# Mechanical-Empirical Pavement Design Guide Applied to Portuguese Pavement Structures
## 3 Application of MEPDG to the Portuguese Pavement Structures
### Results
The only exception was the variation of the longitudinal cracking value for traffic class T6, which ranged only between 14.1 and 23.9 m/km. One can also see that the longitudinal cracking values were quite far from the threshold value of 200 m/km for the whole design life. Regarding the alligator cracking (bottom-up fatigue), the analysis of Table 4 and Figure 5 reveals a very small variation (0.38% to 2.91%) at the end of the design life, which corresponded to combinations P13T3F2 and P1T6F4, respectively. Nevertheless, this very small variation continued to occur when changing the foundation class from F2 to F3 and to F4, within the same traffic class. Finally, it is worth mentioning that the alligator cracking values were quite far from the threshold value of 20% for the whole design life. As far as rutting is concerned, the variation in AC rutting (contribution of asphalt concrete layers only) was greater than the variation in total rutting (permanent deformation), as suggested by Table 4 and Figures 6 and 7. There was a large variation in the AC rutting, ranging from 5.1 to 15.8 mm at the end of the design life, which corresponded to combinations P3T6F2 and P12T1F4, respectively, exceeding the threshold of 15.0 mm in only one situation, i.e., pavement structure P12. This is the pavement structure recommended in the Portuguese manual for the combination of traffic class T1 and pavement foundation F4. Total rutting varied between 11.5 and 19.7 mm, corresponding to combinations P1T6F4 and P12T1F4, respectively, not exceeding the threshold of 20.0 mm in any situation. The maximum AC rutting and maximum total rutting were verified for the same combination P12T1F4. It can also be observed that the variation of AC rutting and total rutting was small within the same traffic class. Finally, Table 4 and Figure 8 show a very small variation in IRI, ranging from 1578 to 1847 mm/km at the end of the design life, which corresponded to combinations P3T6F2 and P10T2F4, respectively. Therefore, the IRI was the pavement performance indicator with the most homogeneous results for all the pavement structures recommended in the Portuguese manual for each combination of traffic and pavement foundation. Furthermore, the IRI values were found to be much lower than the threshold value of 3500 mm/km (for 100% of the length of the project) but were close to the threshold value of 2000 mm/km (for 50% of the length of the project). Those results are particularly relevant within a context where increasing attention has been paid to the excessive contribution of the road transportation mode to the greenhouse gases (GHGs) emissions [42]. Vehicle energy consumption and emissions are strongly affected by pavement surface characteristics due to a phenomenon known as rolling resistance. Among the pavement surface properties influencing rolling resistance, pavement roughness plays a prominent role. Given the long service life of pavements and the potentially high volume of traffic they carry, ensuring that pavement roughness, as measured by IRI, remains low over time is of supreme importance to mitigate and reduce the impacts of the road transport mode on climate change. To summarize, by using the MEPDG, values in the range of 80% and 100% of the threshold values would be expected for at least one of the following pavement performance indicators: alligator cracking (bottom-up fatigue) or total rutting (permanent deformation). However, when analyzing the results presented in Table 4, it can be seen that this was neither the case for these pavement performance indicators nor for the others. The pavement performance indicator closest to this situation was total rutting. These results demonstrate that by applying the MEPDG design method to the Portuguese conditions, the most critical distress is total rutting, since it presented values close to its threshold, i.e., 20.0 mm.