A presentation on industrial retrofit as a transition solution for decarbonizing the existing vehicle fleet. Industrial solutions are available and scaling up, but lack of harmonized regulatory requirements is hindering deployment. Differences in national regulatory frameworks directly affect retrofit sector development across countries. Testing at vehicle level is necessary to account for retrofit system impacts. A forthcoming UNECE Regulation should provide a clear approval framework, establish a streamlined approval process, and ensure mutual recognition of approvals granted by Contracting Parties.