## 3 Case Study: Structural Factor Analysis for Public Transportation Bus
### Discussion  
#### 3.6.1 Summary of Analysis Findings  
Identifying and evaluating the structural factors contributing to the failures of public transportation will lead to successful maintenance management. This study reveals that out of 30 critical factors, the transmission cable (CF3), lubricating oil (CF6), engine speed sensor (CF8), diesel injector (CF9), engine cylinder (CF10), EBS sensor wire (CF14), EBS valve (CF15), alternator belt components (CF28), electrical appliance central control system (CF29), transmission computer (CF1), transmission (CF2), transmission speed sensor (CF4), water tank fan pump motor (CF5), and high-pressure fuel pump (CF12) are more important than others. Among the 14 important factors above, the ones belonging to the cause group (CF3, CF6, CF8, CF9, CF10, CF14, CF15, CF28, CF29) are key factors for intervention as improving these factors can lead to significant overall benefits. Meanwhile, the ones belonging to the effect group [CF1, CF2, CF4, CF5, CF12] also require attention as they significantly impact the whole system, and ensuring their reliability is crucial for maintaining overall system performance. Factors with a high cause degree and high centrality degree, i.e., ignition switch sensor (CF7), turbocharger (CF11), battery (CF26), alternator (CF27), and starter motor (CF30), are crucial as they significantly influence other factors and occupy a central position within the fault network. The high cause degree suggests that this factor is prone to faults, while the high centrality degree means its malfunction can lead to potentially severe operational disruptions. Such factors should be prioritized for both maintenance schedule and maintenance resources. To optimize current maintenance processes for high-cause and high-centrality factors, engineers should increase inspection frequency and implement strict test procedures to ensure these critical components are always in optimal condition. The current regular inspections conducted at bus depots involve engineers checking each bus component one by one, which consumes a lot of time, money, and manpower. Therefore, optimized regular inspections can start by focusing on factors with high cause and high centrality. Preventive maintenance must be a key focus, with proactive measures such as scheduled replacements, upgrades, and the use of high-quality materials to enhance durability and performance. Maintenance resources should also be prioritized for these high-cause and high-centrality factors. For human resources, experienced technicians should be assigned to inspections and maintenance, and they should receive regular training to stay updated on the latest maintenance techniques. For material resources, it is essential to ensure an adequate inventory of spare parts to minimize downtime and avoid cascading failures. Additionally, real-time monitoring systems can be developedand integrated into practical maintenance procedures to continuously track the condition of these critical components. By integrating these comprehensive maintenance strategies, organizations can significantly reduce the transport bus risks associated with high-cause and high-centrality factors, thereby ensuring the safety of the bus system and optimizing maintenance efficiency. Factors with a high cause degree but low centrality degree, i.e., transmission cable (CF3), lubricating oil (CF6), EBS sensor wire (CF14), EBS valve (CF15), and alternator belt components (CF28), act as critical triggers for failure events but have a more isolated impact. In maintenance decision-making, the high-cause and low-centrality factors require regular inspections and preventive maintenance to address their propensity for failure. Additionally, maintenance resources should be efficiently allocated to minimize the down-time and repair costs. However, given their limited impact on the whole bus system, the related components may not necessitate the extensive redundancy monitoring compared with the more central components.