## 4 Mechanistic-Empirical Pavement Analysis Considering Dynamic Axle Loads  
### Analysis Inputs and Assumptions  
Asphalt overlay is commonly used for rehabilitating asphalt pavements with or without milling part of original surface layer. In this study, two AC overlays with different thicknesses of existing AC layers (254 mm and 152.4 mm) were designed as representative pavement structures of major and minor highways in M-E pavement design. The thickness of the new AC layers was 50.8 mm. Table 2 shows the inputs of material property, traffic, and climate. Figure 5 presents the dynamic modulus of asphalt mixture in overlay at different temperatures and loading frequencies, which was set as the Level 1 input in MEPDG. The material properties of mixture in AC overlay were obtained from producer at construction, while the default material properties of mixture were designated for the existing AC layer. For both pavement structures, a 254-mm base layer and a 254-mm subbase layer were laid on the subgrade, and the typical material properties in NJ were designated for the base layer, subbase layer, and subgrade.  
\begin{table}
\begin{tabular}{c c c} \hline
**Input** & **Parameters** & **Major Highway** & **Minor Highway** \\ \hline \multirow{8}{*}{AC Overlay} & Thickness (mm) & 50.8 \\  & Air Void (\%) & 6.2 \\  & Total Binder Content (\%) & 5.4 \\  & Effective Binder Content by & 10.5 \\  & Volume (\%) & 9.5M64 (level 3) \\ \hline \multirow{8}{*}{Existing AC Layer} & Thickness (mm) & 254 \\  & Air Void (\%) & 5 \\  & Total Binder Content (\%) & 5 \\  & Effective Binder Content by & 11.6 \\  & Volume (\%) & 9.5M64 (level 3) \\ \hline \multirow{8}{*}{Material Property} & Thickness (mm) & 254 \\  & Classification & A-1-a \\  & Resilient Modulus (MPa) & 552 \\ \hline \multirow{8}{*}{Subbase} & Thickness (mm) & 254 \\  & Classification & A-1-b \\  & Resilient Modulus (MPa) & 414 \\ \hline \multirow{2}{*}{T Traffic} & Two-way annual average daily traffic (AADT) & 2202 \\  & Operational speed (km/h) & 104 \\ \hline \multirow{2}{*}{Climate} & Mean annual air temperature (\({}^{\circ}\)C) & 11.7 \\  & Mean annual precipitation (mm) & 1306 \\ \hline \end{tabular}
\end{table}
Table 2: Pavement structure and material inputs for Pavement ME.  
The dynamic axle load spectra were modified using Equation (2) based on the estimated DLC by Equation (1) and static axle load spectra from WIM data in LTPP database. Vehicle class distribution and axles per trucks were updated according to the modified axle load spectra. The default monthly adjustment factor was used. The two-way annual average daily traffic (AADT) of minor and major highways was 1575 and 2202, respectively. The operational speeds of minor and major highways were 80 km/h (50 mph) and 104 km/h (65 mph), respectively. Environmental data were required to perform an analysis in the MEPDG. Climate data at the station US NJ-144169 (latitude: 40.05; longitude: \(-\)74.4) in Jackson Township, NJ, were applied for pavement structures on major and minor highways using M-E pavement design. The default parameters in transfer functions were applied for M-E analysis to quantify the impact of dynamic loads on pavement performance.