Study On Multi-Objective Optimization Method For Signal Timing At Roundabouts Considering Emission Characteristics

The roundabout has played an active role in the early stage of urban road traffic development.However,with the growth of road traffic demand,the shortcomings of insufficient traffic capacity at the roundabout are highlighted,which has become a bottleneck restricting the development of urban traffic.Congestion at roundabouts has become the norm,and even“deadlock” and “traffic flow overflow” have occurred,which in turn affects the traffic efficiency of the roads around the intersection.At the same time,the increase in vehicle exhaust emissions has worsened the urban traffic environment.Intersection signal control is one of the effective ways to solve the problem of traffic congestion and serious pollution at roundabouts.Reasonable design of signal control scheme has become one of the hot spots of engineers and scholars.Based on this,this paper establishes a multi-objective timing optimization model for intersections with the goal of minimizing vehicle emissions,average parking times and average vehicle delays,and proposes an improved dandelion algorithm to solve the model.The research results can provide decision support for urban traffic management departments.This paper introduces the development and research status of roundabouts at home and abroad,summarizes three common methods of signal control at roundabouts,introduces the content,phase structure and intersection channelization scheme of each control method in detail,and analyzes the applicable conditions of three signal control methods.A vehicle emission calculation model based on vehicle trajectory is proposed to study the total emission of vehicles at roundabouts.The trajectory tracking software Tracker is used to obtain the vehicle speed and acceleration of each inlet,and the average speed and acceleration of the vehicle are used as parameters to construct the specific power calculation model,so as to obtain the total vehicle emissions of the inlet and intersection in the cycle.The multi-objective optimization model of signal timing is established by taking the total vehicle emission,average vehicle delay and average number of stops as the objective function,and the effective green time and cycle time as the constraints.The multi-objective dandelion algorithm is improved to solve the timing model.The non-dominated solution protection mechanism is added in the breeding mutation stage.The immune function and threshold are set to protect the non-dominated solution to prevent its mutation,reduce the mutation probability of the non-dominated solution,and ensure the reproduction of excellent genes,so as to speed up the search efficiency of the dandelion algorithm and improve the computational efficiency and accuracy of the algorithm.Finally,the TOPSIS method based on entropy weight is used to obtain a single solution from the optimal solution set.The project case of Weihai Haibin Road-Shanghai Road roundabout is selected to investigate and analyze the current situation of intersection channelization and the dynamic change law of traffic flow.The timing scheme is optimized for the three periods of working day peak,flat peak and non-working day peak.Vissim simulates the traffic flow operation of different optimization methods,and compares the effects of NSGA-Ⅱ,multi-objective dandelion optimization algorithm and signal timing optimization scheme of this algorithm.The results show that the proposed method can effectively improve the traffic efficiency of the roundabout and reduce the total vehicle exhaust emissions at the intersection.