# Effects of Vehicular Speed on the Assessment of
## 3 Results and Discussions
### Estimation of Road Users Running Speed  
Using the approach described in ISO 2631, it is possible to estimate for each road section the speed values according to which the road users may accept a particular level of discomfort due to road roughness. In this sense, the first step should consist in defining the target comfort level but this activity presents certain difficulties since it depends on several aspects as also confirmed by the overlapping zones between adjacent levels provided in ISO 2631 standard. For these reasons, it was decided to consider for this analysis, two different target comfort levels:  
* _Fairly uncomfortable_ or better (\(a_{wz}<1\) m/s\({}^{2}\));
* _Little uncomfortable_ or better (\(a_{wz}<0.63\) m/s\({}^{2}\))  
Considering for example the 190 sections of Road 04, the maximum speed values for which the perceived comfort level is equal or better to the target comfort level defined above were determined for all the sections adopting the procedure described in Figure 10. The results are reported in Figure 11.  
Once the estimated road users speed is calculated along the whole road for each of the two comfort levels, the results can be compared with the design speed to found the sections where the unevenness level does not allow running at speeds compatible with the specific speed range of the examined road. Figure 11: Cont. Figure 10: Methodology adopted to estimate traveling speed. Analyzing the graphs in Figure 11, the sections that are expected to be run at speed lower than the minimum value of the design speed interval of the examined road (equal to 60 km/h) can be located. Furthermore, it is possible to compare the speeds of adjacent sections, assessing if the transition between them is adequate and acceptable in terms of safety and performance criteria. In this way, road agencies can properly locate the priority needs, also evaluating the overall level of service (LOS) through a comparison with the geometric characteristics of the road. The results obtained with the aforementioned approach were then compared with the ones obtained for the same sections using the IRI approach. In particular, the comparison concerns the application to Road 04 of the speed-related thresholds found for IRI and the traveling speed estimated considering the \(a_{uz}\) method. Thus, the speed obtained (with an approximation of 10 km/h) considering a \"_Fairly uncomfortable_\" level (or better: \(a_{uz}<1\) m/s\({}^{2}\)) for each section of Road 04 and the corresponding IRI values are reported in Figure 12. In the same figure, the IRI threshold between _Fair_ and _Mediocre_ ride quality (IRI = 2.31-3.30 mm/m) proposed by [PERSON] and [PERSON] [17] or [PERSON] et al. [15] (these limits are very close) for a maximum value of design speed is also reported. Figure 11: Speed values for fairly and little uncomfortable level perceived by road users (**a**) for the road sections of Road 04 from 1 to 100; (**b**) for the road sections of Road 04 from 100 to 190. Figure 12: IRI thresholds and speed values comparison for _Fairly uncomfortable_ level (IRI = 2.31–3.30 mm/m) for Road 04. The indications provided by IRI threshold seems, in general, to be in agreement with the ones provided by the speed diagram (for _Fairly uncomfortable_ level or better, see Figure 12) but, for some sections, they can induce the road agencies to intervene while speed and users comfort could still be acceptable. This circumstance should be considered also because, in general, this kind of choices is influenced by financial constraints and availability of resources. In these sections (highlighted with arrows), there is no correspondence in the diagram between the exceeding of the proposed IRI threshold and the occurrence of a speed reduction to guarantee an acceptable level of comfort.