Driver-assistance technology can fail in rain, leading to crashes in AAA study

Human drivers don't necessarily see the road ahead as well when it rains, and it turns out that driver-assistance technology doesn't either. The systems used to help your car automatically brake and stay within its lane is significantly impaired by rain, according to a study by AAA released Thursday.

American Automobile Association researchers found that automatic emergency braking, in several instances during testing conducted in simulated moderate-to-heavy rainfall, failed to detect stopped vehicles ahead, resulting in crashes. Lane-keeping technology also faired badly.

AAA cautioned drivers, who should always be vigilant of these systems even in ideal conditions, to not rely on them in the rain.

“Vehicle safety systems rely on sensors and cameras to see road markings, other cars, pedestrians and roadway obstacles. So naturally, they are more vulnerable to environmental factors like rain,” said Greg Brannon, AAA’s director of automotive engineering and industry relations. “The reality is people aren’t always driving around in perfect, sunny weather so we must expand testing and take into consideration things people actually contend with in their day-to-day driving.”

Advanced driver-assistance systems, or ADAS, are common in newer vehicles. They do not perform autonomous driving, but they can automate some limited driving tasks such as adaptive cruise control and staying centered in one's lane. Auto emergency braking has been shown to significantly reduce rear-end crashes in tests by insurance groups.

For its tests, AAA employed a 2020 Buick Enclave Avenir, a 2020 Hyundai Santa Fe, a 2020 Toyota RAV4 and a 2020 Volkswagen Tiguan.

No test car crashed into a stopped vehicle under dry, ideal conditions. But then researchers turned on the simulated rainfall — and 17% of the test runs resulted in crashes at speeds of 25 mph (40 km/h). At 35 mph, the instances of crashes increased to 33%.