# Geospatial Simulation System of Mountain Area Black Ice Accidents
## 1 Introduction  
Since Korea has an average winter temperature of 0.5 \({}^{\circ}\)C and an average humidity of 65%, traffic accidents caused by snow and frost are frequent in the winter season. In particular, Korea has many mountainous areas and is surrounded by the sea on three sides, which often causes black ice on road surfaces around the mountains. Black ice is a thin coating of glazed ice on roadways or other transportation surfaces [1] and has an appearance that is identical to the black pavement and wet roads on which it forms [2]. Since the black ice is highly transparent and difficult to see, it causes fatal accidents in the winter season. Black ice is usually formed at night or in the early morning due to sudden temperature drops. This phenomenon is more pronounced on bridges and overpasses due to their elevated and exposed nature [3]. Black ice is more critical as the winter weather gets warmer. According to the Korea Transport Institute [4], the fatality rate of traffic accidents caused by black ice is highest, at 4.2%, when the temperature in winter is above 2 \({}^{\circ}\)C to 3 \({}^{\circ}\)C, but is lower, at 0.7%, when the temperature is between minus 1 \({}^{\circ}\)C and 0 \({}^{\circ}\)C. This is because black ice is created when there is increased water vapor due to higher air temperatures, which meets the cold road surface.  
As the development of mountain areas has recently increased, several roads are being renovated, and new bridges and tunnels are constructed, leading to increased driving speeds. However, the mountainous areas of Korea, especially the area close to the sea, are more likely to incur black ice due to higher humidity and temperature change [3]. While traffic accidents have decreased due to the implementation of government policies, black ice accidents in winter are steadily increasing. Among the total traffic accidents in 2015, the proportion of traffic accidents due to black ice and snowfall was about 6%, but had increased to about 10% by 2018. For this reason, the need for research on black ice prediction and warning systems has been emerging.  
With the recent development of sensor technology, research has been conducted to collect and utilize real-time weather information for each road section and road state information. Meteorological information monitoring systems are installed on national highways and major bridges. For example, the Korea Expressway Corporation has determined highway freeze sections and collected road freezing information and road weather forecasting information [5]. That information has been used for highway management. However, these monitoring systems are operated mainly for highways and major roads in urban areas. Meanwhile, most local roads along mountain areas are managed by local governments, so it is not economically feasible to apply the above systems. This study, therefore, aims to develop a risk assessment and warning system to prevent local traffic accidents caused by black ice by integrating spatial and meteorological information and local road networks. With the spatial information, the risk level of black ice for each time zone is estimated by simulating changes in the shadow area based on precise 3D terrain information. In addition, road structure information such as slope and curvature are considered for traffic accident risk assessment.