Study On The Safety Evaluation Of Merging Area Of Expressway Based On Traffic Conflict

The expressway is the highest grade road in the city,which bears the main traffic volume of the whole city and serves the medium and long distance transportation inside and outside the city,occupying a pivotal position.Among them,the merge area is the entrance of the expressway and other urban roads,generally by the ramp access to the main line,compared to the basic section,the construction form is more complex,resulting in which the traffic flow operation state is more complex,the vehicle driving process is also more interference.And as the number of motor vehicles on the road continues to grow,the interaction between vehicles will also intensify,easily leading to traffic accidents.Therefore,it is necessary to study the merging zone of expressway,understand its traffic flow operation characteristics,analyze the mechanism and characteristics of traffic conflicts in the merging zone,investigate the causes of traffic accidents,and take corresponding measures to improve the safety level of the merging zone of expressway and reduce the incidence of traffic accidents.The paper firstly determines the research scope of the merging zone of the expressway,understands the construction form of the merging zone and the characteristics of vehicles driving in it,adopts the traffic conflict technology as a research tool,studies its meaning and mechanism in the merging zone,classifies it according to different characteristics,divides it into tailgating conflict and lane change conflict,and analyzes the effectiveness and substitutability of the traffic conflict technology.The evaluation indexes of traffic conflicts are introduced,and Time to Collision(TTC)is selected to evaluate tailgating conflicts,and Post Encroachment Time(PET)is selected to evaluate lane change conflicts.The Taiyi interchange merging area and Xinjiamiao interchange merging area were used as the research objects,and multiple videos of the morning peak,flat peak and evening peak of the two interchanges were obtained by field investigation and overhead filming with a UAV.The software was applied to extract the required traffic flow parameters and analyze the traffic volume distribution,vehicle speed distribution and lane change behavior distribution in the merging area of the two interchanges at different time periods respectively.The TTC and PET values were calculated using image processing combined with manual observation to obtain the tailgating and lane change conflicts,and the general and severe conflict thresholds for tailgating and lane change conflicts were determined based on the 85% cumulative frequency quantile:2.16～5.05 s for general tailgating conflicts,0～2.16 s for severe tailgating conflicts,1.88 ～4.39 s,and severe lane change conflict is 0～1.88 s,from which various types of traffic conflict data are derived.Based on the general conflict data and severe conflict data of tailgating conflicts and lane change conflicts,the correlation between traffic volume,speed and lane change behavior and various types of traffic conflicts were investigated,and the negative binomial distribution model and the binomial logistic regression model were selected to construct the prediction models for various types of traffic conflicts in Taiyi Interchange merge area and Xinjiamiao Interchange merge area.The results of the negative binomial distribution model were found to be better in the severe tailgating conflict in the Taiyi interchange merge area when the data volume was insufficient,and in the severe tailgating conflict and severe lane change conflict in the Xinjiamiao interchange merge area,while the results of the binomial logistic regression model were better in the other types of conflicts when the data volume was sufficient.When the amount of data was insufficient,it was difficult to construct the binomial logistic regression model.Further comparison of the influencing factors of traffic conflicts within the two interchange merging zones shows that the influence of traffic volume is more significant in the Taiyi interchange merging zone,while the influence of vehicle speed is more significant in the Xinjiamiao interchange merging zone.By comparing and analyzing various safety evaluation methods,the gray clustering safety evaluation model is selected,and the evaluation matrix is constructed with the general tailgating conflict rate,serious tailgating conflict rate,general lane change conflict rate and serious lane change conflict rate as evaluation indexes to determine the safety level of Taiyi Interchange merging zone and Xinjiamiao Interchange merging zone in different time periods,and it is concluded that the safety level of Xinjiamiao Interchange merging zone is the highest during the flat peak hours,and the safety level of Taiyi Interchange merging The safety level of the merging area in the evening peak hours is the lowest.The safety level of the merging zone is improved by proposing corresponding control measures in three aspects: traffic flow,speed and lane changing behavior in the merging zone,and improving the safety level of the merging zone.