How seriously is Elon Musk taking his quest to solve traffic congestion by digging underground tunnels for roads? Well, if the gigantic hole outside SpaceX headquarters wasn't enough proof that the SpaceX and Tesla CEO is fully committed to his big "boring" plans, then perhaps official merchandise will.

In a tweet on 6 March (embedded below), Musk posted a photo of a black baseball cap emblazoned with The Boring Company's logo – the name of the 45-year-old billionaire's bizarre tunnel-boring project. A follow-up tweet later read "Thanks JJ!", which suggests that the cap was made by New York hat-maker JJ Hat Center.

Unfortunately for those looking to grab their own piece of promotional headwear, Musk made no mention of a public release, although he did promise to send one to Anton "Zedd" Zaslavski after the Russian-born record producer noted that he "needed one".

The (somewhat fittingly) unspectacular merchandise again confirms that developing faster methods of digging underground tunnels with boring machines is high on Musk's busy agenda.

Initially announced in a series of stream-of-consciousness tweets in December 2016, The Boring Company became a reality several weeks later after a gigantic hole appeared in the ground opposite the SpaceX offices in California.

Musk later claimed that the team is "optimistic that tunneling can be improved by at least fivefold, maybe tenfold," and that he sees an underground tunnel network as "key to a lot of technologies: road tunnels, Hyperloop tunnels, train tunnels."

Musk's self-proclaimed passion for digging holes ("I find holes in the ground exciting") has been met with skepticism, however. While the entrepreneur has been keen to stress that the company is operating a "limit-of-physics approach" to improve boring speeds and is merely "muddling along" in the short term, the fact that work on the first hole began without a permit has raised a few eyebrows about the start-up's viability.

Digging tunnels is far from Musk's only business venture though, something IBTimes UK quickly found when tallying up his current to-do-list – a list that has only grown larger after recent announcements that he intends to fly two paying customers around the moon in 2018, and potentially has plans an in-house rollercoaster for staff at Tesla HQ.