Risk Assessment of Horizontal Curves Based on Lateral Acceleration Index: A Driving Simulator-Based Study

This study aims to evaluate the risk level associated with the geometric parameters of two-lane horizontal curves. It is measured using critical average lateral acceleration (a ](c)), a new performance index derived from lateral acceleration profile data and representing a normalized lateral acceleration beyond a threshold value. The required data for the study were obtained from a fixed-base driving simulator in which 41 drivers drove through the geometric configurations comprising 26 horizontal curves. The hierarchical clustering analysis provided three risk clusters for a(c) values represented as low-, moderate-, and high- risk events. These risk clusters were analyzed for the geometric parameters, such as radius, design speed, gradient, and preceding tangent length. The cross-tabulation results indicated that the curve radius less than 100 m represented 2-10 times higher crash risk than the curves with a larger radius (> 100 m). The curves on the descending gradient exhibited two times higher risk than the one on the flat and ascending gradient. Further, the decision tree provided design speed and its interaction with gradient and preceding tangent length as the significant parameters to assess risk along curves. Overall, this study establishes the suitability of the newly developed performance parameter as a surrogate safety measure for evaluating the risk associated with different geometric configurations.