Capturing time effect of pavement carbon footprint estimation in the life cycle

The carbon footprint of pavement in the life cycle is regularly calculated by aggregating the inventory of greenhouse gases (GHGs) at different timings. Comparisons by the nominal values, therefore, ignore the temporal information and may lead to biased estimation of the environmental impact. This study proposed a time-dependent methodology to dynamically assess the global warming potentials (GWPs) incorporating two time parameters, time of evaluation (TE) and time horizon (TH). The former defines the time period of life cycle assessment (LCA) and the latter decides when the GWP is evaluated. Two case studies were conducted. The first case study indicated for design lives (viz. TE) of 20 y and 40 y, the GWPs are significantly overestimated by 59.7% and 33.0%; the second case study indicated that 66 y is the threshold value for TH that brings different policy preference for two emission plans. Together with the concept of “time dominance”, a generic implementation framework was established for the methodology so that users can justify the preferences of alternatives at any THs. The developed methodology can assist decision makers in understanding the real impacts of carbon emission within and beyond pavement life cycle.