# Research on a Collaborative Control Strategy of an Urban Expressway Merging Bottleneck Area
## 4 An Illustrative Example  
### Simulation Platform Construction  
This paper selects as the survey object the urban expressway of Xi'an City, Shaanxi Province, China. Comparing the second ring road and the third ring road in the Xi'an loop line system, it is found that compared to the third ring road, the second ring road has more and denser entrances and exits on both sides, and the closure is poor, which is closer to the urban trunk road in function. In contrast, the third ring road is more in line with the functional positioning of the urban expressway. Therefore, the survey objects matching the research of this paper are selected on the third ring road. Select the evening peak survey data as research data. As shown in Figures 7-9, the total length of the investigated segment is 2.46 km. The distance between the two merging areas is about 396 m, and the distance between the merging area and the downstream diverging area is about 200 m. The first merging area is Guang'an Road (expressway), which is connected to the mainline of the East Third Ring Road through the entrance ramp of Andi Interchange. The second merging area is the East Third Ring Road, which is connected to the main line through the entrance ramp. The merging area adopts parallel acceleration lanes. VISSIM is selected to simulate the experimental road to obtain the real-time traffic flow data required for the control strategy, and the effect of the control strategy is evaluated according to the output data of each detector. Based on the two principles of diverging area and merging area as a separate segment and similar road conditions in each basic segment, the experimental segment is divided. Figure 10 shows the division of the experimental segment and its cell division results. The expressway mainline is divided into nine segments, of which Cell3 and Cell6 are merging segments, Cell8 is a diverging segment, Merge1 and Merge2 represent the entrance ramp segments of the two merging areas, and Diverge is the diverging ramp segment. Figure 7: Survey site and objects. The simulation needs to accurately reflect the road operation and provide a reliable experimental basis for the effective evaluation of the subsequent control strategy. In order to avoid congestion caused by the insufficient capacity of the mainline, this paper considers the running state of the mainline traffic flow without a ramp and finds that it is not the congestion caused by excessive traffic flow of the mainline. Therefore, the relevant parameters in VISSIM software should be calibrated according to the actual operation of road traffic. As shown in Figure 11, the simulation road network is constructed according to the actual road conditions. According to Figure 10, the simulation road section is divided into different segments. Data detectors are set in each segment and queuing, and flow detectors are set at the entrance ramp. Based on the measured data on Friday, December 11, 2020, the simulation road path decision, traffic rules, vehicle composition, traffic flow, etc., are input. The simulation duration is set to 2 h, and the peak hours are 1800 s-5400 s. As shown in Figure 12, the split path decision point is set at the starting point of the split zone, and the split ratio is set to 0.15; according to the actual observation situation, the conflict area at the connection between the entrance ramp and the mainline is set as the alternate traffic rule; according to the actual data statistics, the vehicle composition of the mainline and the entrance ramp is shown in Table 1. In order to simulate the uneven arrival  
Figure 8: Survey road satellite map. Figure 10: Simulation segment structure and Cell division results. Figure 9: Survey road diagram. characteristics of the ramp vehicles, the flow type is set to random arrival. The merging area 2 flow is larger than the merging area 1, and the interference to the mainline is stronger.