The Rastatt Tunnel represents the core engineering structure in planning approval section 1.2 of the new/upgraded Karlsruhe–Basle rail route. It will be tackled from May 2016 using two hydro-shield TBMs. The two single-track, roughly 4270 m long tunnel tubes will be lined with 50 cm thick reinforced concrete segments. The shallow location of the tunnel with minimal overburdens of less than 4 m, the subsidence-prone infrastructure and the presence of buildings, quite apart from having to undertunnel the Federbach low-lying conservation area protected by a frozen cover, place high demands on the engineering and process technology. Undertunnelling the busy Rhine Valley Railway, secured in advance by a ring-shaped brine freezing zone represents a particularly sophisticated task.