ABSTRACT
Road safety depends on
humans, vehicles, and highway conditions. These factors influence road safety
separately or in combination. Despite these facts, the police report indicated
that only a single cause of accident has been reported for a given accident in Ethiopia
and the number of accidents that had been caused by road defect accounted
around 1% of total accidents per year, which underestimates its contribution to
road accidents. Beside these facts, only a few studies were carried out in
Ethiopia on this issue. Even though dangerous road segments were identified and
ranked 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 expected
number of traffic accidents and the geometric conditions of the road under
study to reduce accidents and provide safe driving environment. The main
objective of this study was to quantify the influence of road geometric
parameters on road safety. Using historical accident data, traffic data, and
road 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 road
geometric parameters at a time. Accordingly, the identified dangerous road
segments in the previous publication (DOI: 10.4236/jtts.2018.83009) were
further analyzed to estimate the influence of road geometric parameters on road
safety based on expected accident frequency. The result of the analysis shows
that the radius of horizontal curve, superelevation, transition curve length,
lane and shoulder widths were negatively correlated with the expected
frequencies of accidents. Whereas the numbers of horizontal and vertical curves per segment,
grade of the road, the occurrence of left turn horizontal curves with down
grade and right turn horizontal curves with upgrade were positively correlated
with the expected number of accidents. Therefore, it has been concluded that
the influence of road geometry has significant effect on the occurrence of
accidents along this study area.