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Autonomous cars confused by San Francisco’s fog

Driving in thick fog is a big enough challenge for humans, but it turns out self-driving cars find it pretty tricky, too.

Overwhelmed by dense fog in San Francisco early on Tuesday morning, five of Waymo’s fully driverless vehicles suddenly parked by the side of a residential street in what appeared to be a precautionary measure, the San Francisco Chronicle reported. Another of its cars apparently came to halt in the middle of the street, the news outlet said.

Other vehicles were unable to pass as “baffled motorists flashed headlights and tried to maneuver around the jam,” the Chronicle said.

The traffic problems persisted until the fog cleared and the autonomous cars were able to resume their journeys.

Alphabet-backed Waymo confirmed the incident in a statement on Wednesday, saying that at around 6 a.m. PT, “multiple Waymo vehicles in San Francisco encountered very dense fog and determined they should pull over temporarily.”

It said that after a “brief” stop, its cars continued on their way, adding: “We have software updates planned to improve our fog and parking performance to address such situations in the future.”

San Francisco is of course famous for its fog, and a couple of years ago Waymo addressed the issue in a blog post. “The low-hanging clouds are iconic to the city, but they also pose several challenges for drivers, both human and autonomous,” it said. “Fog is finicky — it comes in a range of densities, it can be patchy, and can affect a vehicle’s sensors differently. Sometimes, we see fog thick enough that it deposits tiny droplets on surfaces, like our optical sensors, while other times its microdroplets just form on our sensors, impacting how far one can see. Fog can also trap other particles, such as smoke from wildfires or pollution from gasoline, creating a more opaque fog or smog that’s hard to see through.”

It said in the post that its fifth-generation imaging radar uses microwaves instead of light and therefore can see through things like fog and mist, while a new cleaning system had been designed to keep the cars’ sensors extra clean. But something clearly failed on Tuesday.

The incident is the latest in a growing list of mishaps involving autonomous cars operated by both Waymo and General Motors-backed Cruise in San Francisco. Both firms are vying to become the first to offer full-fledged autonomous taxi services, and while they are currently carrying paid passengers, the vehicles are still operating under strict rules while engineers continue to refine the hardware and software that powers them.

Just last month, a Cruise self-driving vehicle was involved in a low-speed collision when it became confused by the movement of an articulated bus. No one was hurt in the crash. The incident led to Cruise issuing a voluntary recall for its fleet of 300 cars so that it could add a software update to its onboard computers to ensure this type of accident doesn’t happen again.

In another recent incident, cameras and sensors on several Cruise cars apparently failed to spot cables that had come down in a storm, and ended up becoming entangled in them.

The list of blunders prompted San Francisco officials to call on regulators to slow the expansion of autonomous-car pilot tests in the city until the technology has been further improved.

Keen to steer clear of tighter regulations, both Waymo and Cruise point out that their autonomous vehicles have driven more than a million miles in complex urban environments without any serious injuries or fatalities, and that their respective autonomous systems are being improved all the time.

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Trevor Mogg
Contributing Editor
Not so many moons ago, Trevor moved from one tea-loving island nation that drives on the left (Britain) to another (Japan)…
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