Research On Theory And Method Of Active Prevention And Control For Cascading Failure In Urban Regional Road Network

Urban road traffic network serves as the carrier of the traffic system function service and carries the mission such as traffic flow transportation.However,as GDP grows,the traffic demand increases sharply.It increases traffic congestion frequency that the contradiction between the increasing traffic demand and the backward road traffic network infrastructure.So far,most cities in China are faced with serious traffic congestion problems.And traffic congestion no longer happens at a single intersection(or road),but quickly spreads to the whole line.The time-space range of traffic congestion expands,which even leads to traffic congestion in the regional road network and paralyzes the regional road network transportation function.Once the traffic congestion occurs in the regional network,it not only affects the traffic flow efficiency,but also reduces the traffic safety and aggravates the traffic environment pollution.At present,the studies of urban regional traffic congestion mainly focused on the microscopic congestion parameter problem,such as analyzing the traffic flow operation features,predicting traffic flow queue length in the regional road network and putting forward specific traffic signal control plans.Traffic congestion not only depends on the traffic flow,but also occurs because of the unreasonable infrastructure design.Therefore,how to combine network dynamic characteristics and network topology to analyze urban regional traffic congestion and put forward effective protection methods of regional traffic congestion on the network operation essence,becomes the main research focus of this article.Based on exploring how to control and solve the problem of urban regional traffic congestion,the scientific method of the complex network is adopted.From the perspective of network cascading faiure,a two-layer network model of urban regional road network is established to combine network dynamic characteristics and network topology.From the perspective of complex network cascading failure,the urban regional traffic congestion problem is transformed into two urban regional road network cascade failure problems from accidental traffic congestion and recurrent traffic congestion.On the basis of establishing the failure model to simulate the failure evolution process,the vulnerability of the road network is clarified.And finally,a reasonable identification method and active prevention and control method are proposed to realize the effective control of regional traffic congestion.Therefore,the research content of this paper is mainly divided into three aspects: regional road network failure model,failure identification method and failure active prevention and control method.Among them,the failure identification method research is divided into two aspects: sub-area road network traffic state recognition and road traffic state recognition from the perspective of traffic state recognition.Then,the specific implementation ideas of the three main research contents are as follows: from the perspective of saving monitoring cost,firstly,according to the specific location of the vulnerable road and the vulnerable intersection,the monitoring sub-area of the urban road network is divided;then,the sub-area road network traffic status is monitored in real time.When the traffic state of the sub-area changes phase,it is transferred to monitor the roads and intersectiosn in the sub-area,and then the traffic state of a certain road(or an adjacent road of the intersection)in the sub-area is identified as being in a state of failure or in failure.In the state,the sub-area is actively prevented and controlled.In this paper,the failure identification method mainly focuses on the regional road network traffic state identification method.For the road traffic state recognition,the specific road segment failure identification threshold is given and the existing road traffic state threshold identification method can be used.The main research works and results of this paper are shown below.1.Urban regional traffic network cascading failure model under accidental traffic congestion In order to describe the impact of accidental traffic congestion on regional road network,the optimal power flow(ORNL-PSerc-Alaska,OPA)model is introduced to construct an OPA-based urban regional traffic network cascading failure model,which aims to analyze traffic accidents by means of OPA model and analyzes the vulnerability of the regional road network in the crowded environment.First assume that there are three processes in the state of nodes and edges in the network under the occasional congestion—— "normal" state,"transition" state and "failed" state,and further give the traffic meaning of these parameters,which can reflect the traffic characteristics of urban network road network.Taking the roads and intersections in the traffic network as the initial attack targets,the vulnerable components under accidental traffic congestion are determined by simulating the impact of the attack on the network operation of the regional road network.This part of the study points out that the network dynamics model under accidental traffic congestion indicates that the type of components in the regional road network can easily trigger the network cascading failure in this mode,which provides a theory for determining the reasonable supervision area and controlling the occurrence and spread of network cascading failure.2.Urban regional traffic network cascading failure model under recurrent traffic congestion In the operation of the urban traffic system,because of rising traffic demand for road network due to morning and evening peaks,the traffic congestion occurs with high frequency under regional traffic network in a certain period of time and this kind of phenomenon is the so-called recurrent traffic congestion.Similar to the network deliberate attack,the purpose is stronger.Therefore,aiming at this kind of attack mode,the urban regional road network cascading faiure model is proposed based on Edge transmission efficiency update(Crucitti-Latora-Marchiori,CLM)model.Through a series of model assumptions,the actual road network operation characteristics can be described as far as possible to simulate the influence of different complex network attribute components on network maximum connected chip and network global efficiency.This part study determines the vulnerable position of the regional road network under recurrent traffic congestion,which lays a foundation for protecting the road network normal function and improving network survivability.3.Quantitative model of urban regional network traffic state based on CNM Due to the lack of unified criteria of urban regional road network traffic status,the research on discriminating network traffic state mostly established on the criterion of traffic status of urban trunk road.In order to objectively and accurately reflect the traffic state in urban regional road network,this paper puts forward a quantitative model of urban regional network traffic state based on CNM(Clauset-Newman-Moore).According to the idea of data mining,the model transforms collected regional network traffic parameter data into the network traffic state evaluation parameter—global efficiency.All the elements of global efficiency samples are recognized as nodes in complex,and the global efficiency sample set is abstracted as undirected complex network.From the perspective of community classification in complex network,the quantitative level of regional road network traffic state can be obtained.Through the correlation between global efficiency and average velocity,the fuzzy regional traffic status criterion can be obtained for reference.With unified regional traffic state discrimination standard,this section of the research put forward a regional traffic state quantitative method,which provides a reasonable theory method for obtaining the traffic status information of the supervised regional road network more accurately.4.Model of discriminating urban regional network traffic status based on EMV-Ada Boost-SVM With using pattern recognition,it is necessary to train network traffic status classifiers to obtain real-time traffic status information.By introducing the Ada Boost(Adaptive Boosting)method and SVM(Support Vector Machine)method,combine both methods as the training learning method of regional traffic state classifiers,which improves the multi-classification performance of SVM method and improves the classification accuracy of Ada Boost method.Due to the fact that Ada Boost method and SVM method spend more time in the process of training samples,put forward three methods by optimizing the allocation of sample weight method,using EMV(Embedded Multi-view learning)parallel training all classifier and adopting DAG(Directed acyclic graph)as discrimination process to reduce the number of the called strong classifiers,which achieves the purpose of efficiently obtaining the regional traffic state information.The research work of this part focuses on the proposed method of regional traffic state discriminant without the criterion of traffic condition,which provides reliable information source for real-time monitoring urban supervised area network traffic status.5.Failure limited flow defense model for the regional network To study urban area network cascading faiure aimed at how to improve the network survivability against random attack and attempted attack in order to control network cascading faiure.After mastering the attributes of the fragile components of the regional network,research which method can control the propagation of failure and reduce the degree of the network damage in the early stage of network failure.Under the above research background,this paper puts forward regional traffic failure control model.Taking the road failure control as an example,the concepts are given new traffic meanings by redefining total control flow limit,failure defense response threshold,and failure control response threshold.Based on the developed failure control process,the control model is simulated and analyzed from the perspective of different failure resource allocation strategies and the total amount of different control limited.Besides,verify the feasibility of the model with the VISSIM simulation platform.Through the early determination of the road network vulnerable positions,the research results of this section real-time monitors these positions,and defense the network until the load reaches the failure resource allocation threshold,in order to realize to build the cascading faiure control system for urban regional network.