## 2 Construction of the Evaluation Indicator System
### Indicator Grading Criteria  
Based on the risk assessment indicator system determined in Figure 3 and considering the operational safety requirements for the tunnel entrance segment and the middle segment, the safety risk levels of each indicator were classified into five levels. This classification was established based on the current design standards and specifications in China and was informed by relevant research findings from both domestic and international sources. The corresponding grading criteria have been determined and are presented in Table 2.  
Qualitative indicators, such as the level of emergency management, which are difficult to quantify but have an impact on operational safety, were categorized into five risk levels ranging from low to high. To provide a quantitative representation of these qualitative indicators, a corresponding numerical scale was established, consisting of five interval values: 80-100, 60-80, 40-60, 20-40, and 0-20. Based on the subjective judgments of experts, the evaluated indicators were scored to roughly represent their impact on tunnel operational safety.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Risk Level** & **Low** & \begin{tabular}{c} **Relatively** \\ **Low** \\ \end{tabular} & **Medium** & \begin{tabular}{c} **Relatively** \\ **High** \\ \end{tabular} & **High** \\ \hline Civil Engineering Structural Techniques (Score) & \(\geq\)85 & [70,85) & [55,70) & [40,55) & \(<\)40 \\ \hline Electromechanical Facilities Technical Condition (Score) & \(\geq\)98 & [95,98) & [91,95) & [81,91) & \(<\)81 \\ \hline Technical Condition of Other Facilities (Score) & \(\geq\)85 & [70,85) & [55,70) & [40,55) & \(<\)40 \\ \hline Tunnel Length (m) & \(<\)1000 & [1000,3000) & [3000,6000) & [6000,10,000) & \(\geq\)10,000 \\ \hline Length of Tunnel Entrance Transition & \(\geq\)5 V & [3 V,5 V) & [2 V,3 V) & [V,2 V) & \(<\)V \\ \hline \multirow{3}{*}{\begin{tabular}{c} Tunnel Condition \\ Indicators \\ \end{tabular} } & Minimum Radius & 80 km/h & \(\geq\)2500 & [1500,2500) & [700,1500) & [400,700) & \(<\)400 \\ \cline{2-6}  & 100 km/h & \(\geq\)4000 & [2000,4000) & [1100,2000) & [700,1100) & \(<\)700 \\ \hline Maximum Slope (\%) & (0.3,1] & (1,2) & (2,2.5) & (2.5,3) & \(>\)3 \\ \hline \multirow{3}{*}{\begin{tabular}{c} Sideways Force \\ Coefficient (SFC) \\ \end{tabular} } & \begin{tabular}{c} Concrete \\ pavement \\ \end{tabular} & \(\geq\)56 & [46,56) & [39,46) & [31,39) & [0,31) \\ \cline{2-6}  & \
\begin{tabular}{c} Asphal \\ pavement \\ \end{tabular} & \(\geq\)61 & [51,61) & [41,51) & [31,41) & [0,31) \\ \hline \multirow{3}{*}{
\begin{tabular}{c} Provision of cross passages and \\ emergency stopping lanes (score) \\ \end{tabular} } & \multirow{3}{*}{[80,100]} & \multirow{3}{*}{[60,80)} & \multirow{3}{*}{[40,60)} & \multirow{3}{*}{[20,40)} & \multirow{3}{*}{[0,20)} \\ \cline{2-6}  & Operating speed \(|V_{85}-V_{0}|\) (km/h) & \(\leq\)5 & (5,10) & (10,15) & (15,20) & \(>\)20 \\ \cline{2-6}  & Coordinated nature of operating speeds & \(|\Delta V_{85}|\) (km/h) & \(\leq\)7 & (7,10) & (10,15) & (15,20) & \(>\)20 \\ \cline{2-6}  & Coefficient of variation of vehicle speed & \(\leq\)0.1 & (0.1,0.15) & (0.15,0.20) & (0.20,0.25) & \(>\)0.25 \\ \cline{2-6} Indicators of traffic characteristics & \multirow{3}{*}{Service level (V/C)} & \(\leq\)0.2 & (0.2,0.3) & (0.3,0.4) & (0.4,0.5) & (0.5,0.6) \\ \cline{2-6}  & & \(>\)0.9 & (0.8,0.9) & (0.7,0.8) & (0.6,0.7) & (0.5,0.6) \\ \cline{2-6}  & Overload ratio (\%) & \(\leq\)0.5 & (0.5,3.0) & (3.0,5.0) & (5.0,10.0) & \(>\)10.0 \\ \cline{2-6}  & & \(\leq\)20 & (20,25) & (25,30) & (30,40) & (40,60) \\ \cline{2-6}  & & \(>\)80 & (75,80) & (70,75) & (60,70) & (40,60) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Grading Criteria for Risk Assessment Indicator System.