Most vehicle detection today relies on inductive loop detectors. However, problems with installation and maintenance of these detectors have necessitated evaluation of alternative detection systems. Replacing loops with better detectors requires a thorough evaluation of the alternatives. This research included examination of the performance characteristics, reliability, and cost of these technologies. The detection technologies included in this study were: video image detection, radar, Doppler microwave, passive acoustic, and a system based on inductive loops. Research results clearly indicate promising non-intrusive alternatives to loops, but their limitations must be understood. This research solicited information from a variety of agencies pertaining to installation and use of non-intrusive technologies and conducted field tests on a high volume freeway to determine their suitability for implementation. Findings indicate that non-intrusive detectors have improved since recent detector research sponsored by the Texas Department of Transportation. Count accuracies of 95% and speed accuracies within 5 mph of true values are common during free-flow conditions. During slower congested flow traffic, all non-intrusive device count accuracies degraded to the range of 70 to 90%, and most speed accuracies worsened as well--differing by 10 to 30 mph from the baseline system.
Abstract