Rain Dropped: AAA Says Driver Assist Systems Can Fail In Poor Weather

With perhaps only a relative handful of exceptions, today’s fleet of cars, trucks, and SUVs offer an array of advanced driver assist systems (ADAS) that can provide an added layer of safety. Primary among them is forward automatic emergency braking that can slam on the brakes to avoid hitting a stopped vehicle or other obstruction if the driver isn’t reacting quickly enough. A study conducted by the Insurance Institute for Highway Safety determined that systems with forward collision warning and automatic braking cut rear-end crashes in half.

The latest ADAS gear, which also includes lane departure/lane keeping, blind spot warning, and adaptive cruise control systems employ various sensors to detect the presence of other vehicles and roadway lane markers. Unfortunately, tests conducted by the AAA found that a car’s electronic eyesight, which usually comes from a camera that’s mounted at the top of the windshield, can be compromised in bad weather, leading to crashes that would otherwise be avoidable on a clear day.

“Vehicle safety systems rely on sensors and cameras to see road markings, other cars, pedestrians and roadway obstacles, says Greg Brannon, AAA’s director of automotive engineering and industry relations. “So naturally, they are more vulnerable to environmental factors like rain.” 

The AAA, in collaboration with the Automobile Club of Southern California’s Automotive Research Center, tested key safety systems in four SUVs fro the 2020 model year, a Buick Enclave, Hyundai Santa Fe, Toyota RAV4, and Volkswagen Tiguan, to see how their ADAS fared in simulated rain and other adverse environmental conditions, like bugs and dirt.

In closed-course testing with simulated rainfall sprayed onto the windshield, the AAA’s research found that cars equipped with forward emergency braking traveling at 25 mph nonetheless collided with a stopped vehicle 17 percent of the time. At 35 mph the vehicles crashed a whopping 33 percent of the time. One could assume there would be even higher percentages of system failures at highway speeds. 

Neither of the test vehicles, however, managed to crash while driven under ideal conditions.

The AAA also tested the mettle of lane keeping systems that help keep a car from inadvertently wandering across lane markers via steering and/or braking intervention. This system’s efficiency seems sketchy at best, with vehicles jumping the markers in 17 percent of its tests under ideal road conditions, and a failure rate of 69 percent of the time when the weather turns foul.

Fortunately for those traversing the roads—and trails—less traveled, the study found that driving with a dirty and/or bug-smashed windshield did not significantly affect the systems’ performance.

While some vehicles may flash an alert or deactivate under severe situations, none of the systems in the models tested provided no warning that their performance may be compromised. While valuable assets in their own right, the AAA cautions that advanced safety systems are no substitute for a fully engaged driver. 

Another issue here, the AAA notes, is that such systems are typically tested only under pristine operating conditions. “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,” Brannon says. “Fine-tuning their performance and providing drivers with a more consistent experience will go a long way in unlocking their true potential.”

In the meantime, the AAA recommends those buying ADAS-equipped vehicles take the time to read the owner’s manual or the automaker’s online assets to determine, where and when such systems operate most effectively, and how to use them appropriately. Beyond that the AAA suggests motorists take these precautions when driving in bad weather:

• Keep the windshield clean and ensure that wipers are not streaking the windshield—if you can’t see the road clearly, don’t expect the ADAS sensors to do any better.
• Slow down and drive smoothly, increasing your distance from the traffic ahead. If you can, follow in the tracks of other vehicles.
• Avoid using cruise control to remain alert to changing conditions and respond quickly if the car’s tires begin to lose traction. If the vehicle begins to skid, gradually decrease speed until the tires regain traction, and continue to look and steer in the direction you want the car to go. Don’t slam on the brakes, which can only aggravate the situation.