Influence of Calibration Factors on Crash Prediction on Rural Two-Lane Two-Way Roadway Segments

Calibration factors are applied in the Highway Safety Manual predictive method for rural two-lane, two-way roadway segments to adjust the estimate for local conditions. This research aims to evaluate and recommend improvements related to the estimation of these calibration factors. An aggregated and disaggregated analysis was performed to study the influence of different calibration factors on the prediction of the number of crashes in North Carolina. As a result, those calibration factors based on both types of road elements (horizontal curves and tangents) led to overestimating and underestimating the number of crashes on tangents and horizontal curves, respectively. Furthermore, the calibration factors based on fatal and injury crashes allowed a more accurate estimation of the predicted number of crashes than those calibrated considering all severity levels. Therefore, it is recommended to apply different calibration factors for each type of road element and each type of crash severity.