The run-off road crash (RORC) is a representative type of lethal crash. The severity of RORC has increased owing to a combination of factors, such as roadside geometry, traffic conditions, and weather/climatic conditions. In this study, a model for estimating the RORC severity was developed based on various factors, including fixed objects, roadway geometry, traffic conditions, and road traffic environment. To develop the model, the accident data of crashes with roadside fixed objects on highways, as well as information on fixed object-related variables and roadway geometry-related variables, were collected. To improve the model in terms of implementing a close reflection of the real world, a learning method with tree augmented naïve Bayes (TAN), which takes into account the causal links between variables, was applied. The results of the analysis showed that the severity of crashes with roadside fixed objects increased sharply when the vertical slope was ≥4%, the radius of the curve was ≥250 m, the distance between the fixed object and the roadway was less than 3 m, or the density of fixed objects installation was greater than 2 for every 10 m. The proposed model allows for an analysis of sections with a high RORC severity on the roadways in operation and provides improvement measures to reduce the severity of RORC.

Hi-Pass was introduced at the meeting of the Ministry of Land, Transport and Maritime Affairs and was first opened in June 2005. Since the utility rate of Hi-Pass in 2011 was 50.7%, it has been increasing by nearly 10% annually. With the increase in the use of Hi-Pass, however, there are growing safety problems. At this point of time, a criterion on Hi-Pass lane arrangement is required. Thus, this research suggests a three-stage highway lane arrangement method of mainline toll booths. This study is mainly based on conflict analyses and a conflict model is established.