Evaluation of Sensors for Monitoring Truck Speeds (1232-21)

This study evaluated the applicability, durability, and accuracy of two general systems of sensors that were used to monitor truck speeds on a freeway connector: 1) pavement sensors mounted on the surface or submerged into the pavement, and 2) roadside sensors using an infrared beam technology. Pavement sensors were predominantly temporary piezoelectric sensors, although inductive loops complemented one set of piezo sensors. These pavement sensors generated signals that were processed by vehicle classifiers to produce either "binned" data or "raw" data for all vehicles using the monitored roadway. Roadside sensors monitored vehicles that exceeded a preset height, length, and speed. Findings indicate that temporary piezo sensors are accurate for use as speed, count, and classification studies, but their service life (durability) was highly variable and undesirably short in many cases. Installation and maintenance of these sensors were problematic due to interference with traffic. Infrared sensors, on the other hand, were less intrusive to the traffic stream during installation and maintenance, and they performed well with little maintenance for time periods of one year or longer.