Application of Sustainable Infrastructure Criteria in Railway Projects with the Input–Process–Output–Outcome Approach

Present-day societies face unprecedented dependence on built infrastructure amid escalating sustainability challenges including climate change and social inequality. Railway infrastructure, positioned as the most environmentally sustainable transport mode, presents a critical paradox: while essential for sustainable mobility, much of the existing network was built when environmental awareness, accessibility and innovation-driven technologies were not design priorities. This creates a significant research gap in how railway infrastructure can be systematically aligned with current sustainability frameworks such as the UN Sustainable Development Goals (SDGs), Paris Agreement and regional policy initiatives. This study addresses this gap by developing a comprehensive decision-making model that integrates railway-specific sustainability criteria defined in the previous study within an input-process-output-outcome (IPOO) framework. The approach enables infrastructure management organizations to evaluate investment projects beyond immediate operational efficiency, incorporating medium- and long-term impacts that strengthen system resilience. The framework was validated through application to Latvian railway infrastructure investment scenario. Results demonstrate that the IPOO methodology enables infrastructure managers to trace causality from resource allocation decisions through transformation processes to both immediate outputs and long-term societal impacts. Expert panel validation confirmed practical applicability while identifying critical enhancement requirements across all IPOO components. These findings contribute to sustainable infrastructure assessment theory by providing 64 railway sector-specific indicators aligned with broader SDG frameworks. Practically, the model enables railway infrastructure management companies to systematically assess investment projects for medium- and long-term transformative potential, while offering policymakers a structured approach for developing targeted resilience strategies. This research advances the integration of sustainability science with infrastructure decision-making.