## 4 A Study on the Application of Nine Bridges in the Proposed Prioritization Model
### Data-Based Bridge Maintenance Priorities Analysis
For bridges F and G, they have single-lane entrances leading to the merge points between the bridges, resulting in fewer lanes in both directions. Therefore, they received the lowest comparison score of 0.48. Additionally, since these two bridges are located in the same area, they received identical scores in other evaluation categories, leading to the same final score. The facility type did not have a significant impact, as all bridges were classified similarly. In all, bridges with high scores in risk, criticality, and comparison factors ranked higher in BMP score priority. Bridge A received the highest scores in the risk and criticality sections among the nine bridges, and the second-highest score in the comparison section, giving it the highest overall BMP score. Relying solely on the BMP score may not fully reflect the precise condition and specific structural defects of bridges. To enhance the reliability of the prioritization process, Priority Index (PI) scores were introduced. These scores are derived from detailed safety inspection reports for each bridge's six structural categories and incorporate the weights of the investment prioritization index guide. This method allows for a more thorough assessment of the structural condition of each bridge. Bridge A achieved a high PI score of 0.138 among the nine bridges, indicating serious structural defects in the girder and deck slab sections, which were rated with grades E and D, respectively. This high PI score suggests that Bridge A has significant vulnerabilities in its superstructure's safety, likely due to its longer service life compared with the other bridges. Thus, Bridge A is prioritized for urgent maintenance according to its BHI score. Conversely, Bridge B had the lowest PI score of 0.0539, mainly because its overall structural condition is good and no severe defects were found in the detailed safety inspection. While BMP scores consider a comprehensive range of factors, such as risk, criticality, and comparison, PI scores provide a precise evaluation of individual component conditions. The difference between BMP and PI scores therefore reflects the broader range of factors included in the BMP assessment. The introduction of PI scores significantly enhances the reliability of maintenance prioritization assessments. By complementing the detailed structural and safety information that might be overlooked when only using BMP scores, the combined BHI score offers a more comprehensive evaluation. This approach allows for the clear identification of urgent maintenance needs, as demonstrated by Bridge A, and supports the safe and sustainable use of the bridge. The maintenance prioritization results are illustrated in Figure 9.  
The nine bridges were analyzed based on their BMP score (social importance), PI score (structural risk), and BHI score (composite score) and subsequently categorized into three priority groups, as shown in Figure 10.  
Priority 1 includes bridges requiring urgent maintenance, such as Bridge A and Bridge E. Bridge A, with the highest BHI and PI scores, is at significant structural risk and demands immediate attention. It also holds the highest BMP score, reflecting its high social importance. Bridge E, with the second-highest BHI score, shows notable structural deficiencies. Priority 2 consists of bridges requiring preventive maintenance, including Bridges B, F, and G. These bridges have high BMP scores, indicating significant social importance, but relatively low PI scores, suggesting a lower structural risk. As such, they require medium-term preventive management. Priority 3 includes bridges with a lower need for frequent inspection, such as Bridges D, H, and I. These bridges, characterized by low BHI and PI scores, have minimal structural risk and lower social importance and can be managed effectively through periodic inspections. Figure 10: Bridge priority categorization by BMP, PI, and BHI Scores. Figure 9: Results by maintenance priority.