Study On Traffic Conflict Mechanism In Diverging And Merging Segment Of Expressway Interchange

The expressway carries a large amount of motor vehicle traffic in the city.It plays a pivotal role in serving long-distance travel and mitigating urban traffic congestion.As a traffic node,interchange is a concentrated area where vehicles diverge and merge.The traffic flow state is complicated in these segments.Compared to general road segments,the mutual interference between vehicles is more intense.Grasping the traffic flow and traffic conflict characteristics of the diverging and merging segment effectively,exploring the formation mechanism of traffic conflicts,and formulating effective management and control methods are the key works to ensuring the safe and efficient operation of interchange and even expressway systems.The paper is based on the content of National Natural Science Foundation of “Study on Traffic Flow Self-Organization Mechanism and Associate Design Parameters Optimization of Short-distance Interchanges on Expressway(No.51878236)”.The thesis focused on the traffic conflicts in the diverging and merging segments of the urban expressway interchange.Video images of morning peak,evening peak and off-peak times were obtained by aerial photography with Unmanned Aerial Vehicle.Traffic flow characteristic parameters such as vehicle speed and lane change behavior were extracted by image processing.TTC and PET models and indicators were used to calculate rearend conflicts and lane-change conflicts respectively.Descriptive statistics analysis,oneway ANOVA,LSD multiple comparison test,independent-sample T test,Spearman correlation analysis,and partial correlation analysis methods was used to analyze the data of traffic flow and traffic conflicts.The binary Logistic regression model was used to establish traffic conflict probability.According to the characteristics of vehicles involved in conflicts and areas where conflicts occurred frequently,the management measures aiming at reducing the frequency of conflicts were proposed.The comprehensive evaluation of the application of management measures could be carried out by means of simulation.The results showed that the probability of traffic conflicts in the diverging and merging segments increased with the increase of the traffic flow rate.There was a significant difference of headway between conflict vehicles and non-conflict vehicles.Vehicles involved in conflicts were significantly slower than vehicles that did not have conflicts.In the diverging segment,conflict occured less when the main line and the ramp speed were higher.However,this relationship was not obvious in the merging segment.The spatial distribution of traffic conflicts was significantly related to the occurrence of lane change behavior.The regression model showed that the lane when entering,lane change frequency and speed distribution of the vehicles also significantly affected the occurrence of the conflict.Comprehensive evaluation of the effectiveness of management measures,with traffic conflict rate as the safety indicator and vehicle delay as the efficiency indicator.This leads to the conclusion: The application of low-speed vehicle speed control and illegal lane change control in the diverging segment,and speed control of the low-speed vehicle and control of the main line vehicle lane change in the merging segment could effectively reduce the occurrence of traffic conflict while ensuring the traffic efficiency.