Based on the Theory of Planned Behaviour, this study explains sharing economy platform usage intention. Our results based on PLS-SEM estimations with survey data (N = 655) from the carpooling context show that sharing orientation (i.e. sharing usage instead of owning/buying), grassroots engagement (i.e. non-profit organisation driven by volunteers), and platform authenticity (i.e. loyalty to the original carpooling practice) are strong determinants of people's attitudes towards the carpooling platform, while trend orientation (e.g. the 'sharing economy' paradigm) is not significant. This implies that while digitalisation can optimise older practices (e.g. hitchhiking), online platforms facilitating contemporary sharing practices need to be embedded in the original sharing ethos and values to raise usage intention - even though the sharing economy has become mainstream.