Effect of static weight errors on Weigh-in-Motion (WIM) system accuracy

Weigh-in-Motion (WIM) systems require calibration to account for site conditions and regular calibrations (once or twice a year) to yield accurate and consistent loading data. Generally, the WIM system calibration compares the WIM weights with the reference static weights. However, the ground truth (static weights) accuracy may not be known and is uncertain. WIM protocols (ASTM 1318-09 and COST-323) specify the static error thresholds. Therefore, it is crucial to consider the errors induced due to static weighing procedures during the WIM equipment calibration and pre-validation. This paper uses the long-term pavement performance (LTPP) highquality WIM data to study the effect of static weight measurement errors on the performance of the WIM system. The data analyses address two key concerns (a) modeling gross vehicle weight (GVW) errors while accounting for errors in the static and WIM weights, and (2) quantifying the effect of static truck weight errors for a variety of WIM sites with varying performance levels. The results show that the static weight errors are more critical for the WIM sites marginally meeting the desired ASTM 1318-09 accuracy class. A 2% static error may not change the overall performance of a WIM site (ASTM accuracy class based on tolerance limits), especially the sites with negligible bias or significantly higher bias. However, the ASTM accuracy class can change from higher to lower for WIM sites with intermediate bias (3 to 7%), even with a 1% increase in static weight errors.