By: Deborah Hersman, Chief Safety Officer

My father-in-law was responsible for teaching all of his kids to drive. During the winter, he would ask, “How do we drive on the ice?” And everyone responded in unison, “We don’t!”

Challenging weather conditions, which affect human driver and vehicle performance, are one of the leading contributors to crashes on our roads. The Department of Transportation estimates that weather contributes to 21% of the annual U.S. crashes.

While self-driving cars and human drivers alike are limited by the performance capabilities of the vehicle itself, and there are environmental conditions that no driver, human or technology, should drive in, AVs have the potential to improve one of the greatest performance limitations: visibility.

That’s because humans primarily rely on a set of eyes, and fog, dust, smoke, snow and heavy rain can hinder visibility. Poor perception creates significant risk for other road users including pedestrians, cyclists, and other vehicle occupants. Waymo is working hard to master a variety of weather scenarios as part of our mission to improve road safety. The Waymo Driver, which is comprised of a software and hardware suite developed in-house, has multiple sensors like radar and lidar to rely on when the camera’s view is impaired.

Self-driving cars need to be able to drive in a variety of conditions. We design, test, and continuously improve our system so it will be able to work safely and reliably in the toughest environments. Our vehicles are designed to automatically detect sudden extreme weather changes, such as a snowstorm, that could impact the ability of a human or an AV to drive safely. If weather conditions deteriorate to the point that we believe it would affect the safe operation of our cars, Waymo vehicles are designed to come to a safe stop until conditions improve — just like a motorcyclist might stop under an overpass in heavy rain.

While Arizona may be synonymous with sunshine, what’s often forgotten is that the region experiences severe flash floods, extreme heat as well as haboobs, a type of intense dust storm common in dry regions. Certain weather events may cause reduced visibility that make driving difficult. Using radar and lidar, we are designing our system to help detect other road users in a haboob, even when camera visibility is limited.

But we’re not just driving in Arizona. Early in our program, we made the decision to test in multiple cities to ensure that our vehicles would learn and perform safely in various weather conditions. While our commercial service is currently focused on Metro Phoenix, my father-in-law would be impressed that we’ve tested in 25 cities including snowy Novi, Michigan, rainy Miami, Florida and Kirkland, Washington and foggy San Francisco to ensure that our vehicles learn to drive in a variety of challenging weather conditions. Our work learning how to drive safely in weather isn’t done. Experience is the best teacher, and at Waymo, we are working to build the world’s most experienced driver.

For more on Waymo’s weather testing program, check out our Safety Report.