CHICAGO -- Fresh off the launch of his SpaceX heavy rocket Elon Musk is expressing a down-to-earth interest, an express train from O'Hare International Airport to downtown Chicago.

Musk's The Boring Company is one of four companies interested in designing, building, financing, operating and maintaining the train. The others are Oaktree Capital Management; O'Hare Express Train Partners; and O'Hare Xpress LLC.

Chicago Mayor Rahm Emanuel last year issued a request for qualified companies to make a bid to finance, build, maintain and operate an express train service to O'Hare. The city wants trips to take 20 minutes or less, with fares below the cost of a cab, Uber or Lyft.

Last year, Musk said his plan would involve electric pods using underground tunnels.

In a statement Wednesday, Emanuel called the four companies making bids "visionary," adding they will build on the city's "legacy of innovation."