Benchmarking road transport sustainability: A composite index approach

Road transport plays a critical role in economic development but remains a major source of energy consumption, greenhouse gas emissions, and road-safety risks. Despite extensive research on sustainable transport, there is still no harmonized, road-specific, cross-country benchmarking tool that allows consistent comparison over multiple years. This study addresses this gap by developing the Composite Road Transport Sustainability Index (CRTSI), a transparent and reproducible framework designed to assess and compare road transport sustainability across 32 countries over the period 2011–2021. The CRTSI is constructed using six indicators reflecting the economic (GDP per capita, freight transport activity), environmental (Road energy consumption, road CO2 emissions), and social (road traffic fatalities, motorization rate) dimensions of sustainability. This study applies a harmonized and coherent benchmarking configuration that integrates min–max normalization, objective weighting through Principal Component Analysis (PCA) applied to pooled panel data, and linear aggregation into a single composite index, enabling consistent cross-country comparison and multi-year monitoring of road transport sustainability. The robustness of the index is assessed using the Kaiser–Meyer–Olkin (KMO) measure, Bartlett's test of sphericity, and extensive sensitivity analyses based on alternative weighting schemes. The results of the cluster analysis for the year 2021, using the K-means clustering algorithm, reveal substantial cross-country heterogeneity and a clear three-tier sustainability landscape. Nordic countries emerge as frontrunners, driven by low-carbon energy structures, efficient road transport systems, and strong safety performance. In contrast, Germany, Poland, and Turkey rank lower due to energy-intensive freight activity, higher fossil fuel dependence, and elevated road fatality rates, despite otherwise advanced transport systems. Several Southern European countries, including Tunisia, display intermediate and improving trajectories. The CRTSI provides policymakers with a robust decision-support and benchmarking tool, demonstrating that leadership in road transport sustainability is driven primarily by policy choices rather than income levels alone.