisfy current traffic management requirements. However, improved accuracies and new types of information, such as queue length and vehicle turning or erratic movements, may be required from detectors for future traffic management applications.