This paper is dedicated to developing a risk assessment indicator system applicable to transportation infrastructure investment projects in the public–private partnership (PPP) model. Initially, through practical research, literature reviews, and expert interviews, key risk factors for transportation infrastructure investment projects in the PPP mode were identified. Based on these risk factors, a preliminary risk assessment indicator system was established. Subsequently, the principal component analysis (PCA) was used to reduce the dimensions of the indicators, simplify the structure of the system, and highlight key risk factors. Simultaneously, the CRITIC-EWM method was applied to calculate the weights of the indicators. Furthermore, to validate the effectiveness of the indicator system, a questionnaire survey was conducted, collecting 314 responses. Structural equation modeling was applied to validate the effectiveness of the indicator system and examine its application value in practical risk management processes. The primary contribution of this study lies in proposing a method for constructing a risk assessment indicator system that combines quantitative and qualitative analyses, providing new theoretical and practical guidance for risk management of transportation infrastructure investment projects under the PPP mode.