Integrating system dynamics and fuzzy logic modeling to determine concession period in BOT projects

The concession period is one of the most important decision variables in arranging a BOT-type contract which should be determined considering the existing risks and uncertainties. This research presents an integrated fuzzy-system dynamics (SD) approach for determination of concession period. The complex inter-related structure of different factors affecting a BOT project is modeled using the system dynamics approach. Owing to the imprecise and uncertain nature of different factors affecting the concession period, fuzzy logic is integrated into the system dynamics modeling structure. The values of different factors affecting the concession period are determined by fuzzy numbers based on the opinions of different experts involved in the project. The application of Zadehʹs extension principle and interval arithmetic is proposed for the system dynamics to enable the system outcomes to be presented considering uncertainties in the input variables. To evaluate the performance of the proposed method, it has been employed in a highway project.