<![CDATA[Urban overpass projects require substantial volumes of concrete, reinforcing steel, precast components, heavy equipment, and logistics. When workflow is poorly controlled, waiting, repeated movement, rework, and excess material increase resource consumption and carbon emissions. This study quantifies the emission baseline and determines process-improvement priorities by integrating Lean Construction and Green Construction. A mixed case-study design was applied using MC-0 quantities, an A1-A5 Life Cycle Assessment boundary, Value Stream Mapping, the Waste Assessment Model, a waste-emission source matrix, and engineering expert consensus. The project inventory comprises 1,448.07 m³ of concrete, 171,713.30 kg of reinforcing steel, and 18 girders. A1-A3 emissions amount to 324.35 tCO₂e for concrete and 285.04 tCO₂e for reinforcing steel. Including girders, A4 transportation, and A5 construction activities raises the project baseline to 806.78 tCO₂e. The current-state VSM records a total lead time of 1,253.68 minutes and a process cycle efficiency of 45.32%. The future state reduces lead time to 1,068.55 minutes and increases efficiency to 53.17%. WAM ranks waiting as the dominant waste, followed by transportation and defects/rework. The expert-consensus scenario targets reductions of 40% in rework, 55% in equipment idle time, 10% in inefficient transportation, and 45% in material waste, avoiding 19.25 tCO₂e. The findings demonstrate that carbon management in infrastructure construction must combine low-carbon material decisions with workflow stabilisation, rework prevention, idle-time reduction, and logistics synchronisation.]]>
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