Application of design consistency evaluation tools for two-lane rural roads: a case study from Italy

The operating speed-profile model is an effective tool for the safety analysis of new and existing roads since it can be used for checking speed consistency violations. However, to effectively use the operating speed-profile it is necessary that it accurately predicts the speed along the road. Therefore, the Design Consistency Module (DCM) of IHSDM (Interactive Highway Safety Design Model) and the recently developed model for the Italian context were applied to a real Italian two-lane rural road in rolling terrain with a complex alignment to evaluate their capability to fit the observed speeds. The comparison of the operating speed-profiles revealed that the DCM usually predicts operating speeds slightly higher than the Italian model, whereas the comparison between the predicted speeds and the observed speeds indicates that the Italian model fits slightly better the observed speeds on this type of road. All told, both the models predict quite well the observed speeds, even though there are cases in which the complex alignment strains the construction rules with the results that the predicted speed-profiles are not appropriate. The results of this case study are useful both to practitioners for a correct use of these models and to researchers for identifying the future research needs in an attempt to improve the capability of the models to predict speed-profiles that conform to the real speed observed.