The more (sharp) curves, the lower the risk

The risk of accident in horizontal curves is a complex function of at least the following characteristics of the curve: the radius of the curve; the length of the curve (and the resultant deflection angle); the presence of a spiral transition curve; the super-elevation of the curve; the distance to adjacent curves; and whether the curve is on a flat road, a straight gradient or a vertical curve. The interactions between these characteristics in determining accident risk in horizontal curves is only beginning to be understood. This paper summarises the results of studies that have investigated the interaction between the radius of a horizontal curve and the distance to adjacent curves. The shorter the mean distance between curves, the lower is the increase in risk for a given curve radius. The sharper neighbouring curves are, the lower is the increase in risk for a given curve radius. Thus, overall risk may not be higher on a road consisting mostly of sharp curves than on a road consisting mostly of straight sections with a few curves located far apart from each other.