*2.4. Main Assumptions and Limitations*

Alternative scenarios for powertrain electrification were built considering that each vehicle size class is dominated only by one powertrain. Even though this assumption is not realistic, it allows to estimate the maximum 'technologically realizable' CO2 emissions reduction potential of each powertrain electrification strategy. In that sense, CO2 emissions reduction potential estimated here corresponds to the largest possible CO2 emissions reductions of each strategy considering the dynamics of technology diffusion. Since there are several barriers that prevent the deployment of EDVs in road freight vehicles, the actual CO2 emissions reductions that can be achieved through powertrain electrification are smaller. Furthermore, since EDV diffusion is considered independently from vehicle RCO, road freight vehicle fleet energy consumption and CO2 emissions are not affected by changes in the RCO. This is a limitation of the study, as vehicle RCO affects consumer choices of vehicle type and therefore vehicle fleet energy consumption and CO2 emissions.

The composition of the Japanese road freight vehicle was simplified, assuming that each vehicle size class-powertrain combination is represented by only one vehicle type. Therefore, the model cannot capture the diversity of vehicle types existing in the real road freight vehicle fleet.

It was assumed that annual traveled distance and vehicle service life are identical for all vehicle types within each vehicle size class. Daily travel patterns were not considered and only the average annual traveled distance was used to characterize road freight transport activity. Vehicle service life and annual traveled distance were assumed to remain identical during the whole time horizon. Based on the model calibration for road freight vehicle fleet energy consumption and CO2 emissions, it was assumed that fuel consumption deteriorates as vehicles become older at a rate of 0.3%/year

As fuel production is outside of the scope of this research, fuel prices and CO2 emission factors were considered exogenous to the vehicle stock turnover model. TTW and WTW CO2 emission factors for gasoline and diesel in 2012 were obtained from [74,75]. These values were assumed to remain constant over the time horizon, considering that TTW CO2 emissions are determined by the carbon content in the fuel, and gasoline and diesel production processes are mature. Gasoline and diesel prices in 2012 correspond to the values reported in [76]. Gasoline and diesel prices in 2050 were estimated under the assumption that the ratio between fuel price and crude oil price remains constant between 2012 and 2050. Values for the 4DS scenario from the International Energy Agency's (IEA's) Energy Technology Perspectives [77] were assumed for the crude oil price.

Electricity WTW CO2 emission factor in 2012 was the value reported by the IEA for the electricity generation mix in Japan [78]. Electricity WTW CO2 emission factor in 2050 corresponds to the value of the Nuclear Phase Out scenario from [79], which assumes electricity generation using 50% fossil fuels and 50% renewable energy. Electricity price in 2012 was the historical value reported in [76]; while the electricity price in 2050 was estimated based on the generation cost from [79] and network, retail and other costs from [80]. Steam Methane Reforming (SMR) share in hydrogen production was assumed to go from 100% in 2012 to 50% in 2050. The remaining hydrogen in 2050 is produced using 25% wind electrolysis and 25% solar photovoltaic electrolysis. Prices in 2012 and 2050 were estimated based on the share of each hydrogen production technology and the near term and future delivered hydrogen cost for each technology from [81]. WTW CO2 emission factors in 2012 and 2050 were estimated based on the share of each hydrogen production technology and the technology CO2 emission factor from [75]. Fuel prices and CO2 emission factors are presented in Figure 8.

**Figure 8.** Fuel information: (**a**) Tank to wheel and well to wheel CO2 emission factors; (**b**) price.

## **3. Results and Discussion**
