The Koralm Tunnel, located in Austria and with nearly 33 km one of the longest traffic tunnels in the world, is part of the Trans-European railway network. The paper presents a short project overview and describes the efforts to develop an optimal cross section by questioning general standards valid for shorter tunnels and to justify innovations. Major issues which have to be considered are tunnel lining, tunnel systems, drainage systems, traction system, track superstructure and aerodynamics. A project specific issue is the implication of the existing pilot tunnels.