# Median U-Turn Intersection Critical Parameter Research and Operational Performance Evaluation
## 6 Sensitivity Analysis
### Effect of the Separation Distance and the Gap of the Median U-Turn on Average Vehicle Delay
This phenomenon can be attributed to the reason that, when the separation distance on both sides of the modified MUT intersection is sufficiently long, left-turn vehicles will have more queuing space outside the median U-turn. The probability of congestion at the intersection will be reduced to a certain degree. In addition, a longer separation distance allows the intersection to accommodate more traffic flow while minimizing the impact of left-turn traffic on through traffic. However, an excessively long separation distance may increase complexity in traffic environments. Left-turn vehicles must drive a longer distance to detour around the intersection, which increases the travel time. Drivers may misjudge the traffic conditions at the intersection, which can lead to unsafe driving decisions. Moreover, when left-turn traffic weaves with through traffic, it increases the risk of confusion and congestion, which can contribute to increased average vehicle delay. Therefore, in practice, the traffic departments need to carefully balance the separation distances and the gap in the median U-turn to optimize the operational performance of MUT intersections. Effect of the Vehicle Free-Flow Speed and the Proportion of Left-Turn Vehicles in Corresponding Road Traffic Volume on Average Vehicle Delay  
The vehicle free-flow speed and the proportions of left-turn vehicles on both the major and minor roads may critically influence the delay reduction at the modified MUT intersection. In this subsection, the proportions of left-turn vehicles on the major and minor roads are set between 0.1 and 0.9. The vehicle free-flow speed is set between 2 m/s to 11 m/s. All other simulation parameters remain unchanged. Next, the impact of these factors on delay reduction will be analyzed. Figure 12 presents the delay reduction for various combinations of left-turn vehicle numbers on major and minor roads and vehicle free-flow speeds. Figure 11: Vehicle delay reduction for different gaps at median U-turns and separation distances. As shown in Figure 12, when the proportion of left-turn vehicles on both the major and minor roads is at its minimum, increasing the vehicle free-flow speed leads to an improvement in delay reduction. Subsequently, as the proportion of left-turn vehicles on the major and minor roads continues to increase, delay reduction initially increases accordingly with a higher vehicle free-flow speed, but then begins to decrease. When the proportion of left-turn vehicles on the major and minor roads becomes sufficiently large, further increases in the vehicle free-flow speed cause the delay reduction to decrease steadily. Appropriately increasing the vehicle free-flow speed can help dissipate queuing vehicles and reduce average vehicle delays to some extent. However, an excessively high vehicle free-flow speed means that more vehicles will pass through the intersection during a green phase. This can result in the excessive queuing of left-turn vehicles outside the median U-turn, which may not dissipate in time. In addition, drivers may need to spend more time avoiding fast-moving vehicles while turning around. Consequently, the degree of delay reduction will decrease. Figure 12 also demonstrates that, at low vehicle free-flow speeds (2 m/s to 3 m/s) and low proportions of left-turn vehicles on both the major and minor roads (0.1 to 0.3), there is a significant increase in delay reduction. Under normal traffic conditions, MUT intersections are generally considered effective for enhancing the operational performance of urban intersections when either the major or minor road has a high proportion of left-turn vehicles. However, in most cases, the proportion of left-turn vehicles on both roads is negatively correlated with delay reduction. The higher the proportion of left-turn vehicles, the less significant the degree of delay reduction becomes. This phenomenon is commonly observed at different vehicle free-flow speeds.