Life cycle greenhouse gas emission of wooden guardrails: a study in Nagano Prefecture

Greenhouse gas (GHG: specifically CO2, CH4, and N2O) emissions over the life cycles of type no. 1 and no. 3 wooden guardrails widely used in Nagano Prefecture were evaluated. A comparison with steel (guardrail and guard pipe) types was conducted to investigate the GHG emission reduction effect of wooden guardrails. It was shown that the greatest GHG emissions for all types of guardrails occur during the raw material procurement and production process. The amount of total (life cycle) GHG emissions for pressure-injected wooden type no. 3 guardrails (92 % of steel guardrails and 72 % of steel guard pipes) shows that replacing steel with this type of wooden guardrail can reduce GHG emissions. On the other hand, comparison of the GHG emissions for pressure-injected type no. 1 guardrails with steel (175 % of guardrail; 138 % of guard pipe) shows that no reduction is achieved. When the disposed wooden beams (painted type no. 1; painted and pressure-injected type no. 3) are chipped and used for energy as a substitute for Type-A heavy oil, the volume of the GHG emission reduction significantly exceeds the GHG emission volume, and GHG emissions can be reduced by up to a maximum of 117.67 kg-CO2-eq/m.