Initial Evaluation of Selected Detectors to Replace Inductive Loops on Freeways

Problems with installation and maintenance of inductive loop detectors, especially on freeways, have necessitated evaluation of alternative detection systems. The approach used in this research relied on recent evaluations of non-intrusive detectors and knowledge of researchers to identify three detection systems that warranted further evaluation in Texas. These were the Videotrak® 900 by Peek (video image processing), the non-invasive microloop by 3M¿ (magnetic), and the SAS-1 by SmarTek (acoustic). Testing of these detectors utilized the Texas Transportation Institute's (TTI) freeway test bed for conducting full-scale field-testing. The parameters measured for accuracy were vehicle presence and speed, but installation cost and ease of setup and calibration were also considered. The 3M microloop was the most consistent detector overall, and performed well both on a freeway as well as under a bridge. The Peek VideoTrak system's presence and speed accuracy both declined to unacceptable levels during nighttime and during rain. It was also the most difficult to set up and the most expensive. The SAS- 1 by SmarTek was the least expensive and demonstrated reasonable accuracy. TTI recommends continued evaluation of the SAS-1 and the 3M microloops.