Research On Variable Speed Limits Integrated Control Of Freeway Network

Freeways are important bridges between different urban centers,and between nurban centers and regions.They can often provide road users with convenient,quality traffic services,producing an accelerating effect in promoting the equilibrium of a regional economy.The rapid in crease in the motor vehicle population,and the subsequent gradual appearance of traffic congestion on freeways,have caused arise in a series of traffic-related problems,such as heavier environmental pollution,increasing fuel consumption,low efficiency of traffic flow,and interrupted traffic flow hampering the social progress and improvement of social service levels.Research methodology employed in solving the problem of traffic congestion within freeway network susually always adopts a single traffic control method,or traffic flow guidance,to tackle common traffic congestion.However,these researches aiming to integrate control to improve overall traffic flow have not formed the reliable and reasonable control system.As such,there is still large room for improvement with regards the issue of traffic control and proposing a reasonable,succinct and efficient solution to traffic congestion on freeway networks.Therefore,this paper aims to propose reliable traffic control methods and attempt to offer timely and efficient solutions to traffic congestion on freeway networks to ensure the improvement of overall traffic service levels.In addition,this paper considers the causes and the regional type of high frequency traffic congestion on freeway networks,and classifies traffic congestion into three types:linear congestion,regional congestion and regional network congestion.Aseries of integrated methods to confront these common traffic congestion issues are proposed and these aim to provide technical support to future discussion and consideration of constructions of an intelligent traffic system.The major works and research results of this paper are divided into four aspects and are further detailed below.1)Research on the basic of mainline variable speed limits control and a short-time traffic flow prediction method.Based on the current research,the mainline variable speed limits control method and its action mechanisms are analyzed,and the effect of variable speed limits controls on traffic flow operation is considered.The classical macroscopic traffic flow model has been extended in this paper to provide true descriptions of the changes of traffic parameters effectively.Furthermore,a short-time traffic flow fusion prediction model is given and a finished design flow,based on the predictive self-correcting,two dimensional weights allocation,that takes into account the requirement of traffic control and the efficiency,is offered.The results of this research provide necessary theoretical support and an accurate data basefor in-depth research of mainline variable speed limits on freeways and the promotion and construction of intelligent traffic control systems.2)Research of the mainline variable speed limits control method.On the basis of the analysis of the formation process of traffic congestion,the original region of traffic congestion is defined as the static or dynamic region existing within the freeway network that causes the decrease of traffic capacity.Two kinds of common linear traffic congestion problems caused by bottleneck links in the original region of traffic congestion are described.Based on the current research results,the idea of applying the mainline variable speed limits control method to deal with the two kinds of traffic congestion as mentioned above is proposed.In particular,a few concrete control measures are outlined:in aiming to solve the first category of traffic congestion caused by the self-factor of bottleneck links,the proposed models are intended to tackle traffic operation in bottleneck region.An isolated mainline variable speed limits control method is presented,based on the analysis of the traffic operation in bottleneck regions and the thought of the model predictive control to solve this specific problem;additionally,for the sake of solving the second category of traffic congestion caused by bottleneck links,where there is an off-ramp exit on the upstream mainline,a novel integrated variable speed limits control method is proposed based on the exploration of feasibility and the necessity of integrating the variable speed limit controls.The results of this research provide data on the efficiency of traffic control methods to solve two kinds of linear traffic congestion problems due to bottleneck links,the methodology of a scientific transportation decision,and the optimization of traffic conditions.3)Coordination between mainline variable speed limits control and ramp metering.Based on the analysis of the traffic flow characters in merging regions,the necessity of coordinated control involving variable speed limits and ramp metering is discussed.Two kinds of coordinated control methods are then presented.Coordination is considered,in particular,in relation to solving traffic congestion in merging regions caused by the self-factor of merging regions,based on the balance of traffic and the character ofthe first category of traffic congestion.Following on from this,an evaluation index of traffic condition has been designed,including the traffic density parameter.A model of coordinating mainline variable speed limits control and ramp metering has also been established.Turning to the second category of traffic congestion in merging regions caused by overcrowding in bottlenecks on the downstream mainline road,traffic density and queue parameters are selected as the primary parameters to achieve the most efficient system.A coordinated control method has been applied in the regional network of the merging region downstream with the existing bottleneck.The results of this research can offer considerable technical support to dynamic traffic control within freeway networks.4)Coordination of the variable speed limits control and traffic route guidance.After consideration of less effective traffic control methods and serious traffic congestion in freeway network,the necessity of coordinating the variable speed limits control and traffic guidance is explored.The feasibility of using the ideal of the bi-level programming problem to deal with the coordinated problem is discussed.Furthermore,coordinated variable speed limits control and traffic route guidance bi-level methodsare presented in an attempt to solve common traffic congestion in the regional network.The upper optimal control model mainly considers the user equilibrium and system optimization,while the lower optimal control model refers to the single path optimization problem.The results of this research provides new ideas in dealing with traffic congestion in merging regions,improves methodological thinking and provides support for the construction of freeway traffic controls.Taking into consideration liner traffic congestion,regional congestion and network congestion,this paper proposes a series of traffic control methods to solve common traffic congestion.It also aims to combine advanced traffic control methods and the engineering application closely.The content,methods and conclusion presented in this paper are all centered round discussion of the development and improvement of existing freeway traffic control systems.The outcomes of this research are of important academic significance and practical value to further improve freeway traffic service quality,enhance the safetyof traffic operations,and develop the level of transportation planning,traffic management and traffic control in the future.