When a Waymo pulls up and parks in front of her home on a residential street in West Los Angeles, 10-year-old Morgan rushes to the window.

“The Waymo is home!” she says, calling to her parents, Lisa Delgin and Zach Tucker.

It certainly isn’t the first occasion when a Waymo has returned to this exact location. Last year, a Waymo robotaxi dropped Delgin and Tucker off after a New Year’s Eve celebration and lingered for several minutes before heading off to its next assignment. Ever since, these Waymo vehicles have consistently parked in the same spot, sometimes for mere minutes, other times for hours.

“It would always come back here, like a beacon,” Delgin said. “Like it knew there was a spot here that it could take.”

Much like the introduction of Uber rideshares and Bird scooters, Waymos represent the newest tech-driven transportation model entering people’s daily lives—though not without causing some tension in the cities where they are first introduced.

The AI component adds a certain vagueness to these encounters. Driverless cars creating unexpected stops can seem arbitrary, and their mandatory beeping noises can be grating, leading to questions about whether they adhere to traffic regulations. Some locals express frustration over Waymos taking up neighborhood parking, feeling uneasy about their ever-watchful cameras and sensors. Many residents are merely curious as to why their streets appear to have become unofficial Waymo hotspots.

“Of all the blocks…” Delgin wonders. Why hers?

Morgan, however, welcomes the Waymo’s repeated visits, interpreting it as a nod of approval from the autonomous vehicles towards her family. Her parents, intrigued by the pattern, have conducted some informal tests.

Their observations reveal that different Waymos occupy the spot, as Tucker has noted various license plates. These vehicles seem to prefer only two parking spots: directly in front of their house or straddling the property line with their neighbors to the south. Delgin has noticed that if these preferred spots are occupied, a Waymo will slow down but refrain from stopping or parking elsewhere on the street, despite available spaces nearby.

The Delgin/Tucker family isn’t the only one noticing the consistent presence of parked Waymos in Los Angeles, where these robotaxis have been active since November 2024. Tal, a resident of the Pico/Fairfax neighborhood, observes a Waymo frequently stationed in front of a nearby apartment building. Reports from The Verge have noted similar sightings on a street in Brentwood, and several users on Nextdoor have inquired or expressed concerns about this occurrence in neighborhoods throughout LA, including Palms, Playa del Rey, and Westchester.

The practice has also been ongoing in Arizona, where Waymo has operated since 2020. One Scottsdale family says a Waymo often parks around the corner from their home, which is adjacent to a shopping center. In recent months, Reddit users in Phoenix have documented the robotaxis’ frequent spots, while a 2023 AZCentral article first documented the phenomenon. “How do you stop Waymo from storing cars in front of your house between trips?” asks one Reddit thread.

Whether a human or AI drives a taxi, it makes sense that a car would idle for some time before it’s dispatched on its next ride. But what makes Lisa Delgin’s home or the Pico / Fairfax building a safe haven for the robotaxis, with such apparent specificity? Neighbors have their theories: proximity to high-traffic areas, central locations, a lack of parking restrictions, ample curb space. But none of that accounts for the repeated specificity of the parking choice.

And unfortunately, not even Waymo the company necessarily fully knows the answer.

Can a robot catch a break?

Where does a Waymo go on its downtime? The company acknowledges that street parking may be a part of a Waymo’s daily routine. There are parking depots throughout LA where Waymos get charged and cleaned. But when not in use, the company says that the cars park outside the Waymo lots, too.

“Our vehicles will find appropriate parking spots to wait for short periods between trips, either in Waymo’s parking facilities or on-street parking locations,” Vishay Nihalani, Waymo’s director of product management, said in a statement. Waymo is even participating in a forthcoming study from UC Berkeley and UC Irvine analyzing street parking behavior, and its impact on ride wait times and curb and road congestion, by providing researchers with aggregate / hypothetical data.

Waymo street parking behavior differs from a cab or other rideshare vehicle. After the morning rush, Uber driver / actor Josh Myra heads home, which is naturally where he parks his car when he’s not taking rides. Otherwise, Myra does not make a practice of parking in residential neighborhoods between rides. When he’s not working, he’s parked at home. And if he is looking for rides, he will usually drive around high-traffic areas, a practice known as “deadheading,” since he gets far more ride requests when he’s in motion versus when he’s stopped. Myra said this is typical of most of the Uber drivers he knows.

But if a Waymo isn’t at a depot, or doesn’t need to head to a depot for a charge or service, it’s not necessarily going to act like an Uber driver and chase rides. If Waymo isn’t seeing a high amount of traffic for ride requests, it may choose to park to conserve energy and avoid contributing to traffic, while also ensuring there’s some Waymo coverage in non-high-traffic zones.

“When Waymo vehicles are idle and don’t have charging or maintenance needs, they choose between parking in nearby spots or driving to areas of high demand,” Nihalani said. The Waymos opt to drive to these “high-demand” areas when “they’re likely to quickly receive the next hail.” If high-demand areas have an adequate number of Waymos nearby, the cars may choose to park. “This allows us to best match ride-hailing demand and vehicle supply, while conserving energy and reducing traffic congestion,” Nihalani said.

