# Analyzing Delay and CO Emissions: A Simulation Study of the Median U-Turn Method at Intersections
## 5 Conclusions  
* Through VISSIM software simulation, it can be seen that when the through traffic volume Qs \(\leq\) 400 veh/h, the average delay curve of the intersection using a direct left-turn method and that of the intersection using a median U-turn method have one intersection point, and the left-turn ratio corresponding to the smaller intersection point is relatively concentrated, while the left-turn ratio corresponding to the larger intersection point decreases rapidly as through traffic volume increases. When the through traffic volume Qs > 400 veh/h, the average delay curve of the intersection using a direct left-turn method and that of the intersection using a median U-turn method have one intersection point, and the left-turn ratio corresponding to the intersection point shows a trend of rapid decrease followed by stabilization with the increase in through traffic volume. * Through VISSIM software simulation, it can be seen that when the through traffic volume Qs < 934 veh/h, the CO emission curve of the intersection using a median U-turn method is lower than that of the intersection using a direct left-turn method under each through traffic volume. When the through traffic volume Qs \(\geq\) 934 veh/h, the CO emission curve of the intersection using a direct left-turn method has a single intersection point with that of the intersection using a median U-turn method, and the left-turn ratio corresponding to the intersection point shows a trend of increase followed by stabilization with the increasing through traffic volume. * When the through traffic volume is between 0 and 3000 veh/h and the left-turn ratio is between 0 and 4, three critical left-turn ratio boundary curves named Rdcri(1), Rdcri(2), and Rdcri(3) can be obtained by fitting the left-turn ratios corresponding to the intersection points of the average delay curve of the intersection using a median U-turn method and that of the intersection using a direct left-turn method under different through traffic volumes, and a critical left-turn ratio boundary curve named RCOcri can be obtained by fitting the left-turn ratios corresponding to the intersection points of the CO emission curves of the intersection using a median U-turn method and that of the intersection using a direct left-turn method under different through traffic volumes. 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\({}_{\text{dcri(2)}}\) or, 0-4, 0-R\({}_{\text{dcri(3)}}\), and R\({}_{\text{COcri}}\)-R\({}_{\text{dcri(3)}}\). It should be noted that the research in this article is based on the following conditions: the research object is a flat four-way intersection with three entrance lanes and three exit lanes in each direction; each entrance includes a left-turn lane, a straight lane, and a right-turn lane, and each of four central medians with a width of 4 m has a U-turn opening with a length of 8 m located 400 m away from the intersection. Under the geometric conditions of the road intersection mentioned above, only the through traffic volume and left-turn traffic volume are considered to seek the suitable conditions of an intersection using a median U-turn method. Further research is needed on the through traffic volumes and left-turn ratios that are suitable for using a median U-turn method at intersections under other road intersection geometric conditions. Additionally, safety issues and pedestrian movements were not considered in the current analysis and are left for future work. Conceptualization, Z.Z. and Q.G. ; methodology, B.G. ; software, Z.Z. ; validation, B.G., C.T., and Q.G. ; formal analysis, Z.Z. ; investigation, Q.G. ; resources, B.G. ; data curation, B.G. ; writing--original draft preparation, Z.Z. ; writing--review and editing, B.G. ; visualization, Q.G. ; supervision, B.G. ; project administration, C.Z.