Driverless cars are here.

Waymo, the Alphabet self-driving car company, now has cars driving on public roads in the Phoenix metropolitan area with no one in the driver's seat. Waymo CEO John Krafcik plans to announce the news today in a speech at the Web Summit in Lisbon, Portugal.

For the last year, Waymo has offered free taxi rides to ordinary people who live near the Phoenix suburb of Chandler. Until recently, the company's modified Chrysler Pacifica minivans had a Waymo employee in the driver's seat ready to take control if the car malfunctioned.

Waymo is now confident enough in its technology to dispense with a safety driver. The company has released a video showing Waymo cars driving around the Phoenix area with no one in the driver's seat:

At first, most of Waymo's driverless cars will have an employee in the back observing the vehicle's behavior. If something goes really wrong, they'll be able to push the "pull over" button to stop the car. In the coming months, participants in Waymo's early rider program will start getting the option to ride in fully driverless vehicles.

Some time after that, Waymo will launch a commercial driverless taxi service that's open to members of the general public in the Phoenix metropolitan area and beyond.

Waymo’s first product will be a taxi service

Industry watchers have long assumed that a Phoenix taxi service would be Waymo's first product. But as recently as last week, Waymo was still playing coy about the question, suggesting that it might get into the trucking business instead. Now, Waymo is officially announcing that its first commercial product will be a driverless taxi service.

There's a dichotomy in the industry when it comes to autonomous cars. On the one hand, you have companies like Tesla and Volvo that want to sell you a car that drives you around. Others, including Waymo, want to operate fleets of robotaxis themselves. Some car companies, including GM, BMW, and Volkswagen, are pursuing both strategies simultaneously.

Companies selling cars to customers envision a future where today's driver-assistance systems—like lane-keeping and adaptive cruise control—gradually evolve into more sophisticated self-driving software, with human drivers intervening less and less frequently over time.

Google initially considered this same gradualist approach, which could have led to licensing partially self-driving technology to automakers. But early tests convinced the company that it was a bad idea. Google employees who got to test early prototypes started trusting the technology way too quickly. Google captured videos of test drivers looking at their smartphones, putting on makeup, and even napping in the driver's seat while cars zoomed down the freeway.

So Google changed its strategy. The company decided that instead of selling cars, it would build a taxi service built around cars designed from the ground up for driverless operation. Customers would never be required—or even allowed—to take the wheel.

This strategy allows Google—now Waymo—to pursue a different kind of gradualism. In the old model, cars could go anywhere, but at first the software would only drive some of the time. In the new model, the software drives all the time, but at first the cars can only go certain places.

Specifically, Waymo's fully driverless cars will initially only navigate in a small portion of the Phoenix metropolitan area around the southeastern suburb of Chandler. Within this zone, the cars are able to go anywhere a conventional taxi can go. But the cars will refuse any trip that would take them outside of this carefully chosen area.

To aid with navigation, Waymo has built high-resolution three-dimensional maps of its service area. Self-driving software in each car can compare the objects identified by sensors to objects on the map, allowing it to quickly distinguish stationary objects like trees and buildings from mobile objects like cars and pedestrians.

As Waymo expands its map and acquires more vehicles, it will also expand its service area. Before too long, Waymo expects to offer service across the entire Phoenix metropolitan area. Eventually, Waymo will extend service to other metropolitan areas using the same incremental approach.

Why Waymo is launching first in Phoenix

A big advantage of starting in Phoenix is the region's excellent weather. It's warm and sunny there almost every day. Tricky situations like rain, snow, and ice are rare—though Waymo says its cars are able to drive safely in light rain. Waymo recently expanded its testing into Detroit to prepare for an eventual expansion of the service into colder parts of the United States.

In addition to nice weather, the Phoenix area has wide, well-maintained streets and less traffic congestion than most major cities.

"I'm not going to say Phoenix drivers are the best drivers, but the Phoenix metro area is an easy place to drive," Phoenix resident Eric de Gaston told Ars last month.

Perhaps the most important factor is the regulatory climate. Arizona's leaders have bent over backward to attract Waymo and other self-driving car makers to the Phoenix area. Arizona Gov. Doug Ducey signed a two-page executive order in 2015 designed to encourage self-driving car testing in the state. Besides that, Arizona doesn't have any special legislation or regulations related to self-driving cars.

Last month, I asked Ryan Harding, a spokesman for the Arizona Department of Transportation, if there were any legal barriers to launching a fully driverless self-driving taxi service in the state. "I'm not aware of any current law that would prohibit" fully driverless taxis on public streets, Harding said. "We don't have a problem with that."

In the last year, Waymo's minivans have become a common sight in the Phoenix suburb of Chandler.

"I live in Chandler. You see Waymo units all over the damn place," a Redditor wrote last month.

"When it first started, a lot of people I think were kind of afraid," said Scott Suaso, who lives near Chandler and sees Waymo cars on a daily basis. "That was a year ago. These days, no one really seems to care. Everybody has become so used to seeing them."

Ars got a preview of Waymo’s fully driverless cars last week

Last week we were invited to visit Waymo's secretive test facility in the California desert to see Waymo's fully driverless cars in action.

In a conventional car, the main user interface is the steering wheel, pedals, and other controls on the dashboard. But no one will be allowed in the driver's seat in Waymo's cars. So the company has had to think about building a user interface for a car where everyone is a passenger.

Customers hail cars with an Uber-style app, so the car itself barely needs a user interface at all. There's a pair of video screens mounted on the backs of the front seats, and a row of four buttons on the ceiling above the middle row of seats.

The main function of the video screens is to increase passengers' confidence in the safety of the self-driving software. The screens show a stylized map of the area immediately around the car, with outlines of pedestrians, other cars, bicycles, and so forth marked. Passengers will be able to compare what they see on the screen to what they see out the window and confirm that the car really does understand the road situation.

The leftmost button initiates a call to Waymo's customer service center. The second button locks and unlocks the doors. The third button causes the car to pull over—though Waymo says the car won't stop in an unsafe place, like in the middle of an intersection. The rightmost button tells the car to start the ride.