Since January 1, 2017, 25.25 m EuroCombis (ECs) with a maximum gross vehicle weight rating (GVWR) of 40 t are allowed in German national freight transport on a specified part of the road network. This decision was based on a field test of the potential risks of the EC operation that was carried out under the surveillance by the Federal Highway Research Institute (BASt). However, the assessment mainly focused on safety concerns rather than on environmental impacts. To gain additional insights on the climate effects related to the EC use, a dedicated study was initiated by the state government of Baden-Württemberg and Daimler AG. In this paper, we present the impact of ECs on the modal split of national road and rail freight transport and the corresponding impact on greenhouse gas (GHG) emissions. Analysis was carried out for a 2010 scenario mirroring the conditions of the field test and for a 2030 scenario with a non-restricted highway network.