Operating Speed Prediction for Italian Two-Lane Rural Roads Using Speed Profiles from GPS Data

"The main objective of the present research consisted in verifying if a low cost Global Positioning System (GPS) installed in a medium passenger car could be used to study drivers speed behavior in order to provide predictive models of operating speed and speed differential. GPS data have the great advantage of providing directly the speed profiles and not only spot speed values, on which the most of the current speed predictive models are based. Moreover, as several previous studies have demonstrated that the speed behaviour significantly differs among different Countries, as generally influenced by education, desire, driving regulations and enforcement, the present study proposed speed models specific for the Italian two-lane rural roads.. For this aim 36 driving test were performed along a segment of a two-lane rural road characterized by 13 tangent-curve configurations. Results demonstrated the effectiveness of the equipment for processing speed continuous data, and allowed to propose new speed models. Specifically a predictive model for operating speed on tangent was calibrated and it was found that the length of the tangent and the local grade were the most significant explanatory variables. Moreover a predictive model of operating speed on curve was proposed and the predictors were the length and the radius of the horizontal curve and the local grade. Finally tangent-curve speed variations were evaluated, and a model for predicting 85MSR was developed. The length of the approaching tangent and the deflection angle were found as the most significant predictors