*1.4. Organization of the Article*

The rest of the article is organized as follows: the mathematical formulation of the model and the description of the scenarios are presented in Section 2; the results are presented and discussed in Section 3; finally, the conclusions are presented in Section 4.

## **2. Methods**

### *2.1. Formulation of the Vehicle Stock Turnover Model for the Road Freight Vehicle Fleet*

This research focused on energy end-use in road freight vehicles. Other stages of the vehicle cycle and the fuel cycle were not considered. Energy flows in the energy system are shown in Figure 1. The energy system is made of four energy carriers, diesel, gasoline, electricity, and hydrogen; which

are used in 12 vehicle types. The 12 vehicle types result from combining four powertrains, ICEV, HEV, BEV, and FCEV; and three vehicle size classes, normal, compact and mini-sized vehicles.

**Figure 1.** Energy system diagram.

The criteria from the Japan Ministry of Land Infrastructure, Transport and Tourism (MLIT) [49] were used for road freight vehicle size classification. These criteria divide road freight vehicles in normal, compact and mini-sized classes according to the external dimensions and engine displacement. It should be noted that according to MLIT's classification, all mini-sized vehicles are LDVs. However, not all LDVs belong to the mini-sized vehicle size class; and there are LDVs that belong to the compact vehicle size class. MDVs belong to the compact and normal vehicle size classes; while HDVs belong to the normal vehicle size class. The Gross Vehicle Weight (GVW) ranges for road freight vehicles in Japan were extracted by analyzing MLIT data [50]; with GVW for mini-sized vehicles varying between 0.9 and 1.5 ton; compact vehicles between 1.6 and 3.4 ton; and normal vehicles between 2.8 and 59.1 ton.

The Long-range Energy Alternatives Planning system (LEAP) software was used to model the energy system [51]; based on previous work developed by the authors in [52,53]. The model developed can be classified as a dynamic bottom-up accounting energy-economics model. The description of the main components of the model is presented below. For more details, the reader can examine the previous references.

For a given fleet of vehicles type *t* and vintage *v* in a calendar year *y*, the vehicle fleet tank to wheel (TTW) energy consumption is calculated by multiplying the vehicle stock *N*, the annual traveled distance *M* and the vehicle fuel consumption *R*, as indicated in Equation (1):

$$E\_{TTW,t,y,\nu} = N\_{t,y,\nu} M\_{t,y,\nu} R\_{t,y,\nu} \tag{1}$$

The vehicle fleet TTW CO2 emissions are calculated by multiplying the fleet energy consumption *ETTW,t,y,v* and the CO2 emission factor *EFTTW,t,y* of the fuel used by the vehicle type *t* in the calendar year *y*, as indicated in Equation (2):

$$G\_{TTW,t,y,\upsilon} = E\_{TTW,t,y,\upsilon} E\_{TTW,t,y} \tag{2}$$

The vehicle fleet well to wheel (WTW) CO2 emissions are obtained similar to Equation (2), replacing the TTW CO2 emission factor with the WTW CO2 emission factor.

The economic assessment was performed using the relative cost of ownership (*RCO*), defined as the sum of the capital cost, the operating and maintenance (O&M) cost and the energy cost, as indicated in Equation (3):

$$RCO\_{t,y,\nu} = S\_{t,x=y}c\_{\text{cap},t,x=y}CRF + N\_{t,y,\nu}c\_{OM,t,y,\nu} + E\_{TTW,t,y,\nu}c\_{\text{enc},t,y} \tag{3}$$

where *S* is the new vehicle sales, *ccap* is the vehicle capital cost, *CRF* is the capital recovery factor, *cOM* is the annual O&M cost, and *cene* is the energy price.

It should be noted that Equations (1) and (2) are built under the assumption that annual traveled distance and vehicle fuel consumption are constant for all vehicles of a given type and vintage during a calendar year. In that sense, differences in vehicle usage across users cannot be captured in the model. Regarding the economic evaluation, it was assumed that costs other than capital cost, O&M cost and energy cost are identical for ICEVs and EDVs [54]; and therefore, excluded in the estimation of the RCO in Equation (3). Road vehicle fleet energy consumption, CO2 emissions and RCO for a given calendar year *y* are estimated by summing across all vehicle types and vintages existing in the road freight vehicle fleet.

