WASHINGTON -- How would you like to have breakfast in New York and be at your desk in Washington, D.C., in time for your morning coffee break?

If tech entrepreneur Elon Musk has his way, it will take only 29 minutes to commute between New York and Washington one day, traveling on ultra-fast trains underground.

Musk, the founder of Tesla and SpaceX, tweeted yesterday that he'd just "received verbal government approval" to build a hyperloop tunnel connecting Manhattan, Philadelphia, Baltimore and D.C.

Just received verbal govt approval for The Boring Company to build an underground NY-Phil-Balt-DC Hyperloop. NY-DC in 29 mins. — Elon Musk (@elonmusk) July 20, 2017

"Musk is the modern day, infrastructure P.T. Barnum, and it's a testament that we are even talking today, about this idea that is really decades away," said Adie Tomer, a transport futurist.

Maybe. But several companies are now working to make hyperloop trains a reality. One completed a successful test recently on a special track built in the Nevada desert.

In 2013, Musk dreamed up the idea of a hyperloop, where passengers travel in pods that levitate and glide in a vacuum sealed tube with almost no aerodynamic drag.

The D.C. to New York loop would be the world's longest tunnel, with trains traveling at 700 mph.

Airliners fly closer to 500 mph and America's fastest passenger train tops out at 150 mph.

If it gets built, it would be a game changer:

"All of a sudden folks who maybe have friends and family in Washington can actually work in Philadelphia and New York on a daily basis. Hyperloop is capturing our imagination because the thought of moving at that fast a speed is nothing short of exciting," he said.