Elon Musk's huge and varied successes with finance, electric cars, space transportation, levitating trains and solar roofs have put him in a strange position; no one knows whether his Twitter musings are a joke or the foundations of a major new company.

In the same year Musk announced an affordable electric car for the masses and revealed his plan for colonising Mars (and seriously suggested life is probably a videogame), a series of tweets explaining how he wants to solve traffic problems by digging underground tunnels suddenly seems plausible.

On 17 December, Musk said on Twitter: "Traffic is driving me nuts. Am going to build a tunnel boring machine and just start digging...It shall be called 'The Boring Company'...Boring, it's what we do".

Two hours later the billionaire added: "I am actually going to do this" and changed his Twitter bio to read: "Tesla, SpaceX, Tunnels (yes, tunnels) and OpenAI".

This isn't the first time Musk has shown a fondness for building a network of underground tunnels. After an event in January where Musk spoke about the Hyperloop, an 800mph train he conceptualised in 2013, a question-and-answer session brought up tunnels. "It's a really simple and obvious idea and I wish more people would do it: build more tunnels.

Elon Musk boring tweets
Twitter rant about traffic sees Musk muse about boring out underground tunnels for new roads Twitter

"Tunnels are great. It's just a hole in the ground, it's not that hard. But if you have tunnels in cities you would massively alleviate congestion and you could have tunnels at all different levels; you could probably have 30 layers of tunnels and completely fix the congestion problem in high-density cities. So, I strongly recommend tunnels."

Although the tweets would ironically pass for those written by parody account Bored Elon Musk, the plan echoes a concept produced in early December by London architecture practice PLP. called the CarTube, the plan sees newly bored underground tunnels become home to a fleet of electric, autonomous vehicles shuttling passengers beneath city streets.

Translated into Musk-speak, these tunnels could be used by vehicles produced by Tesla, which already sells a range of electric cars with advanced autonomy. Musk, 45, has already outlined plans this year for future Tesla cars to be intelligent enough to act as autonomous taxis while the owner is asleep, at work or on holiday.

CarTube underground road tunnel
Musk's plans are similar to those revealed by architects PLP in early December PLP

Lars Hesselgren, director of research at PLP, said: "CarTube is a direct response to mass transit and traffic congestion in the world's largest cities. Moving high-speed car traffic below ground will revolutionise our concept of the city, allowing our urban spaces to be designed not for cars, but for people."

So where does The Boring Company fit on the Musk Scale Of Plausibility? More likely than colonising Mars? Less realistic than the Hyperloop? As strong a Muskism as that time he reckoned there was a "billions to one" chance humanity was not a computer simulation?

Answers on a postcard, please.