Evaluation of Dynamic Weight Threshold Algorithm for WIM Operations using Simulation

In the past decades, states have utilized weigh-in-motion (WIM) technology to reduce delay and increase enforcement of overweight vehicles. Usually a threshold value is used to filter and sort the trucks by weight. If the WIM reading of a truck is over the threshold, the truck would be sent to a static scale for further inspection. To fully utilize the WIM technology and enhance the operational efficiency at WIM sites, the authors devised a dynamic weight threshold (DWT) algorithm. The threshold value is increased when the queue at the weigh station is long so as to avoid the closure of the weigh station while still catch the worst weight limit offenders. The threshold value is lowered when the queue at the station is short to maximize the number of trucks inspected. This paper focuses on the evaluation of the design and operations of the dynamic weight threshold algorithm. A microscopic simulation model based on a real-world ramp WIM weigh station site was first developed and calibrated. Subsequently the dynamic threshold adjustment strategy was modeled and tested. The results show that under a wide range of conditions DWT algorithm always outperforms the traditional static threshold operations. Under heavy demand conditions, DWT catches 16 times more overweight trucks than the static operations while keeping the average delay per truck at only 30% of the delay under static operations. In other words, DWT is both more effective in weight enforcement and more efficient for traffic flow.