Research On Vehicles Operation Characteristics At The Small-Radius Ring Road Of Expressway Interchange

As an indispensable part of expressway interchange,the ramp plays the role of connecting channels for traffic flow in different directions.Small radius ramp as a form of ramp,although it can meet the requirements of the design specification,in the actual operation there are great safety risks,not conducive to the on-ramp traffic safety.To further understand the operating characteristics of vehicles on the small-radius ramp and improve traffic safety on the ramp,this paper takes the small-radius ramp of the expressway interchange as the research object.Based on the aerial video of the UAV,the "AI.Datafromsky" analysis platform is used to obtain the vehicle operating parameter data,such as speed,acceleration,trajectory,etc.The accuracy of the platform data was verified through the real vehicle test.Based on this,the operating characteristics of vehicles on the small radius ramp of the expressway interchange were studied.First of all,based on the vehicle speed data,the overall operating speed of vehicles on different small radius ramps is analyzed,and it is found that the operating speed variation trend has obvious differences.According to the classification of vehicle type,the difference and dispersion of operating speed between passenger cars and heavy vehicles are compared.The operating speed and dispersion of passenger cars are higher than that of heavy vehicles.According to the changing trend of operating speed,the small radius ramp is divided into three feature locations(starting point,easing curve segment,and circle curve segment).It is found that the mean speed of different small radius ramp feature locations has obvious differences.According to the distribution of deceleration endpoints of different vehicle types,the differences in deceleration length and deceleration amplitude between passenger cars and heavy vehicles are analyzed,and the deceleration modes of vehicles on the small radius ramp are divided.Secondly,based on the vehicle acceleration data,the tangential(lateral)acceleration distribution characteristics and changes of vehicles on two small-radius ramps are analyzed respectively.It is found that the lateral acceleration amplitude of passenger cars is significantly higher than that of heavy vehicles,while the tangential acceleration amplitude difference is small.Analysis of variance was used to test the tangential(lateral)acceleration of vehicle mean under the conditions of different on-ramp radius segment radii.The results showed that there were statistical differences in the longitudinal(lateral)acceleration of passenger cars(tangential acceleration: F=7.409,P<0.05;Lateral acceleration: F=33.503,P<0.05);The tangential and lateral driving behaviors of vehicles on ramps were evaluated respectively.Combined with the speed and acceleration data of different vehicles,the acceleration distribution characteristics of vehicles on different small-radius ramps were compared.According to the tangential(lateral)acceleration amplitude of different vehicle types,the risk assessment G-G diagram is used to study and analyze the dangerous driving behavior of vehicles on the on-ramp.Finally,based on the vehicle trajectory data,the distribution characteristics of the tracking harness of the ramp easing curve segment with a small radius and the circle curve segment with a small radius were expounded.According to the differences in the ramp trajectory,the vehicle trajectory preference was divided into three models,and combined with the operating speed,the influence of the operating speed on the different preferred trajectories was analyzed.The vehicle UTM coordinates were obtained from "AI.Datafromsky" analysis platform were used to calculate the vehicle traveling curvature,and the curvature distribution characteristics of vehicles on the small-radius ramp were studied and the differences between them and the road design curvature were analyzed.The concept of the equivalent radius was introduced,and the small radius ramp round curve segment was divided into three stages: entry,middle,and exit,and the difference of equivalent radius in different stages were analyzed according to different vehicle types.Finally,based on the above analysis,the driving high-risk area of the small radius ramp is divided,and the corresponding improvement suggestions are put forward.The research of this paper can provide reference and data support for the safety design,traffic safety improvement,and parameter calibration of the traffic simulation model of the small radius ramp of freeway interchange in the future.