## 4 Life Cycle Assessment (LCA)
### Inventory Analysis  
In the present study, raw material production and transport for each case study were included in the inventory. Tables 2 and 3 showed the inventory of materials and transport considered for each reinforcement arrangement, respectively. This inventory considered the own volumes of each disposal alternative. The life cycle analysis software SimaPro 7.3.3 was used to quantify the impact categories in a straightforward manner. The specific consumption of raw materials, energy, fuels, and emissions released to air, water, and soil during the construction of the transition zone located in Portugal was considered. In addition, it was deemed that the backfill material and BB sleepers already arranged in storage sheds were located 10 km and 200 km, respectively. SimaPro software was implemented to evaluate the potential environmental impacts of creating transition zones reinforced with BB sleepers. It is important to note that in \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & **NRM** & **BM** & **HA** & **PA** & **SHA90\({}^{\circ}\)** & **SHA90\({}^{\circ}\)** & **DHA90\({}^{\circ}\)** & **DHA90\({}^{\circ}\)** & **Units** \\ \hline Ballast & 71.04 & 71.04 & 71.04 & 71.04 & 71.04 & 71.04 & 71.04 & 71.04 & m\({}^{3}\) \\
**Sub-Ballast** & 125.24 & 125.24 & 125.24 & 125.24 & 125.24 & 125.24 & 125.24 & 125.24 & m\({}^{3}\) \\
**Track-bed** & 238.95 & 186.98 & 234.33 & 237.75 & 237.24 & 237.58 & 233.48 & 232.11 & m\({}^{3}\) \\
**Landfill** & 2530.43 & 2992.75 & 2508.88 & 2517.27 & 2522.45 & 2521.53 & 2520.39 & 2511.62 & m\({}^{3}\) \\
**Foundation** & 6733.48 & 4472.31 & 6733.48 & 6733.48 & 6733.48 & 6732.11 & 6733.48 & 6726.64 & m\({}^{3}\) \\
**Wedge 1** & N/A & 500.12 & N/A & N/A & N/A & N/A & N/A & m\({}^{3}\) \\
**Wedge 2** & N/A & 1051.94 & N/A & N/A & N/A & N/A & N/A & m\({}^{3}\) \\
**NS** & N/A & N/A & 459.00 & 252.00 & 170.00 & 180.00 & 272.00 & 450.00 & unit \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Inventory of material inputs for each reinforcement arrangement. Figure 16: Processes considered in the environmental analysis of the different arrangements of BB sleepers and the study boundary. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & **NRM** & **BM** & **HA** & **PA** & **SHA90\({}^{\circ}\)** & **SHA90\({}^{\circ}\)** & **DHA90\({}^{\circ}\)** & **DHA90\({}^{\circ}\)** & **Units** \\ \hline Ballast & 127.87 & 127.87 & 127.87 & 127.87 & 127.87 & 127.87 & 127.87 & 127.87 & tkm \\ Sub-Ballast & 275.53 & 275.53 & 275.53 & 275.53 & 275.53 & 275.53 & 275.53 & tkm \\ Track-bed & 525.69 & 411.35 & 515.53 & 523.04 & 521.93 & 522.68 & 513.65 & 510.64 & tkm \\ Landfill & 4681.29 & 5536.59 & 4641.43 & 4656.94 & 4666.52 & 4664.84 & 4662.73 & 4646.49 & tkm \\ Foundation & 12,456.94 & 8273.77 & 12,456.94 & 12,456.94 & 12,456.94 & 12,454.41 & 12,456.94 & 12,444.29 & tkm \\ Wedge 1 & N/A & 1075.26 & N/A & N/A & N/A & N/A & N/A & N/A & tkm \\ Wedge 2 & N/A & 2188.04 & N/A & N/A & N/A & N/A & N/A & tkm \\ Slepers & N/A & N/A & 87.21 & 47.88 & 32.30 & 34.20 & 51.68 & 85.50 & tkm \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Inventory of transport inputs for each reinforcement arrangement. Portugal, BB sleepers removed from the railway track are considered waste and therefore do not have an economic value, so only the environmental impacts of their transport to the transition zone, and not those of their production, are considered. The information was collected from one of the most internationally accredited generic environmental databases of the Ecoinvent V2.2 report [20].