## 3 Environmental Product Declaration EPD  
The development of the index for the quantification of the environmental impact of the asphalt concrete production and paving cycle developed in this article stems from the information and the adopted procedures for the production of the Environmental Product Declaration (EPD) certification. EPD certification has been presented and described in the standards ISO 14025 and EN 15804 [13,14]. It is based on the adoption of common criteria and calculation rules derived from the Life Cycle Assessment (LCA) methodology applicable to a very wide range of products and processes. As discussed in the introduction, several scientific works, including the not previously mentioned work [15], have demonstrated their effectiveness in assessing the production process and use of asphalt concrete. Furthermore, in the present work, it was decided to adopt this certification because it allows the use of common and internationally recognized criteria and calculation rules for a large number of product categories, reporting information in a common and uniform format. To ensure this uniformity and harmonization of EPD certification formats, documents called Product Category Rules (PCRs) have been defined. These PCRs define the principles and requirements for the drafting of EPDs for each specific category of product or service. Specifically, the PCRs for asphalt concrete have been developed by the National Pavement Association [16]. For the entire life cycle of materials, the assessment of environmental impact is carried out through the determination of several environmental factors described below by means of summary tables: parameters related to emissions (Table 1), consumption of resources intended as raw materials and as energy (Table 2), generation of waste and the management of different output flows (Table 3). All the pollutant components shown in the respective tables are quantified throughout production, installation (construction), use, and end-of-life phases, also assessing the potential for reuse, recovery, or recycling. All the different phases are reported and briefly described in the Table 4. Table 4 also indicates the relative codifications described in the EN standards used and reported in the EPD certifications. The phases considered in this study are highlighted in grey. For the establishment of EPD certifications, it is possible to identify three different approaches that consider different system boundaries by considering only some of the phases described in Table 4. These approaches are referred to as:  
* _From cradle to gate._ This is the most widely used approach to quantify the impact of the production cycle of materials, including the production and procurement of raw materials. In relation to the production phases, it can be said to correspond to phases A1 + A2 + A3. \begin{table}
\begin{tabular}{l l l} \hline \hline
**Parameter** & **Abbreviation** & **Unit of Meas.** \\ \hline \hline \multicolumn{3}{l}{Use of renewable primary energy excluding renewable} \\ primary energy resources used as raw materials & PERE & MJ \\ Use of renewable primary energy resources & PERM & MJ \\ used as raw materials & & PERT & MJ \\ Total use of renewable primary energy resources used as raw materials & PERE & MJ \\ Use of non-renewable primary energy resources & PENRM & MJ \\ Use of non-renewable primary energy resources & PENRT & MJ \\ used as raw materials & PENRT & MJ \\ Total use of non-renewable primary energy resources & PENRT & MJ \\ (primary energy and primary energy resources used as raw materials) & SMI & kg \\ Use of renewable secondary fuels & RSF & MJ \\ Use of non-renewable secondary fuels & NNFS & MJ \\ Use of net fresh water & FW & MJ \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Environmental impact parameters related to use of resources.