Ride-hailing company Lyft announced intentions to move the majority of its rides to self-driving cars by 2021.

Company co-founder and president John Zimmer last month predicted personal car ownership will be phased out as automated cars become cheaper than car ownership. He made the pronouncement in an essay on the future of urban transportation.

Lyft is currently testing self-driving cars in San Francisco and Phoenix in a partnership with General Motors. Uber is starting self-driving car service in Pittsburgh.

“As technology improves, these cars will be able to drive themselves in more and more situations,” Zimmer said.

He also added the self-driving cars are going to be an integral part of helping cities handle increasing density. They’ll free up parking for other uses like parks, he said.

Self-driving or autonomous cars will change the business models for companies like Uber and Lyft, which currently utilize human drivers in their self-owned cars. When they implement self-driving cars on a large scale, it’s likely the companies will own them, rather than the drivers. They’d also be able to eliminate the expense of paying drivers.