The CEO of Cruise, the San-Francisco-based self-driving company backed by General Motors (GM -0.04%), said that it has begun operating autonomous vehicles on San Francisco's streets without safety drivers.

Until now, the company's test vehicles have had human drivers on board, ready to take control of the vehicle if its software got confused or made an unsafe move. But now, CEO Dan Ammann said, Cruise is confident that it's safe to take the next step.

Getting to the point where the company felt it was safe to do without safety drivers took more than five years and over two million miles of test-driving on San Francisco's crowded and confusing streets, said Ammann. GM acquired Cruise in March of 2016. 

"There are no shortcuts to achieving a moment like this," Ammann said. "Especially when the complexity of the driving environment in SF is something like forty times greater than in a typical suburban setting."

A Cruise AV, a self-driving taxi based on the Chevrolet Bolt, is shown parked on a San Francisco street.

Cruise's self-driving taxis have become a familiar sight in San Francisco, but always with human safety drivers aboard -- until now. Image source: General Motors.

Cruise received a permit from the state of California that allows it to operate up to five of its prototype autonomous vehicles in San Francisco without human safety drivers aboard. 

Cruise's human-free test cars will initially operate in just a few neighborhoods, but that will change as the company — and California regulators — gain confidence. 

"We'll be expanding to new parts of the city and different times of day on a steady and continuous basis, until we're operating everywhere and around the clock, with a full fleet of our driverless AVs," Amman said.

Though he wouldn't share a time-frame for that wider deployment, he did say that the company has big plans for 2021, and that its progress will be much more visible to the media and to the public from this point on. 

"I think you can see that these first driverless tests are a small humble step toward a much bigger goal," he said. 

Editors' Note: This article has been updated.