Setting Speed Limit For Highway Circular Curve Based On Vehicle Lateral Safety Boundaries

During recent years,with the rapid development of highway construction and the continuous growth of vehicle population,driving safety attracts a widespread concern from the community and is urgent problem to be solved.Compared with straight highway segments,when the vehicle is driving on a highway circular curve segment,it is easy to cause highway crashes due to lateral instability,and meanwhile speeding further increases the risk of accidents.Therefore,setting scientific and reasonable speed limit values on highway circular curves is of vital importance for improving traffic safety.However,with respect to existing speed limit strategies,there are problems such as inaccurate vehicle stability evaluation index and excessively simplified tire models.In view of the above problems,based on the theory of automobile dynamics,this paper deeply analyzes the lateral instability mode of the vehicle.According to the safety boundary of each instability mode,a high-precision theoretical derivation method for the critical safety speed of the circular curve section is proposed,which provides a reliable theoretical basis for the speed limit of the circular curve section of highway.Firstly,the instability status was decoupled into three modes: steering instability,losing track-holding capacity,and rollover,and then the corresponding safety evaluation index were proposed.Secondly,a 7 degree-of-freedom(DOF)nonlinear vehicle-circular highway segment coupling model was developed,with which the computational models of safety boundaries of the safety evaluation index were deduced.Subsequently,the accuracy of the safety boundaries was validated in various road friction conditions and radius through the employment of Carsim.Finally,based on the 7 DOF nonlinear vehicle-roads coupling model and the computational models of safety boundaries,revised the inferred design speed considering the lateral stability of the vehicle and propose a speed limit strategy for the circular curve segments of the highway based on the lateral safety boundary of the vehicle.The comparisons among the proposed method,the operating speed,the inferred design speed and the design speed were performed through a case study of two highway circular curve segments(Stake number: K46+106.308—K46+267.726,K50+337.028—K50+414.988)of between Banzhuyuan and Tiantangzhai.The results indicate that as speed limit values,design speed and the inferred design speed are too conservative on dry and wet pavement.For highway circular curve segments with small radius and limit sight distance,operating speed often exceeds the revised inferred design,which may cause safety issues.This speed limit strategy fully considers the non-linearity of vehicle’s lateral motion and solves the problems such as inaccurate vehicle stability evaluation index and excessively simplified tire models in existing speed limit strategies,which provides a reliable theoretical basis for calculating the speed limit of the circular curve section of highway and could be used as a complement for other speed limit strategies for highway circular curves.