Nowadays society is strongly sensitive to environmental issues and sustainability. DECO estimates that in Portugal there are about of 800.000 people exposed to excessive noise and complaints concerning this, are the most common complaint with respect to the environment. The noise emission and the right not to occur to disturb are regulated and people are informed of their rights. So the need to reduce the noise to acceptable values is an important priority for many companies. These noise reduction actions are often concerned significant investments, and we must ensure the success of the project and minimizing their costs, and this is a major concern of those responsible for the environment. Give the importance of objective approach exists as regards the assessment of the impacts of investments to make.