## *2.2. Road Freight Vehicles Characteristics*

Due to the variety of vocational uses, there is a large number of road freight vehicle types. In Japan, the MLIT reported fuel consumption data for 5272 road freight vehicle types [55], mainly ICEVs. Considering this number of vehicle types in the vehicle stock turnover model is not practical. Therefore, the structure of the road freight vehicle fleet was simplified, assuming there are only 12 vehicle types: ICEVs, HEVs, BEVs, and FCEV, available in three vehicle size classes, normal, compact and mini-sized vehicles. Additionally, based on the analysis of the same data from MLIT, it was assumed that all normal ICEVs use diesel; and all compact and mini-sized ICEVs use gasoline.

In order to calibrate the model against historical data, 2012 was selected as the base year. It was assumed that all road freight vehicles in the Base year were ICEVs. Each vehicle size class was represented only by one ICEV, with vehicle fuel consumption close to the average value reported in data from MLIT [56]. Mini-sized ICEVs were modeled as a Subaru Sambar with a GVW of 1.2 ton; compact ICEVs were modeled as a Toyota Hiace with a GVW of 3.1 ton; and normal ICEVs were modeled as a Fuso Canter with a GVW of 7.9 ton. Vehicle data for road freight EDVs were constructed extracting relationships between ICEVs and EDVs from the existing literature.

Fuel consumption and capital cost for the road freight vehicles in 2012 and 2050 are shown in Figure 2. Fuel consumption data for ICEVs in all vehicle size classes in 2012 were estimated using data reported by MLIT [56]. Using ICEV fuel consumption as a reference, 2012 fuel consumption for EDVs in the normal size class was estimated assuming the ICEV and EDV fuel consumption ratios are identical to values reported in [35] for HEVs, and in [57] for BEVs and FCEVs. Fuel consumption in 2012 for EDVs in the compact size class and the mini-sized BEV was estimated considering the ICEV and EDV fuel consumption ratios are identical to the values reported for normal LDVs in [53]. Fuel consumption in 2012 for the mini-sized HEV and FCEV was estimated assuming the fuel consumption ratios for ICEV and HEV and for ICEV and FCEV are identical to the values reported for LDVs in [58].

The capital costs for the normal ICEV, HEV and BEV were obtained from [40]; while the capital cost for the normal FCEV was estimated as the capital cost for the HEV minus the capital cost of the internal combustion engine plus the capital cost of the fuel cell, using data from [59,60]. Capital costs in 2012 for compact and mini-sized road freight vehicles were assumed equal to values for passenger vehicles reported in [53]. Fuel consumption and capital cost evolution between 2012 and 2050 were assumed identical to the trends reported in the previous reference.

In order to estimate the RCO, vehicle capital costs were annualized over the vehicle service lives using a discount rate of 10%; corresponding to the average value of the range for typical discount rates for trucks reported in [30]. The same reference was used for the O&M costs for the normal ICEV, HEV and BEV, estimated in 0.124, 0.099 and 0.087 USD/km, respectively. O&M costs for compact and mini-sized vehicles were considered identical, 0.056 USD/km for ICEVs and HEVs, and 0.057 USD/km for BEVs and FCEVs [61,62]. O&M costs for all vehicle types were assumed to remain constant throughout the time horizon.

**Figure 2.** Main characteristics of the road freight vehicles: (**a**) fuel consumption; (**b**) capital cost.

Vehicle usage characteristics are presented in Figures 3 and 4. Annual traveled distance is reported for public and private vehicles for each vehicle size class by MLIT [63]. The shares of public and private vehicles in each vehicle size class were estimated using data from the Automobile Inspection & Registration Association (AIRIA) [64]. These values were used to calculate the annual traveled distance for each vehicle size class as the weighted sum of the annual traveled distances for public and private vehicles. The median vehicle service life for each vehicle size class corresponds to the average value reported by MOE [65]. Similar to Nishimura [66], survival profiles were estimated using the logistic curve shown in Equation (4):

$$\sigma = 1 - \frac{1}{\alpha + \varepsilon^{-\beta(a - a\_o)}}\tag{4}$$

where *r* is the vehicle survival rate, *a* is the vehicle age, *a0* is the vehicle median service life, α is a model parameter set to 1, and β is a growth parameter. The growth parameter β was estimated equal to 0.180, 0.192 and 0.187 for normal, compact and mini-sized vehicles through model calibration against historical data for the road freight vehicle stock.

**Figure 3.** Vehicle service lives and annual traveled distances.

**Figure 4.** Vehicle survival profiles.
