Sankey diagram mapping of greenhouse gas emissions in road infrastructure projects: A cradle-to-laid perspective

• Pavement works may contribute to less than half of road project GHG; • Cement and diesel can be major GHG sources in a road project; • Sankey diagrams improve LCA transparency; • Differentiate pavement scope and road project scope is important. Road projects are key contributors to global greenhouse gas (GHG) emissions of urban civil infrastructure, accelerating climate change. Current assessment boundary focuses on pavement works, neglecting necessary GHG emissions components including subgrade, bridge, culvert, and temporary works at a sub-project level. To address this gap, our study extends the GHG emissions assessment boundary to sub-project levels, comprehensively evaluating cradle-to-laid emissions of a complex road project. Employing Sankey Diagrams, we map detailed emission flows with precision based on the bill of quantities of the project, offering a transparent and holistic visualization of emissions. Our analysis reveals that pavement works contributes 49% of the total GHG emissions in the studied road project. Notably, cement and diesel collectively account for 56.6% of GHG emissions (36.7% and 19.9% respectively), despite constituting merely 3.6% and 0.5% of the total material quantities by mass. This disproportion stems from their exceptionally high GHG emission intensities. Subsequent contributors include steel (12.2%) and bitumen (10.3%). By extending GHG emissions assessment boundaries, this study supports identifying high-impact emission sources from a broader perspective and enables more efficient mitigation strategies.