Elon Musk, founder of SpaceX and Tesla, says he has received "verbal government approval" to build a high-speed underground transport system between New York and Washington, DC.
The hyperloop tunnels - a network of vacuum tubes "through which trains or pods could be shot at high speeds" - will be built by the South African-born billionaire's tunnelling firm, The Boring Company, with the aim of shrinking journey time between the two cities from 2hrs 45mins to a mere 29mins.
While there's "still a lot of work needed to receive formal approval", Musk says he is "optimistic" approval will "occur rapidly."
To help speed up the approval process, he asked his followers: "Please let your local & federal elected representatives know. Makes a big difference if they hear from you."
However, The Guardian reports that representatives from cities between New York and Washington, DC were not aware of plans for the tunnels to be built in their areas.
Eric Phillips, press secretary for New York City Mayor Bill de Blasio, said they knew nothing of the plan.
He added: "The entirety of what we know about this proposal is what's in Mr Musk's Tweet," and asked the inventor: "If you're stopping by City Hall, please bring a copy of the proposal. That would help."
This would be the first major project to be undertaken by The Boring Company, which Musk established earlier this year to begin testing outside SpaceX's headquarters in Los Angeles.
According to the Daily Telegraph, he aims to reduce the costs of tunnel "by a factor of ten or more". The current price of building an underground network in the US is $1bn (£770m) per mile.