*3.3. Primary Assumptions and Limitations*

Firstly, the energy required for energy resource extraction and refining, as well as the water consumption in each productive process, have not been included in this study. Water is usually consumed for refrigeration, and the internal reuse of it is a standard operation in the industry. Moreover, thermal energy has been considered to be an internal process of each facility, which is produced by the input energy resources that are listed in the study.

Secondly, this approach bases its calculation on internal combustion engine vehicles (ICEV), which represent more than 63% of vehicle sales in Japan. Moreover, hybrid vehicles represent 31% of the total sales. Future studies will extend this approach to electric vehicles (EV), which are even more energy-intensive products than our base scenario. On the other hand, the material composition of the vehicle varies depending on the model and the year of production. Thus, final energy and material consumption values per vehicle can vary moderately, but they are also actualized when considering the energy that is required per unit of mass, as shown in Figure 8.

Thirdly, even this approach estimated the total energy consumption of the automotive industry when considering the Japanese market as a case study; not all the productive processes are carried in domestic facilities. Nonetheless, the main conclusions of this study will not change.

Finally, our analysis was centered on the seven principal materials. Miscellaneous materials are expected to vary widely, depending on the analyzed vehicle model (i.e., leader in the case of high-spec vehicle seats, electric and audio equipment, wood in high-end vehicles, and others).
