REFLECTIVITY

The optical properties of road surfaces are essential to many planning issues, both in urban areas and in the field of road infrastructures. Indeed, the interactions of light with these surfaces underlie important challenges such as the adaptation of cities to climate change or the visibility of road signs whether for the human visual system or for the sensors of driving assistance or autonomous vehicles. The BRDF (Bidirectional Reflectance Distribution Function) is the function that describes the ability of a surface to reflect a light wave in all directions in space. Although its use is predominant in virtual reality to address issues of visual appearance, it is hardly available for road surfaces (pavement and markings). It is indeed a complex data, in terms of instrumentation and time required to measure it. Thus, in the field of road infrastructures and equipment, very partial data are used by imposing the geometries of observation of the road. Typical pavement characteristics are considered obsolete nowadays and conventional geometries are not very relevant for urban lighting. The REFLECTIVITY project consortium is composed of three research teams from a Carnot Institute, an industrial company, two university laboratories and two local authorities (urban communities). Its ambition is to demonstrate the importance of the knowledge of the BDRF of the road surfaces to answer the climatic challenge and the development of autonomous mobility. We propose the creation of a shared database describing both the structural characteristics of road surfaces (elementary constituents, formulations, micro and macro textures, surface geometries) and their optical properties (BRDF, photometry, colorimetry, spectral reflectivity). We will develop new techniques to determine the BRDF of road surfaces using in particular a methodology of measurement by virtual gonioreflectometry based on the 3D geometry of the surfaces, usable in laboratory and on road, thanks to the adaptation of existing systems of point or dynamic measurements. The robustness of this approach will be confirmed by comparison with reference measurements made in the laboratory and on site. Accessing the BRDF from dynamic measurements is a technological breakthrough that will allow a large-scale characterization that will consider both the variability and diversity of road surfaces. Temporal evolution aspects will also be addressed via the development of predictive methods of BRDF depending on the formulation of a pavement or a marking but also according to the life cycle of road surfaces by considering the phenomena of ageing of the materials or the evolution of their surface condition (degree of moisture in particular). In addition to the methodological and scientific aspects of the project, experiments will be conducted with the industrial and the partners cities. They will assess the contributions of the project to the optimization of road lighting installations, to better consider the contrast of markings for the deployment of autonomous vehicles and to provide the albedo of materials for urban climatology. This research will provide a global approach to the optimisation of urban pavements and road markings over large areas, combining daytime and night-time issues and taking into account the diversity of users and environmental conditions.