Elon Musk said he’s making “progress” on his tunnel ambitions on Twitter on Wednesday, a project he first mentioned after being stuck in traffic in LA in December. The SpaceX and Tesla CEO shared more details about the project when pressed by fans, specifying that he could actually plan to start digging essentially from near his office at SpaceX.

Musk’s tunnel plans, then, seem possibly aimed at reducing his travel time between SpaceX and LAX, at least initially. LAX is an airport he likely frequents with dizzying regularity, given his commitments at SpaceX, Tesla and SolarCity. In Ashlee Vance’s 2015 biography, he said Musk essentially splits time between SpaceX and Tesla HQs, which means a regular mid-week and end-of week trip to and from Silicon Valley from LA.

Exciting progress on the tunnel front. Plan to start digging in a month or so. — Elon Musk (@elonmusk) January 25, 2017

It’s hard to gauge Musk’s seriousness on Twitter, given his ability to come with fairly dry and playful responses. But he has insisted the tunnel plans were serious previously, and so far, nothing to indicate he’s just joking has emerged. Here, too, he responded to a query from a fan wondering if he was serious with a simple “Yup,” and he does include “Tunnels” as a list item of his concerns in his Twitter biography.