Abstract Among different kinds of infrastructures, tunnels are responsible for a significant proportion of carbon emissions; therefore, the carbon emission reduction of infrastructure is crucial for achieving global carbon neutrality. Previous studies often focused on a particular type of tunnel only, without considering and comparing the carbon emissions of different types of tunnels over the construction and operation phases. This paper compares the carbon emissions across the four common types of tunnels, namely, shield tunnels, New Austrian Tunnelling Method (NATM) tunnels, cut‐and‐cover tunnels, and immersed tunnels, during the construction, operation, and maintenance (O&M) phases. A consistent carbon accounting framework is established, and a case study of a subsea tunnel project in China is conducted to quantify emissions and perform sensitivity analysis. The results show that the construction phase accounts for approximately 60.3% of the total, while the O&M phases contribute around 39.7%. Among the three feasible schemes, the shield tunnel exhibits the lowest unit‐length carbon emissions (33.59 t CO₂/m), followed by the NATM tunnel (35.89 t CO₂/m) and the immersed tunnel (90.99 t CO₂/m). Sensitivity analysis identifies the concrete and electricity emission factor and tunnel segment length as the most influential parameters. Finally, this paper further suggests several key carbon reduction measures to contribute to the sustainability of low‐carbon tunnels.
Long et al. (2026) studied this question.