One of the few people with the wherewithal to actually do something about the legendary traffic in Los Angeles is finally fed up.

Billionaire innovator Elon Musk declared on Wednesday US time that he's ready to move ahead with his recently formulated ambitions to bore holes through the earth.

"Exciting progress on the tunnel front," Musk tweeted. "Plan to start digging in a month or so."

Coming from anyone else, you might assume this is a joke.

But given that this is an entrepreneur who helped reshape mobile payments, formed a business that sent rockets into space and launched an electric-car company from scratch, it would be foolish to shrug it off.

The cofounder of PayPal and current CEO of SpaceX and Tesla Motors first mentioned his boring plans last month.

"Traffic is driving me nuts. Am going to build a tunnel boring machine and just start digging," he tweeted at the time, adding, "it shall be called 'The Boring Company.'"

"Boring," he said, apparently coining a catchphrase, "it's what we do."

To remove all doubt - OK, to remove some doubt - he added, "I am actually going to do this."

In classic Musk fashion, on Wednesday he teased the forthcoming announcement with just enough detail to make you ponder the possibilities.

"Where will your tunnel be?" a Twitter user asked.

"Starting across from my desk at SpaceX," he responded. "Crenshaw and the 105 Freeway, which is 5 mins from LAX."

As these things typically go, it was hard to say immediately whether he was joking. A Musk spokesman was not available for comment.

Good timing

Make no mistake, though: Musk has good timing. After meeting with President Trump on Monday to promote American manufacturing and praising Trump's secretary of State nominee on Tuesday, he renewed speculation about his tunnel ambitions just in time for the president's infrastructure spending push.

A "large investment tunnelling project" like Musk's or the Hudson River rail tunnel project connecting New Jersey to New York "could be considered" as part of the Trump administration's infrastructure spending, International Bridge, Tunnel and Turnpike Association communications director Bill Cramer said in an email.

"In general, the nation's infrastructure is crumbling," Cramer said. "There simply is not enough federal, state and local government funding to address all of the nation's infrastructure needs. Private investors, working with state and local government and policymakers can be effective and efficient."

Musk's tunnel plans face a few, shall we say, bureaucratic hurdles, however.

For starters, the permitting process can be nightmarishly long and meticulous, if not impossible altogether. And then there are cost overruns, which often plague underground construction projects, such as subways, freeways and water pipes.

The consumer watchdog organisation US Public Interest Research Group last year dubbed the underground extension of Los Angeles' San Gabriel Valley Route 710 Freeway as one of the biggest transportation " boondoggles" in the country.

The $US3.2 billion ($4.24  billion) to $US5.6 billion project is the "most expensive, most polluting and least effective option for addressing the area's transportation problems", the group said.

In New York, the first phase of the Second Avenue Subway opened on January 1 after years of astonishing cost overruns.

Bottom line: Digging tunnels is hard, takes a long time and is very expensive. And of course in Los Angeles there are naturally concerns about the impact of earthquakes.

But voters in November passed a balloting measure authorizing massive transportation infrastructure spending.

Sounds like a business opportunity.

The tunnelling industry is poised to grow revenue at an annualised rate of 7.3 per cent from 2016 through 2021, rising to $US5.6 billion, according to research firm IBISWorld. Government investments are key drivers of the growth, representing about 69.5 per cent of industry revenue.

Big companies in the tunnelling business include San Francisco-based Bechtel Group and Omaha, Nebraska-based Kiewit Corp, with market share of 4.1 per cent and 2.4 per cent, respectively.