The visionary billionaire behind Tesla and SpaceX is working on a proof of concept for building a tunnel under Los Angeles to ease gridlock, LeFrak told CNBC's "Squawk Box" on Friday.

Elon Musk 's "imaginative" ideas to alleviate traffic congestion are worth taking seriously, said developer Richard LeFrak, co-chair of President Donald Trump 's new infrastructure council.

"He says that he can build a mile of tunnel," LeFrak said. "He's obviously a force of nature," he added. "This guy is an imaginative guy."

Earlier this month, Musk tweeted a symbol of his tunnel idea, dubbed "The Boring Company."

The tweet showed a hat baring that moniker.

"The real problem with doing this is gaining rights of way, gaining eminent domain, or having the rights of way to get the real estate to build the tunnel," LeFrak said.

"[Musk] still has to prove the concept," he argued. "But at least here's a man ... doing something a little unusual, thinking out of the box, and willing to invest his own capital."

On Thursday, another one of Musk's visions, a super-fast hyperloop transport system, appeared to take a step closer to reality with the release of test track photos.