Managing infrastructure projects often presents challenges in maintaining flexibility throughout their lifecycle, which limits their ability to adapt to evolving and uncertain conditions. This systematic literature review examines the factors that accelerate design flexibility in the management of infrastructure projects. Analyzing 50 articles from a dataset of 11,443, we identified several key factors, organized into seven clusters across three levels: individuals, organizations, and inter-organizational relationships and three operational dimensions of design flexibility. These factors help to expand the concept of flexibility beyond its traditional association with engineering product design to encompass managerial project design. Building on Simon's design theory, this study frames design flexibility as a proactive and strategic asset. We offer future research directions to further broaden the scope of flexibility in project management. This study contributes to ongoing debates in project management on how to enhance project performance in uncertain conditions, by addressing the challenge of balancing flexibility and control.