 The NRLA imitative sought to provide better alternatives to the steep mountain railways across Gotthard, Ceneri and Lötschberg through the construction of a number of base-level tunnels that enabled trains to more rapidly and efficiently traverse the Swiss Alps.The Zimmerberg Base Tunnel (ZBT) was one such tunnel constructioned under the initiative.Phase I of the Zimmerberg Base Tunnel is a major feature of the route between Zurich and Thalwil.