ABSTRACT
Weigh-in-motion (WIM) is a primary technology used for monitoring and collecting vehicle weights and axle loads on roadways. One way to evaluate the quality of WIM measurements is to analyze axle load spectra over time. Class 9 single-axle (SA) normalized axle load spectra (NALS) can be modeled as a single normal or log-normal distribution with a mean value corresponding to the NALS’s peak load frequency value (bell-shaped distribution). The changes in the location of the peak of this distribution can be related to the changes in mean error. Similarly, tandem axle (TA) NALS could be modeled by using a mixture of two normal or lognormal distributions (i.e., the bi-modal distribution). This paper presents a case study for WIM site where the WIM sensor exhibited a drift within a year after calibration. The loading data from single and tandem axles were analyzed to quantify the decline in WIM accuracy and precision. The results presented in the paper can be used as a guideline to select calibration frequency for the WIM sites.
