# Interaction between Rockfalls and Vehicles Studied for Speed Limit Zonation along Mountainous Roads
## 1 Introduction
This aspect has scientific importance, which is reflected in its public utility, because both of the previously reported spatial and temporal correspondences are strongly dependent on the vehicle speed limit posted along roads. Inspired by this topic and with the aim of increasing the scientific knowledge on this relevant problem, this paper presents a rockfall risk analysis along a mountainous road connecting the Ionian coastline of Sicily (Italy) to Forza d'Agro, a historical village offering a medieval atmosphere with narrow streets, charming churches, and aistocratic buildings in the geological context of the Peloritani Mountains (Figure 1a). Thanks to its history and monuments, the village is acknowledged as being among the most popular tourist destinations on the eastern side of Sicily, and the main access route is represented by Provincial Road 16 (SP-16), which runs from 50 to 350 m a.s.l. on a winding path crossing a complex geological setting. These reasons led to the choice of this study area. In particular, most of the road crosses intensely fractured rock masses that show evident signs of instability, thus representing a source of risk for vehicular traffic. Several rockfalls have already occurred along the SP-16 road, and numerous blocks have been surveyed at different spots on the road side, thus testifying to the current rockfall activity. The potential road disruption in case of rockfalls would lead to the partial isolation of the village not only from the touristic point of view, but also for rescue purposes in case of emergency. According to a Civil Protection report published in 2016, the Province of Messina, within which the study area falls, is the most affected by rockfalls along roads in Sicily. In this light, the rockfall risk evaluation was performed herein by using the Rockfall Hazard Rating System (RHRS) proposed by [PERSON] et al. [14] and modified for Italian road standards by [PERSON] [8]. This approach is a semi-quantitative system that takes into account all of the elements related to rockfall hazards and vehicle vulnerability [8], including vehicle speed, and this allows a reliable estimation of the degree of exposure to risk along roads. [PERSON] et al. [16] provided a summary of the most widely used RHRS approaches, which were modified for specific regional conditions and needs (e.g., [8; 22; 23; 24; 25]). Numerous application casesinvolving RHRS methods are available in the scientific literature. [PERSON] et al. [6] applied it to a mountainous road connecting tourist cultural heritage sites, while [PERSON] [26] critically revised the RHRS of Saudi Arabia, which was initially proposed by [27], pointing out hints for future studies. Further applications in different countries were presented by both [28] for alpine regions and [29] for natural slopes at historical sites in Greece, as well as along railways [10]. Nevertheless, the relationship between the final RHRS outcomes and the speed limit to post along roads has not been previously addressed in detail and represents a scientific novelty that this study aims to provide. In fact, in this paper, the RHRS was applied while considering five different vehicle speed scenarios in order to find out the implications of this key parameter when dealing with rockfalls along linear infrastructures. The application of this methodology was supported by field surveys, which were carried out for geomechanical and kinematic purposes. Data arising from the RHRS were used to draft thematic maps and to present the consideration of the possibility of rockfall-risk-related speed limit zonation, which would represent a useful tool for territorial management, with specific reference to the prioritization of slope mitigation work. Figure 1: (**a**) Geographical location of the study area and panoramic view (Google Earth) with the studied road path highlighted; (**b**) geological map of the study area.