# A Methodological Approach to the Study of Retroreflective Pavements
## 1 Introduction
Like the previous studies, the total reflectance was obtained from a UV-VIS-NIR spectrophotometer. [PERSON] et al. [25] identified reflectance in the visible and near-infrared spectra as dominant factors affecting the thermal behaviour of coatings. These authors studied different coatings to improve the pavement reflectance. Other authors have also proposed solutions through the use of coatings [26; 27]. However, these types of solutions can decrease the skid resistance of the surface course and present durability concerns. By these methods, the reflectance could be reduced by up to 50% within a single year [28]. [PERSON] and [PERSON] [29] filled the voids in a porous mixture with magnesium phosphate cement to obtain a reflective grouting compound pavement. They observed a surface temperature reduction of 4.5 \({}^{\circ}\)C compared to the reference mixture after 180 min of exposure. The reflectance in the near-infrared spectrum increased by up to 34.19% related to that of the asphalt. In the study of [PERSON] et al. [30], the maximum surface temperature reduction was 20.2 \({}^{\circ}\)C. In this case, the authors used, in addition to magnesium phosphate cement, titanium dioxide as an additive to improve the reflectance. No recent studies have been found on the design of bituminous mixtures manufactured with synthetic binders and additives that change the colour of the mixtures to lighter shades, thus improving their reflectance. The greatest drawback of reflective pavements is the glare caused by reflected radiation, which can be harmful to skin, cause visual effects on the cornea of the human eye, and affect drivers' perception [31]. This is because reflective pavements reflect solar radiation in all directions. In this way, if the radiation is not reflected to the atmosphere, it can negatively affect the thermal comfort of citizens and affect vehicles and urban buildings. For this reason, reflective pavements will only effectively reduce the heat island effect if they reflect incident radiation to the atmosphere. This highlights the need to modify existing reflective pavement technology towards those capable of reflecting the incident solar radiation back in the same direction, that is, retroreflective pavements [32]. Thus, retroreflection refers to the ability of certain surfaces to reflect incoming light back towards the light source, regardless of the original angle of incidence [33]. In this manner, whereas solar reflectance reflects light in multiple directions and focuses on the amount of light reflected, retroreflectance is characterised by redirecting light directly back to its source, regardless of the angle of incidence. Different authors have studied the retroreflective capacity of materials for their use in buildings, facades, and pavements, aiming to address the limitations of reflective materials [34; 35]. Some findings indicate that for small angles of incidence (10\({}^{\circ}\)), the retroreflective materials predominantly reflect the light towards its source [36]. However, there are few studies in the literature focusing on retroreflective materials specifically for urban pavements. [PERSON] et al. [35] analysed the retroreflective capacity of an urban pavement within a canyon using a spectrophotometer with an integrating sphere, as well as an ad hoc pyranometer that enabled measurement of both the incident light and that reflected in the same direction. The results demonstrated an increase in the albedo of the retroreflective surface by 4.6% compared to white and beige diffusive materials. Traditionally, a pyranometer or a spectrophotometer with an integrating sphere has been used to determine the optical properties of reflective materials [37]. The former is generally employed in field measurements, while the latter is used in laboratories to conduct measurements on small samples. However, it is not possible to measure the reflective properties directly in specific directions using this equipment to determine a material's retroreflective capacity.