Beyond Infrastructure: Climate-Constrained Transit Transition and Urban Sustainability in Riyadh

This study assesses the multi-dimensional impacts of large-scale urban mass transit infrastructure on network sustainability and individual mobility behavior, using the newly operational Riyadh Metro as a case study. Adopting a qualitative interpretive synthesis method, the research integrates peer-reviewed literature, institutional policy reports, and early operational datasets to evaluate transit outcomes across network accessibility, spatial equity, and localized environmental constraints. The study shows the interactions between infrastructure provision, urban form, and climatic conditions. The results reveal that while the infrastructure significantly enhances raw corridor accessibility, its systemic impact is heavily constrained by extreme climatic conditions, institutional fragmentation, and critical first- and last-mile gaps. Extreme heat significantly reduces effective walking. Additionally, continued reliance on private vehicles, resulting in a hybrid mobility regime rather than a full modal transition. The analysis also further reveals uneven spatial distribution of the metro for easy accessibility. To overcome these barriers, this paper introduces the Climate-Constrained Sustainable Transit Transition Framework (CSTTF) as an analytical tool. The study concludes that infrastructure-led urban transformation in hyper-arid megacities requires a comprehensive policy shift that integrates land-use reform, behavioral incentives, and climate-adaptive urban design. The proposed Climate-Constrained Sustainable Transit Transition Framework (CSTTF) provides a transferable decision-support framework that can assist policymakers, urban planners, and transit agencies in designing climate-resilient metro systems, optimizing first- and last-mile connectivity, and informing sustainable transport planning in Riyadh and other hot-arid metropolitan regions facing similar environmental and urbanization challenges.