## 3 Research Methodology
### Emission Simulator for GHG Emission Estimation  
The U.S. EPA has developed and upgraded an emission simulator named the motor vehicle emission simulator (MOVES) for estimating the amount of CO, NO\({}_{\rm x}\), and CO\({}_{2}\) emitted by vehicles at different levels from on-road and non-road sources. MOVES depends on the operation modes defined by vehicle speed and vehicle specific power (_VSP_) as explanatory variables that were noted as highly correlated with the emissions of interest [50]. The concept of _VSP_ is the instantaneous power demand of the vehicle divided by its mass, which is used in the evaluation of vehicle emissions. As can be seen in Equation (1), it is the value obtained by dividing the sum of the loads resulting from aerodynamic drag, acceleration, rolling resistance, and hill-climbing by the mass of the vehicle [4; 51].  
\[\textit{Vehicle specific power}\ (VSP)=(Av+Bv^{2}+Cr^{3}+mv(a+gsin\theta))/m_{fixed} \tag{1}\]  
where:  
\(VSP:\) Vehicle specific power \((\rm kW/ton)\);  
\(A:\) Rolling resistance \((\rm kW\cdot s/m)\);  
\(B:\) Rotating resistance \((\rm kW\cdot s^{2}/m^{2})\);  
\(C:\) Drag resistance \((\rm kW\cdot s^{3}/m^{3})\);  
\(m:\) Source mass \((\rm ton)\);  
\(v:\) Speed \((\rm m/s)\);  
\(a:\) Acceleration \((\rm m/s^{2})\);  
\(\theta:\) Road grade;  
\(g:\) Acceleration of gravity \((\rm 9.8m/s^{2})\);  
\(m_{fixed}:\) Fixed mass factor \((\rm ton)\)[52; 53].  
Table 1 shows the weighted average of CO\({}_{2}\) emissions of all vehicles for 23 operating modes in MOVES such as braking, idling, coasting, cruising, and accelerating by referring to the emission rate of CO\({}_{2}\) associated with _VSP_, vehicle speed, vehicle type, and fuel type.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline  & & & & & & & **Unit: Kg/h** \\ \hline  & & \multicolumn{3}{c}{**Passenger Car**} & \multicolumn{3}{c}{**Transit Bus**} & \multicolumn{1}{c}{\
\begin{tabular}{c} **Passenger** \\ **Truck** \\ **Diesel** \\ \end{tabular} } & \multicolumn{1}{c}{
\begin{tabular}{c} **Long-Haul** \\ **Vehicle** \\ **Diesel** \\ \end{tabular} } \\
**Op. Mode** & **Op. Mode Description** & **Gasoline** & **Diesel** & **Diesel** & **CNG** & **Diesel** & **Diesel** \\ \hline
0 & Braking & 3.03 & 3.03 & 15.15 & 8.32 & 4.37 & 15.47 \\
1 & Idling & 2.81 & 2.81 & 7.46 & 6.58 & 3.37 & 7.62 \\
11 & _VSP_ \(<\) 0 & 4.41 & 4.41 & 10.02 & 8.85 & 5.45 & 10.23 \\
12 & 0 \(\leq\)_VSP_ \(<\) 3 & 6.09 & 6.09 & 29.14 & 21.02 & 6.82 & 29.76 \\
13 & 3 \(\leq\)_VSP_ \(<\) 6 & 1 \(\leq\) Speed \(<\) 25 & 8.47 & 8.47 & 53.38 & 61.00 & 9.81 & 54.50 \\
14 & 6 \(\leq\)_VSP_ \(<\) 9 & 10.70 & 10.70 & 77.89 & 101.67 & 12.43 & 79.53 \\
15 & 9 \(\leq\)_VSP_ \(<\) 12 & 12.76 & 12.76 & 98.51 & 142.34 & 14.99 & 100.58 \\
16 & 12 \(\leq\)_VSP_ & 15.41 & 15.41 & 135.50 & 203.34 & 18.72 & 138.35 \\ \hline
21 & _VSP_ \(<\) 0 & 6.00 & 6.00 & 8.08 & 11.77 & 7.30 & 8.25 \\
22 & 0 \(\leq\)_VSP_ \(<\) 3 & 6.83 & 6.83 & 37.46 & 24.84 & 7.83 & 38.25 \\
23 & 3 \(\leq\)_VSP_ \(<\) 6 & 8.32 & 8.32 & 62.12 & 65.28 & 9.67 & 63.43 \\
24 & 6 \(\leq\)_VSP_ \(<\) 9 & 10.68 & 10.68 & 89.92 & 77.35 & 12.52 & 91.81 \\
25 & 9 \(\leq\)_VSP_ \(<\) 12 & 50 & 14.25 & 14.25 & 115.62 & 108.29 & 16.08 & 118.05 \\
27 & 12 \(\leq\)_VSP_ \(<\) 18 & 50 & 18.78 & 18.78 & 159.71 & 154.71 & 22.14 & 163.07 \\
28 & 18 \(\leq\)_VSP_ \(<\) 24 & 25.31 & 25.31 & 223.59 & 216.59 & 29.57 & 228.30 \\
29 & 24 \(\leq\)_VSP_ \(<\) 30 & 34.68 & 34.68 & 287.47 & 278.47 & 40.54 & 293.52 \\
30 & 30 \(\leq\)_VSP_ & 43.55 & 43.55 & 351.35 & 340.35 & 47.76 & 358.76 \\ \hline \end{tabular}
\end{table}
Table 1: CO\({}_{2}\) emission rates for multiple operating modes in MOVES.