A Risk-Based Multiobjective Optimization Framework to Enhance the Safety of Horizontal Curves with Limited Sight Distance

This study introduces a multiobjective optimization framework for the redimensioning of the cross-sectional elements of rural horizontal curves with limited sight distance. The optimization aims at minimizing both the risk associated with the limited sight distance and the expected collision frequency corresponding to the cross-sectional elements’ dimensions. The risk component was assessed using an index known as Pnc, which is developed based on reliability theory using the First-Order Reliability Method (FORM). The change in collision frequency corresponding to the change in the cross-sectional elements was extracted from the literature. The risk and the safety components were then combined into one measure, a combined crash modification factor (CMFcombined), to develop a direct measure of the safety impacts of the optimization. The proposed framework was applied to five restricted curves in British Columbia, Canada, considering various scenarios. The results showed a considerable reduction in the Pnc value (ranging from 12% to 73%), the expected collision frequency (ranging from 10% to 31%), and the estimated combined collision reduction CMFcombined (ranging from 48% to 76%). The framework presented in this study would support transportation engineers in selecting optimal dimensions of cross-sectional elements of restricted horizontal curves, understanding the safety consequences of selecting a specific cross-sectional configuration, and assessing the economic viability of different design options.