Current standard decision-making models for transport are based on a so-called ‘weak’ concept of sustainability, in which any negative impact can be offset by any positive impact, so as to recommend ‘optimal’ solutions. In reality, practitioners often do not follow these recommendations, and theoreticians increasingly criticise the fundaments of weak sustainability. In STUNT we therefore explore alternative theoretical concepts of sustainability, but we also systematically analyse past transport projects to identify the factors that are decisive in real-world planning. We use these insights to build and test a new framework for strong sustainability appraisal. STUNT is a collaboration between VUB-MOBILISE and VUB-COSMOPOLIS and is sponsored by FWO.