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

Driver behavior in both normal and abnormal (stress, fatigue, risk) circumstances are not taken into account by geometrical indicators. Such circumstances are often created by road environment and way of driving. Repeated transversal accelerations and other dynamic stresses while driving, for example, may induce abnormal behaviors. A new, advanced, and effective indicator has been proposed and validated to assess road infrastructure safety which considers investigating transversal acceleration variability as an unbiased indicator of discomfort. Its main theoretical assumption is that a driver on a self-explaining road will assume a safe, correct trajectory and local transversal accelerations depend on the geometrical curvature of the road. The road is not self-explaining and may be unsafe if correction of the vehicle's trajectory is greater than what the road curvature imposes. Local transversal accelerations are biased by the driver's corrections of trajectory if they do not depend on actual road curvature. The proposed indicator accounts for the frequency and amplitude of anomalous corrections of trajectory. Use of an advanced driving simulator has verified the theoretical hypothesis of high correlation between the proposed indicator and the observed accident rate. The authors also present an analysis of the correlation between such an indicator and a geometrical parameter. The numerical results of two Italian case studies also confirmed such a theoretical hypothesis through numerical results. Correlation parameter values are much higher than expected. Additional case study validations are suggested before model generalization, although outcomes are extremely promising.