Develop Calibration Factors for Crash Prediction Models for Rural Two-Lane Roadways in Illinois

This paper documents the development of calibration factors for crash prediction models in the new Highway Safety Manual (HSM) for rural two-lane roadways in Illinois. The crash prediction modes (so called Safety Performance Functions (SPF)) in the HSM were developed using data from multiple states, therefore the models must be calibrated to account for local factors, such as weather, roadway conditions, and drivers’ characteristics. In this study, two calibration factors were developed for two different SPFs to give a better prediction of crash frequencies on rural two lane roadways in Illinois.