CO2 emissions mitigation from road construction activities is one of potential pathways to deal with climate change.Aiming to estimate the magnitude of CO2 emissions and identify the uncertainty from construction phase of real entire road projects including road structures and earthworks apart from pavement,this paper applied Life Cycle Assessment on 20 asphalt and 18 concrete road projects which were classified into high-grade road and low-grade road.The impact of uncertain data source and system boundary on results was checked,followed by discussion with previous studies.The findings show that average total emissions per kilometer per lane are variety but nearly 500t for concrete and 1500t for asphalt road (1.92 times higher than that of studies only considering pavement,27% higher than that of studies without considering bridge and tunnel).Materials contribute to largest emissions,but off-road machinery even accounts for 45% of total emissions in concrete road.Emission of off-road machinery in asphalt road in this study is 13.6 % higher than that of studies only considering pavement.Efforts should focus on earthworks and structures,and on improvement in off-road machinery performance not only on materials.Lack of chemical reactions for cement and pre-consumption for fuel could underestimate 15% of total emissions for asphalt road and concrete road,respectively.Recycling steel and electricity structure improvement play a weak role in road construction emissions reduction.For both concrete road and asphalt road,emissions of low-grade are about 13% lower than that of high-grade road.