Elon Musk really doesn’t like flying cars. The Tesla CEO, who has been working on a tunnel-digging venture called The Boring Company to solve traffic congestion, slammed suggestions that Uber’s flying taxi plan could alleviate the need for hyperloop and other underground transit.

“If you love drones above your house, you’ll really love vast numbers of ‘cars’ flying over your head that are 1000 times bigger and noisier and blow away anything that isn’t nailed down when they land,” Musk wrote on his Twitter page Thursday, in response to a question from journalist Anirban Ghoshal.

Musk may want to transport humans to Mars, and plug in brains to computers to avoid A.I. dominance, but even he finds flying cars an outlandish idea. His criticism focuses on safety: when a car runs out of gas, it can glide to a stop. When a flying car runs out of gas, you have a serious problem.

“Obviously, I like flying things, but it’s difficult to imagine the flying car becoming a scalable solution,” he told Bloomberg Businessweek last year in a story about The Boring Company. “If somebody doesn’t maintain their flying car, it could drop a hubcap and guillotine you.”

Instead, Musk is focused on ideas like the hyperloop, a vacuum-sealed tube that transports pods of up to speeds of 700 miles per hour, as well as tunnels that use existing cars but transports them at higher speed:

Musk announced in November 2017 that the team wanted to build a “loop” — like a hyperloop, but without the vacuum seal — from Chicago’s O’Hare Airport to downtown. The company also wants to build a hyperloop from Washington D.C. to New York.

Musk isn’t entirely against the idea of taking some lessons from aerospace technology and applying it to cars. The entrepreneur also heads up SpaceX, and in November 2017 he suggested that the second-generation Tesla Roadster supercar due for launch in 2020 could “enable it to fly short hops.” Musk is known for his tongue-in-cheek suggestions and this may fall into that category, but even he has to admit that practicalities aside, the idea of a flying car is pretty cool.

If you liked this article, check out this video: "Three Times Elon Musk Failed Harder Than You Ever Will"