# Interaction between Rockfalls and Vehicles Studied for Speed Limit Zonation along Mountainous Roads
## 2 The Study Area  
The study area is located along the northeastern coastal sector of Sicily (Italy) (Figure 1), where the medieval village of Forza d'Agro, a popular tourist destination and one of the most charming mountainous villages of the region, stands on a 420 m high promontory. The village was first settled by Greeks, who arrived between the 8 th century and the 5 th century BC and named the town \"Arghennon Akron\", meaning \"Silver Promontory\". Over time, Akron changed into Argon, then into Agron, and finally into Agro. A few remains of a fort-like structure located at the top of the promontory suggest that the village used to be a fortress. Thanks to its narrow streets, charming churches, and aristocratic buildings, the old town center offers a wonderful medieval and ancient atmosphere that attracts tourists from all over the world. To reach this destination, the main route is represented by a two-lane mountainous road (Provincial Road 16, SP-16) that climbs from 50 to 350 m a.s.l. on a winding path (Figure 1). From the geological point of view, the study area is located on the southern part of the Calabria Peloritani Orogen, which made up of a Hercynian metamorphic basement covered by Mesozoic-Cenozoic units [30]. Regional fault systems displace the geological formations along the E-W and NW-SE directions as a result of the complex tectonic history that characterizes the area. In particular, [PERSON] et al. [31] reported a pervasive set of oblique extensional NW-SE faults that were measured just west of the Forza d'Agro village, which affect the carbonate rock masses and dislocate the previous WNW-ESE trending thrust faults. In this peculiar setting, the SP-16 road crosses two main geological formations that are characterized by different physical-mechanical features, i.e., Jurassic gray dolostone-limestones and polygenic conglomerates in a red matrix (Figure 1b). The first ones crop out as heavily jointed rock masses bordering the road along one or two sides with relevant wall heights and suffering from evident features of rock mass instability; on the other hand, the road portion crossing the red conglomerates (northernmost sector) is affected by deformation of the road pavement due to local movements. The carbonate rock masses show signs of heavy tectonics and past rockfall activity. The first one is testified by the intense degree of fracturing (Figure 2a,b), while the rockfall activity can be inferred from the numerous empty rock mass sectors that can be regarded as past rockfall source areas (Figure 2a,b). Moreover, numerous loose rock mass sectors hang over the road path (Figure 2b,c). Based on this field evidence of instability that threatens the infrastructure of SP-16, this paper is focused on the road path that is bounded by the carbonate rock masses. The latest documented rockfalls date back to 2009 and 2014, when a series of large blocks impacted on the roadway. Similar events have periodically occurred over the years, as testified by numerous blocks found along the roadside (Figure 2d). Therefore, rockfalls represent a risk to elements with value in terms of human life and economy (i.e., people, vehicles, road infrastructure), especially considering the tourist vacation of the area. In fact, in addition to the historical village, the studied road offers some stopping spots (not equipped for parking) for religious and scenic purposes. These include a pilgrimage spot located at a natural cave, which hosts a religious statue of the [PERSON] and some benches under the bare rock roof. This spot, as well as a few others along the road, also offers a breathtaking view of the coastal landscape (Figure 2e), thus prompting tourists and drivers to stop under the rock cliff.  
Figure 2: **(a,b)** Examples of rock masses hanging over the road and showing features of instability and past rockfall source areas; **(c)** previously fallen blocks surveyed at a road bend segment; **(d)** unstable block hanging over the road; **(e)** panoramic view from inside the religious cave.