Evaluation of Portable Automated Data Collection Technologies: Final Report

Portable automated traffic data collection systems were evaluated by means of a series of field demonstrations. Systems demonstrated included (a) temporarily mounted microwave radar sensors intended to provide volume, speed, and/or length classification data for traffic census or various traffic studies; (b) similar sensors mounted on a semi-permanent basis and intended to serve as substitutes for loop detectors in traffic surveillance systems; and (c) low-mounted infrared sensors used for axle counting. The field demonstrations focused on the issues of sensor accuracy for all systems and the reliability of wireless transmission systems for semi-permanent installations. Microwave radar sensors tested included the Wavetronix SS-105 and Wavetronix SS-125 (HD) models. A planned demonstration of the EIS RTMS sensor had to be cancelled because of inability to download per-vehicle data required for evaluation. Performance of the Wavetronix SS-105 sensor was satisfactory. Performance of the SS-125 sensor was acceptable but not as good as the SS-105 sensor in non-congested traffic and marginal in congested traffic. In all cases, a majority of the errors were in the lanes farthest from the sensor. Performance of the communications system used in the semi-permanent installation demonstration varied greatly depending on circumstances. Possible problems included bandwidth limitations in the Caltrans statewide computer network, cellular telephone system maintenance activities, problems with the interface between the modem and the cellular telephone system, and sensor failure. The low-mounted infrared sensor system demonstrated provided accurate axle-classification counts under low-volume traffic conditions but was seriously inaccurate under high-volume conditions. Although portable automated data collection systems are practical and potentially cost-effective for the data collection tasks investigated, problems with sensor accuracy and the reliability of wireless communications for semi-permanent systems have not yet been fully resolved.