# Evaluation of Bridge Maintenance Priorities in Megacities
## 1 Introduction  
Bridges are important social overhead capital (SOC) facilities that help connect national transportation networks. They are directly related to the safety of people in social and economic aspects [1]. Many bridges in South Korea were completed during the country's rapid economic growth period of the 1970s and the 1980s. They account for about 63% (c. 19,000 bridges) of all bridges in Korea as of 2022, and the number of old bridges over 30 years old, which will increase rapidly, is expected to increase to about 72% (c. 21,000 bridges) by 2035 [2; 3; 4; 5]. The sudden overwhelming number of aging bridges was the result of the conservative evaluation of SOC facilities when they were designed and constructed several decades ago. The aging of bridges can heighten people's worries about the potential for major structural failures. Down the line, considerable funds need to be spent on ad-hoc repairs, squeezing funding in other important areas for future generations. Unfortunately, bridge aging is accelerating in Korea, and preventive, preemptive, and economic maintenance must be carried out to effectively cope with the problem. Ideally, a systematic maintenance system should be established to improve maintenance efficiency at the national level, and the appropriateness and adequacy of investment in maintenance should be determined based on quantitative and qualitative indicators such as bridge size, age, and risk [6; 7]. A lack of means for determining a maintenance system for old bridges is not a new problem. There are plenty of past cases in other highly developed nations in which bridges shockingly collapsed, leading to loss of life and public inquiries [8]. In the United States alone, there have been several hundred documented bridge collapses since the 1980s. These include the Mianus River Bridge in 1983, the Schoharie Creek Bridge in 1987, the Interstate 35W bridge over the Mississippi River in August 2007, and the Interstate 5 bridge in Washington state in 2013. Also, in August 2018, the Polcevera Bridge collapsed in Genoa, Italy, killing approximately 40 people. [PERSON], warned of the danger of collapsing the Polcevera Bridge about 20 years ago before it collapsed [9]. Even though structuraldefects were discovered, the bridge was not maintained properly, as it was believed that maintenance could damage aesthetics. Italy's bridge management regulations have been significantly impacted by this accident, and the importance of bridge maintenance has been reconfirmed. In Japan, the importance of paying greater attention to aging SOC facilities was recognized because of the 2012 Sasago Tunnel collapse near Tokyo, resulting in a fresh $3.5 billion investment in maintenance projects for bridges, roads, and schools. Following similar disasters, other countries such as the UK, Canada, and Australia have introduced and operated evaluation systems for infrastructure by moving away from centralized government schemes to localized schemes. Korea needs to prepare for upcoming bridge aging by adopting good examples of maintenance system practices and more efficient investment principles from those who have already learned harsh lessons. Presently, in the case of Korea, the investment in maintenance costs compared to the asset value of facilities is only about one-third of that of other developed countries. In order to solve this problem, studies that can evaluate the stability of bridges are being actively conducted, and the representative methods for evaluating the stability of bridges include the probabilistic method and the neural network method [10; 11; 12; 13; 14; 15; 16; 17]. However, probabilistic and neural network methods are limited to evaluating single bridges based on complex correlations [18]. Therefore, simplification is needed to evaluate numerous bridges and use them in government.