The Need for Uncertainty Propagation in Life Cycle Assessment of Vehicle Technologies

The aim of this article is to enhance the interpretation of the environmental burden of different vehicle technologies, by incorporating uncertainty and variability in the end result and understanding the sensitivity of the results. In most life cycle assessment studies, environmental impacts are shown with single values. The complexity, uncertainty and variability of the life cycle system are not well approximated with single values. Single values approximate the environmental impact of a vehicle but fail to provide a wider view on the possible effects. The article argues that uncertainties are an inherent part of LCA and should be made explicit in the result. Many sources of uncertainty have been identified and included in the results. In this paper two distinct classes of uncertainties are investigated, namely parameter uncertainty and modeling uncertainty. Firstly, parameter uncertainty deals with the variability of the car market, the mismatches between the theoretic values derived from homologation Driving Cycles and the unrepresentativety and inaccuracy of the background data (data from general life cycle inventory databases). The most spectacular differences between tailpipe emissions measured from a homologation driving cycle and the real- life values concern the emissions of NOx and CO. The contribution of the market variability to the overall uncertainty is included in the result and is more significant compared to the uncertainties generated by the driving cycle. Secondly, modeling uncertainty deals with the uncertainty in life cycle impact assessment due to normalization, weighting and methodology. The choice of the Life Cycle Impact Assessment method itself introduces an uncertainty and is analyzed.