The former Google driverless car company will begin charging pre-approved passengers in the Chandler, Arizona, area for rides on its self-driving ride-sharing service Wednesday.

Waymo officials said the robot cars will be offered to the general public “over time,” but initially only a limited number of people screened and invited by the company will be able to hail a ride from the new Waymo One commercial service.

The company had previously said that it would launch a public service by the end of 2018 in the metro Phoenix area.

Waymo has the same parent company as Google, Alphabet Inc. Since April 2017, more than 20,000 people have applied to participate in the Early Rider program. The company said it has accepted "more than 400" participants in the program.

Arizona is the only market where the program is available, though Waymo officials said they expect to expand it nationally and beyond.

In an interview with The Arizona Republic, Dan Chu, Waymo's head of product, called the Wednesday announcement "a beginning."

"We are excited to bring more members of the public into this service and expand it over time," Chu said.

That program offers rides in autonomous Chrysler Pacifica hybrid minivans in Chandler and nearby areas. Nearly all of the rides still have a safety driver behind the wheel to take over when the autonomous system needs help.

How Waymo One will roll out

Waymo began testing pricing with early riders this year, and now will move some of its riders to the Waymo One paid service and new phone app, much like Uber and Lyft.

Chu said the paid service's rollout will go slowly and will focus on preapproved riders to ensure enough cars to meet demand.

Waymo doesn't disclose how many of its Chrysler Pacificas are on the road in Arizona but reports 600 in operation nationally. The company also placed orders for 62,000 more Chryslers and 20,000 Jaguar I-Pace electric vehicles this year that it says will be used to expand the ride service in the coming years.

The Waymo test vehicles operate in areas in multiple cities where the company has mapped the roads, driveways and other features.

The company won't disclose the exact boundaries of that area in Arizona but says it covers large parts of Chandler, Mesa, Tempe and Gilbert and that it is expanding.

Does testing create hazards for public?

One expert who has followed the self-driving vehicle industry said Waymo's work in Arizona is exciting, but he also worries that people could get hurt as the technology is perfected.

This fear was realized in March when a self-driving Uber vehicle in Tempe struck and killed 49-year-old Elaine Herzberg on Mill Avenue.

The Uber Volvo had a collision-avoidance system that was disabled, and the car's autonomous emergency braking also was turned off by the company to smooth the ride. The safety driver was responsible for stopping the vehicle, but she was watching "The Voice" on one of her cell phones, police records show.

After the Uber accident, Waymo CEO John Krafcik said his company's vehicles would have avoided it.

But Jim McPherson, a California attorney and self-driving car consultant said requiring human test drivers to interact with the autonomous technology creates potential hazards.

"I am less concerned about the fact that Elaine Herzberg was also killed in Arizona (by an Uber) than I am that a Waymo car recently crashed into a motorcyclist in Mountain View, California," McPherson said.

The Oct. 19 Waymo accident he referred to was caused by the safety driver taking control of the Waymo and changing lanes when another driver moved into the Waymo's lane, the company said.

"In this case, our test driver reacted quickly to avoid what he thought would be a collision, but his response contributed to another (collision)," Waymo's Krafcik wrote in a blog about the California accident.

Krafcik said the autonomous vehicle would have avoided both vehicles if the test driver had not intervened.

McPherson said that creates a dangerous interaction between man and machine.

Waymo officials say their intent is to develop the world's safest driver and then replicate that driver into all of its vehicles.