REFLECTIVITY project organisation

WP 1 : Constitution of a database of road surfaces characteristics

This work package will bring together the characteristics of the samples collected and specifically manufactured, the experimental protocols and the description of the equipment used. Thus, all of the previous measurements available but also carried out on samples within the framework of this project will be compiled within a database which will include

• the structural characteristics of the road surfaces characterised (elementary components, formulations, micro- and macro-textures, surface geometries)
• the contextual elements of the measurement (surface condition of the sample, etc.),
• measurements of their optical properties: classical (table-r, retro-reflection, etc.), BRDF, colorimetric coordinates, spectral reflectivity, albedo, etc.

Within the framework of the project, this database is expected to feed the modelling and prediction work packages 2 and 3. It will also be made available to all in accordance with the FAIR (Findable, Accessible Interoperable, Reusable) principle and in compliance with the ANR's data management plan.

WP 2: Estimation and prediction of the BRDF of road surfaces

This work package includes the main simulation work carried out within the framework of the project in order to estimate the BRDF of road surfaces and then predict its evolution as a function of the degradation of the surface condition.

• Numerical simulation of the BRDF from the 3D geometry of the surface and a virtual gonioreflectometer:
  the method consists of digitising the 3D geometry of road surfaces and then estimating the BRDF with a virtual gonioreflectometer as a function of the micro-geometric properties of these surfaces. This will require the use of data structures specific to the simulation of surfaces with complex geometry and appearance to take into account the heterogeneity (diversity of materials) of a pavement. The evaluation of the numerical simulations will be based on the BRDF measurements carried out in the work package 1.
• Prediction of the evolution of the BRDF as a function of the degradation of the surface condition:
  the objective here is to predict the evolution of the BRDF of a road surface as a function of the ageing of the materials (effects of road traffic and climatic conditions) or of the temporary modification of its surface condition (wetting, presence of dirt). Parametric functions will be determined to describe the actual BRDF of the surfaces, and then models of the evolution of the parameters according to the degradation factors will be developed.

The work package 2 is structured in two tasks, each of which will be the subject of a doctoral thesis.

 WP 3: In situ and large-scale characterisation of the BRDF of road surfaces

In the objective of better considering the heterogeneity of road surfaces and their diversity on a territorial scale, measurements will be carried out by instrumented vehicles.

The challenge here is to use field measurements to implement the workpackage 2 in order to

• Carry out numerical simulations of BRDF based on in situ measurements of the 3D geometry of the pavement
• Estimate the albedo of a linear pavement
• Develop relevant indicators for both the pavement and the markings in order to estimate visibility more globally.

The validation of this work will be carried out by comparison with punctual measurements on site.

The objective is both to carry out a transition to a large scale and also to consider the reflectivity of surfaces for multiple geometries, corresponding to both human vision and the cameras used by automated vehicles.

WP 4: Enhancing the value of BRDF for industry and authorities

This work package constitutes the application of the work carried out in the other work packages. It will be strongly dependent on "real-life" needs, those of road surface manufacturers as well as those of local authorities and infrastructure managers. The role of the industrial and local authority partners in the project will be predominant here in order to guarantee the usefulness of the research work. Three levers for enhancing the value of the BRDF have been identified.

• Prediction of the optical properties of pavements from their design:
  with the knowledge of the precise formulation of the road surfaces that constitute the database, it will be a question of examining the links that exist between the nature of the materials and the BRDF obtained. The challenge will be to anticipate the optical properties of pavements as soon as they are developed and then to consider their evolution in order to obtain decision-making tools for the choice of a pavement within an urban development according to the desired use.
• Optimisation of lighting installations and reduction of urban heat highlands (UHI):
  the possibility of measuring the BRDF of pavements on a large scale will offer very interesting levers of action to local authorities to optimise the operation of their public lighting installations and to better consider the impact of the pavement on the UHI phenomena.
• Management of road markings for all users (human and VA):
  the impact of the BRDF of road surfaces and markings in visibility calculations will be studied in partnership with road infrastructure managers. The visibility of markings will be calculated from models using luminance contrast, which in turn will be determined from the BRDF of pavements and markings under different conditions.