As for where to pull over, there are a few things that definitively go into Waymo’s parking choices. First is “local parking regulations,” so that includes the actual curb restrictions such as time limits or street sweeping. Next is “the number of our vehicles that are parked in a given area.” If there are already Waymo vehicles servicing that neighborhood, the individual Waymo is likely to move on. And finally, “how long they remain parked.” If they tend to hang out there for long periods of time, that could mean a Waymo might not park in that neighborhood (or spot) in the future, since it indicates there’s not much demand in that area.

The decision to park or head to a depot or a high-traffic zone appears to be a balancing act. If a neighborhood doesn’t have another Waymo nearby, and high-traffic areas are saturated with Waymos, parking in a place with minimal curb restrictions might be the best choice. The curb traffic study supports this: UC Irvine lead researcher on the curb study Michael Hyland said data showed that street parking reduces wait times and road congestion. Although it does, obviously, take up more parking spots.

While Waymo provides general insight into its parking choices, it does not address the specificity of the places its vehicles choose to stop — in front of the same house or apartment building, over and over again.

Waymo acknowledges the specific repeat parking phenomenon, but says that the cars’ AI is making so many dynamic decisions in driving as well as parking — about safety, accessibility, and congestion — that it can’t say why a Waymo selects a spot for idling or parking.

Neither the repetition nor the lack of clarity around the behavior shock Phil Koopman, a Carnegie Mellon professor and autonomous vehicle expert. “A computer just doing exactly the same thing the same way every time should not be a surprise to anyone,” Koopman said. “That’s how computers are.” Essentially, they’re smart enough to find an absolutely optimized parking spot — but not necessarily elastic enough in this instance to choose a nearby spot if the optimal spot is not available, the way a human would.

As for how the computers are arriving at that result, Koopman has another theory. Waymo saying that only the car’s computer really knows why it does what it does leads him to believe that Waymo is using machine learning to direct its curb parking decisions. Machine learning means that Waymo engineers provide the cars with data that allows them to make their own decisions based on that data, rather than provide specific instructions via a human-written algorithm.

“Machine learning looks at statistical information and comes up with an answer, and nobody has any idea how it got there,” Koopman said. “And it seems that they are currently not optimizing to vary the location for whatever reason.”

Waymo does not confirm or deny its use of machine learning, instead saying “several elements go into the vehicles’ determination of where to park,” according to Nihalani.

Koopman says that while Waymo may not have insight into how the cars are arriving at their parking choices, they absolutely understand what it’s basing those decisions on. “They don’t know why it made the decision, but they know what data they’re feeding it,” Koopman said. Where it’s legal to park is certainly in this data, but one Reddit user suspects that Waymos have “designated safe spots” — a suspicion that Koopman shares. However, Waymo does not confirm the existence of such designations, and only says that it prohibits parking in certain places.

Tal, the Pico / Fairfax resident, feels slightly uncomfortable about the constant presence of the Waymo with its always-on cameras; Redditors have expressed similar sentiments. Delgin and Tucker have been mostly amused, though sometimes annoyed by the car taking up a spot. Once, while about to head out on an errand, Delgin even made a quick U-turn back into her street spot when she saw a Waymo coming to block it. This sort of moderate annoyance is the overwhelming sentiment on forums where people raise the issue, too.

Some residents have taken their complaints directly to Waymo, the company says. The thing is, Waymo is not technically doing anything wrong, as long as parking doesn’t exceed three hours. Regarding parking regulations governing Waymo parking, Los Angeles Department of Transportation spokesperson Colin Sweeney cites Los Angeles Municipal Code 80.69.2(b), which says that commercial passenger vehicles under 22 feet must follow the same parking regulations that personal vehicles do, and that they can’t park in the same spot for over three hours.

Neither Tal nor Delgin is sure whether Waymo has overstayed this time limit. But researcher Hyland says that, according to the aggregate / hypothetical data, very rarely did any rideshare vehicle park for more than two hours.

Waymo can, and has, told its vehicles to steer clear of certain spots. Waymo confirmed that it is technically possible to mark a spot as a no-parking zone for Waymo vehicles, which it has done in response to neighbor complaints. The police departments of Los Angeles and Phoenix weren’t able to say whether they had gotten any general “loitering” complaints, as these types of information requests require that inquiries be pinpointed to specific locations.

“We are committed to being good neighbors in the communities we operate in,” Nihalani said. “We have received a few pieces of feedback from neighbors, and have made adjustments accordingly.”

Being a “good neighbor” is all well and good, but not providing clarity into the specific parking behavior could indicate larger problems if it is also using machine learning for other functions.

“[Parking] is not high stakes,” Koopman said. “But companies like to use, ‘Well, the computer just did what it did, we don’t know,’ as an excuse for shirking accountability for decisions that might be somewhat harmful.”

Lately, the Delgin / Tucker family’s Waymo has been around less. Waymo confirms that, while usage fluctuates, it has seen a significant uptick in recent months. So chances to stop and take a breather for the robotaxis might be fewer and farther between as the supply of Waymo’s 500-strong Los Angeles fleet begins to meet Angelenos’ demand. Lisa Delgin just hopes, in the future, a Waymo will be around when she needs it.