A sustainable governance index for public infrastructure: integrating lifecycle retrospective analysis and structured expert assessment

Sustainable Development Goals (SDGs) are increasingly referenced in infrastructure policy but remain insufficiently integrated into early-stage decision-making. This study proposes a Sustainable Governance Index (SGI) to evaluate governance risks and sustainability performance across the lifecycle of public infrastructure projects. The framework integrates a lifecycle retrospective–feed-forward governance model with case-anchored weighting across six dimensions: design interface risk, cost escalation, schedule delay, social adaptability, environmental resilience, and procurement governance. Empirical baseline weights were derived from documented governance events in 30 purposively sampled cross-national infrastructure cases spanning eight economies. A structured professional review involving 24 infrastructure practitioners provided contextual and content-level support for the governance structure rather than independent weight calibration. The resulting Sustainable Governance Decision Framework (SGDF) was applied to four infrastructure projects in Taiwan and Lithuania, with robustness examined through ±10%, ±20%, and ±30% sensitivity analyses. Results show that design interface coordination remains the dominant influence on lifecycle cost risk across all tested perturbations. The SGI provides a transparent, recalibratable diagnostic framework for integrating SDG-oriented governance considerations into early-stage infrastructure planning rather than a universal ranking instrument.