Risk ranking on existing two-lane rural roads with respect to alignment and at grade intersections

Matragos, Vassilios; Apostoleris, Konstantinos; Psarianos, Basil; Mavromatis, Stergios · 2021 · Crossref

DOI: 10.5592/co/cetra.2020.1309

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Summary

This paper addresses the critical issue of road safety on existing two-lane rural highways, where approximately 51% of traffic fatalities in Greece and similar proportions in Europe and the USA occur. The research is motivated by the prevalence of inconsistent geometric designs and poor intersection layouts that violate driver expectations, leading to increased accident risks. The primary objective is to develop a methodology for evaluating built-in road safety by ranking risk levels based on geometric elements (horizontal and vertical alignment, superelevation, sight distance) and at-grade intersection characteristics. The methodology integrates operating speed ($V_{85}$) with specific geometric and intersection parameters to calculate hazard scores. The study utilizes a mathematical expression for $V_{85}$ derived from Greek regulations, incorporating curvature change rate, lane width, and longitudinal gradient. For road sections, critical parameters include minimum horizontal curve radius, consecutive curve radii, longitudinal gradient, required superelevation, and stopping sight distance. For intersections, the evaluation considers sight distances, turn lane adequacy, presence of dividing islands, signage, lighting, and operating speed. Data were collected from approximately 1000 km of the Greek rural road network, comprising over 4000 intersections. Road geometry was extracted using topographic surveys from a moving vehicle, while intersection features were assessed using Google Earth, Street View, and video recordings. Statistical analysis and regression factors were employed to derive weight coefficients for a combined rating system. The results establish a quantitative ranking system for both individual curves and road sections. Individual horizontal curves are rated on a scale where scores above 150 indicate a very low safety level, while road sections are rated such that scores above 450 signify very low safety. The methodology also calculates a weighted hazard factor per kilometer for road segments to account for the frequency of intersections. The study successfully applied this approach to the Greek dataset, identifying critical areas and "black spots" with high accident probabilities. The findings were validated by correlating the hazard scores with recorded accidents and results from the Interactive Highway Safety Design Model (IHSDM). The significance of this work lies in providing a rapid, comprehensive tool for prioritizing safety improvements on existing infrastructure. By assigning distinct scores to each design parameter, the methodology highlights specific deficiencies responsible for high hazard ratings, thereby guiding targeted interventions. The approach is modular, allowing for the inclusion of additional parameters such as pavement conditions or roadside clear zones. Furthermore, the researchers developed specialized software to automate the evaluation process, enabling the efficient assessment of large road networks and facilitating the identification of safety hazards for preventive maintenance and upgrade planning.

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-26; verification: verified.

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• road geometry

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• Empirical Findings: crash risk outcomes