# Evaluation of Bridge Maintenance Priorities in Megacities
## 2 Concept of Risk  
The International Organization for Standardization (ISO) defines \"risk\" as the effect of uncertainty on objects [23]. [PERSON] noted that risk-based approaches provide a methodological framework formed by three elements (hazard, exposure and vulnerability) [24]. In addition, studies using the framework to which these three factors are applied are being actively conducted. However, such methods are particularly suitable for low-probability high-impact events, such as floods and seismic [25].  
Risk management can be understood as the process of assessing the probability and outcome of risk, establishing a response plan, and achieving objectives through active and continuous management. As shown in Figure 1, the National Health Service (NHS) in England refers to the repeated relationship between risk identification, risk assessment, risk response, planning, and risk monitoring [26].  
Risk analysis is divided into quantitative risk analysis and qualitative risk analysis. Quantitative risk analysis is a process of numerically deriving and analyzing the influence of various factors on the target, and qualitative risk analysis is derived from the relationship between possibility and weight by analyzing the impact of each factor and evaluating the degree of risk relative advantage.  
[PERSON] described the necessity of a complex management system that included risk analysis so as to effectively perform bridge asset management [27]. He also stated that standardized inspection programs, inspection cycles, efficient distribution of repair and reinforcement costs, and priority determination are required for risk analysis. Elsewhere, the International Infrastructure Management Manual (IIMM) [28], published by the National Asset Management Steering Committee (NAMS), presents research on SOC facilities and recommends how to apply findings. In IIMM, improved bridge management procedures are described. These include details on risk analysis, added procedures such as condition evaluation and performance measurement, damage type and risk assessment, response evaluation and selection, and optimal response.  
[PERSON] et al.'s \"Risk Management Strategy for Bridges and Structures\" puts forward a risk index combining status ratings with road classification indicators, forming a business plan network (BPN) for risk analysis. This was limited to the direct function of bridges, and existing research analyzing risk levels was improved to additionally derive risk factors for indirect functions [29].  
[PERSON] proposed evaluating risk through qualitative evaluation because of the challenge of quantitatively deriving the probability and associated effects of an event that did not occur [30]. He emphasized the need for continuous correction through expert consultation to increase the accuracy of qualitative evaluation.  
[PERSON] describes the bridge management guidelines in Italy and points out their differences from other approaches adopted worldwide [31]. In addition, open data such as Google street view and OpenStreetMap were used for additional data required for the study. Through this, considering the characteristics of the risk classification results, a higher evaluation level and a method of prioritizing bridges were proposed.