# System Dynamics Modeling for Estimating the Locations of Road Icing Using GIS
###### Abstract  
Road icing can cause large traffic accidents on highways because, unlike snowy roads, its location is difficult to identify and it can occur rapidly, even during rainy weather. In this study, the amount and location of road icing were modeled and simulated over time based on the system dynamics theory. The simulation is expressed on the geographic information system (GIS) and facilitates advance detection of the location and amount of road icing that occurs unexpectedly unlike previous studies. Modeling was designed to process spatial and meteorological data after combining them. The spatial data used for modeling were Hillshade, Water System, Bridge, and Road (Highway). Air temperature, cloudiness, vapor pressure, wind speed, and precipitation were used as meteorological data. The amount of road icing was estimated by scientifically designing the parameters related to its occurrence between spatial and meteorological data. Based on this, the amount of road icing by location was simulated per 1m\({}^{2}\) using the GIS. The simulation results showed that the amount of road icing that began to increase from AM 08:00 reached its peak (an average of 213.62 g/m\({}^{2}\)) at noon and then slowly decreased. Additionally, when simulated with GIS, the sum amount of road icing between AM 12:00 and PM 13:00 was a maximum of 1707.292 (g/14 h) and a minimum of 360.082 (g/14 h) for each location. Hypothesis testing was conducted on whether road icing significantly occurs at actual points vulnerable to traffic accidents. Based on the results, the average significance level was calculated to be less than 0.05. Therefore, the alternative hypothesis that the model can estimate road icing in vulnerable areas was adopted. The verified simulation can be useful data to government agencies (e.g., road traffic authority) in their programs to prevent traffic accidents caused by road icing. road icing; highway; system dynamics; geo-information system 2021 11 8537 1188537 1188537 1188537 1188537 1188537 1188537 1188537 1188537 11  
42 injured [3]. In the morning of 15 November 2019, a 20-vehicle chain collision occurred on the 2 nd Yeongdong Highway due to road icing [4]. Road icing has continuously caused extensive property damage and human casualties each year [5]. Table 1 shows the average conditions for the occurrence of road icing. Scenarios were selected and data were acquired based on these figures. Various studies have been conducted on the occurrence of road icing and some of the causes have been identified. These causes include nighttime freezing of rain that fell in the daytime, freezing of moisture on the road surface during wet weather due to fog, and freezing of water that flowed down the slope on roads. The main cause, however, is the \"freezing rain\" generated by the application of a weak impact in the unfrozen supercooling state despite temperatures below 0 \({}^{\circ}\)C when it rains on roads at sub-zero temperatures [6]. As freezing rain instantly occurs as soon as rain falls on roads, its generation and location are difficult to estimate [1,7,8]. Therefore, fast and efficient responses to prevent traffic accidents due to road icing is important, but it is also important to select vulnerable sections where road icing is expected through modeling and to prevent it through structural and non-structural measures. To establish such measures, research is required to estimate the occurrence time, amount, and location of road icing. Spatial and meteorological data were used to model road icing in this study, then road icing was estimated and verified by constructing scenarios focused on \"freezing rain\". The modeling was performed using the system dynamics theory to estimate the time of occurrence and amount of road icing [9]. After modeling, the target road section was divided into multiple areas and each of them was substituted into the model. In addition, the amount of road icing by location was simulated using the geographic information system (GIS).