# Research on a Collaborative Control Strategy of an Urban Expressway Merging Bottleneck Area
## 4 An Illustrative Example
### Effect Evaluation
#### 4.3.2 Traffic Efficiency Improvement Analysis  
(1) Operational efficiency comparison  
VISSIM outputs the operation efficiency indexes of merging area 1 and merging area 2 under no control and cooperative control during the simulation period, as shown in Tables 7 and 8 (In order to avoid the influence of the control of merging area 2 on the operation efficiency of merging area 1, when the cooperative control of merging area 1 is turned on, the control system of merging area 2 is closed, which is the same as that of merging area 2). It can be seen that for merging area 1, after the coordinated control is applied, the operation efficiency indexes of the main line are improved to a certain extent, and the ramp operation efficiency decreases, but the decrease of each index is within 10%. For merging area 2, the traffic operation at the mainline and ramp is more stable than that in the uncontrolled state after applying cooperative control. Figure 19 shows the comparison of the overall travel time and turnover index of the experimental road segment under uncontrolled and coordinated control when the control systems of the two merging areas are both open. By analyzing the following figure, it is found that during the peak period, due to the application of the coordinated control strategy at the merging area, the overall travel time and turnover of the road segment are improved. It can be seen from Tables 9 and 10 that the total travel time during the simulation period under the uncontrolled state is 542.351 veh-h, and the total turnover is 27,643 veh-km. The total travel time after adopting the coordinated control strategy is 502.564 veh-h (reduced by 7.34%). The total turnover is 29,319 veh-km (an increase of 6.06%), indicating that the overall operational efficiency of the expressway under the cooperative control strategy is effectively improved. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Mainline**} & \multicolumn{3}{c}{**Ramp**} \\ \hline
**Evaluating Indicator** & **Uncontrolled** & \begin{tabular}{c} **Cooperative** \\ **Control** \\ \end{tabular} & \begin{tabular}{c} **Optimized** \\ **Ratio** \\ \end{tabular} & **Uncontrolled** & \
\begin{tabular}{c} **Cooperative** \\ **Control** \\ \end{tabular} &
\begin{tabular}{c} **Optimized** \\ **Ratio** \\ \end{tabular} \\ \hline Total travel time & 103.980 & 94.600 & +9.02\% & 9.280 & 10.109 & \(-8.93\%\) \\  (veh-km) & 11.956 & 10.272 & +14.09\% & 4.759 & 5.141 & \(-8.04\%\) \\ Maximum queue & 293 & 237 & +19.11\% & 44 & 47 & \(-6.82\%\) \\   length (m) & 266 & 239 & +10.15\% & 144 & 157 & \(-9.03\%\) \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Comparison of operation efficiency before and after control of merging area 1. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Mainline**} & \multicolumn{3}{c}{**Ramp**} \\ \hline
**Evaluating Indicator** & **Uncontrolled** & \begin{tabular}{c} **Cooperative** \\ **Control** \\ \end{tabular} & \begin{tabular}{c} **Optimized** \\ **Ratio** \\ \end{tabular} & **Uncontrolled** & \
\begin{tabular}{c} **Cooperative** \\ **Control** \\ \end{tabular} &
\begin{tabular}{c} **Optimized** \\ **Ratio** \\ \end{tabular} \\ \hline Total travel time & 122.690 & 99.311 & +19.06\% & 18.887 & 15.874 & +15.95\% \\  (veh-km) & 30.893 & 20.070 & +35.03\% & 13.082 & 8.739 & +33.20\% \\ Maximum queue & 368 & 268 & +27.17\% & 89 & 67 & +24.72\% \\ Stop times (veh-times) & 359 & 307 & +14.48\% & 475 & 369 & +22.48\% \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Comparison of operation efficiency before and after control of merging area 2. (2) Safety comparison  
The mutation and discreteness of speed is the main cause of traffic conflicts and accidents, and the probability of traffic conflicts and accidents increases with the speed difference. Therefore, in order to analyze the change in the overall operational safety level of the road segment before and after the cooperative control, the speed difference is selected as the evaluation index for analysis.