The implementation of MARPOL Annex VI in the North and Baltic Sea Sulphur Emission Control Area (SECA) has raised economic concerns among shippers and shipowners, as well as spurred policymakers to appeal to various interests, such as citizen health, export industry competitiveness, and consumer prices. To justify their cases, policymakers and stakeholders have commissioned various agencies to monitor the implementation’s effects upon sustainability, especially regarding a potential modal shift from sea to road transport. This article thus reviews some of these commissioned studies in order to analyse the effects of the implementation and the possibility of modal shift. It also provides an agent-based simulation study of route choice for comparatively high-value cargo from Lithuania in the east to the United Kingdom in the west. Ultimately, the results of our TAPAS study do not provide concrete evidence supporting a modal shift from sea to road transport and indeed, they indicate that a shift is unlikely to occur.