SUNNYVALE, Calif. — Karen Brenchley is a computer scientist with expertise in training artificial intelligence, but this longtime Silicon Valley resident has pangs of anxiety whenever she sees Waymo self-driving cars maneuver the streets near her home.

The former product manager, who has worked for Microsoft and Hewlett-Packard, wonders how engineers could teach the robocars operating on her tree-lined streets to make snap decisions, speed and slow with the flow of traffic and yield to pedestrians coming from the nearby park. She has asked her husband, an award-winning science-fiction author who doesn’t drive, to wear a shiny vest while cycling to ensure autonomous vehicles spot him in a rush of activity.

The problem isn’t that she doesn’t understand the technology. It’s that she does, and she knows how flawed nascent technology can be.

“I’m not skeptical long-term,” said Brenchley, who has lived in Silicon Valley for 30 years. “I don’t want to be the guinea pig. I don’t want my husband to be the guinea pig.”

Brenchley and others who live among the world’s technology giants represent a surprising Silicon Valley paradox: Residents believe in the power of technology to change the world for the better, but they are skeptical of the role it might play in their daily lives. This is especially visible as driverless cars from numerous tech giants arrive en masse in the streets of Silicon Valley neighborhoods.

Some residents say they’re confident the technology can work in limited settings, such as test tracks or simulations. But the software that controls the cars needs to be trained on real-life situations: left-hand turns, bikers, children running out into the streets. And, some residents say, that brings a form of disruption that will tangibly change the fabric of their communities and could even prove dangerous. That became apparent last year, when an Uber robocar struck and killed a pedestrian in Arizona.

Google self-driving subsidiary Waymo says safety is core and the company’s highest priority, and that the technology could make roads safer. The company’s employees and families work and live there, said spokeswoman Alexis Georgeson, and test the vehicles, too. It’s also educating the public at local events. “Our vehicles are programmed to be safe and cautious drivers,” she added in a statement.

Silicon Valley types can be most skeptical of advanced technology because they know how it works and what its risks are. Parents with experience at large tech firms have famously cracked down on screen time for their children. Some tech executives won’t let female family members ride alone at night with ride-sharing cars. Others keep their kids off social media indefinitely.

That same skepticism has landed on Silicon Valley streets. Residents are showing up to community meetings to express their concern about driverless cars, even though they still have safety drivers in the front seat. Posts on community site Nextdoor debate safety risks.

George Azzari, 39, spent five years in the Mountain View neighborhood on the doorstep of Waymo. He said the cars tended to form a trail down a small road near his home at rush hour, clogging up traffic.

“I basically would run into a bunch of these cars coming back to headquarters at 25 miles per hour on this tiny road. You can’t pass them,” said Azzari, chief technology officer at Palo Alto-based social impact start-up Atlas AI. “I definitely drive different when I’m around those things,” coming to a hard stop or pulling around one driving particularly slowly.

Tech companies in the area have seized on automation as the solution to the problems of an aging population, pollution and congestion, and the collective ravages of the United States’ car dependence, pitching it as a way to significantly cut down — or even eliminate — the dangers of driving. Contrary to the notion that self-driving cars are just another one of tech’s sci-fi innovations, executives have argued that robocars are an inevitability of society’s march forward, relegating the manually driven car to the status of horse and buggy.

California has awarded permits to 63 different companies to test self-driving vehicles on state roads, according to state figures from Aug. 9. Among them are a slew of tech companies with a substantial Silicon Valley presence: Lyft, Tesla, Alphabet-owned Waymo, General Motors’ Cruise division, Ford-affiliated Argo AI, and start-ups such as Aurora and Zoox.

The companies outfit their autonomous cars with complex sensors such as radars and cameras. They are frequently equipped with a cone-like lidar sensor atop a roof-mounted contraption that looks like an upside-down sled. Most are small SUVs or vans that stop and start with regular traffic — driving tasks normally left to the human brain. Safety drivers are in the vehicles to monitor the cars’ performance.

While much of the testing is done on closed courses imitating city streets or virtual simulations, real roads are essential in teaching the cars’ artificial intelligence the myriad real-life situations it could encounter, the companies say.

That happens in Silicon Valley, one of the early homes for such testing. Companies have also started rolling it out in other states where it’s allowed, including Arizona, Nevada and Pennsylvania, to add a diversity of weather, road conditions and driving cultures.

