1 INTRODUCTION Life-cycle assessment (LCA) is one of the sustainability measurement tools used to quantify life- cycle environmental impacts of a product. Recently, pavement LCA applications have been in- creased with an emphasis on sustainability for the construction industry aiming at reducing carbon footprint of pavements. In order to accurately characterize the environmental impact of pave- ments, Federal Highway Administration (FHWA) recently published pavement LCA framework following the International Standards Organization (ISO) 14040 and 14044 standards (Van Dam et al; 2015; Harvey et el., 2016; ISO, 2006 ). There is certainly a need for an easy-to-use, and yet reliable, model capturing the nature of pavement–environment interaction that can be incorporated in pavement LCAs for the use of LCA experts as well as LCA users in agencies and industry. This can facilitate implementation of LCA with its most needed components related to the use-stage and improve sustainability of pavement systems. In general, some studies ignore the use-stage component completely (i.e., tex- ture, albedo, and carbonation) or simplify it to a degree that renders the need to use other software platforms unnecessary (Wang et al., 2012). Finally, most previous studies focused on energy con- sumption and/or GHG only as part of the impact characterization and the sole outcome of the LCA (Wang et al., 2014, Shakiba et al., 2016). However, a comprehensive pavement LCA, similar to other products and services, should ultimately include environmental impact categories other Functional Unit Choice for Comparative Pavement LCA Involving Use-Stage with Pavement Roughness Uncertainty Quantification (UQ) Mojtaba Ziyadi Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign 205 N Mathews Ave., Urbana, IL 61801, e-mail: ziyadi2@illinois.edu Hasan Ozer Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign 205 N Mathews Ave., Urbana, IL 61801, e-mail: hozer2@illinois.edu Imad L. Al-Qadi Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign 205 N Mathews Ave., Urbana, IL 61801, e-mail: E-mail: alqadi@illinois.edu ABSTRACT: An analysis of the use-stage for pavement life-cycle assessment (LCA) is pre- sented within a framework of an LCA tool developed for Illinois Tollway. Methodological choices that can significantly affect LCA results were evaluated in this study. The share of the use-stage in a comprehensive pavement LCA framework was evaluated with all life-cycle stages including materials, construction, use, maintenance, and end of life. The scope of the use-stage includes albedo, carbonation, and rolling resistance (including pavement roughness and texture components). Uncertainty of the pavement roughness and its effect on the results are investigated using Monte Carlo sampling technique. A discussion on the choice of functional unit and its effect in comparative LCA is presented and an appropriate functional unit is suggested. Four projects were selected as case studies to demonstrate the capabilities of the tool and proposed framework. A multi-point environmental performance evaluation was performed using four environmental indicators for comprehensive interpretation of results. The effect of each stage of LCA was eval- uated with emphasis on the results of the use-stage. Additional fuel consumption and emissions, resulting from roughness and texture, constituted the largest share of use-stage impacts while the effect of carbonation was limited. As traffic reduced and the share of the materials and construc- tion stage increased, the share of the use-stage could be decreased to 50% levels.