Freeway Interchange Traffic Safety Analysis Method Based On Traffic Conflict Technique

The interchange of expressway is a kind of traffic engineering facility with continuous flow characteristics,which takes the turning function of traffic flow in freeway network,and plays an important role in improving freeway service capability.For a long time,the focus of the study of interchange has been to improve the capacity of traffic,in order to enhance the capacity of the entire freeway network,and on the interchange of traffic safety research is inadequate."National Highway Network Planning(2013-2030)" requires greater connectivity to the freeway network,faster access to freeway network,which inevitably requires an increase in the number of interchange.In this context,the study of the interchange of traffic safety analysis methods will help to enhance the interchange traffic safety level of the new and alteration.Traffic accident evaluation method is a kind of macro traffic safety evaluation method.It is difficult to analyze the traffic safety of freeway interchange by traffic statistics,such as irregular statistics,no system and low sample size.Traffic conflict technology has the characteristics of observable,high efficiency and quantitative,and it is a non-accident traffic safety analysis method.Under the unmanned aerial vehicle technology support,we can obtain the traffic flow video and the video tracking technology to realize the traffic parameter acquisition function of the traffic flow This completes the data acquisition task of the interchange regional traffic conflict.Based on the data,this paper studies the traffic conflict which is applied to a number of key technologies of expressway interchange,thus forming a traffic safety analysis method of freeway interchange based on traffic conflict.The interchange of freeway interchange is divided into connection,basic segment and ramp.Only the traffic flow of the connection is unstable,so the traffic safety research of freeway interchange is limited to the three functional areas in the connection,i.e.diverging area,merging area and weaving area.This paper will focus on the key technologies of traffic conflict in these three regions,and establish the traffic conflict analysis model of three functional areas to analyze the traffic safety of freeway interchange.(1)The traffic conflict indicators selection.The traffic conflict is divided into two types:lane-change conflict and rear-end conflict.The traffic conflict of different functional areas is defined,and TTC(time to collision)is selected as the evaluation index of traffic conflict.(2)Traffic conflict severity.Training traffic observers,and achieving consistent awareness of traffic conflicts;and then jointly determine the type and severity of all traffic conflicts.The observers judges the conflict type and severity of the High Definition video from the Unmanned Aerial Vehicle;then uses the Track software to calculate the conflict index TTC value.Excluding the exception point,according to Pareto method to take the 85%value of the traffic conflict as the upper threshold.(3)HCRI(the hourly traffic conflict risk index).Based on the accident data of freeway infrastructure and the direct economic loss of different grades,the traffic risk index of freeway interchange at different severity is established,and the traffic risk index is used as an indicator to describe the traffic risk index the severity of the conflict.(4)Traffic simulation test design.The traffic simulation software VISSIM and SSAM(Surrogate Safety Assessment Model)to obtain more traffic conflict data.Using the two steps of "travel time-traffic conflict",the parameters of the traffic simulation model of each functional area are calibrated according to the traffic survey data.The orthogonal test method is used to design the traffic simulation test scheme,and the data of traffic collisions with sufficient representative traffic conditions are obtained with fewer test times,and the data base of modeling is laid.(5)Traffic conflict analysis model construction.The relationship between road condition and traffic condition and traffic conflict is analyzed by using the control variable method.The simulation experiment is designed by orthogonal test method for data modeling.In the three functional areas were selected from the common form of construction:weaving area selection of collector-distributor road form and four-lane weaving form,merging&diverging area selection of single-lane lane and two-lane ramp form.Through the data regression analysis,the corresponding form of traffic conflict analysis model is established.The validity of the analysis model is verified by the field data.(6)Traffic conflict evaluation model system construction.According to the gray clustering method,the traffic safety evaluation level of different indexes is defined,and the different levels of traffic safety service level are defined.The traffic safety assessment level is defined as the traffic safety rate of the three functional areas.(7)Application of traffic safety evaluation method based on traffic conflict.Relying on the demonstration project as an example,the paper puts forward the improvement strategy of traffic safety improvement.Taking the traffic simulation to obtain the traffic conflict before and after the improvement,the traffic safety evaluation method is used to evaluate the improvement effect.