The Application Of Vehicle Dissipation Index In Road Network Capacity Control

In recent years,the urbanization process has obviously accelerated,which is a doubleedged sword for social development.It injects an army of fresh blood into the city and brings vigorous development opportunities and motivation;but it has also been accompanied by quite a few challenges.With the rapid increase in urban population and the number of motor vehicles,the demand for transportation has also gradually increased.Urban traffic congestion has become a major obstacle to economic development.Under this background,the analysis and research of urban road network traffic flow is of great significance.Urban traffic flow status is particularly crucial in intelligent traffic management and control.Accurately describing the traffic flow status and predicting its changing trend,and early warning of the roads that are about to be congested can effectively guide the traffic management department to do congestion work in advance.Using the average speed of the floating car section the calculated congestion index is the current mainstream method to describe the traffic status,but the threshold is divided according to the road grade and obtained by empirical values,which is different from the actual road conditions.Therefore,in the 2018 Shenzhen Cup Mathematical Modeling Challenge D question < based on Research on Reconstruction of Urban Road Traffic Flow State Based on Multi-Source Monitoring Data > in the article,Fan Xinyue et al.Proposed the evaluation index of road section ”dissipation index” based on the fusion of multi-source data with video detection equipment for urban intensive construction.On the basis of the dissipation index of the road section,the following four aspects are studied:(1)Research on Road Network Operation State Based on Road Section Dissipation IndexThe function of the road network operating state is mainly to describe the congestion of the overall road network.Based on the road segment dissipation index,a spatial network system of ”road section-road-road network” is established,which aims to divide from a single road section to a road of the same level to the overall road network evaluate the traffic state at different levels.Select the parameters such as average travel speed,average design speed,and design capacity as indicators to build a road network operation state evaluation system.Due to the uncertainty of the road network,the multi-index fuzzy comprehensive evaluation model is used to run the road network.Solve the state,and use the entropy method to solve the index weights.(2)Road network carrying capacity in different statesBased on previous achievements,the concept and model method of road network capacity is analyzed from different angles,and the research definition of this paper is proposed.The author believes that the road network capacity in different states is different,so the classic headway spacing model is used to determine the theoretical capacity of the road network,and a new calculation model based on the time and space consumption of vehicles,to solve the road network carrying capacity under different traffic conditions,that is,the maximum number of vehicles the road network can withstand in this state,this is a macro road network capacity.(3)Traffic flow state prediction model based on dynamic bayesian networkThe traffic flow has the characteristics of randomness,uncertainty and time variability,so a dynamic Bayesian network model is constructed to predict the traffic state.First,the time slice is added to the static Bayesian network structure diagram,and the DBN structure diagram is constructed in combination with the upstream and downstream relations of the road section;then the maximum likelihood estimation of each node in the Bayesian network is calculated by using the maximum likelihood function;finally,the traffic operation state at the next moment of the study section is determined by the maximum membership degree.(4)Example analysisIn order to verify the feasibility of the model,this paper takes the middle ring road of Guiyang as an example,based on the traffic data of September 2,2019,and calculates and analyzes all road sections of the middle ring road through examples.A detailed example study is conducted and good results are obtained.Finally,this paper summarizes,points out the questions existing in the research process,which provides directions for the improvement of the following model,hoping to help the urban road network planning.