## 3 Evaluation of Damage in Turnout System Using FMEA
### Definitions of Items for AHP Analysis and Results of Survey  
The damage risk factors for the wooden sleeper turnout systems of urban railways were classified into 7 categories (rail, rail joint, joint, baseplate, sleeper, fastening, and bolt) and 25 subcategories based on the existence or nonexistence of a history of maintenance and replacement. A survey was conducted among a group of experts, each with over 10 years of experience in railway maintenance. 1. Survey item: Survey of risk priority for sleeper floating track (known as STEDEF) wooden sleeper turnout system;
2. Participants: Experts with over 10 years of track maintenance experience in urban railway operating agencies;
3. Period: 1-20 August 2020 (for 20 days);
4. Method: A total of 15 copies of the questionnaire were distributed to 15 field management personnel through on-site visits, and 40 copies were distributed to 40 employees at head offices, business offices, and outside personnel. A total of 55 people were surveyed;
5. Main characteristics of survey respondents: With regard to the number of years in service for the respondents: 60% of the selected experts had 25 to 30 years in service, 20% had between 20 and 25 years of experience, and 20% had between 10 and 20 years of experience. The score distributions of occurrence, sensitivity, and detection for 66 turnout damage risk factors were each provided in a range of 1 to 5 points. Occurrence was defined as the likelihood of failure occurrence in the sleeper floating track (STEDEF) wooden sleeper turnout. The criteria for occurrence scores are presented in Table 1.  
The descriptions of the level of sensitivity for each failure mode of the sleeper floating track (STEDEF) wooden sleeper turnout are presented in Table 2. \begin{table}
\begin{tabular}{c c c c} \hline
**Item** & **Likelihood of Failure Occurrence** & **Range of Frequency** & **Score** \\ \hline Very High & Inevitable and certain occurrence of failure & \(\geq\)25 & 5 \\ High & High likelihood of failure occurrence & 20 \(\leq\)\(n\)! \(<\) 25 & 4 \\ Medium & Medium-level likelihood of failure occurrence & 15 \(\leq\)\(n\)! \(<\) 20 & 3 \\ Low & Low likelihood of failure occurrence & 10 \(\leq\)\(n\)! \(<\) 15 & 2 \\ Very Low & Almost no likelihood of failure occurrence & 0! \(<\) 10 & 1 \\ \hline \end{tabular}
\end{table} 
Table 1: Occurrence criteria. \begin{table}
\begin{tabular}{c c} \hline
**Item** & **Severity of Damage Impact** & **Score** \\ \hline Very High & Failure of turnout will lead to devastating accidents with loss of human life. & 5 \\ High & Failure of turnout will lead to large-scale accidents. & 4 \\ Medium & Failure of turnout will lead to medium-scale accidents. & 3 \\ Low & Failure of turnout will lead to small-scale accidents. & 2 \\ Very Low & Failure of turnout will lead to microscale accidents. & 1 \\ \hline \end{tabular}
\end{table} 
Table 2: Sensitivity criteria. The impact represents the level of influence on related components and the turnout system when failure occurs in the sleeper floating track (STEDEF) wooden sleeper turnout. The impact score criteria are presented in Table 3.  
For detection, we evaluated the level of difficulty in detecting damage on each turnout component. These components were divided into rail and non-rail components. The value of D was calculated based on the score given by categorization according to the methods of inspection and testing for the maintenance of the turnout system and the matters that required inspection by experts. Regarding the sensitivity calculation, importance refers to the degree of influence on the maintenance of the turnout system and was determined using the analytic hierarchy process (AHP) with the participation of 10 or more experts to ensure objective assessment. The major rail components in terms of weight (i.e., significance) were in the following order from highest to lowest: crossing, switch toes, normal rail, check rail, wing rail, stock rail, and closure rail.