Quantitative evaluation of highway safety performance based on design consistency

The concept of design consistency evaluation provides highway designers with a proactive tool for roadway safety improvement. The most promising consistency measures identified in previous research fall into four main categories, namely: operating speed, vehicle stability, alignment indices, and driver workload. For the most part, previous research has focused on the development of models that can estimate these consistency measures with less attention paid to quantitatively relating these measures to safety performance. The main objective of this study was to quantify the relationships between individual and combined consistency measures to actual collision experience through regression analysis. Model development was based on a database of horizontal curves representative of the different classes of two-lane rural highways in Eastern Ontario. Several statistically significant models relating the consistency measures to collision frequency were developed, and the sensitivity of each model to safety performance was examined. The models constitute a quantitative tool for evaluating the safety benefits of design improvement, and can therefore be used by designers in a safety-explicit highway design.