Switzerland’s 57 km Tunnel Is the World’s Longest—But a French Project Could Soon Break the Record

Stretching over an astonishing 57 kilometers and plunging as deep as 2,300 meters beneath the Swiss Alps, the Gotthard Base Tunnel stands as a true marvel of modern engineering. Connecting Erstfeld to Bodio, this colossal rail tunnel has held the title of the world’s longest and deepest railway tunnel since its opening for freight traffic in December 2016. Yet, this record could soon be challenged by an ambitious French-Italian venture aiming even longer.

The Gotthard Base Tunnel: A Swiss Engineering Triumph

Construction on the Gotthard Base Tunnel began in 1999 and took 17 years to complete. Unlike some large European infrastructure projects notorious for budget overruns, the Swiss managed the enormous task with remarkable discipline. Initially estimated at 6 billion Swiss francs (about 6.3 billion euros), costs ultimately doubled to 12 billion francs (roughly 12.3 billion euros). However, since 2008, spending stabilized and the project finished a full year ahead of its planned 2017 completion.

The tunnel consists of two parallel tubes dedicated to rail traffic, linked every 325 meters by safety passages. In total, it encompasses 152 kilometers of galleries, nearly 290 kilometers of track, and over 380,000 sleepers. Its nearly flat gradient was engineered to maximize speed and reduce energy consumption—vital for high-volume freight and passenger trains alike.

At 57 km long, the Gotthard Base Tunnel surpasses other famous tunnels like the 53 km Channel Tunnel between the UK and France and Japan’s 54 km Seikan Tunnel by a significant margin.

A Record-Breaking Construction Feat

At the height of construction, up to 2,400 workers labored around the clock in three shifts. The project deployed gargantuan tunnel boring machines—each about 450 meters long and weighing 2,700 tonnes, with a diameter reaching 9.5 meters. These mechanical giants bored through tough Alpine granite at an impressive rate of six rotations per minute, carving out 80% of the tunnel; the remaining 20% was excavated via controlled blasting.

This massive undertaking not only required technical excellence but also meticulous project management to maintain safety and schedule.

Connecting Northern and Southern Europe

The tunnel serves as a critical link in the rail corridor connecting northern European industrial hubs—Belgium, Germany, the Netherlands, and Switzerland—with southern centers in Italy. The logistics benefits are profound, accelerating freight transport between the key ports of Rotterdam and Genoa. For travelers, the tunnel slashes travel times and enhances reliability on routes like Zurich to Milan.

From Vision to Reality: The Tunnel’s History

The idea for a base tunnel under the Gotthard was first conceived back in 1947 by Swiss engineer Carl Eduard Gruner. However, it wasn’t until national referendums in the 1990s that the project gained official approval. Construction officially commenced in 1999, culminating in the final breakthrough in 2010.

Four named tunnel boring machines—Sissi, Heidi, Gabi I, and Gabi II—performed the arduous task of excavation while simultaneously installing pre-fabricated concrete lining to stabilize the tunnel walls. Today, one of the massive 9.5-meter cutting discs is displayed in a museum, commemorating this monumental engineering achievement.

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Trains Whizzing at 200 km/h and Environmental Gains

Passenger trains now speed through the tunnel at up to 200 km/h, with two trains running each hour in both directions. The connection between Zurich and Milan has been cut by about 30 minutes, a substantial improvement for commuters and tourists alike.

Besides improving travel efficiency, the tunnel plays an essential role in reducing road traffic in the sensitive Alpine environment. By facilitating increased freight movement by rail and coupling this with higher tolls on trucks, it helps preserve the region’s natural beauty by lessening truck traffic.

France’s Mont d’Ambin Tunnel: A New Challenger on the Horizon

Not far from this Swiss engineering wonder, another tunnel project is underway that promises to surpass the Gotthard Base Tunnel’s length. The Mont d’Ambin Base Tunnel, spanning approximately 57.5 kilometers, will form part of the vital trans-Alpine rail link between Lyon and Turin.

Once completed—expected around 2032—it will connect Saint-Jean-de-Maurienne in France with Susa in Italy via two parallel tubes designed for both freight and high-speed passenger trains. The maximum speed inside this tunnel will reach 220 km/h, aiming to further ease road congestion across the Alps.

Currently, about 14 kilometers have been excavated out of the 115 km required for the twin tubes. This major infrastructure project is co-funded by France, Italy, and the European Union, highlighting its strategic importance for European connectivity.

The World’s Longest Tunnels: A Quick Overview

To put these giants in perspective, here are the top ten longest railway tunnels completed or in progress worldwide:

As the Mont d’Ambin tunnel progresses, it will likely set a new global benchmark for tunnel length and reinforce the importance of efficient, sustainable transport links across Europe’s formidable Alpine barrier. Meanwhile, the Gotthard Base Tunnel remains a shining testament to Swiss precision and engineering excellence—a true colossus beneath the mountains.