Can joint-contract functions promote PPP project sustainability performance? A moderated mediation model

Purpose The role of conventional contracts in achieving sustainability goals in public–private partnership (PPP) projects has been questioned. From the multifunctional perspective of contract theory, joint-contract functions that combine contractual control, coordination and adaptation may be a potential approach for improving PPP project sustainability performance. This research intends to investigate the link between the joint-contract functions and PPP project sustainability performance, and their underlying mechanism, by analyzing the mediating role of relationship quality and moderating roles of environmental uncertainty and behavioral uncertainty. Design/methodology/approach Based on 170 valid survey data collected from the Chinese PPP professionals, partial least squares structural equation modeling (PLS-SEM) was adopted to test the hypothesis. Findings The results reveal that joint-contract functions are positively associated with the PPP project sustainability performance. This relationship is strengthened by environmental and behavioral uncertainty. Moreover, the relationship between the joint-contract functions and PPP project sustainability performance is mediated by relationship quality. Research limitations/implications This research extends contract governance theory and sustainability research in PPP projects. The research implications are as follows: (1) joint-contract functions are a second-order construct consisting of three first-order dimensions: control, coordination and adaptation and are positively associated with PPP project sustainability performance; (2) joint-contract functions enhance the sustainable benefits of PPP projects during environmental uncertainty and behavioral uncertainty; (3) informal relationships are a critical bridge connecting formal institutions with the sustainability performance of PPP projects. Practical implications In general, these findings guide project participants who aim to achieve sustainable outcomes in PPP projects. (1) Project participants should consider the process of contract design and sign contracts that focus on joint-contract functions. (2) Project participants should investigate the degree of uncertainty of a PPP project before designing contracts, and design the contracts with corresponding complexity. (3) Project participants should work to enhance PPP sustainable benefits by improving the relationship between partners, such as encouraging mutual trust and joint problem-solving. Originality/value This research verifies the relationship between joint-contract functions and PPP project sustainability performance, and the boundary and intermediary conditions between them.