Smart vs conventional motorways: environmental impact assessment under realistic traffic conditions

This research aims at assessing the environmental impacts exerted by a smart motorway compared to those of a traditional motorway. The study has global policy implications: it takes into account the impacts due to the construction and maintenance of the infrastructure and the environmental effects produced by the traffic emissions, taking into account smart technologies and truck platooning regulation. Through a classical LCA approach, 1 km-long smart motorway with 2 m-high embankment was assumed as the functional unit for the analysis. A realistic traffic condition has been considered. A comparison between environmental effects produced by the use of virgin material and by Reclaimed Asphalt Pavement was made by assuming two maintenance plans. Thanks to C-ITS systems the greater safety featured by smart motorways has a significant effect on the environmental impact, compared to conventional motorways. The impact produced by safety barriers during the life cycle was also estimated. For smart motorways the impact categories GWP, POCP, AP and EP are observed to be considerably reduced in the maintenance phase of zinc-coated steel safety barriers and in those associated to traffic emissions. It must be noted that in smart motorways vehicle emissions are markedly influenced by the percentage of heavy vehicles travelling in Truck Platooning mode. The results show that concomitant use of lime stabilization and RAP leads to a significant reduction in energy consumption (up to 35%) and pollutant emissions (up to 34% of CO2) than in case of exclusive use of virgin material. The accidents reduction produce a 30% decrease of GWP, POCP, AP and EP related to safety barriers maintenance phase than the corresponding values of traditional motorway. Truck platooning mode generates GWP reduction close to 4%. The environmental advantages of a smart motorway increase progressively with the increase of AADT, platooning truck percentage and heavy vehicles percentage.