Elon Musk isn't the only person who wants to build this kind of transport. However, he is one of the most successful ones who manage to popularize it. Recently he did it when he replied to a tweet from journalist Johnna Crider. His tweet was a part of a discussion about cities with the worst traffic in the world.
“From a known physics standpoint, this is the fastest possible way of getting from one city center to another for distances less than ~2,000 miles”, Musk wrote.
As a reaction Musk's The Boring Company, which develops Hyperloop, answered that full testing will start later this year.
Hyperloop is an ultra-high-speed public transportation system in which passengers travel in autonomous electric pods at 600+ miles per hour. A Hyperloop trip from Washington, D.C. to New York would take less than 30 minutes and similarly, a trip from Washington, D.C. to Baltimore would take less than 8 minutes.