# Analyzing Delay and CO Emissions: A Simulation Study of the Median U-Turn Method at Intersections
## 4 Discussion  
From the introduction section, it can be seen that many scholars have given examples of applying the median U-turn method based on the average delay at an intersection. In order to verify the applicable zone of the median U-turn method determined by the Formulas (4)-(6), as shown in Figure 12, the suitable left-turn ratios that used a median U-turn method under different through traffic volumes in some of the literature are also plotted in Figure 12. From Figure 12, it can be seen that all suitable left-turn ratios of the intersection using a median U-turn method under different through traffic volumes fall within the applicable grey zone of the intersection using a median U-turn method determined by Formulas (4)-(6), which proves that the applicable zone of the median U-turn method determined in this paper is correct and feasible.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Conditions** & **1** & **2** & **3** & **4** & **5** \\ \hline \(\rm Q_{s}\) (veh/h) & 0–87 & 87–400 & 400–416 & 416–934 & 934–3000 \\ \(\rm R_{ls}\) & 0–\(\rm R_{dcri(2)}\) & 0–\(\rm R_{dcri(2)}\) or \(\rm R_{dcri(1)}\)–4 & 0–4 & 0–\(\rm R_{dcri(3)}\) & \(\rm R_{COcri}\)–\(\rm R_{dcri(3)}\) \\ \hline \hline \end{tabular}
\end{table}
Table 2: The suitable left-turn ratio \(\rm R_{ls}\) for the intersection using a median U-turn method.  
Figure 12: The schematic diagram of the applicability of the intersection using a median U-turn method in the relevant literature [3,5,7,11,16,17].  
According to the \"Evaluation Method for Road Traffic Congestion\" (GA/T 115-2020) in China, it can be concluded that the intersection is in a slight congestion state when the average delay at an intersection exceeds 55 s, and the intersection is in a serious congestion state when the average delay at the intersection exceeds 145 s [37]. The unobstructed intersection means that the average delay of the intersection is less than one signal cycle. The slight congestion intersection means that the average delay of the intersection is greater than one signal cycle. The congested intersection means that the average delay of the intersection is greater than two signal cycles. According to Figures 6a and 10a, when the through traffic volume Qs > 500 veh/h and the left-turn ratio RIs = 1, the average delay at the intersection exceeds 145 s and the average stop times at the intersection are more than 4 times (Figure 7), and the intersection is in a serious congestion state. When the through traffic volume Qs \(\geq\) 1000 veh/h, the average delay at the intersection far exceeds 145 s and the average stop times at the intersection are more than 4 times (Figure 7), and the intersection is also in a serious congestion state under all left-turn ratios. As this kind of congestion state may occur at urban intersections, it is still necessary to give the suitable left-turn ratios for an intersection using a median U-turn method based on the average delay and CO emissions as indexes. However, it is not enough to only consider whether or not to use a median U-turn method to alleviate the congestion at the intersection. Some other measures to alleviate traffic congestion also need to be comprehensively considered such as road network traffic organization, intersection space channelization, signal timing optimization, and so on.