✓ Link copied to clipboard! The $20 trillion "Transatlantic Tunnel" construction that could connect the U.S. and the U.K. by rail has been branded a "high-risk" project by one of the world's leading megaproject experts. Why It Matters The concept of a transatlantic tunnel has existed for several decades without significant progress, but recent breakthroughs in vacuum technology have made the idea much more viable, with tech CEO Elon Musk even suggesting that he would be capable of getting the construction started for a fraction of estimated costs. What To Know While a variety of different proposals for a transatlantic tunnel have been floated, the most common one is a tunnel between New York City and London, which is a distance of over 3,000 kilometers. On paper, the concept has a lot of appeal. New York and London are both large cultural and financial hubs, and linking them by rail opens up incredible opportunities for economic and recreational growth. The environmental impact of long and steady transatlantic flights would also be reduced. A transatlantic communications tunnel on October 17, 2008 in London. The city has been floated as one end of a transatlantic tunnel connecting Europe to America. A transatlantic communications tunnel on October 17, 2008 in London. The city has been floated as one end of a transatlantic tunnel connecting Europe to America. Getty Images The idea recently reentered the public imagination after developments in vacuum train technology. A flight between London and New York currently takes around eight hours and it had previously been unclear if trains running underneath the ocean could compete with this, but breakthroughs in vacuum tube technology have indicated these speeds may soon be possible. Tests of "Hyperloop" technology in India, which involves sending pressurized cabins through vacuum tubes, have theoretical top speeds of 1,100 kph, and it has been estimated that other "Vactrains" could reach top speeds of around 5,000 mph (8,000 kmph). This would theoretically make the journey between New York and London, which is 3,400 miles long, take around 54 minutes, much faster than an overseas flight. However, not everyone is convinced that 3,000 kilometers of underwater construction will be as easy as it sounds. What People Are Saying