*4.1. Global Change Assessment Model*

GCAM was chosen as an integrated assessment model for creating representative concentration pathways for the Intergovernmental Panel on Climate Change (IPCC)'s Fifth Assessment Report (AR5) [18]. GCAM represents various sectors including energy systems, agriculture, land use, land use change and forestry (LULUCF), economy, water, and climate for an analysis of their interactions. GCAM runs in five-year time steps, solving for market equilibrium. At the equilibrium, supply equals demand in all markets. The transportation sector is one of the end-use sectors in GCAM's energy system. One of the advantages of using GCAM is a well-represented hierarchical structure of the sector (for example, passenger road sector), mode (for example, small, medium, large car, and sport utility vehicle (SUV)), and technology (for example, ICEV, BEV, and FCEV) [19]. Mishra et al. [20] explain the methodological details of the GCAM transportation module. Kyle and Kim [21] and Yin et al. [22] can also be used as reference studies for an analysis of the transportation sector using GCAM.

The passenger transportation service demand at time *t* is given as

$$D\_t = \sigma(\mathcal{Y}\_t)^a (P\_t)^{\beta} (\mathcal{N}\_t) \tag{7}$$

where

*D*: Passenger transportation demand (passenger kilometers travelled or PKT),


*Energies* **2020**, *13*, 4533

The price of transportation services (*P*) is calculated from the weighted average cost of sector, mode, and technology as

$$P\_t = \sum\_{i} S\_{i,t} P\_{i,t} \tag{8}$$

$$P\_{i,t} = \sum\_{s} S\_{s,i,t} P\_{s,i,t} \tag{9}$$

$$P\_{s,i,t} = \sum\_{j} S\_{j,s,i,t} P\_{j,s,i,t} + \frac{W}{SP\_{s,i,t}} \delta\_{i} \tag{10}$$

$$P\_{j,s,i,t} = \frac{FP\_{j,s,i,t}EI\_{j,s,i,t} + NFP\_{j,s,i,t}}{L\_{j,s,i,t}} \tag{11}$$

where

*i*: Sector (for example, passenger road sector, passenger rail sector),

*s*: Mode (for example, small car, medium car),

*j*: Technology (for example, ICEV, BEV),

*W*: Hourly wage (\$/h),

*SP*: Speed of mode (km/h),

δ: A parameter for the calculation of value of time,

*FP*: Fuel price (\$/joule),

*EI*: Energy intensity (joule/VKT),

*NFP*: Non-fuel price (\$/VKT),

*L*: Load factor (PKT/VKT),

*S*: Market share.

For example, the share of technology *j* in mode *s* is determined as

$$S\_{j,s,i,t} = \frac{\left(SW\_{j,s,i,t}P\_{j,s,i,t}\right)^{\lambda\_i}}{\sum\_{j} \left(SW\_{j,s,i,t}P\_{j,s,i,t}\right)^{\lambda\_i}}\tag{12}$$

where *SW* means share-weight as a parameter for calibration and λ denotes the logit exponent.

Figure 5 shows the structure of the transportation sector used in this study. The passenger car sector includes four different modes—small sedan, medium sedan, large sedan, and SUV. Each mode has three technology options—ICEV, BEV and FCEV. The input data for modeling the transportation sector are based on Jeon and Kim [23], Jeon et al. [24], Korea Energy Economics Institute [3], Korea Transport Institute [12], Korea Energy Agency [17], and Korea Transportation Safety Authority [25].

**Figure 5.** Representation of the transportation sector's structure used in this study.
