Evaluation of Design consistency: a new operating speed model for rural roads with different grades

Achieving an effective evaluation procedure of geometric design consistency is among the most promising strategies to increase the road safety level. Actually, it is estimated that accident probability is higher where alignment homogeneity lacks. In the last years many research works were developed with the aim of addressing the different effects of geometric parameters on the prediction of the operating speed. Based on this parameter, the design consistency on road elements can be evaluated, and different approaches have just been worked out to estimate the operating speed on two-lane rural highways. However, the current operating speed predicting models are reliable if applied at horizontal curves, but when they have to evaluate the operating speed in high-graded and high-curved sections, the obtained results are significant different from the observed values. Consequently, these models can be employed successfully for estimating the operating speed in horizontal highways, but they are still lacking when applied on roads characterized by sharp curves, hairpin bends, highlongitudinal grades and long successions of curves with short tangents. The purpose of the present research work was to develop a new operating speed predicting model for this kind of alignment, using data detected on two-lane rural roads, involving totally nine curved sections.