Evaluation of the Safety Performance of Highway Alignments based on Fault Tree Analysis and Safety Boundaries

<p><b>Objectives</b>: To overcome the limitations of previous highway alignment safety evaluation methods, this paper presents a highway alignment safety evaluation method based on fault tree analysis (FTA) and the characteristics of vehicle safety boundaries, within the framework of dynamic modeling of the “driver-vehicle-road” system.</p> <p><b>Methods</b>: Approaches for categorizing the vehicle failure modes while driving on highways and the corresponding safety boundaries were comprehensively investigated based on vehicle system dynamics theory. Then, an overall crash probability model was formulated based on FTA considering the risks of three failure modes: losing steering capability, losing track-holding capability, and rear-end collision.</p> <p><b>Results</b>: The proposed method was implemented on a highway segment between Bengbu and Nanjing in China. A driver-vehicle-road multi-body dynamics model was developed based on the three-dimensional alignments of the Bengbu to Nanjing section of Ning-Luo expressway using Carsim, and the dynamics indices, such as sideslip angle and, yaw rate were obtained. Then, the average crash probability of each road section was calculated with a fixed-length method. Finally, the average crash probability was validated against the crash frequency per kilometer to demonstrate the accuracy of the proposed method. The results of the regression analysis and correlation analysis indicated a good consistency between the results of the safety evaluation and the crash data, and that it outperformed the safety evaluation methods used in previous studies.</p> <p><b>Conclusion</b>: The proposed method has the potential to be used in practical engineering applications to identify crash-prone locations and alignment deficiencies on highways in the planning and design phases, as well as those in service.</p>