Design speed based reliability index model for roadway safety evaluation

The risk level evaluation for a highway segment is difficult because traffic crashes are characterized by a complex combination of highway alignments, vehicle speed, and speed dispersions. This paper provides a means of evaluating risky expressway segments by combining the design speed, observed speed, and their variations. A reliability index model was introduced for this purpose. The design speed and observed speed were used as the input capacity and demand, respectively, in the reliability index. Highway alignments, observed speed, and crash data from eighteen segments of expressways obtained from road safety audit projects in Korea were used to evaluate the model applicability to observed road conditions. The results imply that reliability indices and associated variables can explain the level of crash statistics. The new reliability index approach can therefore provide easily combined reflections of highway design and driver elements in the evaluation of risky expressway segments.