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The safety of a horizontal curve (by means of accident frequency and degree of severity) is examined in this paper by features internal and external to it; both of these characteristics affect the driver attitude and the curve approach speed. Based on a review of the available literature on the subject, first the relationship between accident rate and some of the most important curve characteristics is examined. Then data from rural highways in Greece are used to investigate the relationship between accident rate and degree of curve or the curve radius. The flexible family of Gamma distributions is selected for this analysis and models using a special form of it (the shifted negative exponential distribution) are defined. The estimated functional forms are presented in conjunction with those from the literature and conclusions are drawn.
Horizontal alignment, horizontal curves safety, road geometric characteristics, rural roads
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