# A Methodological Approach to the Study of Retroreflective Pavements
## 4 Conclusions  
In this study, the retroreflectance of different bituminous mixtures for use in the top layer of pavements has been examined, considering the influence of colour, aggregate type, and surface texture. The investigation was carried out by measuring total reflection and directional reflectance. The main conclusions are detailed below as follows:  
* When determining total reflectance using a spectrophotometer with an integrating sphere and directional reflectance at 45\({}^{\circ}\) with a spectroradiometer, similar trends were observed. The reflectance values measured by the spectroradiometer were lower than those obtained through the integrated reflectance across all directions. The ratio between these values for white mixtures is approximately 90%, while for black mixtures, it is around 30%. Nonetheless, both methods proved effective for analysing the reflectance. * When the shade of the mixtures is white or warm, the reflectance increases with wavelength as it approaches the infrared range. However, for mixtures with a cooler shade (blue), the reflectance is higher at shorter wavelengths near the ultraviolet range. * The effect of the aggregate depends on the shade of the mixture. For dark mixtures, the differences between aggregates are minimal (around 3% when measuring global reflectance and 0.2% for directional reflectance). For light-coloured mixtures, the reflectance values are higher when using a limestone aggregate (white). For the same shade, no differences in the reflectance were observed between granite and porphyry aggregates. * By reducing the entrance angle between the incident light direction and the measurement direction, the spectroradiometer provides an approximation of the retroreflectance, which yield higher values than those obtained with the usual 45\({}^{\circ}\) angle. * When measuring the retroreflectance and increasing the entrance angle of the light on the surface to a more grazing angle, the values increase, especially for the lighter mixtures (for AUTL mixtures, values increase by approximately 42%). * The effect of the mixture type has been demonstrated, with higher retroreflectance values obtained for the AUTL mixtures manufactured with limestone aggregate and synthetic binders pigmented with titanium oxide (white). However, for light-shaded mixtures, the texture differences between the different mixtures were very small. Consequently, light-coloured mixtures with high texture levels may be suitable for the construction and maintenance of urban roadways, particularly in areas susceptible to the urban heat island effect. Conceptualization, R.M., T.L.-M. and A.H.M. ; methodology, R.M., T.L.-M. and A.H.M. ; formal analysis, R.M. and T.L.-M.; investigation, R.M., A.M.i.R., T.L.-M., R.V.M., A.H.M. and E.P.-C.; resources, R.M., T.L.-M., A.H.M., A.M.i.R., E.P.-C. and M.S.M. ; data curation, R.M., T.L.-M., A.M.i.R. and R.V.M. ; writing--original draft preparation, R.M., T.L.-M. and A.M.i.R. ; writing--review and editing, E.P.-C., M.S.M., A.M.i.R. and A.H.M. ; visualisation, R.M., T.L.-M. and A.M.i.R. ; funding acquisition, A.H.M. All authors have read and agreed to the published version of the manuscript. This publication is part of the R&D&I project \"Heat island mitigation to prevent global warming by designing sustainable pavements with reflective and photoluminescent properties (RELUM)\", supported by grant TED2021-132077B-I00, funded by MCIN/AEI/10.13039/501100011033/, and by the European Union \"NextGenerationEU/PRTR\". Two authors ([PERSON] and [PERSON]) acknowledge the financial support of the project with reference (PID2020 tool14582 RB-I00/ AEI/10.13039/501100011033). Not applicable. The original contributions presented in the study are included in the article; further inquiries can be directed to the corresponding author. [PERSON] is a Serra Hunter Fellow. **Conflicts of Interest:** The authors declare no conflicts of interest.