Research On Reliability Of Road Network In Small And Medium-sized Cities

The reliability analysis of the road network in small and medium-sized cities can predict the growth degree of traffic volume that the urban road network can bear,identify the key road sections in the road network,then we can control the growth of traffic demand in advance,improve the key road sections to ensure the service level of road network.Considering that most small and medium-sized cities are in a period of rapid development and strong plasticity,the reliability analysis of road network can effectively guarantee the sustainable and high-quality development of cities.This paper summarizes the main analysis methods of the road network,which includes three stages: network connectivity reliability,travel time reliability and reliability based on network capacity,then optimizing the model and algorithm design of road network reliability analysis.In terms of model: the essence of reliability analysis based on road network capacity is to calculate reserve capacity coefficient.This paper optimizes its bi-level programming model,the upper-level model has been added service level coefficient and travel time limit,which realizes the unification of capacity and travel time reliability analysis to a certain extent.Stochastic user equilibrium(SUE)model based on origin has been selected as the lower-level model,which added capacity constraints to optimize distribution results,and the equivalence and uniqueness of the model are proved.In terms of algorithm: This paper designs the framework of reliability analysis based on the capacity of road network,and the enhanced Lagrange multiplier method is chosen to solve the SUE problem with constraints.The model avoids the listing of paths,so it is possible to design an efficient algorithm: the iterative step size of method of successive averages can be optimized to improve the efficiency of the algorithm.According to the sensitivity matrix,we can easily get a new equilibrium solution when the input variables change after getting a set of initial solutions.It is an important part of reliability analysis based on road network capacity.Based on the mathematical programming method,this paper designs the sensitivity analysis algorithm of SUE model with capacity constraints,and simplifies the calculation of the sensitivity matrix under the constraint conditions.Then,the correctness and feasibility of the algorithm are verified by simple single origin and multi origins examples.In the example,the paper gives the method to deal with the rank deficient problem,and the analysis results can be obtained.The capacity of urban road network is the basis of reliability analysis.Considering that there are many openings on both road sides,pedestrian crossing at random,serious mixed traffic in small and medium-sized cities,the section capacity is greatly affected by the external environment.It is difficult to obtain accurate results through direct calculation by deterministic mathematical model for ignoring the random influence factors.The section capacity can also be obtained by speed-flow model which is a kind of fuzzy recognition method,it needs more survey data.At the same time,the method is more used in high-speed roads,and urban roads need to deal with the speed.Considering that the radial basis function(RBF)neural network is a kind of network with simple structure,fast convergence speed and can approach any nonlinear function,it is well applied in fuzzy recognition.Based on RBF neural network,combined with the speed-flow model,the paper designs the flow chart of road capacity calibration,and takes the example of Xiangshui old city as an example,and the prediction effect is goodThis paper summarizes and analyzes two mainstream methods of calculating link capacity.The method of calculating link capacity by modifying the ideal capacity is simple,but it is a deterministic mathematical model and ignores the influence of random factors on the results,so it is not applicable in the complex traffic environment of small and medium-sized cities.The method of obtaining link capacity through speed-flow model is essentially a fuzzy identification method,it can take into account the random factors,but it needs a lot of investigation to calculate the link capacity of large-scale road network directly.At the same time,when the method is applied in cities,it needs to process the speed to get better results.Considering that the radial basis function(RBF)neural network is a kind of network with simple structure,fast convergence speed,and can approximate any nonlinear function,it has a good application in fuzzy recognition.Based on RBF neural network,combined with the speed-flow model,this paper selects some representative road sections as training sections,constructs RBF neural network,designs the section capacity calibration process.The method is applied in the road network of Xiangshui old city,compared the prediction results with the calculation results,the error is within the acceptable range of the project.The road network of Xiangshui old city is more representative in the road network of small and medium-sized cities.This paper takes the road network of Xiangshui old city as the research object.Firstly,the road network topology of the old city area is studied.Secondly,the paper studies how to get the traffic zones and OD matrix.Finally,based on the capacity of the road network,the reliability analysis is carried out,and the "sensitive" section is identified.Based on the reliability analysis of the road network in Xiangshui old city,this paper puts forward specific measures and improvement suggestions from three aspects,what is traffic demand management,topology optimization and key section improvement,and evaluates the reliability improvement after the road network optimization and road section improvement.After the improvement,the reliability of the road network in the old urban area has been significantly improved.At the same time,the recognition of key road sections is also discussed in addition,a recognition method based on contribution degree and comprehensive intersection is designed which is applied with an example.Finally,the paper summarizes the planning methods of high reliability road network.