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An EMPIR project provides updated data on the minimum luminance levels for night-time roads which will reduce energy consumption but improve safety

Road lighting accounts for 14 to 19 % of all energy consumed globally. As more than 40 percent of all fatal car accidents occur at night – despite traffic being 60 % less than during the day - designers need to balance this energy usage with safety.  

Driver visibility doesn’t just depend on how bright the lighting is but also on the overall ‘luminance’ of a road or pavement. This includes how ‘reflective’ the surface is, whether it is dark or light and the type of material it is composed of.

The EN 13201 series of standards provide values, based on data from the International Commission on Illumination (CIE), which link the luminance coefficient of a road surface with a visual model of a driver at a height of 1.5 meters with a viewing angle of 1^o to the lit surface and corresponding to a viewing distance of 83 meters away.
However, these standards are based on luminance coefficient data from the 1970s and on a limited number of surface types. They do not take into account new types of surfaces nor the introduction of new lighting systems such as LEDs. In addition, the viewing angle and distance in the model is an unrealistic condition for urban driving where visibility is much more limited than 83 meters.
Studies have shown that the use of CIE data as a reference can lead to errors over 30 % on average and, in worst cases, up to 50 % on expected road luminance.

These problems have been addressed by the now completed EMPIR project Pavement surface characterisation for smart and efficient road lighting (16NRM02, SURFACE).

During its lifetime the SURFACE project:

• Published “Review of road surface photometry methods and devices – Proposal for new measurement geometries”. The recommendations include increasing the driving viewing angle from 1o to 2.29^o for urban environments.
• Published “Road Surface Photometric Characterisation and Its Impact on Energy Savings” where the energetic impact of using old and SURFACE provided new data on luminance coefficient of asphalts is compared.
• Used 3D printing to manufacture reference materials representative of different road surfaces.  This represents one of the first actual applications of the ‘internet of things’ to metrology. The reference material kit has now been patented.
• Compiled a database containing around 250 different types of current road surfaces.
• The project defined, in accordance also with EN 13201-5 suggestions, a reference set to compare performances of road surfaces and lighting systems. This SURFACE test set includes 5 different reference road surfaces from the SURFACE database, a reference road profile and lighting class and a reference lighting system of given geometrical and photometrical characteristics.
• Developed the software LUMCORUN to compute the uncertainty of road surface luminance coefficient measurements for any type of setups involving light sources and detectors.
• Initiated the first intercomparison between European metrology institutes on luminance coefficient to ensure the necessary traceability and uncertainty evaluation of measurements.
• During the COVID-19 travel restrictions, organised 4 open access webinars for the scientific and stakeholders’ communities. These webinars are available on the project website.

The project results will be used by CEN TC169/WG12 in the next revision of EN 13201 series, and by CIE TC4-50 in the revision of pertinent publications such as CIE 144.

The use of SURFACE data can lead to energy savings of up to 27 % for bright pavements and can be more than 50 % with the use of new pavement installations and ‘smart’ adaptive lighting and, with the more realistic luminance values, improve safety on European roads.

The project coordinator Paola Iacomussi (INRiM) who is also a co-chair of CIE’s TC4-50, said about the work:

“Just as the safety of today's cars is not comparable to that of cars of the 1970s, so is the performance of asphalts. But until now it has not been possible to account for this on a regulatory level due to a lack of coordinated research results. People are often unaware of how important the reflection behavior of asphalts is and how crucial it is to ensure the safety of our roads at night. The SURFACE project carried out the metrological research necessary to improve and update the scientific knowledge underlying the CIE technical document that form the basis of the European regulations. If we will have better-lit roads with optimized energy consumption, it will also be thanks to the commitment of all the members of the SURFACE project consortium. Although the most important project achievements have been disseminated in guidelines, papers, to CIE and CEN, the most relevant it has been within the consortium itself: researchers of SURFACE consortium have been able to turn difficulties into opportunities, working together toward project objectives despite distances and difficulties in the different countries during the most endeavor times of the Covid pandemic. I’m really honored of having led this project, and of the results we achieved.”

This EMPIR project is co-funded by the European Union's Horizon 2020 research and innovation programme and the EMPIR Participating States.

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