Zimmerberg Base Tunnel II Thalwil–Zug remains in planning

Zimmerberg Base Tunnel II is the roughly 10.6 km second stage of the overall project (20 km in total, following the first stage ZBT I completed in 2003), intended to make the Thalwil–Zug line fully double-tracked as far as Litti north of Baar. Switzerland's parliament included the project in the 2019 STEP 2030/35 expansion programme, and in March 2022 SBB presented a feasibility pre-study commissioned by the Federal Office of Transport (BAV). Realization is expected at the earliest from the late 2030s; concrete costs have not yet been specified.