Absence of transition curves


Goldenbeld, Ch.; Schermers, G.; Petegem, J.W.H. van



Transition curves are defined as the transition between a tangent and a circular curve. In a transition curve, the curve radius is not constant but gradually changes. These curves are often designed as clothoids (i.e. curves where the radius of curvature decreases linearly as a function of the arc length). Theoretically, a curve transition should improve safety because it gradually leads the driver into a natural safe path on the circular curve and it provides a space for superelevation to gradually change, thus minimizing excess side friction forces. The analysis of coded studies reveals that curved roads with transition curves are associated with improved driving performance and lower crash risk. Studies have shown a significant relationship between the absence of transition curve and risk, but this relationship is dependent upon various external factors including type of terrain (level, rolling, mountainous), road width, and ADT. There is an apparent interaction between the landscape and road design elements in curves, and the application of transition curves strengthens these interactions and results in improved safety. However, the influence of transition curves on crashes is much smaller than the radius of the curve. On the basis of these results, it is expected that the measure of implementing transition curves may have analogous positive effects on road safety, dependent upon external factors.

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European Road Safety Decision Support System, developed by the H2020 project SafetyCube



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European Commission, Brussels