Elon Musk is serious about tunnels. Last night, the Tesla / SpaceX CEO provided Twitter with an update on his Tunnels venture, showing off a drilling machine in action. Earlier this week, he began work on an experimental tunnel on SpaceX’s headquarters in Los Angeles. Now, it seems that he’s considering putting his tunnels to work with another idea that he’s had: hyperloop.

When Musk tweeted out his frustrations with traffic back in December, we weren’t sure if this a serious pitch or a passing musing by Musk, who has used Twitter as both platform for his company plans, but also as a space to riff about wild ideas. But since then, he’s spoken about how he believes that tunnels could be a way to avoid traffic congestion in the future.

Answering a question from a follower on Twitter, he's implied that Boring could be wrapped into another of his visionary ventures — the hyperloop:

@elonmusk

So Mr. Musk, are you thinking to combine Hyperloop and Tunnels to make transportation revolution. — OMAR (@OfficeOfOMAR) February 4, 2017

Ever since Musk revealed hyperloop — a transportation system that shoots pods through low-pressure tubes — in 2013, he’s made it clear that his priorities are on his two bigger ventures: SpaceX and Tesla, letting others handle the design and implementation, even as he built a test track for prototypes. The fact that he’s publicly musing about merging the two ventures shows that the potential that the hyperloop offers is at least still on his mind, and he’s willing to provoke some outside speculation.

On the face of it, the two ventures seem to be a good match. Rather than building above-ground tunnels, you could put most of your transportation infrastructure underground, where it’s out of the way, much like cities discovered with the introduction of subway systems in the late 1800s. If this is the direction that Musk decides to take his idea, it would be a new face on an old concept: pneumatic tubes were not only proposed, but demonstrated, with the short-lived Beach Pneumatic Transit line in New York in 1869.