 The LBT has been divided into two phases of work; as of 2020, only Phase I is operational while Phase II remains in the planning and preparation stages.Zimmerberg I is about 10 km long and links Zurich with Thalwil and bypasses a section of the Lake Zürich left-bank railway line, allowing rail traffic to traverse the mountains more efficiently than traditional routes.During the 1990s, Switzerland embarked upon a major programme of modernisation and improvements across its railway infrastructure.