环形交叉口待行区设置与信号控制方法

为解决环形交叉口左转通行能力不足的问题，提出一种借助内侧环道与外侧环道设置左转待行区和直行待行区，并建立环道交通信号与进口道交通信号协调控制的环形交叉口信号控制方法。在饱和度等约束条件下，基于进口道停车线和环道停车线后不同的交通状态建立相应的延误计算模型，以延误最小为优化目标建立信号控制参数优化模型。案例分析表明：当左转交通量低于左转二次停车控制法适用的左转临界值时，所提出方法的延误较高；而当左转交通量高于该临界值时，左转二次停车控制法的延误快速上升并高于所提出方法的延误，且将导致环道锁死，而采用该方法仍能稳定运行，验证了提出方法的有效性。进一步分析进口交通量、不同类型环道数量和环岛半径等差异对所提出方法控制效益的影响，结果表明：随着环形交叉口进口交通量增大，该方法适用的临界左转比例随之降低；当进口交通量的左转比例低于临界左转比例时，交叉口处于非饱和状态且延误低；反之，交叉口处于过饱和状态且延误高。当左转交通量高于450 veh·h^-1时，增加左转环道有利于降低车均延误；而当直行交通量高于1 150 veh·h^-1时，增加直行环道效果更佳。当进口交通量小于800 veh·h^-1时，环岛半径对交叉口延误影响不大；而一旦进口交通量高于800 veh·h^-1后，环岛半径对车均延误的影响随进口交通量的增长愈加显著，环岛半径越大，交叉口车均延误就越高。

Design and Signal Control Method for Waiting Areas of Roundabout

This paper proposes a signal control method and design for a large roundabout to address the problem of insufficient capacity. This involves setting up waiting areas for left-turn and through vehicles at the inner and outer loop lanes of the roundabout, respectively, as well as adopting a coordinated control method for the traffic signals of the loop and approach lanes. Under the saturation constraint, a delay calculation model was established based on the traffic conditions of the loop and approach lanes, and a signal control optimization model was established with the goal of minimizing the delay. A case study showed that when the volume of traffic turning left was lower than a critical value applicable to the left-turn secondary stop control method, the delay of the method proposed in this paper was higher. When the volume of traffic turning left was higher than the critical value, the delay of the left-turn secondary stop control method rapidly increased, and was higher than the delay of the method proposed in this paper. Meanwhile, the left-turn secondary stop control method led to the loop lanes locking, whereas the method proposed in this paper could operate with stability, which verified its validity. Furthermore, the influences of the approach traffic volume, number of different types of loop lanes, and radius of the roundabout on the control efficiency of the proposed method were analyzed. The results showed that with an increase in the traffic volume at the approach to the roundabout, the critical left-turn proportion of the proposed method decreased. When the left-turn proportion of the approach traffic volume was lower than the critical left-turn proportion, the intersection was in the unsaturated state and the delay was low. In contrast, when the left-turn proportion of the approach traffic volume was higher than the critical left-turn proportion, the intersection was in the oversaturated state and the delay was high. When the volume of traffic turning left was higher than 450 veh·h^-1, increasing the left-turn loop lanes helped reduce the average vehicle delay. However, when the traffic volume of through vehicles was higher than 1 150 veh·h^-1, increasing the through-loop lanes was more effective. When the approach traffic volume was less than 800 veh·h^-1, the influence of the radius of the roundabout on the average vehicle delay was insignificant. When the approach traffic volume was greater than 800 veh·h^-1, the influence of the radius of the roundabout on the average vehicle delay was more significant; an increase in the approach traffic volume and larger radius of the roundabout led to a higher average vehicle delay at the roundabout.