## 3 Results
Particularly, the relationships between the identified physical and geometrical characteristics (i.e., speed limit, inbound and outbound ramp slopes, elevation difference) have been examined. The measurements from Dipstick have been processed in order to have symmetrical longitudinal profiles of the surveyed RPCs (Figure 9--some symbols will be explained after). The overall length \(L_{t}\) is composed of a two-branch approach curve where the parts are \(L_{a,1}\) and \(L_{a,2}\), the flat top length \(L_{c}\), and a two-branch exit curve where the parts are \(L_{e,1}\) and \(L_{e,2}\). Particularly, approach and exit ramps have the same longitudinal slope (i.e., \(i\)) and length (i.e., the sag curves \(L_{a,1}\) and \(L_{e,1}\) have the same length, and the crest curves \(L_{a,2}\) and \(L_{e,2}\) have the same length). The flat top surface is parallel to the road pavement before and after the RPC (i.e., the RPC height is constant and equal to \(h\)). Primary data about geometry of the surveyed RPCs are in the Supplementary Materials. Table 4 lists the results. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{\(i\) (\%)} & **Percentage** & **Number** & \multirow{2}{*}{\(h\) (cm)} & **Percentage** & **Number of** \\  & **of RPCs (\%)** & & & **of RPCs** (\%) & **RPCs** \\ \hline
0 \(<i<2\) & 0.00\% & 0 & 0 \(<h<4\) & 0.00\% & 0 \\
2 \(\leq i<3\) & 12.50\% & 3 & 4 \(\leq h<6\) & 20.83\% & 5 \\
3 \(\leq i<4\) & 12.50\% & 3 & 6 \(\leq h<8\) & 8.33\% & 2 \\
4 \(\leq i<5\) & 0.00\% & 0 & 8 \(\leq h<10\) & 3 In Table 4 the majority of the RPCs have a slope between 5% and 10%, and are 4-12 cm high. Moreover, 4.17% and 12.50% of the surveyed RPCs do not fit the maximum longitudinal slope and the maximum sidewalk height (i.e., 10% and 15 cm, respectively) permitted by the Italian standard [47]. The obtained results highlight a great variety of configurations: Figure 10 represents the measured longitudinal profiles for roads where the administrative speed limit is 30 km/h. On the other hand, the normalization of profiles with respect to the RPC overall length points out the geometrical differences better: The curves in Figure 11 allow comparison qualitatively of the slopes of RPCs in Figure 10. Moreover, the values of the 85 th percentile of measured speeds (\(v_{85}\)) are reported because they are correlated with \(i\): In most of the analyzed cases as slope index of the ramp increases, the speed of vehicles decreases. Figure 11 represents the measured longitudinal profiles for roads where the administrative speed limit is 30 km/h. Figure 11: Normalization of longitudinal profiles for RPCs with 30 km/h administrative speed limit. Figure 10: Longitudinal profiles for RPCs with 30 km/h administrative speed limit. The geometric variability of RPCs affect distribution of measured vehicle speed: The lower the administrative speed level \(v\), the higher the dispersion of measured speed values. Figure 12a,b allow comparison between RPCs with 30 km/h and 40 km/h administrative speed limit, respectively. Data about site 5 (administrative speed limit 40 km/h) are lacking. For administrative speed level equal to 30 km/h, the average values of measured speed are between 18 and 45 km/h, and the standard deviation increases with the increase of the average speed (\(v_{a}\)). For administrative speed level equal to 40 km/h, both the average values and the standard deviation are comparable to each other. In Figure 12b, the blue curve differs from the others because of the non-correct geometry and non-adequate marking: Regular users of the road (site 24) limit their speed because they have experienced the RPCs and aim to prevent vehicle damage caused by contact with the pavement (e.g., grooves in Figure 5c,d). It is therefore necessary to build RPCs according to geometrical standards, not overlooking functional requirements. Indeed, the calculation of \(a_{z}\) for different speed values revealed that vertical accelerations on the vehicle occupants are related to the longitudinal slope of the access ramp.