The public decision-making methods in transport are based on cost-benefit analysis, by which the consequences of the decision (standards for vehicles, new infrastructures...) are converted in monetary amounts and compared to the cost of implementation of the decision. But some of these consequences, especially those related to environment, are not directly expressed in monetary terms. The article aims at offsetting this difficulty in the case of noise. The possible methods for getting money values of noise are presented; it is shown that the estimates to which they lead are coherent and consistent. Then a comparison is made between the present procedures and the procedures which could be implemented, and it is shown that large gains of efficiency could be obtained.