. The service life of the tunnel was assumed to be 30 years. The CO2 emission per day from the construction is calculated by dividing by the number of days. Pipelines cannot be constructed in a straight line, so we multiplied by 1.2 as an extension factor. CO2 emissions for installation and transportation of concrete pipelines were ignored because they are negligible. The thickness of a concrete pipeline was estimated to be 1/12 of the inside diameter. Therefore, the LCCO2 emission per day from building the pipeline, 𝐵 (kg-CO2/day), is described as: