A video Musk tweeted of the proposed system confirmed its resemblance to a bus – albeit a very expensive, futuristic, small, underground bus.

Musk described the new mission as a departure from his original concept for The Boring Company, which focuses on drilling tunnels beneath major urban centres. Initially, the company's tunnels were to be filled with moving platforms that carried personal cars.

"Will still transport cars, but only after all personalized mass transit needs are met," he tweeted. "It's a matter of courtesy & fairness. If someone can't afford a car, they should go first."

Musk, who lives in traffic-jammed Los Angeles, has vowed to solve his city's gridlock problem with new tunnels. In late 2016, he vented his frustration with LA traffic, which gave rise to his Boring Company.

"Traffic is driving me nuts," Musk tweeted. "Am going to build a tunnel boring machine and just start digging..."

Last year, local officials said they were welcoming Musk's drills – but the entrepreneur countered quickly that he was "not ready to do a proper announcement yet."