*3.1. Powertrain Electrification of the Road Freight Vehicle Stock*

Results for the road freight vehicle fleet stock are presented in Figure 9. Differences between modeling results and historical data for the years 2012 to 2017 [70] are lower than 2%. Vehicle stock decreases in all scenarios from 14.7 to 12.3 million vehicles between 2012 and 2050. Compared with the base year, there is a small shift from normal and compact vehicles to mini-sized vehicles; with the stock share of mini-sized vehicles increasing to 66.6% and the stock shares of normal and compact vehicles decreasing to 13.3% and 20.1%, respectively. In this research, the selection of the vehicle size in road freight transport is considered exogenously. However, opportunities to reduce energy consumption and CO2 emissions can be unveiled by improving the selection of the vehicle size with a detailed analysis that includes the load capacity utilization rate and the daily travel patterns. This is suggested for future work.

**Figure 9.** Road freight vehicle fleet stock: (**a**) Base scenario; (**b**) HBB scenario; (**c**) HFF scenario; and (**d**) FBB scenario.

By 2050, the share of ICEVs in the road freight vehicle stock decreases in all scenarios compared with the 2012 values; reaching 54.2% in the Base scenario, 40.9% in the HBB and HFF scenarios, and 42.8% in the FBB scenario. The largest diffusion for HEVs occurs in the Base scenario, reaching 42.9% of the vehicle stock by 2050. HEV diffusion is lower in other scenarios, accounting for 12.2% of the 2050 vehicle stock in the HBB and HFF scenarios, and 3.5% in the FBB scenario. Combining ICEVs and HEVs, diesel- and gasoline-fueled vehicles represent more than 46% of the road freight vehicle stock in all scenarios; evidencing the difficulty of reducing the dependence from fossil fuels in road freight transport.

Compared with EDV diffusion in the new vehicle market share presented in Figure 7, diffusion of EDVs in the road freight vehicle stock shown in Figure 9 is slower due to the time lag effect caused by the vehicle service lives; as most of the new vehicles replace current vehicles in use only after their service lives have finished. Long vehicle service lives are a barrier that prevents powertrain electrification in the road freight vehicle fleet. In the case of Japan, vehicle service lives for road freight vehicles are longer than values reported for other countries. For instance, service lives for heavy-duty trucks, medium-duty trucks, light-duty trucks, and mini-trucks in China are 12, 11, 9, and 8 years [82]; while in the United States, values between 7 and 10 years are reported for heavy-duty trucks [31], and 10 years for medium-duty trucks [27]. Even though reducing the vehicle service life for road freight vehicles might seem as a straight forward measure to accelerate penetration of EDVs in the vehicle stock, EDV manufacturing requires more energy and can produce more CO2 emissions than manufacturing ICEVs. Therefore, including vehicle cycle in the assessment of strategies for powertrain electrification in road freight transport is recommended for future research.

It should be noted that the road freight vehicle fleet was simplified considering only one vehicle type for each powertrain and vehicle size class combination. This is unrealistic, particularly for normal vehicles, given the broad range of GVWs for normal vehicles according to the MLIT classification. In that sense, a more detailed assessment of the normal road freight vehicle fleet is recommended. Furthermore, it was not possible to consider road freight EDVs as one existing vehicle model due to lack of data. Instead, vehicle data were constructed using different sources in the existing literature. A more realistic characterization of the road freight vehicle fleet can be achieved by modeling each vehicle type using vehicle modeling software such as Autonomie and PAMVEC. This is also suggested for future work.