For the project for the A4 motorway extension that Salini Impregilo is carrying out in Italy, we have developed a plan to reduce pollution in an underpass located near residential areas and affected by intense traffic. The project consists in applying special photo-catalytic materials on the asphalt, and on the walls and ceilings of the underpass. These materials contain special metal compounds which when irradiated by light cause a chemical reaction that breaks down toxic substances, such as carbon monoxide, nitrogen and sulphur dioxides, benzene and particulate matter, into non-harmful ones like mineral salts and limestone.

The underpass is fitted with special UV-ray lamps to ensure the proper activation of the photo-catalytic process, which reduces the pollution from vehicle traffic to around 75-80%. In addition, as the photo-catalytic materials reflect the light up to 60% more than the traditional surfaces, we reduced the number of illumination sources used in the underpass, thereby cutting energy consumption by up to 50%.  

The project is of particular relevance as it represents a useful test for materials routinely used in tunnels, and could be effectively adopted for other infrastructure projects, such as underpasses, which are very common in urban and non-urban areas.