It's unwise to laugh these days when a billionaire entrepreneur seems to be joking about a new venture he dreamed up while sitting in traffic. Tesla CEO Elon Musk's seemingly jokingly (we thought) tweeted in December that he was going to "build a tunnel boring machine and just start digging" in response to intractable city traffic (possibly referring to LA, but these days it could just as easily have been SF). Fast-forward to May, and he did a whole TED Talk about it, complete with some sophisticated animation showing how it would all work, featuring elevator platforms that cars pull onto at street level and then dump them out into a network of underground tunnels that whisk cars around on tracks. Also in May, he showed the beginnings of a demo tunnel and parts of the boring machine itself.

Behold, the genesis of the idea, the rendering, and now video of one of the actual devices in action:

Entry hole, staging area and starting tunnel for Boring Machine 1 (aka Godot) now complete

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Across the road and below the ground

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And now, Musk's Instagram post from last night, showing video, likely shot on Tuesday, captioned "Testing The Boring Company car elevator."

Testing The Boring Company car elevator

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As TechCrunch reports, Musk remains deadly serious about this crazily ambitious project (is anyone familiar with how much the Big Dig cost in Boston and how long it took to finish that?). He says he's gotten "verbal approval" (from someone!) to build an underground tunnel network connecting New York, Philadelphia, Baltimore and Washington DC, and he's had "promising talks" with the mayor of LA about the project.

The man claims he'll be colonizing Mars and all kinds of other outlandish stuff like a super-fast cross-country monorail, but seriously, if we can't build a high-speed train from LA to SF in under two decades, how in the hell are we going to fund something like this?

Know a few more billionaires who'll donate their fortunes just to avoid sitting in traffic?

Previously: Elon Musk Proposes New Underground Superhighways in Completely Plausible TED Talk