Whilst there are a lot of financial, environmental and material considerations, one of the biggest goals of tunnel construction is to bring people together, and the results of most tunnel projects make the conveyor belt construction, tunnel boring machines and years of work worth it.

Successes such as the Gotthard Base Tunnel and the Channel Tunnel have changed communities, boosted economies and brought the world closer together, and tunnels have connected countless islands and archipelagos since.

However, ever since the concept of the undersea tunnel was invented, there has been one project seen as impossibly ambitious, but what are the challenges and would it take to make it happen?

The Transatlantic Tunnel

The Atlantic Ocean is the second-largest body of water in the water, one that has historically been extremely difficult to cross by boat or ferry but necessary in order to foster cross-continental trade or transportation.

It is one of the most important crossings in the world, but also one of the most dangerous, so people have considered alternative ways of travelling from the “Old World” to the “New World” for almost as long as Europeans have been aware of the existence of the Americas.

It was the subject of a very popular 1913 Bernhard Kellerman book which itself was adapted multiple times into both silent and feature films through the 1920s and 1930s, and multiple other alternative history stories have covered the idea of a transatlantic tunnel.

Rather ironically, whilst the ending of The Tunnel laments that following the (overambitious by modern standards) 26-year construction timeline the tunnel was already rendered obsolete by transatlantic aircraft, it has been reevaluated as a viable alternative to aeroplanes in recent years.

Whilst for over a century it was confined to the pages of science fiction, interest was revived in the concept following the success of the Channel Tunnel in the early 2000s, and several major publications such as Forbes and Popular Science have claimed it is more feasible than previously thought.

The word “more” is a relative term here, and just because it is not literally impossible based on the world’s collective engineering knowledge, there are still some significant barriers in the way of its construction.

Construction Speed

The sheer distance across the Atlantic Ocean is a huge issue, but one that is often underestimated in many of the proposals.

When it was completed in 1994, the Channel Tunnel became the longest undersea tunnel in the world and still has the longest underwater section of any tunnel in history. This section is 23.5 miles, at least 100 times shorter than the underwater section of any proposed transatlantic tunnel.

Given that it took the Channel Tunnel six years to build a tunnel that distance, a transatlantic tunnel created at the same pace would take 800 years to complete. 

It is difficult to ensure a consistent budget for tunnels that take decades, so a tunnel that will only be enjoyed after entire aeons is difficult to sell.

Undersea Conditions

Unlike the English Channel, which is relatively shallow and has predictable tidal conditions, the Atlantic Ocean is famously deep and famously chaotic at the depths required to create the tunnel.

Even reaching the depths of the Atlantic Ocean via submarine is exceptionally difficult due to the undersea pressure conditions, and most proposals for a transatlantic tunnel are partly or completely underground rather than above the seabed.

Transport Method

To make it a viable transportation option compared to flight, a transatlantic tunnel needs to be faster than a conventional flight across the Atlantic.

This means that a vacuum maglev train or a jet-powered train would be required to ensure that transport would be fast enough to be viable.

Whilst such conceptual forms of transport could cut the time between London and New York City to less than an hour, there are currently no full-scale vacuum trains in operation, and such a design would need to be close to complete before construction on the tunnel could even start.

Cost

Ultimately, the biggest hurdle is cost, as a transatlantic tunnel would be the single most expensive infrastructure project in human history. Originally estimated to cost up to £150bn, the costs have been expanded to as much as £16tn in just the two decades since the revival of the proposal.

For context, this is nearly 30 times the cost of the Trans-European Transport Network, which has linked the entirety of the European Union.

This figure is both a conservative estimate and likely to increase due to inflation and materials costs, as well as the research expenses involved.