## 4 Conclusions, Limitations and Future Work  
Traditional design procedures of asphalt mixtures are based on volumetric parameters and the compliance with the mechanical performance, while functional properties receive less attention. Additionally, even though the potential of sustainable technologies is proven, this is not sufficiently reflected in the technical specifications and their use is not widely spread. In order to overcome these barriers, the development of a useful tool that allows IMs an easy evaluation of the mechanical, functional, and environmental attributes of the designed mixtures, as well as seek the balance between properties, will encourage the optimization of road surfaces. \begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Indictors**} & \multicolumn{2}{c}{**Labels**} & \multicolumn{2}{c}{**Rated Label**} & \multicolumn{2}{c}{**Geometric Mean**} \\ \hline
**Category** & **Mix 1** & **Mix 2** & **Mix 1** & **Mix 2** & **Mix 1** & **Mix 2** & **Mix 1** & **Mix 2** \\ \hline
**Mechanical performance** & & & & & & & & \\ \hline Dry Cantabro losses (\%) & 4.2 & 4.9 & A & A & 3 & 3 & & \\ ITSR (\%) & 92.7 & 93.4 & C & C & 1 & 1 & & \\ \hline
**Functional performance** & & & & & & & & \\ \hline Macrotexture (mm) & 1.06 & 1.08 & D & D & 0 & 0 & 0 & \\ Sideway force coefficient (\%) & 56.8 & 53.7 & D & D & 0 & 0 & 0 & \\ \hline
**Environmental performance** & & & & & & & & \\ \hline Tire–pavement noise (dB(A)) & 85.55 & 86.96 & A & A & 3 & 3 & & \\ Production temperature (\({}^{\circ}\)C) & \(>\)150 & \(>\)150 & D & D & 0 & 0 & 0 & 0+ \\ Reuse of by-products & NO & YES & & + & + & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Mechanical, functional, and environmental properties of the mixtures. ITSR—indirect tensile strength ratio. Figure 26: Global label performance for mixture 2. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
\begin{tabular}{c} Asphalt \\ concrete \\ concrete \\ friction course \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Design parameters of the mixtures. Figure 25: Global label performance for mixture 1. In addition, in the last few years, public administrations are willing to reward those road works whose quality is beyond the thresholds required by the specifications, and recognize this added value in the road construction tendering process. In this sense, a labeling system would smooth the introduction of award criteria into the contracting process. This article is a first attempt to multi-labeling scheme for asphalt mixtures for thin wearing courses according to their mechanical, functional, and environmental performance. The developed labeling system allows the comparison and benchmarking of different designed asphalt mixtures, providing the chance to choose the most safe and environmentally demanding option for each specific situation; therefore, it should function as a potential driver for behavioral change. The aim of this research was to propose a methodology to develop a multi-labeling scheme for asphalt mixtures and to show the potential of this tool to stimulate better road surface practices. The approached methodology is flexible enough to be adjusted to the sample size or to be tailored to suit countries' specific requirements. In this case, the study focused on the Spanish case because different Spanish IMs were involved and all the collected data belonged to the Spanish road network; however, the described methodology can be easily applied to any other study case. This guideline proposes four label classes (A-D) based on the sample size, but the range of characterization can be scaled up as data arise. The limits of the non-acceptable performance were defined according to the requirements established by the road administration and the boundaries of the acceptable labels were established according to the defined percentiles of the statistical distribution.