Safety effects of highway terrain types in vehicle crash model of major rural roads

Abstract

This paper presents the safety effects of highway terrain types in a crash model developed for South Korean rural national roads. This research was necessary because despite terrain type being one of the major factors determining the design speed of highways, their specific safety effects on actual crash occurrences and severity have not been fully investigated. It is the author’s view that when the design speed is changed, the terrain types will have some safety effects. To check this view, a statistical analysis was performed with an ordinal logistic regression model in order to relate several independent variables of highway geometric elements such as terrain type, tangent length, curve length, radius of curvature and vertical grade to actual crash occurrences. Through this investigation, terrain type was found to be a significant independent variable that explains crash occurrences for rural arterial roads in South Korea. Next, an attempt was made to develop crash cost estimation models for each terrain type. This was necessary because practicing engineers should be able to estimate the impacts of using different highway geometric designs on accrued crash costs. The models developed indicate that highway radius of curvature and median designs influence crash costs noticeably in flat areas, whereas vertical grade and shoulder width do so in mountainous areas. These findings seem to capture more detailed crash trends using different highway geometric designs and they should be helpful in designing safer highways.