| As a special type of intersection node,roundabouts have advantages such as high efficiency,low accident rate,and beautification of the environment.However,with the rapid development of cities and the sharp increase in motor vehicle ownership,priority rules control the frequent occurrence of congestion in the weaving area of roundabouts,leading to a significant increase in average vehicle delay.To solve congestion,signal control of the roundabout should be considered first.Currently,the most common signal control method at roundabouts is single signal control.This control method adds signal lights at the entrance to ensure the normal operation of traffic flow inside the roundabout to a certain extent,but there are still congestion problems during peak hours.In this case,it is necessary to implement dual signal control on the roundabout,completely separating conflicting traffic flows,and allowing different traffic flows to drive out of the roundabout in an orderly manner.This article aims to study the dual signal control methods at roundabouts.Firstly,it elaborates on the traffic management and control methods at roundabouts,introducing the control principles and application scope of priority rule control,single signal control,and dual signal control;Secondly,by conducting data surveys on roundabouts in Changchun City,the characteristics of headway and speed in the circulation area were analyzed,and four models were used to fit the headway and speed data.Analyzed two dual signal control timing methods and provided the calculation of phase transition time.Based on existing timing theories,the overall idea of timing scheme design was determined,and the phase sequence was designed.The concept of left-turn traffic storage time was proposed,and based on this,a loop cycle calculation method was designed based on the storage time of left-turn traffic flow,which takes the maximum storage time of actual left-turn traffic flow at different phases of the loop as the loop cycle.In terms of phase connection,the potential conflict judgment of left-turn traffic flow was given based on the actual left-turn flow,and the lighting time of the left-turn green light on the entrance lane was optimized.Based on the operating characteristics of the second left-turn vehicle and the flow of left-turn vehicles,the optimization time for the green light on the circular road is given;Finally,four experimental schemes were designed based on average vehicle delay and average maximum queue length as indicators,and PTV VISSIM 9 was used for simulation.Through comparative analysis,the feasibility of a dual signal control timing method based on the storage time of left-turn traffic flow was determined,and the applicability of different timing methods was explored.The main conclusions were as follows:(1)The experiments of irregular roundabout show that the new method has the smallest overall delay.When the total flow rate is about 2200～6500veh/h,the new method reduces the average vehicle delay by about 32% compared to the Yang method and about 21% compared to the Cakici method.(2)The experiments of regular roundabout show that when the total flow rate is about2200～5800veh/h,the single signal controlled symmetrical release method has less delay for vehicles;When the total flow rate is about 5800～6500veh/h,the "two steps left-turn" control vehicles have less delay.When the total flow rate is about 2200～6500veh/h,the overall delay of the new method is relatively small,reducing by about 12% compared to the Yang method and about 20% compared to the Cakici method.(3)The experiments of changing the left-turn proportion show that the new method is suitable for left-turn traffic flow with a proportion less than about 35%;The Yang method is suitable for left-turn traffic with a proportion of approximately 35% to 50%.(4)The experiments on the diameters of different roundabouts show that the new method is suitable for diameters less than 80m;The Cakici method is suitable for circular intersections with a diameter of no less than 80 m. |
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