Safety Evaluation Process for Two-Lane Rural Roads: A 10-Year Review

Abstract

A practical procedure was developed that explicitly considers the driving behavioral and safety rules of a horizontal alignment for the evaluation of roadway new designs; redesigns; and projects of rehabilitation, restoration, and resurfacing. Design classes were developed to classify, from a traffic safety point of view, roadway sections as good, fair, or poor; these design classes are associated with three safety criteria to develop an overall quantitative safety evaluation procedure for two-lane rural roads. The safety criteria are introduced to analyze and evaluate by ( a) Safety Criterion (SC) I: the difference between design speed and actual driving behavior as expressed by variations in observed 85th percentile speed; ( b) SC II: the difference between observed 85th percentile speeds on successive design elements; and ( c) SC III: the difference between side-friction assumed and side-friction demanded at the 85th percentile speed level on curves. Furthermore, the issues discussed include design speed, operating speed, sound tangential, and side-friction factors, as well as the application of tangents in the design process. A comparative analysis of the actual accident situation with the results of the safety criteria reveals a convincing agreement. Thus, the great advantage of the new concept is that as early as in the design stages, safety criteria can predict the endangerment (low, medium, and high) for new alignments or allow statements about the safety conditions of existing (old) roadway sections or whole road networks.