["Oxford Bulletin of Economics and Statistics, Volume 88, Issue 2, Page 198-212, April 2026. ", "\nABSTRACT\nHow does withdrawing from a free trade agreement affect maritime cargo volumes? Are there external effects on freight transport between third‐party countries? Using Brexit as a case study, in a difference‐in‐differences analysis of 2013–2024 port‐level data, I find a 21% decrease in EU‐UK roll‐on roll‐off (Ro‐Ro) volumes, and a 60% decrease in Ireland‐UK volumes. I find an 88% increase in Ireland‐France cargo, indicating a diversion from the UK ‘land‐bridge’ between Ireland and mainland Europe to the direct route. I estimate that emissions would be roughly 35% lower on the direct route, revealing an externality on transport between two third‐party countries.\n"]