Effect of Weigh-in-Motion System Measurement Errors on Load-Pavement Impact Estimation

Abstract

Weigh-in-motion (WIM) technology has found increasing application in the highway and transportation areas for traffic data collection for the purpose of highway capacity analysis, aiding enforcement and, most recently, pavement design. The measurement accuracy of a WIM scale is critical. There are numerous existing studies involving the measurement accuracy per se; however, the implications and effect of the accuracy in the context of pavement design have been rarely examined. To address this issue, two particular aspects are considered in this study. First, with traffic data obtained from WIM stations in Texas, axle load spectra are developed from both statistical data fit and load-pavement impact perspectives. Axle load spectra are shown to be captured best by mixed-lognormal distributions. Second, based on the first aspect, two scenarios are investigated by incorporating two types of errors into the load measurements: (1) A random error component due to the WIM scale intrinsic properties; and (2) a systematic error component due to the improper calibration of WIM system. The relationship between jointly varying measurement error levels and load-pavement impact estimation errors is established. It is demonstrated (and quantified) that both types of errors contribute to load-pavement impact estimation inaccuracy. The random error leads to overestimation of load-pavement impact. The results also show that WIM system calibration is of more importance because load-pavement impact estimation is more sensitive and significantly related to systematic error than random error. In addition, the estimated load-pavement impact is found to be more sensitive to overcalibration (positive bias) than undercalibration (negative bias) condition. In summary, the findings in this study provide an effective and efficient approach to evaluate WIM measurement errors in conjunction with load-pavement impact in pavement design and rehabilitation. The findings in this study could be further applied for the determination of adequate pavement design reliability standards. Results can also be useful to highway agencies in assessing and selecting WIM equipment.