Self-driving cars in Arizona are starting to navigate local roads without a human in the driver's seat.

In a show of confidence, Alphabet's autonomous car unit, Waymo, is phasing out the need for a test driver in its vehicles. Save for the passengers inside, a subset of the company's self-driving cars will operate by themselves on public roads in the Phoenix metro region, Waymo announced on Tuesday.

Ditching the human test driver may sound alarming, but it brings Waymo closer to offering a truly autonomous vehicle. For eight years, the company has been developing the technology and doing test runs on public roads across 20 US cities. For safety reasons, a human test driver was always nearby to take over.

Not anymore. The fleet of self-driving cars will at first operate in a limited area in Phoenix, but Waymo will gradually increase the coverage area to the size of "Greater London," it said, and add more vehicles over time.

The completely autonomous vehicles will at first only transport Waymo employees, but the public will eventually be invited to ride inside, too.

As part of its public trials, the company has been enlisting local Arizona residents to try the cars through Waymo's "early rider program." Those participants will be among the first to test out these new fully self-driving vehicles over the next few months, Waymo said.

Arizona residents in the Phoenix metropolitan can still apply, and receive free rides from Waymo.