The Decarbonization Potential of a New Short-Sea Ro-Pax Corridor in the Baltic Sea: Methodology and a Case Study of the Gdynia–Liepāja Connection

Maritime transport entered the EU Emissions Trading System (EU ETS) in 2024, turning a route’s carbon performance into an economic variable. Existing studies examine this on established routes; the case for a new (greenfield) short-sea corridor under the post-2024 regime remains unaddressed, particularly in the under-served south-eastern Baltic. This study proposes a transparent, transferable methodology linking multi-criteria route selection, a lane-metre demand model, a speed-dependent fuel-consumption model and a consignment-level modal-shift carbon balance, applied to a prospective Gdynia–Liepāja Ro-Pax connection (148 nautical miles). At high deck utilization, each freight unit shifted from the 850 km road alternative avoids roughly 300–380 kg of CO2 (a 44–55% reduction), because a short-sea leg replaces a long road haul rather than because the ferry is cleaner per tonne-kilometre. The benefit is conditional: the corridor is climate-beneficial only above a break-even freight-deck occupancy of about 45% at design speed, falling to about 34% under slow steaming. Across the demand scenarios (about 17,900–35,900 units per year), it avoids on the order of 10,000–13,400 t of CO2 annually under high demand, while under low demand the annual balance ranges from a small net increase at design speed to a modest saving under slow steaming. The corridor relieves the congested Suwałki Gap and aligns with smart-port enablers, providing a replicable decision tool for operators and port authorities.