City of Fairbanks

Snow is a problem the self-driving industry hasn't fully solved. Waymo operates in 15 major U.S. cities and has logged more than 300 million fully autonomous miles, according to Alphabet. But its own safety data, which runs through June, includes no snow.

"There is no commercial [automated driving] service operating in winter conditions or freezing rain," Steven Waslander, a University of Toronto robotics professor who studies winter driving, told Heatmap in February. "We don't have it completely solved." He added: "But our research has shown that a lot of the winter conditions are reasonably manageable."

Waymo started giving public rides Sept. 1 in Denver, which a company spokesperson told the Denver Gazette is "the first true winter weather market." In snowy cities, Waymo says, it validates its system "with trained human drivers behind the wheel." When the weather goes beyond what it has validated, it plans to limit or pause service, and "those pauses may last for hours or even days."

Winter can trip up a self-driving car in several ways. Falling snow can clutter the readings from lidar, the laser sensors that map a car's surroundings, with false detections and missed objects, researchers have found. Snow can bury the lane lines, curbs and signs the cars rely on. Black ice is "nearly invisible even to advanced sensors," Frances Zhu, a Colorado School of Mines researcher, told Denver's Westword.

And a 2022 study found that car exhaust condensing in cold air creates "ghost object detections" in lidar. In Fairbanks, at about 30 below, that exhaust freezes into ice fog. Car exhaust is "the main cause of limited driving visibility," UAF science writer Ned Rozell wrote in 2024. Ice fog has become rarer, averaging about six days a year from 1990 to 2020.