One of the most frequent roadway characteristics that affects accidents is the horizontal curve. Accident rate increases in proportion to a decrease in the radii of curves, in particular for sharp radii on two-lane rural roads. Usually, driver behavior along the horizontal curve is represented by the speed because it is an important element in the general design process and can be used to create a speed profile along the alignment to verify design consistency. The consistency check is very effective in identifying sequences of elements that require a considerable speed reduction, such as a sharp isolated curve on a flowing alignment. Such inconsistencies are dangerous because they violate driver expectancy. Moreover, there are important differences in accident rates between similar curves, because the speed chosen by the driver to traverse the curve depends not only on the geometric curve characteristics, but also on other factors of the upstream horizontal alignment and of the overall road environment. To improve the validity of the speed profile previously proposed, environmental speed was introduced and a prediction model to estimate it was elaborated. The introduction of environmental speed into the prediction model of the horizontal curve operating speed improves its reliability. The results show that the model effectively estimates the operating speed along the road alignment, according to its geometric features. Consequently, this simulation model can be used in order to evaluate the consistency of new and existing roads and to promote traffic safety.
Samenvatting