Estimating quantity and equity of carbon emission from roads based on an improved LCA approach: the case of China

Purpose

Carbon emission from roads is an important contributor of a nation’s greenhouse gas emission that causes climate change. However, the existing life cycle assessment (LCA) analysis of road carbon emissions focus on project-level, ignoring regional differences. Significant challenges remain in developing regional road’s carbon emission mitigation strategies. This study estimates the quantity of carbon emissions from roads in China and calculated the regional equity of road carbon emissions.

Methods

An improved LCA approach, which considered the regional difference of raw materials’ carbon emissions, carbon emissions caused by traffic jam and road category, was applied to calculate the quantity of carbon emissions of roads. Sensitive analysis was conducted to find the key influential factors. Gini coefficient was used to calculate the equity degree of carbon emissions by roads based on the LCA results. The decomposition model of Gini coefficient is applied to analyze the causes of carbon emission differences.

Results

The total national carbon emissions by roads in 2019 increased by 2.2 times compared to 2009. Carbon emission from roads in the operation phase increased from 62% in 2009 to 83% in 2019. The functional unit for expressway in this study ranging from 1646 to 1794 t CO₂e/km in 31 provinces. An estimated uncertainty of plus or minus 4% of the traffic flow allocation between expressway and other roads makes an increase of 38% or a decrease of 15% of the life cycle emission. The overall Gini coefficient of carbon emissions from roads in China is under the warning line of 0.4. Outer inequity between regions contributes 88.83% of the whole inequity and the most developed three regions contribute 66.23%.

Conclusions

Large quantity of road construction in the past in China makes the burden of carbon emission transfer from the construction phase to the operation phase. Regional differences of raw materials’ carbon emissions, traffic jam, and road hierarchy are important factors influencing the LCA-based estimation of road carbon emission. To improve the national equity degree of road carbon emission, quota allocation of road carbon emission rights between regions and cross-regional carbon emission reduction policies would help.