# Analyzing Delay and CO Emissions: A Simulation Study of the Median U-Turn Method at Intersections
###### Abstract  
To improve traffic efficiency and reduce pollutant emissions at urban road intersections, VISSIM software was used to simulate traffic states to compare the median U-turn method with the direct left-turn method under various traffic volumes and left-turn ratios. Based on the average delay and CO emissions, suitable conditions were identified for using the median U-turn method at intersections. The results show that there are three critical left-turn ratio boundary curves named R\({}_{\text{dcri}(1)}\), R\({}_{\text{dcri}(2)}\), and R\({}_{\text{dcri}(3)}\) based on the relatively smaller average delay and there is a critical left-turn ratio boundary curve R\({}_{\text{COcri}}\) based on the lower average CO emissions at the intersection when the through traffic volume is in the range of 0-3000 veh/h and the left-turn ratio is in the range of 0-4. The median U-turn method is considered applicable at the intersection when the through traffic volumes are in the range of 0-87 veh/h, 87-400 veh/h, 400-416 veh/h, 416-934 veh/h, and 934-3000 veh/h, respectively, and, accordingly, the left-turn ratios are in the range of 0-R\({}_{\text{dcri}(2)}\), 0-R\({}_{\text{dcri}(1)}\) or R\({}_{\text{dcri}(1)}\)-4, 0-4, 0-R\({}_{\text{dcri}(3)}\), and R\({}_{\text{COcri}}\)-R\({}_{\text{dcri}(3)}\). These findings can provide a reference for traffic managers to organize the left-turn traffic at an intersection reasonably. urban road intersection; left-turn ratio; median U-turn; traffic delay; CO emission; VISSIM 4.0.0.0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-00000-00000-000000-0 The median U-turn method for left-turning traffic at an intersection has been extensively studied and widely applied in practical applications; as an example, of the median U-turn method has been applied at the intersection of Dongguan Road and Hongwei Road in Dongguan city in Guangdong province, China, and it is shown in Figure 1. Some researchers [3; 4; 5; 6; 7; 8; 9] studied the left-turn traffic organization method at intersections using the VISSIM software and found that the U-turn scheme can reduce the average delay and increase the traffic capacity. Other researchers [10; 11; 12; 13; 14; 15; 16; 17] found that the average delay of the intersection using a median U-turn method is related to the traffic volume. Under some traffic volume conditions, the average delay of using a U-turn method is less than the direct left-turn method, while under some traffic volume conditions, the direct left-turn method has less average delay. [PERSON], [PERSON] et al. [18] studied the models of U-turn and traditional intersection using the VISSIM simulation software. They found that the U-turn performed better in overall intersection emissions levels. [PERSON], [PERSON] et al. [19] studied the traffic delay due to U-turns to understand the causes of the delay and develop control measures for improved traffic performance. [PERSON], [PERSON] et al. [20] found that median U-turn intersections can provide superior safety performance when used in the appropriate conditions. The above research studies show that using an U-turn method at an intersection can reduce the average delay and improve the intersection's capacity under suitable conditions. However, most of the literature only focused on the delay and capacity effect of using the U-turn method at some specific intersections, and the quantitative relationship between the applicability of using the U-turn method and the traffic volume is not yet clear enough. In addition, more and more scholars are paying attention to the relationship between traffic organization and pollutant emissions at intersections under the background of China's Double-Carbon Policy. Some researchers [21; 22; 23; 24; 25; 26] studied the pollutant emissions at signalized intersections using the Vehicle Specific Power (VSP) method.