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Quantifying the Influence of Road Geometric Parameters on Road Safety (Case Study: Hawassa-Shashemene-Bulbula Rural Two-Lane Highway, Ethiopia)

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Document pages: 27 pages

Abstract: Road safety depends onhumans, vehicles, and highway conditions. These factors influence road safetyseparately or in combination. Despite these facts, the police report indicatedthat only a single cause of accident has been reported for a given accident in Ethiopiaand the number of accidents that had been caused by road defect accountedaround 1 of total accidents per year, which underestimates its contribution toroad accidents. Beside these facts, only a few studies were carried out inEthiopia on this issue. Even though dangerous road segments were identified andranked along the same study area of this paper in our previous publication,Hawassa-Shashemene-Bulbula two-lane rural highway, the influences of road geometric parameters on road safety were not correlated along this study area.Therefore, it is imperative to clarify the relationship between the expectednumber of traffic accidents and the geometric conditions of the road understudy to reduce accidents and provide safe driving environment. The mainobjective of this study was to quantify the influence of road geometricparameters on road safety. Using historical accident data, traffic data, androad data, the expected numbers of accidents were estimated by using the empirical Bayes (EB)method. Then, the expected numbers of accidents have been correlated with one or more roadgeometric parameters at a time. Accordingly, the identified dangerous roadsegments in the previous publication (DOI: 10.4236 jtts.2018.83009) werefurther analyzed to estimate the influence of road geometric parameters on roadsafety based on expected accident frequency. The result of the analysis showsthat the radius of horizontal curve, superelevation, transition curve length,lane and shoulder widths were negatively correlated with the expectedfrequencies of accidents. Whereas the numbers of horizontal and vertical curves per segment,grade of the road, the occurrence of left turn horizontal curves with downgrade and right turn horizontal curves with upgrade were positively correlatedwith the expected number of accidents. Therefore, it has been concluded thatthe influence of road geometry has significant effect on the occurrence ofaccidents along this study area.

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