The traffic congestion between the Anatolian and European sides of Istanbul calls for an urgent solution. This paper focuses on the selection of the most suitable and comprehensive remedy for the Bosphorus crossing problem. For this purpose, the study proposes an integrated decision aid, which brings together all the stages from the problem structuring to the evaluation of alternatives. An aggregated cognitive map initially derived through information gathered from 19 experts is converted into a hierarchical structure with the fundamental objectives at the top. In the second stage of the analysis, a rule-based approach is used. The values gathered from the same 19 experts for each alternative corresponding to each subcriterion at the lowest level of the hierarchical model are transformed into the descriptors of the fundamental objectives. Finally, the decision matrix of these aggregated values is evaluated by PROMETHEE I and PROMETHEE II and is also analyzed for robustness. (C) 2001 Elsevier Science BN. All rights reserved.