The incredible organisation of tunnel construction and repair projects often betrays the scope, complexity and work that goes into them, with everything from the conveyor belt systems to the gargantuan tunnel boring machines designed to perfectly suit the project.

An excellent example of both an ambitious construction project and indeed an ambitious repair project can be found with the world’s longest railway tunnel, the Gotthard Base Tunnel.

Decades in the marking and with a need that has existed for centuries, the Gotthard Base Tunnel was a significantly faster, safer and shorter route through Switzerland, fundamentally changing the route between the south and north of Europe in the process.

However, just seven years after it was opened, it would be faced with a repair job almost as ambitious as the initial tunnel.

The Great Gotthard

On 10th August 2023, a freight train on the northbound part of the tunnel derailed whilst inside the tunnel. Whilst nobody was injured, sixteen wagons derailed, smashing against the rails and tunnel edges, as well as scattering huge amounts of cargo destined for northern Europe.

According to an official report, eight kilometres of track, 20,000 sleepers and a lane change were significantly damaged. The latter issue was arguably the most significant in the short term, as it was a vital part of the separation between the two tubes, and meant that the second, undamaged tunnel could not initially be used to run passenger trains.

The Swiss Transportation Safety Investigation Board found that a wheel tread broke, which caused the wagon to be dragged along for several kilometres before finally flying off the rails near a tunnel tube switching point.

A temporary maintenance gate was fitted to allow freight trains to pass in the other tunnel, but passenger services were completely redirected through the so-called “panorama route” that added several hours and rail changes to the journey.

This route was the old Gotthard Pass route, a much longer railway route that goes through the older Gotthard Tunnel but largely climbs up and over parts of the Alps through the former historic route.

Whilst the Gotthard Base Tunnel takes roughly 35 minutes from one side to the other, the older Gotthard railway takes several more hours, something that was accepted due to its nature as an aesthetically pleasing tourist route rather than the primary freight and commuter line through the Alps.

There was a hope that the repairs would be completed by the end of 2023, but when it turned out that the eight kilometres of damaged railway would not only need to be cleared, repaired and realigned but outright replaced, this added another year to the timetable.

Passenger trains were allowed to slowly circle through the tunnel in the undamaged tunnel, but the capacity was still significantly lower than before.

The complication with using the second bore is one of safety; freight trains were effectively using the emergency safety tunnel, and there was a fear that passengers would not be able to evacuate in case of an emergency.

Ultimately, this led to the decision to close and completely repair the underlying concrete slabs, the rails and the sleepers, an astonishingly complex operation rivalling a lot of major tunnelling projects in the first place.

The capacity would be gradually increased as the sections were repaired, and weekend passenger services did see some expansion as a result as well.

However, it would take until 3rd September 2024 and 13 months of round-the-clock repairs for the tunnel to be fully reopened again, with a level of service mirroring what had been seen up until that point.

The consequences of the derailment have been severe. Outside of the estimated £150m costs in repairs and lost revenue, the incident highlighted the importance of redundancy and a weakness in the contingency developments in the tunnel itself.

When the tunnel reopened, there was a temporary speed restriction at the lane changes to avoid derailment, reducing the top speed of trains from 140 mph to 100 mph, as well as an increase in the use of train control equipment and imaging data to provide early warning signs of a derailment and allow action to be taken quickly.

As well as this, there has been some consideration for installing a trackside derailment detection system that would provide an early warning and potentially prevent incidents, but this would require a substantial level of planning and is unlikely to appear any time soon.

Finally, it highlighted the value of one of the oldest, longest railway tunnels in the world, and in 2025, there is set to be upgrades and renovations to the historic Gotthard railway route to ensure that it is an effective redundancy system in the future.