The project had been challenged by environmental groups which argued that the project could threaten water resources in the Semmering region and the UNESCO World Heritage status of the existing railway.

Last year the Administrative High Court ruled that some of the expert testimonies in the environmental assessment were inaccurate and would need to be amended. As a result, the court imposed a temporary ban on construction. These expert testimonies were subsequently amended but another appeal was launched against the updated assessment. This appeal has now been rejected and the court says the assessment is now in line with legal requirements.

The court also decided that the UNESCO World Heritage status is secure because this covers only the existing railway line, which will not be affected by the construction of the tunnel.

The court decision enables Austrian Federal Railways (ÖBB) to restart construction and the tunnel is expected to open in 2025 as scheduled.

The 27.3km tunnel will cut journey time from Vienna to Graz and Villach by 40 minutes.