The idea first became public when the billionaire tweeted that traffic “was driving him nuts” and that he wanted to start a tunneling machine company.

Get it?

The proposed location for Musk’s trial tunnel is hard to suss out. Crenshaw Boulevard runs across the front of SpaceX headquarters, dividing it from a company parking garage. Three SpaceX employees were hit by a rogue driver crossing the road late after a shift on Dec. 17, 2016, just hours before Musk tweeted out his idea about a tunneling company.

It’s not clear if the two incidents are connected, but a tunnel across Crenshaw could make it safer for employees to cross the busy street. From there, though, Musk’s suggested path becomes more interesting. Highway 105 is about a quarter mile away, and takes a hard left straight for Los Angeles International Airport.

Tunneling underground in an urban environment is a regulatory nightmare, given the maze of underground pipes and wires in most cities, abutting properties, and rules around noise and debris removal. If Musk truly has gone from idea to groundbreaking in just a few months, that would be unusual. More likely is that Musk will pilot the idea on his own property, though going under a busy road like Crenshaw won’t be simple.

This isn’t the first Musk transit spin-off; his scheme for a pneumatic train called the Hyperloop attracted lots of attention when he unveiled it in 2013. SpaceX has been hosting engineering teams in a contest to develop the technology, but hasn’t been involved in trying to commercialize it. Two companies that have picked up on Musk’s idea have so far produced mixed results, with the leading firm finding itself embroiled in a messy lawsuit.

But Musk’s tunneling tweets may also reflect new tricks he’s learned as an outside adviser to the new Trump administration: A timely tweet can always change the subject.

Yesterday (Jan. 24), Musk offered measured support for US president Donald Trump’s nominee for secretary of state, former ExxonMobil CEO Rex Tillerson, praising his competence and his support for a carbon tax. Musk, who regularly warns about the dangers of global warming and founded his electric car company, Tesla, to move the auto industry away from fossil fuels, came in for some criticism from environmental activists who fear Tillerson won’t leave his oil biases behind. Musk appeared disappointed with the quality of internet discourse on the issue.

Hours later, he was tweeting about tunnels.

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