| During rainfall,the road traffic environment and driver behaviour will change,resulting in new characteristics of road traffic flow.If the traffic signal timing scheme,especially the coordinated control timing scheme for arterial road traffic signals,cannot be responded to in time,the traffic signal control effect will be significantly affected,resulting in a significant reduction in road traffic operation efficiency and safety.Therefore,there is an urgent need to develop a coordinated traffic signal control timing scheme for arterial road traffic in response to the characteristics and control features of traffic flow under rainfall,in order to ensure the safe operation of road traffic flow on the premise of improving the efficiency of road traffic operation as far as possible.Firstly,the rainfall weather classification and the corresponding traffic flow parameter correction coefficients were determined.Based on the characteristics of rainfall weather,the rainfall weather is classified into three rainfall classes: light rain,moderate rain and heavy to heavy rain;based on the data survey,the change characteristics of traffic flow parameters such as road section speed,intersection speed,starting loss time,saturation flow rate and traffic volume under rainfall weather are analysed,and the optimum recommended values of traffic flow parameter correction coefficients under the three rainfall classes are solved by SA.Secondly,four strategies for coordinated control of arterial road traffic signals in rainfall conditions are developed and their application scenarios are identified.Taking road operation efficiency and road operation safety as the main considerations,combined with the degree of intervention in the original trunk line coordination and control,the trunk line road signal coordination and control strategy under rainfall weather is formulated.Strategy 1 is no interference with the original arterial coordination control idea;strategy 2 is light interference with the original arterial coordination control idea,through the adjustment of traffic signal timing scheme to achieve;strategy 3 is moderate interference with the original arterial coordination control idea,through the adjustment of traffic signal timing scheme and speed limit to achieve;strategy 4 is heavy interference with the original arterial coordination control idea,through the yellow flash control to achieve.According to the three principles of rainfall level,rainfall duration and saturation,18 kinds of rainfall scenarios are constructed,and the road traffic signal coordination control strategies for different rainfall scenarios are determined by the Delphi method.Again,an optimisation method is proposed for the coordination and control of road traffic signals on trunk lines under rainfall.In order to optimize the strategies and objectives of the mainline road traffic signal coordination control under different rainfall conditions,the traffic flow parameters correction coefficients under different rainfall levels are introduced,and the optimization method of the mainline road traffic signal coordination control under rainfall conditions is proposed.As Strategy 1 adopts the original traffic signal timing scheme and Strategy 4 adopts yellow flashing control,the proposed optimisation method is only for Strategy2 and Strategy 3.In this paper,the optimisation method is divided into intersection layer optimisation and arterial layer optimisation.The intersection layer optimisation determines the common cycle duration and green time for arterial traffic signal coordination control,and then the arterial layer optimisation regulates the phase difference between the intersections.In Strategy 2,a multi-objective optimisation model is established with the objective of maximising the number of vehicles passing and minimising delays,which is solved by a flower pollination search algorithm;in Strategy 3,speed constraints are added to Strategy 2,and the solution algorithm and process are the same as in Strategy 2;in Strategy 2,a phase difference optimisation model is established taking into account the changing speed characteristics of the road section,and an iterative search algorithm is used to find the If the speed of the road section is less than the safety limit of the road section,the phase difference is still calculated using the speed of the road section;if the speed of the road section is greater than the safety limit of the road section,the phase difference is calculated using the safety limit of the road section.Finally,the effectiveness of the optimization method for coordinated control of arterial road traffic signals under rainfall weather is verified.The data obtained from the survey on Weiyang Road(Fengcheng Road 3-Fengcheng Road 5)in Xi’an were matched to 18 rainfall scenarios according to the principles of rainfall level,rainfall duration and saturation,and it was found that Strategy 2 was applicable to the light and medium rainfall weather and Strategy3 to the heavy to torrential rainfall weather investigated in this paper.After determining the control strategy,three coordinated control timing schemes for arterial road traffic signals under rainfall weather are calculated and verified by example using SUMO simulation software.In addition to analysing the two optimisation objectives of the number of through vehicles and delay times,the average queue lengths in the simulation results are also analysed.The results show that the optimised traffic signal timing scheme can respond more effectively to the chosen control strategy,resulting in a 5%-17% improvement in the number of through vehicles,a 5%-16% reduction in delay times and a 2%-25% reduction in average queue lengths. |
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