The opinions expressed and arguments employed herein do not necessarily reflect the official views of ITF or OECD member countries. The work for this report was carried out in the context of the Decarbonising Transport Initiative of the International Transport Forum. The author thanks the participants of the ITF Decarbonising Passenger Transport Workshop, as well as Wei-Shiuen NG, Jari Kauppila, and Michael Kloth for their comments.