**1. Introduction**

Climate change is considered to be one of the major social drawbacks of the last decades. To combat it, the Paris Agreement on climate change was established in December 2015, for which 195 nations have unified its environmental goals and agreed to maintain a global temperature increase well below 2 ◦C [1]. In this sense, different strategies and studies regarding the efficient use of energy are continuously conducted by governmental as well as private entities, demonstrating a global conscience and strong necessity to change the current high energy and resource consumption of society.

The transportation sector accounts for 25% of global energy consumption [2], and it is one of the most challenging sectors for fulfilling the proposed goals. Therefore, several studies centered on the fuel consumption of the vehicle have been conducted over the past few decades. New technologies, such as alternative propulsion methods (hybrid electric vehicles, battery electric vehicles, plug-in hybrid electric vehicles, and fuel cell vehicles) and lightweight materials, have also been developed.

A widely known method to assess the environmental effect of a vehicle is through its life cycle, and previous studies estimate that the production phase constitutes 7–22%, and the use phase 78–93%, of the energy consumption and CO2 emission of a vehicle's life cycle [3,4], whereas the end-of-life vehicle (ELV) phase is considered to be almost negligible. Thus, improving the energy efficiency of the use phase of the vehicle was prioritized and the production and ELV phases have usually been considered less important. However, comprehensively understanding the environmental impact of the transportation sector is also indispensable for correctly evaluating the impact of both phases [5].

Nemry et al. [3] evaluated possible environmental advantages of the transportation sector in Europe, O'Reilly et al. [6] proposed a lightweigh optimization method, Sato et al. [5,7] evaluated the environmental impact of the ELV phase, Lane [8], and Vinoles-Cebolla et al. [9], Messagie et al. [10], and Yang et al [11] evaluated the environmental impact of electric vehicles, all using life-cycle assessment (LCA). However, even those studies included the effect of the production phase, basing its analysis on external energy consumption or CO2 emission constant coefficients; in some cases, even the precedence of the data used for the calculations were clarified. Those coefficients are usually presented as an approximation of the energy that is required to produce a vehicle part and defined per unit of mass of the material that composes it. However, they are usually close values and, in this sense, premises considered, the processes included in their calculation did not make the level of accuracy of the proposed values transparent [12–15]. It is worth mentioning that the International Organization for Standardization [16,17] specifies the necessity of clarifing the sytem boundary and also lists data-quality requirements to ensure the transparency of the LCA.

This study aims to comprehensively evaluate the energy consumption in the automotive industry, clarifying the effect of its productive processes. This study focuses on developing a process-by-process breakdown analysis and elaborates the material flow of vehicle production, from raw material mining to vehicle assembly. Moreover, the results obtained for energy and material consumption have been assessed per unit of produced vehicle as well as per mass of product. This approach is based on open data, and the effects on the Japanese vehicle market were analyzed as a case study.

The results presented in this study allow for a comprehensive understanding of the production phase of the vehicle and proposed values of energy consumption that can be used for upcoming vehicle life-cycle studies, contributing to the improvement of future vehicle production and recycling assessments. Moreover, those values can be adopted and modified, depending on necessity, allowing for possible changes in premises to be incorporated.
