## 3 Model Development
### CO\({}_{2}\) Emissions and Energy Consumption Estimation  
The estimation of CO\({}_{2}\) emissions and energy consumption under the different scenarios required models to be applicable to the actual vehicle types used in the KKTP. Previous research had produced such models for use in Thailand, as described below. Currently, three main approaches are used to estimate CO\({}_{2}\) emissions from the urban transport sector, including the top-down method, the bottom-up 1 method, and the bottom-up 2 method. [PERSON] et al. [29] and [PERSON] et al. [30] provided technical comparisons of these three methods. The three principal methods for calculating CO\({}_{2}\) emissions are briefly summarized as follows. First, the top-down approach is commonly adopted to estimate the quantity of CO\({}_{2}\) emissions from the total amount of energy consumed by examining the historical statistics of energy consumption. Subsequently, the energy consumed is utilized to calculate the amount of CO\({}_{2}\) emissions by adopting the appropriate CO\({}_{2}\) emission factors for each vehicle type and energy type. Second, the bottom-up 1 approach is normally applied to quantify the amount of CO\({}_{2}\) emissions from each vehicle. Then, the sum of all of the CO\({}_{2}\) emissions of all vehicles yields the total CO\({}_{2}\) emissions. Third, the bottom-up 2 approach is typically employed to compute the CO\({}_{2}\) emissions of the traffic volume on each individual road segment of the transport network. Subsequently, the sum of the total CO\({}_{2}\) emissions of each road segment is the total CO\({}_{2}\) emissions of the entire road network. The bottom-up 2 approach is appropriate for utilizing the MTDM output data, which include traffic volumes and average speeds on all segments of the transport network. Consequently, the bottom-up 2 approach was adopted in this study. This method predicts CO\({}_{2}\) emissions and energy consumption using link-based traffic volumes, disaggregated by vehicle type and engine type, and their associated average speeds and link distances in the designated years. Based on the bottom-up 2 approach, the total CO\({}_{2}\) emissions and energy consumption can be calculated using Equation (1) [29; 36; 47]. Additionally, Equation (1) can calculate the amount of energy consumption by replacing the following input variables: (1) \(TE_{k}\) is to be replaced by \"fuel economy in liters\" and (2) \(Ef_{kij}\) is to be replaced by \"specific fuel economy rate in liters per kilometer (L/km)\". \[TE_{k}=\sum_{i}\sum_{j}\sum_{k}\,(Ef_{kij}\times D_{e}\times V_{jje}) \tag{1}\]  
where:  
\(TE_{k}=\) Total daily emissions from energy type \(k\) from all vehicle types \(i\) and engine type j of all links (e) in a road network (g);  
\(Ef_{kij}=\) Emission factor of energy type \(k\) for vehicle type \(i\) and engine type \(j\) (g/km);  
\(D_{e}=\) Road distances of link (e) (km);  
\(V_{jje}=\) Traffic volume of vehicle type \(i\) and engine type \(j\) on all links (e) (number of vehicles per day). The baseline CO\({}_{2}\) emissions and energy consumption were estimated for both the without-project (baseline) cases and the with-project CO\({}_{2}\) emissions and energy consumption scenarios for 2026 and 2046. Assuming leakage emissions (\(LE_{y}\)) are zero, the potential CO\({}_{2}\) emission (and energy consumption) reductions (\(ER_{y}\)) will be the difference between the CO\({}_{2}\) emissions in the without-project (Baseline Emission, \(BE_{y}\)) cases and those in the with-project (project emission, \(PE_{y}\)) cases. The reduction in CO\({}_{2}\) emissions and energy consumption can be estimated using Equation (2) [29].