1998 Volume 77 Issue 12 Pages 1184-1192
Life cycle assessment (LCA) is expected to be a useful measure for us to evaluate environmental impacts associated with products or processes, so that we could improve our production systems for sustainable development. For this purpose, we have developed a novel mathematical tool called Process-relational Model. In the model, we have improved the principle of input-output analysis so as to include joint production. This improvement has enabled us to overcome difficulties of LCA in retracing complicated repercussions among production systems and in allocating environmental emissions among multiple products.
Then life cycle CO2 emissions of electric and gasoline vehicles have been estimated with this model. We have shown that production and driving of electric vehicles cause less CO2 emissions than those of gasoline vehicles. Our analysis has also indicated that the difference detween electric and gasoline vehicles dramatically changes depending on traffic situation. Namely the difference becomes larger, as average velocity of vehicles becomes lower. Concerning electric vehicles, we have compared CO2 emissions caused by production with those caused by driving. The share of production has increased, as average velocity becomes higher.
In conclusion, we have clarified directions of research and development of electric and gasoline vehicles for sustainable energy system.