Environmental assessment with a life cycle approach is an ever more popular method for construction project appraisal. For that purpose, Life Cycle Assessment (LCA) which is standardized (ISO 14040 and 14044) is a robust methodology, adopting a systemic position and calculating environmental potential impacts of a system on a set of quantitative indicators. As ecological prejudices are numerous and delay real advances towards environmental transition, LCA has the advantage to provide quantitative performance ratings and to detect transfer of impacts. In France, LCA may be used to assess the environmental performance of road infrastructure – several road eco-comparators like SEVE, ECORCE or Variways® have been developed in that purpose.
Nevertheless, assessing complex systems by LCA entails methodological choices to make the studied object and phenomena simpler through modelling. Indeed, reality is so complex that modelling it entirely is not possible, because science is not advanced enough: scientific phenomena are not entirely well understood, computers are not powerful enough, etc. Road eco-comparators only consider pavement and earthworks in the system boundaries instead of assessing an entire transport project. In particular, despite the public appealing toward urban plantations that are ever more frequent in infrastructural development projects – green walls and roofs, urban kitchen gardens, miscellaneous green embellishment, the real environmental benefit is rarely calculated. Specifically, in an infrastructure project, LCA uniquely captures environmental burden due to construction, and potentially maintenance of green spaces, but does not take into consideration phenomena related to vegetation growth or end-of-life, namely carbon sequestration, ecosystem services, impact on biodiversity, land, resources consumption, etc.
Whereas it is common belief that greening cities has positive effects on the environment, the objective of the article is to propose a state-of-the-art of knowledge toward an impartial quantitative consideration of the impacts of infrastructure project’s greenery in urban context via LCA.
Results show that if some effects related to few indicators would be relatively possible to intercept like climate change or resource consumption, others seem to be more delicate like biodiversity or land use. Moreover, LCA methodology, either attributional or consequential LCA, would consider different phenomena, with high repercussion on the results. The use of methods associated to consequential LCA such as system expansion allows integrating positive aspects of urban plantation such as additional energy resources provided by maintenance of green spaces (e.g. wood recovery).
Even though all kind of effects are not methodologically taken into account in LCA – like local impacts (landscape, noise, odor, ambience) or even mind changes which are so important when it comes to environment, it may be valuable to take into account more phenomena related to vegetation in LCA of urban projects. The final aim would be to provide robust information to decision-makers in order to rationalize public and private choices.
urban vegetation; environmental benefits; Life Cycle Assessment; infrastructure project; methodology; ecosystem services