Robocars have become a common sight in the tree-lined suburban streets of Silicon Valley, dotted with California’s iconic mid-century Eichler-style homes, where upper-middle-class engineers and tech workers reside and where their children roam on bicycles and skateboards.

Some residents are proponents — or at least indifferent — to the autonomous cars on their streets. And plenty of people here are quick adopters on tech, demonstrated in part by the sheer volume of Teslas on the streets. Plus, some of the communities where the testing is taking place say that so far it has largely been incident free, with few complaints from residents.

Brad Templeton, who lives in testing hotspot Sunnyvale, frequently sees the cars on the road. He worked on them, too, as part of Google’s self-driving car project roughly a decade ago. Most experts in the field say real-world testing is needed, he says, something he agrees with.

Templeton says a small number of crashes are acceptable when considering the eventual overall improved safety when human drivers are off the roads. He compares it to teenagers learning to drive.

“We accept them driving, with very high risk, because it is the only way to turn them into safer middle-aged drivers. And all we get out of that is one safer driver,” he said. As autonomous vehicles are trained, “we get a million safer cars from a prototype fleet of hundreds.”

But John Joss, 85, doesn’t think the robot drivers are that mature. “They drive like either geriatrics or 17-year-olds who have very limited experience of driving,” said Joss, a magazine writer.

He said the behavior of hundreds of vehicles on his Mountain View streets has inspired more questions than confidence. In one instance, he said, a Waymo vehicle drove from 8 mph to 10 mph on a 25-mph street, gathering a “tail” of other vehicles behind, trapping vehicles at a light. In another instance, he said, a Waymo vehicle stacked cars behind a blind curve after struggling to navigate an expressway on-ramp.

Knowing tech workers well has added to his concerns about the risks engineers might be taking on his roads, he said. “I have met, dealt with, interviewed and written about geeks for the last 30 or 40 years,” Joss said. While they understand the tech they’re working on, it doesn’t always translate to a broader understanding of potential impact.

Others here see the testing as a nakedly self-interested push for profit, an arms race to launch the first driverless taxi service and reap the profits that come from being unburdened to paying drivers. They don’t want to be the unwitting subjects of those tests.

Sally Applin lives in Silicon Valley and frequently ends up on the road with robocars. She said she tries to avoid them. She recently took a visitor around the Valley who snapped pictures when he saw a Waymo self-driving vehicle. She slowed down to stay safe. “I keep a distance,” she said.

A review of safety reports in California found self-driving vehicles are at risk of rear-end collisions. Experts say the vehicles behave unlike human drivers and are hard for people behind the wheel to predict, and they jolt to a stop when detecting a hazard.

As Applin recently sat at a red light, she realized a driver next to her was going to make an dangerous illegal turn. “How does an autonomous vehicle sense that?” she asked.

Applin, who studies the intersection of people, algorithms and ethics as an anthropologist but who also feels the impact in her real life, said the introduction of these cars to the road is problematic because it means that she and other drivers are responsible when it comes to training the new tech.

In online neighborhood bulletin boards, at community meetings and elsewhere, skepticism has bubbled up among those in the communities who say Waymo and other companies have not provided enough of a glimpse into their testing methods, and their safety claims have not been independently verified.

Those tensions came to a head in Palo Alto and Mountain View as Waymo held community meetings on its driverless-car testing. “We’re going to storm City Hall if these cars come to Palo Alto,” said one resident at the meeting, according to the local Palo Alto Weekly.

One resident specifically asked Waymo what third-party data, and validation of its testing methods, the company has on hand, according to a newspaper clipping in the Weekly, the local newspaper.

Waymo said earlier this year it had hit 10 billion miles of driving in simulation, and in October 2018 announced it had reached 10 million real-world miles. It has also released a detailed safety report on its vehicles along with publicly available guides for emergency responders on how to respond to incidents.

Still, some residents like Brenchley would like more transparency and data about the robocars they see on the roads. She also wants to make sure developers learn lessons from science-fiction literature: Heed the social implications of your innovations, and don’t let the technology run amok.

“It’s too early,” she said. “They’re too excited. They’re chasing the rainbow, and I just don’t want them driving down my street.”

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