Objective. Provision of social capital may bring large-scale change in a socio–economic system. Therefore, the system boundary of LCA for infrastructure should be larger than that for general products. “Extended Life Cycle Environmental Load (ELCEL)” is a concept for evaluating changes in comprehensive environmental impacts of infrastructure projects. However, uncertainty of the results increases when the boundary of evaluation is extended because it contains some uncertaint data given by forecast models. In this study, a framework for setting the system boundary and analyzing the uncertainty of the LCA results for a transport infrastructure project is proposed.
Results and Discussion. The system boundary is set step-wise, as follows, 1) “System Life Cycle Environmental Load (SyLCEL)” that includes infrastructure’s lifecycle and the activities using it, 2) “ELCEL-1” that includes SyLCEL and another competitive traffic mode, and 3) “ELCEL-2” that includes ELCEL-1 and alternative route. Life Cycle Inventory (LCI) shows the difference between the results of SyLCEL and ELCEL. In a case study for Light Rail Transit (LRT), changes in car traffic conditions and route choices after LRT provision are considered by ELCEL. A sensitivity analysis shows a demand shift from vehicle to LRT in the LCI result. However, this data contains uncertainty caused by the forecast. Uncertainty analysis shows that the result may change if these data have a wide range of errors.
Conclusions. The result of LCI for infrastructure depends on the system boundary setting. It is also important to conduct an uncertainty analysis to improve the reliability of the LCA result. If the uncertainty of LCI results is very large and is caused by the errors of input data, two countermeasures can be employed. One is conducting additional research to decrease the uncertainty of input data. However, in cases where additional research is not possible or effective, it is necessary to determine whether the inclusion of uncertaint data in the analysis must be avoided to ensure high reliability of the result.
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