Normal people are getting their first chance to ride in Google's self-driving cars.

Waymo, the autonomous vehicle group owned by Google parent company Alphabet, is going to begin testing a self-driving car program for hundreds of families in Phoenix, Arizona, the companies said on Tuesday.

Waymo has recently been quietly testing the service for a handful of families, learning what potential customers would want from a ride service, the company said in a blog post.

It is now expanding the test, and buying 500 Chrysler minivans to do so. The Californian firm is urging people to apply to take part in an expanded test, which is the first public trial of Waymo's self-driving cars. The vehicles include human operators from Waymo behind the wheel, in case intervention is required and to take feedback.

"Over the course of this trial, we'll be accepting hundreds of people with diverse backgrounds and transportation needs who want to ride in and give feedback about Waymo's self-driving cars," Waymo CEO John Krafcik wrote in a blog post. "Rather than offering people one or two rides, the goal of this program is to give participants access to our fleet every day, at any time, to go anywhere within an area that's about twice the size of San Francisco."

Silicon Valley is racing to master self-driving technology, betting that it will transform the auto industry and be a gold mine for leading companies. Waymo has one of the best technology track records, and it has an alliance with Fiat Chrysler Automobiles.

Many companies expect that customers will use autonomous vehicles as a service, rather than owning them outright. Ride-hailing service Uber in particular expects to use autonomous cars, and CEO Travis Kalanick has said that the tech will be crucial to the company's future. Amazon is the latest big tech company to show an interest in research self-driving technology.

The new Waymo test in Arizona is meant to help the company understand what people want out of self-driving cars and see how they use and integrate the service. Testers will get access every day at any time.

Waymo already has with 100 Chrysler Pacifica minivans and is acquiring five times more, partly to be able to support the service.

Here's a promotional video Waymo made about some of the "early riders" in the trial: