The railway L890 is an important link between the Zurich area and the Grisons as well as Austria and carries 180 passenger and freight trains every day. The 453 m long, excavated Bommerstein Tunnel was put into operation in 1941. It has a horseshoe profile and consists mostly of masonry. Around a fifth of the vault’s length is sealed only by sprayed mortar. With the planned partial renewal, the railway installations will be renewed and the building structure repaired. The works will guarantee the structural and operational safety as well as the suitability of the tunnel for the next 30 years. Measures: - Sealing of the tunnel lining; - Invert and track lowering; - Construction of rescue niches; - Renovation of the drainage system; - New track superstructure and substructure (concrete sleepers); - Adjustment of the structure gauge; - New conductor rail; - Adjustment of the cable systems; - Repair of the tunnel portals. - Bottom and track lowering, substructure rehabilitation starting at the tunnel portals - Temporary and definitive Tiefrietbach stream culvert The execution of the technical measures takes place under operation in continuous single-track operation phases.