AbstractComplexity creates both challenges and opportunities for the operation and maintenance (O&M) of mega transportation projects (MTPs), making it imperative to explore the O&M complexity. Traditional approaches to the analysis of project complexity followed reductionist thinking and failed to address the relationships between system elements. Therefore, this study proposes a systems thinking–based framework that captures the relationships to prioritize the O&M complexity of MTPs using social network analysis (SNA). First, 47 complexity indicators were identified through a literature review, semistructured interviews, and a Delphi survey. These indicators were applied to map the O&M complexity network of the Chengdu–Chongqing Highway, with the structural characteristics analyzed using SNA. The results reveal that the availability of technologies, skills, methods, and tools is most closely related to other indicators and that the sharing level of operational information most strongly controls other indicators. Furthermore, the management strategies for this case were formulated according to the centrality of network nodes, and a complexity management process that can be applied to prioritize and manage the O&M complexity of any MTP was designed.