| Expressway is one of the typical urban road types in China.It is a high-grade trunk road to meet the important passenger and freight demand in the city.In the process of continuous improvement and construction of urban traffic system,urban expressway also develops rapidly.There are many characteristics in the construction of urban expressway in China,such as a large number of ramps,dense ramp sites and many weaving areas.The main function of urban expressway weaving area is to connect the expressway and the trunk road,so as to meet the smooth completion of the convergence and dispersion of vehicles in the area.As an important traffic node of urban roads,the internal traffic flow operation state is complex.Due to the special structure of the weaving area,the vehicles in this area change lanes for many times,accelerate and decelerate frequently,which leads to the traffic flow disorder in the weaving area,and finally leads to traffic safety accidents,which makes the rapid development of the weaving area gradually become a frequent area of urban road traffic accidents.Therefore,this paper takes the traffic conflict in urban expressway weaving area as the research object,deeply studies the internal causes leading to the conflict,and analyzes the generation mechanism between vehicles in the weaving area.The main purpose is to curb the traffic conflict from the source of the accident.The collision time TTC(time to collision)is selected as the conflict judgment index,and the conflicts in the weaving area are divided into two categories: rear end collision and side collision.The conflict calculation model is established based on the traffic operation characteristics of conflict vehicles.Taking the vehicle as an approximate geometric figure,an improved calculation model in rectangular coordinate system is constructed according to the actual situation.At the same time,the severity of conflict is divided into two categories: general conflict and serious conflict,and the appropriate discriminant factor is selected to define the classification criteria.A comprehensive and systematic conflict judgment process is proposed.The main research process is as followsFirstly,through reading the relevant research content,this paper expounds and summarizes the research results of domestic and foreign scholars at this stage.It is found that there are some deficiencies in the research on the mechanism of traffic conflict between objects in urban expressway weaving area.The application of traffic conflict technology in urban expressway safety research is less involved,and the research on the relationship between the causes of traffic accidents and the mechanism of traffic conflict is not comprehensive.Therefore,the research object and research route are determined.Secondly,according to the conflict angle and driving track between the conflict objects in the weaving area,the operation characteristics of the two conflict parties are summarized and analyzed,and the traffic conflict in the weaving area is divided in detail.Based on the existing time index,this paper selects TTC as the judgment index of traffic conflict,and establishes the calculation model under different types of conflict.Then,the severity of traffic conflict is further divided into general traffic conflict and serious traffic conflict.Taking speed,included angle and headway as discriminant factors and Fisher discriminant method as theoretical support,a multi factor comprehensive discriminant function is established to calculate the threshold.According to the comparison between the value of discriminant function and threshold value,the severity of traffic conflict can be divided.Finally,VISSIM software is selected to simulate the traffic flow in urban expressway weaving area.The simulation parameters are determined according to the weaving section design standard,and the rationality of the improved TTC calculation model is verified by analyzing the output results of vehicle delay time and so on. |
