The present paper aims to identify and evaluate risks in transportation projects carried out through public-private partnerships (PPP) and proposes a model for allocating critical risks among stakeholders. The study utilizes the fuzzy analytic hierarchy process (FAHP) to prioritize risks and a system dynamics (SD) approach to develop a causal model for risk allocation. Thirty risks are identified and categorized into five primary risk categories: government, financing, operational, social, and organizational. Operational risks are found to be the highest priority, followed by organizational, economic, political, and social factors. Using the Pareto principle, eight critical risks are identified. The proposed SD-based risk allocation model is applied to a case study of the Shiraz-Isfahan Freeway Project. The results indicate that the project can be completed within the set timeframe of six years, but it would incur a 46% higher cost than initially estimated if 62% of the risk of exceeding the financial limit is allocated to the employer. This study provides valuable insights into risks associated with transportation projects undertaken through PPP. The proposed model offers stakeholders an effective and efficient approach to allocate risks. By addressing these risks, stakeholders can enhance the success and efficiency of PPP transportation projects.