A survey was carried out on a representative population from the exposed community, who were presented with an exchange scenario at the end of which they were prompted to state their willingness to pay for suppressing the level of nuisance caused by aircraft noise. Statistical calculations were used to estimate the monetary value that the sample population would put on restoring the quality of the noise environment related to aircraft traffic and from this deduce the social cost related to its deterioration. As an extension to our use of this methodology, we decided to try to define the broad outlines of the legitimation mechanisms for expert evaluation procedures in a labile decision-making context in which complexity has become an issue in itself. In so doing we were following one of the current trends in scientific research in response to an accepted state of affairs : the increasing lack of correspondence between transport policy and the new approach to the way public initiatives are constructed is derived in part from the crisis of legitimacy that traditional, technically or economically based expert evaluations are currently experiencing.
In order to measure the acceptability of the contingent valuation method, exploratory interviews were carried out with 15 key players in the area of aircraft noise and two deliberative processes (focus groups) bringing together a panel of residents from the area around Orly airport, who had previously taken part in the contingent valuation survey, were set up. This process, which was designed to shed light on the mechanisms by which decision-making is seen to be legitimate, focused on two main points of view: legitimation through an understanding of the substance of territorial functioning as shown in the results of the survey, and procedural legitimation through the consultative function of the survey mechanism.
The contingent valuation method can be used to show the correspondence between valuation and decision-making. Depending on their different ways of thinking, most of the key players interviewed and residents involved were in agreement in highlighting the advantage not only of a scientific procedure for operational data (intensity of noise nuisance, social cost, cost to people who consider themselves inconvenienced, etc.) but also of gaining an insight through a consultative approach to how territories function, their experience of environmental burdens, individual and collective representations of the attitude of the public authorities, and so on. Formalising certain socio-spatial processes in quantitative terms seems to be the primary vector for legitimating an evaluation tool used at the interface between transport and the environment. Although considered promising in overall terms, however, this methodology still raised further questions and an expectation of further insight. Setting out the problematic nature of the situation (the relationship between theoretical and operational foundations and operational targets in the context of action-oriented pragmatics) then appears as a second vector of legitimation for any evaluation tool used at this same interface. This process therefore presents some undeniable substantial and consultative advantages for building a bridge between evaluation and decision-making. The questions formulated and views expressed, however, prompt us to think that, used on its own in its current state, it is unable to guarantee operational usage, in particular in the field of planning and development. Some methodological mechanisms with strong political connotations would represent major obstacles. In order to exploit this potential for correspondence and thus delimit the contours of its role in the decision-making field, we developed a procedural framework for this method based on the prospect of windows of opportunity.