Safety Evaluation: a new operating speed model for two-lane, undivided rural roads

The main objective of this paper is to examine the influence of road alignment on vehicle operating speed. The authors propose and validate a new operating speed model in which the geometric features of an alignment and the lengths of its elements (curve, tangent) are considered. The results demonstrate that grade, radius, and length affect driver perception and operating speeds and are relevant to safety analysis methods. In contrast, the geometric features of previous and oncoming elements, although essential for an accurate analysis of the single locations and sections, had a negligible statistical influence on operating speed. The paper provides a set of analytical tools for predicting driver behaviour and speed in a given section based on the alignment features (previous and oncoming elements included). Furthermore, a framework for ranking and screening the factors that affect speed profiles is presented. Finally, the model can be used in safety evaluation of horizontal curves and tangents on rural undivided roads.