Quality control of road project: identification and validation of a safety indicator

Geometrical indicators neglect both normal human behavior and driver’s behavior under specific conditions of stress, risk and fatigue. These conditions are frequently induced by the road environment and the way of driving. Repeated dynamic stresses (such as transversal accelerations) during driving can cause abnormal behaviors. This is the reason why a new, advanced and effective indicator is proposed and validated to assess the safety of road infrastructures considering the investigation of the variability of transversal accelerations as an unbiased indicator of discomfort. The main theoretical assumption is: a subject driving on a self-explaining road assumes a correct and safe trajectory and the local transversal accelerations depend only on the curvature of road geometry. If the driver corrects the vehicle’s trajectory more than what road curvature imposes, the road is not self-explaining and, consequently, it can be unsafe. If the local transversal accelerations do not depend only on the actual road curvature, they are biased by the driver’s corrections of trajectory. The proposed indicator takes into account the frequency and the amplitude of anomalous corrections of trajectory. The theoretical hypothesis of high correlation between the proposed indicator and the observed accident rate has been verified using an advanced driving simulator. Moreover an analysis of the correlation between such an indicator and a geometrical parameter has been examined. Two Italian case studies are presented. The numerical results confirmed such a theoretical hypothesis. The values of correlation parameters are much higher than any expectation. These outcomes are extremely promising but validations to other case studies are suggested before model generalization.