The evaluation of environmental impact is a preventive instrument for the protection of the environment. Construction projects, whether public or private, that they can have impacts on the environment, can only be conceded if previously present an environmental impact study which evaluate the possible effects on the environment.
According to the valid regulations, the studies of environmental impact also have to include alternatives and corrective measures. The Town Council of Barcelona makes available for the citizenship the reports of environmental impact from different projects of the city. If you want to know more you, check out the portal of Transparency of Urbanism and Ecology.