A Look at the Longest Deepest Traffic Tunnel in the World

The Gotthard Base Tunnel stretches 35.5 miles (57.5 km) under the Alps in Switzerland. Completed in 2016 after a nearly 20 years of construction, the tunnel overtook the Seikan Tunnel in Japan as the longest passenger tunnel in the world.

Aside from being the longest underground passenger tunnel in the world, it is also the deepest ever constructed. Part of the tunnel bores under Piz Vatgira, a nearly 10,000-foot tall mountain in the Swiss Alps. Underneath the peak of this mountain, the tunnel sits 1.42 miles (2.3 km) underneath the surface. That equates to 1.5 times the deepest point in the Grand Canyon, all sitting over the heads of the passengers on the high-speed trains that travel through the tunnel.

The tunnel itself is actually made up of two different tunnels which run side by side which connect at 2 different points to allow for interchanges in the case of an emergency in either tunnel.

In terms of numbers, 28,200,000 long tons of rock were excavated at the equivalent volume of 5 Great Pyramids of Giza. The end to end length of the tunnel may be just 35.5 miles, but because there are two tunnels, the total tunnel distance in the project is 94.5 miles (152 km). During the first 6 months of operation, the tunnel transported an average of 9,600 passengers per day. Upon completion, the Gotthard tunnel also beat the previous record-holding tunnel in Japan by 2.2 miles (3.6 km)

Image Source: Wikimedia Commons

More astounding than the engineering feats of the tunnel is perhaps the total cost of the project. Over 17 years, 9.56 billion Swiss Francs were spent on the project, which equates to 9.84 billion USD. That’s the equivalent cost of building 23.5 empire state buildings, adjusted for inflation – but money wasn’t the only sacrifice it took to dig this massive tunnel.

9 men lost their lives in the construction of the Gotthard Base Tunnel all from construction-related accidents.

Part of the reason that the tunnels were bored so deep and thus so difficult to construct has everything to do with the possible grade allowed in rail design. Engineers had to construct the tunnel with either a negative grade or at an incline below the ruling grade for the high-speed trains on the track. A ruling-grade is essentially that, a grade that controls whether a train can travel across a rail line or not. Ruling grades vary by train, but if a train tries to travel over a track steeper than it’s ruling grade, then its wheels will slip. In the case of the Gotthard tunnel, the average grade is just .16%, but the maximum grade in certain sections of the tunnel is 6.76%.

Engineers went to such great effort to keep the tunnel and thus the rail line as flat as possible in order to reduce operating costs and increase the safety of the routes.

Image Source: Wikimedia Commons

It can be hard to grasp just how massive in length this tunnel is just by sheer distance, so let’s put it in the context of travel time. It takes the highspeed trains servicing the Gotthard Base tunnel twenty minutes to travel through the tunnel in either direction at an operational speed of 124 mph (200 km/hr).

If you were to try and play the popular game of holding your breath while traveling through the tunnel, you simply wouldn’t be able to make it. While you might not be able to make it, there is one man who could – Aleix Segura Vendrell, the current record holder for longest breath hold at 24 minutes and 3 seconds.

Image Source: Wikimedia Commons

So, you might have to be a world record holder to be able to hold your breath through the tunnel, but anyone traveling on the Gotthard Line in Switzerland can take the journey through the current longest tunnel in the world.

It’s likely that the Gotthard Tunnel won’t be dethroned for quite some time. Given the amount of time each one of these tunneling projects takes and simply the massive amount of money they require to complete, there are no other tunnels slated to overtake the Gotthard Tunnel anytime soon.

Sources: The Guardian, BBC, Newly Swissed

Trevor is a civil engineer by trade and an accomplished internet blogger with a passion for inspiring everyone with new and exciting technologies. He is also a published children’s book author whose most recent book, ZOOM Go the Vehicles, is aimed at inspiring young kids to have an interest in engineering.


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