Decarbonization is one of the key research topics in the marine industry. Nowadays, various sets of measures (e.g., technical, operational, market-based) are being investigated to make this process smooth, efficient, and economically viable. Among these measures, alternative fuels are widely recognized as a very promising solution for reducing shipping emissions in the short term, while slow steaming reduces a ship's primary energy needs, thereby directly lowering emissions if the ship’s power system relies on fossil fuels. Furthermore, numerous studies have shown that a single-measure approach is not the optimal solution, and therefore, combining different measures is recommended. This paper presents research into the simultaneous effects of alternative fuels and slow steaming on the emission reduction of a ferry operating between Italy and Croatia. This work is part of broader transnational goals to establish green ferry and cruise corridors in the ADRION region. The effects of speed reduction on both the ship’s energy needs and transport work are considered. A life-cycle assessment (LCA) and life-cycle cost assessment (LCCA) have been conducted, along with sensitivity and uncertainty analyses of the most dominant parameters. Analysis of ship technical parameters and operational profile shows that the crew is applying slow-steaming principles already, thus contributing to fuel savings and emission reduction. Potential utilization of alternative fuels offers further possibilities towards green ferry corridors in the ADRION region.