Analyzing Delay and CO Emissions: A Simulation Study of the Median U-Turn Method at Intersections

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 Rdcri(1), Rdcri(2), and Rdcri(3) based on the relatively smaller average delay and there is a critical left-turn ratio boundary curve RCOcri 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–Rdcri(2), 0–Rdcri(2) or Rdcri(1)–4, 0–4, 0–Rdcri(3), and RCOcri–Rdcri(3). These findings can provide a reference for traffic managers to organize the left-turn traffic at an intersection reasonably.