# Interaction between Rockfalls and Vehicles Studied for Speed Limit Zonation along Mountainous Roads
## 6 Conclusions  
In this paper, a rockfall risk zonation along a road to a historical village was presented with the aim of evaluating the implications of rockfall threat for vehicular speed. The stretch of road analyzed herein is characterized by tight hairpin bends, causing relevant reduction of visibility. The road is also surrounded by intensely fractured rock masses that show instability problems, and it is frequently affected by rockfalls. The methodological approach followed herein refers to the Rockfall Hazard Rating System after [8; 14], which was applied by considering three different scenarios involving increasing vehicle speeds, namely, 10, 20, 30, 40, and 50 km/h.  
The application of the RHRS allowed the provision of a risk zonation according to the final scores for the five simulated scenarios. The road can be considered to be at high risk, especially along the low-visibility segments. Straight road stretches were characterized by lower risk values, as were road portions surrounded by secured rock masses (with wire meshes or protective barriers installed). The comparison between the simulated scenarios confirmed that the rockfall risk increases with the increase in vehicle speed, although for very low speeds (10 and 20 km/h), no significant difference were highlighted. By assuming the geomechanical characteristics of the rock masses and the structural features of the infrastructure at each analyzed road sub-segment to be constant, the AVR and DSD parameters were the vehicle-speed-related factors that mostly controlled the rockfall risk. The first benefits from a slight improvement with the increase in vehicle speed because it refers to the time during which a vehicle passes within a hazard zone. On the other hand, the DSD parameter, which is related to the road visibility, is negatively affected by the speed limit.  
The achieved results were finally used to draft a zonation map of rockfall-risk-related speed limits along the road, which can be reasonably considered to be suitable for keeping the road segments within the lowest, or at least intermediate, risk class. In this case, rockfall risk cannot be definitively solved due to the coexistence of a rockfall hazard and elements at risk, but it can be reasonably reduced. The approach presented herein is a useful tool for practical purposes in the frame of territorial management and disaster risk reduction, as it allows the evaluation of the most suitable speed limits to be posted along a road with reference to the rockfall risk. It would, indeed, represent a key activity for reducing the rockfall risk, in conjunction with securing operations along unprotected rock mass sectors. This should then be evaluated along with other variables related to specific features of the construction of the road and local regulations so as to achieve a final speed limit value to be established for the studied infrastructure.  
Conceptualization, methodology, and writing: S.M. and G.P.; software, data analysis: S.M. and D.C.; supervision: S.M. and G.P.; funding acquisition: G.P. All authors have read and agreed to the published version of the manuscript.  
This research was financially supported by the University of Catania, \"CH2V--Cultural Heritage Hazard and Vulnerability\" project, Linea 2-PIACERI, granted to [PERSON].  
The authors declare no conflict of interest.