## 1 Introduction  
The increasing occurrence of damage and fractures in continuous welded rails (CWRs) in urban rail systems can be attributed to the characteristics of urban rail systems such as the frequent operation of trains, cumulative tonnage, and environmental factors, including climate change. Fractures in CWR that directly affect operational safety can be classified as a risk factor with an unpredictable occurrence [1]. Risks associated with CWR fractures can range from minor disruptions such as simple signal failures to major defects that can cause train delays and derailments. Previous studies and analyses of CWR fracture occurrences have indicated that fractures most frequently occur in surface ventilation shaft sections, which are directly affected by seasonal temperature variations among various factor-specific correlations. In this study, continuously welded rails installed in Korean urban railway systems are analyzed based on rail expansion theory, wherein axial stress develops in response to temperature fluctuations. Notably, tensile stress increases during winter due to thermal contraction, contributing to a complex failure mechanism in conjunction with residual welding stress and rolling contact fatigue (RCF). Repeated train loading leads to the accumulation of microcracks, while tensile stress induced by temperature drops accelerates crack propagation. It is therefore anticipated that rail fracture may occur even at temperatures below the ductile-to-brittle transition temperature (DBTT) when these mechanisms act concurrently. The thermal expansion and contraction of CWR, attributed to temperature fluctuations in winter and summer, result in concentrated axial forces, which lead to fractures at vulnerable welded joints. However, most existing studies on winter-specific localized CWR fractures have focused on qualitative trends and correlations based on cumulative fracture data. Therefore, research on the quantitative impact of temperature variations on CWR fractures remains lacking. [PERSON] [1] analyzed statistical data on mainline rail defects in South Korea from 1995 to 2014 in a study on correlations between factors affecting rail defects in urban rail concrete tracks and mitigation measures. They identified correlations between different rail defect factors and proposed mitigation strategies. Seasonal rail defects were found to be affected by temperature fluctuations and seasonal temperature differences. Significant temperature-related effects were observed in locations where the installation and fracture temperatures differed by more than 10 \({}^{\circ}\)C and in areas where temperature variations were severe, such as within 100 m of the ventilation shafts. [PERSON] [2] analyzed the causes of rail damage in Seoul Metro by examining the track infrastructure (Lines 1-4) and ten years of rail damage data and categorizing the causes into nine major factors. Analyzing the causes of rail damages, particularly rail fractures near ventilation shafts and those caused by temperature variations, confirmed that brittle fractures occur because of rapid drops in temperature. In underground urban railway systems, rail fractures occurred within 200 m of the ventilation shafts. [PERSON] [3] conducted a statistical analysis of key factors affecting CWR fractures in a study on the causes of CWR fractures in the Seoul urban rail system. The correlation analysis of CWR fracture factors and proposed countermeasures emphasized quality control in rail welding and defect management. [PERSON] [4] estimated the natural ventilation volume generated by train-induced wind in subway tunnels to quantify the magnitude of train-induced airflow (e.g., air displacement) when a train travels through a tunnel. To this end, they performed field measurements in tunnel tracks and natural ventilation shafts and conducted a numerical analysis to compare, analyze, and validate the measurement results.