This study aims to establish an evaluation method for life cycle CO₂ emissions of transport system including vehicle running, infrastructure construction, vehicle production and other elements. The case study treats light rail transit (LRT) development project. Proposed method has a framwork which can analyze effects of route bus abolishment, decreasing private car use and traffic congestion caused by reduction of road lanes. This study utilizes microscopic traffic flow simulation to illustrate traffic congestion from signals and turnings of vehicles and mixed traffic between LRT and vehicles. Using microscopic traffic flow simulation enables to consider running behavior of LRT and vehivles on evaluation of life cycle CO₂ emissions and the sensitivity analysis.