Regional Coordinated Traffic Signal Control Strategy For System Optimal State

The system optimal state in the field of traffic assignment indicates the upper boundary of the network performance.However,because the travelers in the transportation system trend to select the route that is best to them,the ground true operating state is biased toward the user equilibrium state.When the saturation degree of the road network increases,the difference between the system optimal state and user equilibrium state increases,indicating that there is still some "space for adjustment" in the road network.If the travel efficiency of specific travelers is "sacrificed" by a limited amount,the overall operational efficiency of the road network can be further improved.Traffic signal control is a critical way to organize and regulate the road traffic flow.The network performance state can be shifted from a biased user equilibrium state to a biased system optimal state by using the coordinated traffic signal control.In this way,the network flow can be organized more effectively,which can unlock and utilize more potential capacity of the road network and improve its overall operational efficiency.Therefore,there is an urgent need to establish an effective,reliable and easy-to-implement traffic signal control strategy optimization method to organize and regulate the traffic flow of the road network.This study proposes a method for obtaining a network level traffic signal coordination strategy that guide the road network operation state to a biased system optimal state.The proposed traffic signal control strategy should have the ability to guide selected travelers to adjust their travel routes,so as to realize the transfer of the road network operation state.First,after analyzing the formation mechanism of the road network operation state,this paper indicates the control demand of the regional traffic signal cooperative control strategy for the system optimal state.And this control demand can be expressed as the transformation of the road network operation state to a biased system optimal state through the adjustment of the travel routes.This paper also defines the critical route for the transformation of the road network operation state under signal control.In this paper,the critical route refers to the route that determines the road network operation state,i.e.,the route that leads to the difference between the user equilibrium state and the system optimal state.Taking into account the influence of traffic signal control,this study optimizes the path-based traffic equilibrium assignment algorithm,which is used to calculate the traffic assignment results in the user equilibrium state and the system optimal state.Then,the critical routes can be obtained by comparing the traffic assignment results in different states.To improve the proportion of traffic volume on the critical route to the route used by the system optimal state,this paper analyzes the route choice behavior of travelers and predicts the degree of travelers’ response to the strategy through the following research process.First,the travel process is classified according to the step-by-step process of travel route decision and the influencing factors in each decision step.Then,based on the classification results of the travel process,a survey has been designed to investigate the characteristics of travelers’ pre-travel and en-route route choice behaviors.After analyzing the results of the survey,it has been found that travelers choose their routes before or during their travels by referring to navigation information,and they would change the travel routes during their travels due to successive red light intersections.Therefore,based on the cumulative prospect theory,a route choice prediction model is developed by integrating the influence of navigation information and the number of red lights traveler passed.The model predicts the route choice results of traveler under the influence of traffic signal control by calculating the proportion of route adjustment of travelers influenced by various factors.Critical intersections and target critical routes are defined based on the analysis of travelers’ decision making behaviors and the characteristics of the links that the critical routes pass through.Then three coordinated traffic signal control strategies for system optimization are proposed,which are as follows: i)coordinated signal control for critical intersections only;ii)the regulation for the number of sequential red lights on the target critical route only;and iii)after regulating the number of successive red lights passed through,the strategy considers to coordinate the signal control for critical intersections.After that,to implement the coordinated traffic signal control strategies,this paper first develops a regional traffic signal adjustment scheme,and then determines the signal timing plan for each intersection.In order to verify the efficiency of the strategies,an experimental case is designed in this paper.In this case,first,three traffic signal timing adjustment schemes are developed based on the strategies.Then this study predicts the travelers’ route adjustment results based on the route choice model.And finally,this paper verifies the effectiveness and reasonability of the strategy establishment process in details from four perspectives: total travel cost of road network,average travel cost of each vehicle,service level of road links and average delay of intersections.