Reducing carbon dioxide emissions during the construction phase of road projects is pivotal for advancing the zero-carbon agenda. This paper presents a comprehensive approach to estimate carbon dioxide emissions and analyze their sources in road construction, leveraging the principles of life cycle assessment (LCA). Additionally, it introduces an innovative uncertainty analysis method that combines spectral matrix and Monte Carlo simulation, providing a robust examination of major uncertainties affecting assessment outcomes. By examining four road construction projects as case studies, the paper elucidates the characteristics of carbon dioxide emissions in terms of sources, temporal and spatial distribution, and scrutinizes the uncertainties inherent in inventory data. Findings reveal that concrete utilization stands out as a primary source of carbon dioxide emissions during road engineering construction, with material production representing the most significant emission stage. Furthermore, carbon dioxide emissions from key construction activities such as surface layering, retaining wall construction, and subgrade preparation exhibit notable concentration. The paper concludes with actionable measures for emission reduction during road construction, including the adoption of recycled materials, optimization of construction machinery configuration and use of clear energy.