Hierarchical Quantification of CO ₂ in Transportation Infrastructure Maintenance: Identifying Key Contributor and Targeting Reduction Department

This paper introduces a hierarchical quantification framework based on process-based life cycle analysis for evaluating CO 2 emissions from departments in transportation infrastructure maintenance. The method decomposes the maintenance process into a carbon responsibility chain consisting of “Maintenance Department–Maintenance Task–Maintenance Activity–Resource Utilization,” enabling a systematic mapping of CO 2 emissions to the corresponding responsible departments. The method allows users to quantify the itemized CO 2 emissions and identify high-emission activities and resources that are responsible by department, assisting in the development of targeted CO 2 reduction strategies. Case studies of expressway, bridge and tunnel maintenance in Shanghai show that the road maintenance department for expressways, the structure maintenance department for bridges and tunnels contribute 70.2%, 69.7%, and 84.7% of emissions in their categories, with annual values of 32.69, 23.60, and 41.40 ton/single-lane kilometer, respectively. At the activity level, “Mechanical paving of SMA asphalt concrete,”“Manual paving of medium-graded asphalt concrete,” and “Tunnel segment joint sealing” are the primary high-emission activities in their respective categories, accounting for 29.4%, 13.2%, and 25.2% of their respective emissions. Accordingly, relevant government agencies and enterprises should prioritize targeted CO 2 reduction strategies for them, such as warm-mix asphalt substitution, low-carbon material replacement, and engineering efficiency optimization. In the case studies, these measures are estimated to reduce CO 2 emissions by 16.2% for expressway maintenance, 9.0% for bridge maintenance, and 3.8% for tunnel maintenance. The proposed framework offers a flexible and effective tool for reducing CO 2 emissions in transportation infrastructure maintenance and provides valuable insights for policymakers and industry stakeholders.