Where do driverless cars go when they're on break? Some idle in Phoenix neighborhoods

In downtown Phoenix, cars with no drivers are slowly becoming part of the landscape.

Since Waymo rolled out its robo-taxi service to the metropolitan center last year, it's more and more common to see the autonomous vehicles nimbly — or not so nimbly — navigating Roosevelt Row.

The smart white SUVs prowl the streets, cameras and detectors whirring, picking up and dropping off passengers in what seems like a seamless dance.

It's still odd to glance into a passing car and see nobody at the wheel. But the Waymo vehicles have a job to do: pick people up and take them where they want to go.

Simple, kind of.

What's harder to grasp — at least existentially — is what they do in their downtime.

In between passengers, a taxi driver might grab a snack. Use the restroom. Read a book. Browse social media. Call their parents.

But a self-driving car doesn't need to eat, or go to the toilet. It doesn't yearn for the escape of literature, or curate an Instagram feed, or have a mom.

So what's an unoccupied Waymo vehicle to do?

'It's just kind of weird'

Downtown Phoenix resident David Clarke knows.

“They’re picking spots where it’s perfectly legal to park. And they’re taking themselves there," he said. "And they’re waiting, with the lights on, and the sensors still running."

"It might seem less strange if they turned off."

Clarke lives in Garfield, an eclectic neighborhood just east of downtown. Last fall, he began to notice Waymo vehicles congregating on the street outside his apartment.

"Pretty much any time I’m home I can look out and there’s a 50/50 chance of one being there," he said.

He would watch them pull up smoothly and stop at the curb, lights on, motors running, signature lidar detectors spinning endlessly. Sometimes there would be more than one, as if they had planned to meet at that very spot and hang out.

And then what happens?

"They just sit there and they wait," Clarke said. "It's just kind of weird. It’s creepy because it’s new. I’m sure that in a few years when this kind of thing is more commonplace it won’t seem creepy."

"It doesn't bother me," he added. "It's just unusual."

Clarke has wondered what makes his street so enticing to Waymo vehicles. He has a theory: "I think they must be picking spots that are geographically central to their average call location."

Keep reading: Waymo vehicles are stalling in Phoenix. What to know about the driverless rideshare service

So what's going on?

According to Waymo, there are multiple factors that cause autonomous vehicles to park in certain spots.

First, parking locally makes the most sense, a company spokesperson explained over email.

Continuing to drive around would add to traffic congestion and be inefficient, he said, and waiting nearby — as opposed to going back to a Waymo facility — means vehicles can arrive quickly when called.

The company identifies potential parking spots using publicly available information and by following city curb restrictions.

"Some examples of criteria for determining parking spaces could include proximity to anticipated pickup locations, streets with consistent availability, type of maneuver required, style of space, etc," he said.

The sensors keep running to maintain awareness of what's going on around the vehicle, he said.

"This awareness lets us understand the environment and helps us protect the vehicles from any actions like unintended interference," he said, a category that includes things like random people touching or trying to get into the car or if the car is struck by another vehicle.

So that's what's happening as the Waymo vehicle sits and waits.

"Once the vehicle is matched with another rider," the spokesperson said, "it continues on its way."

Honking the horn

Sometimes the waiting Waymo SUVs make themselves heard.

On a recent Saturday evening, an autonomous vehicle drove into a mostly empty parking lot just north of downtown. It sat there and waited, sensors whirring, not pulling into a car space.

After a couple of minutes of sitting there, it honked its horn.

A short period passed before it honked again. Then a longer pause. Another honk. All in all, the self-driving car honked four or five times before a passenger finally appeared at the other end of the parking lot, walked over to the vehicle and got inside.

Again, the taxi driver comparison comes to mind. Were the honks an oddly human show of irritation toward a tardy passenger?

No, according to Waymo.

"Similar to a car horn on a typical key fob, riders can use the app to honk the horn to locate and identify their vehicle," the spokesperson said.

The feature is useful for those who simply can't find their waiting ride, he added, but particularly useful for people with visual impairments and other accessibility needs.

'They seem very polite'

The Waymo rollout hasn't gone without a hitch.

On April 7, a busy First Friday night downtown, a number of self-driving Waymo vehicles came to a stop along First Street, the resulting traffic jam captured in a viral TikTok.

And on Wednesday morning, an autonomous Waymo vehicle stopped unexpectedly in the middle of Roosevelt Row, forcing commuters to drive around it.

And when it comes to illegal parking, self-driving vehicles can be hit with tickets like any other car.

Sgt. Phil Krynsky from the Phoenix Police Department told The Republic that if an autonomous vehicle was parking illegally it could receive a citation, as it goes to the registered owner, not the driver. He said Phoenix police do not maintain a database of whether tickets were issued to autonomous vehicles.

Waymo said its autonomous vehicles have not received any parking citations in Phoenix to date.

"They seem very polite," said Clarke. “They’re very courteous. They always use their blinkers. They yield to pedestrians. They’re actually probably very safe.”

But despite these kind observations — which Waymo vehicles would probably appreciate, if only they were sentient — Clarke has yet to hop in for a ride. The technology is neat, he said, but just a little too new for him.

“I’ll probably take them in a few years," he said. "I’m looking forward to a vacation on the moon someday, after 50,000 other people have gone and returned safely."

"I will not be the first one.”

This article originally appeared on Arizona Republic: Driverless Waymo cars idle in neighborhoods, raising suspicions