The implementation of his proposal that many first viewed as a joke started last week, with the building team having excavated a 30 feet wide and 50 feet long test trench.
The businessman announced that the whole undertaking is so far just an experiment.
"We're just going to figure out what it takes to improve tunneling speed by, I think, somewhere between 500 and 1,000 percent," Musk said, cited by wired.com. "We have no idea what we're doing-I want to be clear about that."
Musk announced his idea in late December 2016. He complained that he was very annoyed by the traffic jams in LA and therefore wanted to dig underground tunnels. Many interpreted this statement as a joke, but later the business magnate confirmed his intention.