Public-private partnership (PPP) projects have the features of extended investment cycles, diminished returns, and high demand for technology. Inadequate utilization of these projects may result in an accumulation of new implicit debt for the government. Consequently, it becomes imperative for the government to manage and mitigate implicit debt risks associated with urban rail transit PPP projects, which is a crucial prerequisite for ensuring the progression of such projects and the unhindered functioning of the financial system. The objective of this study is to investigate the factors that influence government implicit debt risks in urban rail transit PPP projects from the perspective of policy. This study employs the grounded theory method to develop a comprehensive framework model that identifies the influencing factors of government implicit debt risk in urban rail transit public-private partnership (PPP) projects. The contributions of this study are twofold: (1) it highlights the role of policy as a significant determinant of implicit debt risks of urban rail PPP projects, which contain governmental subsidies, external environmental risk sharing, and supporting measures. Specifically, government subsidies directly contribute to the government's implicit expenses, thereby impacting the level of implicit debt risks associated with urban rail transit PPP projects. Supporting measures exert an indirect influence on the implicit debt risks of the government, thereby imposing a significant burden on local fiscal expenditure. External environmental risk sharing, as an external factor, leads to an increase in fiscal expenditure due to the government's social responsibility; and (2) it provides a qualitative method that examines the government implicit risk factors associated with urban rail trait PPP projects based on grounded theory. The model that examines the influencing factors of government implicit debt risk in urban rail transit PPP projects adopts a policy perspective, which can inform policymakers on a heretofore unexplored adverse effect of guarantee policy.
