EFFECTS OF THE ROAD ALIGNMENT CONSISTENCY ON THE ROAD STRATEGIES SELECTION: CASE STUDY OF UNDIVIDED RURAL ROAD

The research aims to assess the relationships between the crash rates and road consistency. Design consistency assessment is a tool employed by designers to improve road safety. The case study involved a rural two-lane two-way road in Southern Italy that is located on a flat terrain without spiral transition curves between tangent segments and circular curves. Road alignment consistency was examined in two steps: a) by adopting Standards in force in Italy based on the design speed profile; b) by plotting operating speed profile to determine the area bounded by the speed profile and the average weighted speed, and the standard deviation of operating speeds for each geometric segment. Operating speed prediction model that returns the 85th percentile of the speed distribution of the only cars under free flow conditions, good weather conditions, and lighting was adopted. A negative exponential function was performed to predict the global consistency of a road as a whole. Finally crash rate prediction model was calibrated and it confirmed that as design consistency increased, the crash rates decrease significantly. The consistency model can be used during the geometric design process or during the evaluation process for two-lane rural highways.