# Interaction between Rockfalls and Vehicles Studied for Speed Limit Zonation along Mountainous Roads
## 4 Results
### Rockfall Risk Zonation  
The risk assessment procedure along the road was repeated by taking into account five different scenarios that considered different likely vehicle speeds. This is because this methodological approach involves both fixed and dynamic factors. Fixed factors are those related to geology, rock mass condition, presence of mitigation measures, and road engineering features. The dynamic factor is the vehicle speed. The five scenarios modeled herein refer to vehicle speeds of 10, 20, 30, 40, and 50 km/h, and for each model, the highest RHRS value between the two directions of travel was taken as representative. These speed values are reasonable in mountainous roads, where, on the one hand, vehicles are induced to travel slowly due to the presence of narrow bends, while, on the other hand, the low traffic rate could lead some drivers to experience higher velocities. The geological parameters involved in the assessment were taken from the geostructural and geomechanical characterization of rock masses presented above. In particular, with specific reference to the boulder volume, the average volume of already fallen boulders surveyed along the road was considered as a cautious value. The geometrical features of the road were measured during field campaigns, along with the traffic volume. The latter was estimated through daily monitoring, which allowed the counting of the passing units. The representative value of 1500 vehicles per day was considered by including a rate of tourist units, whose maximum peak is usually registered during summer and weekends. The 10 and 20 km/h scenarios (Figure 5) were characterized by high similarities in terms of risk zonation. In particular, 47% of the analyzed road sub-segments fell within the low class, with a minimum RHRS value of 177, while the remaining road sectors were in the intermediate risk class, with a maximum RHRS score of 365. The 30 km/h scenario (Figure 5) returned rockfall risk RHRS values ranging between 194 and 494. The analyzed road was, therefore, at intermediate risk for 67% of the analyzed stretches, while the remaining 33% were within the low risk class. The risk zonation was conditioned by the road visibility; in fact, the highest rates were found at bends, with scores close to those of the highest risk class, while the lowest ones occurred at the straightest portions. A further influence on the rockfall risk zonation was provided by the presence of mitigation measures, which, in the study area, occurred at sub-sections 14, 19, and 20 (Figure 5). These were rockfall barriers and wire meshes, which surely reduced the potential impact of rockfalls for the benefit of a risk reduction. In this study case, their occurrence on a straight road portion led to a downgrade by a risk class. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Station** & **RMRb** & **[PERSON] Class [38]** & **c\({}^{\prime}\) (kPa)** & **\(\Phi\) (\({}^{\circ}\))** & **SMR** & **Romana Class [37]** \\ \hline S1 & 50 & III Fair rock & 250 & 30 & 53 & III Fair \\ S2 & 53 & III Fair rock & 265 & 31 & 55 & III Fair \\ S3 & 51 & III Fair rock & 256 & 30 & 52 & III Fair \\ S4 & 54 & III Fair rock & 274 & 32 & 51 & III Fair \\ S5 & 55 & III Fair rock & 277 & 32 & 52 & III Fair \\ S6 & 48 & III Fair rock & 243 & 29 & 50 & III Fair \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Summary of the outcomes of geomechanical classifications. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Station** & **Planar Sliding** & **Wedge Sliding** & **Flexural Toppling** \\ \hline \hline \multicolumn{4}{c}{Kinematically unstable sets} \\ \hline S1 & S1/RD & S1-S4/S1-S2 & S2 \\ S2 & S1 & S1-S4/S4-S3/S1-S3 & S2 \\ S3 & RD & / & S2 \\ S4 & S1 & S1-S4/S3-S1 & S2 \\ S5 & S1/RD & S1-S3/S1-S4 & S2 \\ S6 & RD & / & S4/RD \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Summary of the main unstable kinematic patterns at each surveying station. Figure 5: Risk maps for 10, 20, and 30 km/h vehicle speed scenarios considered.