Safety and Consistency Assessment of a Two-Lane Rural Highway Passing through Mountainous Terrain

Abstract

This paper assesses the implications of vehicle-specific operating speed and crash data on the geometric design consistency evaluation of rural highways passing through mountainous terrain. The consistency was evaluated based on the operating speeds of passenger cars, empty trucks, and loaded trucks, and the results reveal the vehicle type has a significant impact on the assessment. Regardless of the vehicle type, Safety Criterion II has shown a consistent agreement with the degree of endangerment. The endangerment of trucks has a better agreement with the overall safety criteria (82%–86%) than passenger cars (58%–61%). These findings suggest that safety criteria, particularly Safety Criterion II, can be used to analyze the geometric design consistency of undivided roadways that traverse mountainous terrain. However, Safety Criterion II also classified several geometric elements as Fair or Good in spite of a significant number of crashes occurring at these elements. A further investigation of the operating speed using continuous speed profile data revealed a significant variability in vehicle speed on the curve, and that the operating speeds estimated using the spot speed data do not reflect this variability. This study highlights the need to consider speed variability when assessing design consistency using operating-speed-based consistency criteria.