Research On Safety Evaluation Method Of Highway Alignment Based On Fault Tree Analysis

In recent years,with the increasing density of highway network and the improvement of infrastructure,the highway transportation in our country has also achieved a unprecedented development.However,the highway traffic safety is still facing a serious situation and has become a widespread concern of all sectors of society.The highway alignment and traffic crashes are closely related,evaluating the safety of highway alignment accurately and quantitatively,is great significance to propose countermeasure for improving highway alignment and to reduce the risk of highway traffic crashes.The correlation between the result of the existing highway alignment safety evaluation method and the actual traffic crashes data is not strong.In this paper,a calculation method of average comprehensive crashes probability of highway sections based on fault tree analysis was proposed,which can accurately and directly evaluate the safety of highway alignment using the probability of crashes.Firstly,considering the good weather and the free-flow condition,this paper decouples the vehicle lateral instability and re-divides the instability mode of single vehicle crashes into losing steering capability,losing track holding capability,rollover and considering the rear-end crash caused by lack of stopping distance.The traffic crashes probability calculation model was developed based on fault tree analysis.Secondly,The yaw rate of the vehicle's center of gravity,the sideslip angle of the vehicle's center of gravity and latera load transfer ratio are selected as the risk assessment indexes to characterize the losing steering capability,losing track holding capability,rollover crash,respectively.The risk evaluation index of rear-end crash was constructed considering the insufficient stopping distance.According to the vehicle dynamics theory and highway geometry,the dynamic safety boundary of each index was determined.Then,taking the geometrical alignment data of Ben-Ning section of Nan-luo expressway(G36)as a safety evaluation example,the accuracy of this method was verified.The driver-vehicle-road multi-body dynamics model was developed using CarSim,and the dynamics indexes changing with the stake number was obtained.A fixed-length method was utilized to determine the highway sections length,and the average comprehensive crash probability of each sections was calculated.Results of regression analysis and correlation analysis reveal that the correlation between average comprehensive crashes probability and actual crashes frequency is very significant and has a high level of consistency.The average comprehensive crashes probability of highway sections can be used to accurate and effective assess the highway alignment safety.Finally,the method of this paper was used to analyze the impact of highway geometry on the probability of traffic crashes based on the orthogonal test with interaction.The results of range analysis and variance analysis show that circular curve radius and pavement adhesion coefficient have the greatest influence on the probability of traffic crashes.The proposed method in this paper can improve the accuracy and targeting of the safety evaluation method of highway alignment,and it provide a new prospective for the black spot identification of both design-phase and in-service highways.