Applying the UNECE PIERS Evaluation Methodology for the SDGs to Support the Implementation of Green PPP Projects and Infrastructure: Lessons from Slovenia

Robust evaluation methods are essential for assessing the sustainability of public–private partnerships (PPPs) and advancing the Sustainable Development Goals (SDGs). This study examines the United Nations Economic Commission for Europe (UNECE) People-first PPP and Infrastructure Evaluation and Rating System (PIERS) through three green PPP initiatives in Slovenia, focusing on energy efficiency, renewable energy and sustainable mobility. Using structured scoring across five dimensions—access and equity, economic effectiveness, environmental sustainability, replicability and stakeholder engagement—the analysis considers project-level performance, national SDG alignment and methodological applicability. The results indicate strong overall sustainability performance, but identify stakeholder engagement as a significant weakness, largely due to institutional constraints. Comparison with Slovenia’s national SDG progress in 2023–2025 shows broad alignment between project outcomes and wider sustainability achievements. The methodological review also identifies scope for improving the applicability and adaptability of PIERS indicators. Although primarily designed as a self-assessment tool, PIERS provides a systematic framework for integrating SDG principles into PPP management, especially in relation to SDGs 7, 9, 11 and 13. The study contributes empirical evidence and methodological insights for more sustainable public investment governance.