## 4 Mechanistic-Empirical Pavement Analysis Considering Dynamic Axle Loads
### Impact of Overweight Traffic on Pavement Performance under Dynamic Loads  
Previous studies have proved that overweight trucks accelerate pavement deterioration and shorten pavement service life, using the M-E pavement design method [30; 31]. [PERSON], [PERSON], and [PERSON] [32] quantified the fatigue life reduction of asphalt pavement caused by combined traffic on the basis of the axle load distribution and percentage of overweight vehicles. They found that an increase in percentage of overweight vehicles from 0% to 20% could induce as much as 50% reduction in the fatigue life of asphalt pavement. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Type**} & \multicolumn{2}{c}{**Existing**} & \multirow{2}{*}{**IRI**} & \multirow{2}{*}{**3-Year**} & \multirow{2}{*}{**5-Year**} & \multirow{2}{*}{**7-Year**} & \multirow{2}{*}{**10-Year**} & \multirow{2}{*}{**15-Year**} & \multirow{2}{*}{**20-Year**} \\  & & & & & & & & \\ \hline \multirow{8}{*}{Major} & \multirow{3}{*}{5\%} & 1 m/km & 1.4\% & 1.6\% & 0.5\% & 0.0\% & 0.1\% & 0.1\% \\  & & 2 m/km & 3.2\% & 3.4\% & 1.0\% & 0.1\% & 0.1\% & 0.2\% \\  & & 3 m/km & 5.7\% & 6.1\% & 1.6\% & 0.1\% & 0.2\% & 0.3\% \\ \cline{2-10}  & & 1 m/km & 2.1\% & 2 [PERSON], [PERSON], and [PERSON] [33] investigated the influence of overweight truck traffic on the pavement performance of four flexible pavement structures in Wisconsin using the M-E pavement design method and field investigation. It was suggested that the proportion of pavement damage induced by overweight trucks increased most of the pavement distresses by 0.5% to 4%. Few studies have investigated the overweight impact on pavement distresses considering dynamic loads due to rough surface conditions. In this study, the impact of overweight traffic on reflective fatigue cracking of AC overlay on asphalt pavement would be investigated using the dynamic axle load spectra in M-E pavement design. The New Jersey Department of Transportation defined 356 kN (80 kips) as the legal limit of gross vehicle weight (note 1 kip (1000 pound force) equals to 4.45 kN). The legal weights of single axle on non-Interstate and Interstate highways are 100 kN (22.4 kips) and 89 kN (20 kips), respectively. The legal weight of tandem axle is 151 kN (34 kips) [34]. WIM data were categorized into two traffic groups. The first group included trucks within the legal weight limit and overweight trucks (total traffic), while the second group only included trucks within the legal weight limit (non-overweight traffic). The considered legal weight limits on single, tandem, tridem, and quad axles were 89 kN (20 kips), 151 kN (34 kips), 187 kN (42 kips), and 240 kN (54 kips), respectively. Figure 8 presents the static and dynamic axle load spectra of non-overweight traffic on major and minor highways. The overweight weight percentages were 5.4%, 5.8%, 6.2%, and 6.5% corresponding to the scenarios of static load on smooth pavement surface and dynamic load on rough pavement surface with IRI values of 1 m/km, 2 m/km, and 3 m/km. For minor highways, the overweight percentages were 3.5%, 3.6%, 3.7%, and 3.9% when static load and dynamic loads were induced on the rough pavement surfaces with IRI values of 1 m/km, 2 m/km, and 3 m/km. Figure 9 illustrates reflective fatigue cracking in pavement structures on major highways under static and dynamic loads of total and non-overweight traffic. Slower propagation of reflective fatigue cracking was observed when dynamic loads were considered because of the exclusion of heavier axle loads in a non-overweight traffic scenario. The exclusion of dynamic overweight axle loads decreased reflective fatigue cracking when dynamic loads were considered. However, the terminal percentages of reflective cracking under total and non-overweight traffic were identical due to the dominant role of existing cracking in cracking development in pavement overlay design.