Is it a train? Is it a plane? No, it’s the “Hyperloop,” a hybrid new form of transportation that is the brainchild of Elon Musk, a serial entrepreneur who was a co-founder of PayPal and is chairman of Tesla Motors. On Monday, Mr. Musk announced his plan to unveil designs for this new type of train, which he hopes to build and which, he says, can travel as a puck does on an air hockey table.



“Will publish Hyperloop alpha design by Aug. 12,” Mr. Musk wrote on Twitter on Monday. “Critical feedback for improvements would be much appreciated.”



A trip from San Francisco to Los Angeles takes almost six hours in a car. By bus it’s an excruciating nine hours. Although a flight takes one hour and 15 minutes, when the drive to the airport and tarmac time are factored in, it’s a four-hour trip. Bloomberg Businessweek quoted Mr. Musk in September as saying that the Hyperloop would be able to take people to San Francisco from Los Angeles in 30 minutes. That’s a speed of almost 800 miles an hour.



Mr. Musk has described the Hyperloop as the “fifth mode of transportation” and says it is a hybrid between a train and a plane.



The proposed cost of the Hyperloop between Los Angeles and San Francisco is $6 billion. California is now working on plans to build a far slower train system between the two cities that is expected to cost $60 billion.



While responding to people on Twitter, Mr. Musk said the design he planned to release in August would not be patented. ”I really hate patents unless critical to company survival,” Mr. Musk wrote. “Will publish Hyperloop as open source.”



“What you want is something that never crashes, that’s at least twice as fast as a plane, that’s solar-powered and that leaves right when you arrive, so there is no waiting for a specific departure time,” Mr. Musk told Bloomberg while describing his vision of the Hyperloop last year.