Waymo is taking back-up drivers out of some of its Chrysler Pacifica minivans, shown here in California, a significant step in setting up a commercial driverless service. (Waymo)

The brain-bending, potentially earth-moving technology that allows self-driving cars to drive themselves has generally come with an asterisk – in the form of an old-fashioned flesh-and-blood driver sitting behind the wheel, just in case.

But Waymo is taking human chaperones out of some of its driverless vehicles in Arizona, a significant step toward launching an ambitious, paid car service to ferry around the general public.

Waymo Chief Executive John Krafcik said Tuesday that the company, which grew out of Google’s self-driving car initiative, has begun running some of its fully autonomous Chrysler Pacifica minivans without a human backup in the driver’s seat.

It’s starting in a swath of Chandler, Az., and will spread over time through “the entire Phoenix region, which is larger than Greater London,” according to remarks by Krafcik at the Web Summit in Lisbon.

Initially, passengers will be engineers and other company representatives, continuing an eight-year testing program with 3.5 million miles under its belt, the company said. But the next step, carrying members of the public, is coming fast – “in the next few months,” Krafcik said.

It will open up first to families in Waymo’s Early Rider program, who are already using its autonomous cars (with a just-in-case driver) as part of their routines, giving the company insights into everyday use.

Waymo executives see removing the human backstop as a natural part of the evolution of their rigorous technology – and as a vital step in finally tapping all the commercial and social benefits they and other advocates of autonomous driving promise. It will be good for the old and the young, the blind and blotto, and save lives in the process, by starting to remove fallible humanity from the highway equation, boosters say.

Numerous companies are competing to take a bite out of the massive global transportation sector, trying to create a new profit center in the process. Waymo competitors, including Uber have said ditching human drivers could remake the economics of taxi services, ridesharing and freight hauling.

Critics however continue to warn that technologists are too rosy about their ability to tame the confusing, treacherous and potentially deadly randomness of road travel. Skeptics also say federal regulators have not done enough to set basic safety standards for technology firms or car companies to meet.

The U.S. Department of Transportation has set up a voluntary system that allows companies to describe their safety features to officials in Washington, but does not require them to do so. Congress is considering putting some safety disclosure requirements in place.

Waymo last month became the first company to make a voluntary safety self-assessment public, according to the National Highway Traffic Safety Administration.

Krafcik said Waymo’s cars have already driven autonomously the equivalent of 140 times around the globe, and in just the last year have driven billions of miles in simulation. Now, the company is contemplating what’s next.

“You can re-imagine the very idea of what a vehicle is. Because they no longer have to be designed around a driver, just people,” Krafcik said. That will allow them to be built for very specific tasks, he said – “one for napping, a personal dining room, a mobile office.”

And the norms of ride-sharing, like grabbing an Lyft for a 20-minute ride to work or from a bar, will be shaken up, offering numerous new options. “You can even have that eight-seater SUV for your weekend trips. You could take these vehicles for one ride, for a day, for a week, or even longer,” Krafcik said.

“Our role will shift from a driver to that of a full-time passenger,” he said. “We want the experience of traveling with Waymo to be routine, so you want to use our driver for your everyday needs.”