The Gotthard Base Tunnel was hailed as the “project of the century” when it opened in 2016 after twenty years of work. Stretching 57 kilometres under the Alps, it remains the longest railway tunnel in the world, an engineering feat that overcame enormous technical challenges despite some unexpected complications. The road tunnel project, by contrast, is turning into a nightmare for the contractors. Although the new bore is less than a third the length of its rail counterpart, uncertainty over the geological conditions has thrown any realistic completion date into doubt.
Excavation of the new road tunnel, which runs parallel to the existing one opened in 1980, began in February 2025 with an estimated cost of €2.3 billion. Two tunnel boring machines (TBMs) were deployed, one from the north and one from the south. While the TBM starting from Göschenen has been progressing without incident, “Paulina”, the machine operating from the Airolo side, has suffered more stoppages than metres advanced. The first halt occurred in July 2025 after just 192 metres, when the cutterhead was swallowed by an internal landslide.
Investigations by the Federal Roads Office (Ustra) have revealed further problems caused by unstable rock in the 500 metres beyond the blockage. The authorities therefore decided—inevitably, though not without debate—to suspend the TBM and continue excavation using traditional methods with explosives and hydraulic hammers. This has also required the construction of an access gallery to enable counter-excavation towards Göschenen. The change is expected to add around €20 million in costs and extend the works by up to eight months.
A legitimate question now arises: was this simply an unforeseen event, and what might the future hold? Beyond the official statements from Ustra, doubts persist, reinforced by an investigation by the Swiss-German and Romansh public broadcaster Srf. According to information and testimonies gathered three months after the incident, the stoppage may be linked to ignored geological reports, unheeded warnings and an overly superficial approach to mountain engineering—particularly troubling given that experience from the first tunnel was available and seemingly overlooked.
Confidential sources within the site, cited by Srf, suggest the situation could prove even worse than the official estimates. The completion of the new tunnel might be delayed by up to two years, pushing the opening date from 2030 to 2032. This would also postpone the renovation of the first road tunnel, which has been in operation since 1980.
How could such a catastrophic scenario have arisen? According to the same Srf investigation, early warnings date back to 2016, when a simple exploratory borehole in the same area was swallowed by crumbling, unstable rock. Two years later, a detailed geological report advised excavating the first 400 metres using traditional methods before deploying the TBM in more stable ground. However, a subsequent, more optimistic assessment revised that guidance, leaving the project team uncertain and divided over how to proceed.
The cost increase will not be limited to the €20 million estimated for switching from mechanical to traditional excavation. The stoppage of the TBM is also driving up operational costs, particularly for labour, as the site has shifted from two shifts over five days to round-the-clock work—three shifts, seven days a week.
Piermario Curti Sacchi
