ADAS features can struggle to 'see' in bad weather

Oct. 22, 2021
AAA finds that rain can greatly reduce performance of automatic emergency braking and lane keeping assistance

New research from AAA finds that moderate to heavy rain affects a vehicle safety system’s ability to “see," which may result in severe performance degradation. During closed-course testing, AAA simulated rainfall and found that test vehicles equipped with automatic emergency braking traveling at just 35 mph collided with a stopped vehicle one third (33%) of the time. Lane keeping assistance performance was even worse, with test vehicles departing their lane 69% of the time. Vehicle safety systems, also known as advanced driver assistance systems or ADAS, are typically evaluated in ideal operating conditions. However, AAA believes testing standards must incorporate real-world conditions that drivers normally encounter.

“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.”

Research shows rain has the biggest effect on vehicle safety systems

AAA, in collaboration with the Automobile Club of Southern California’s Automotive Research Center (ARC), simulated rain and other environmental conditions (bugs and dirt) to measure impact on the performance of ADAS, such as automatic emergency braking and lane keeping assistance. Generally, both systems struggled with simulated moderate to heavy rain, with results showing:

Automatic emergency braking engaged while approaching a stopped vehicle in the lane ahead

  • In aggregate, testing conducted at 25 mph resulted in a collision for 17 percent of test runs
  • In aggregate, testing conducted at 35 mph resulted in a collision for 33 percent of test runs

Lane keeping assistance engaged to maintain the vehicle’s lane position

  • In aggregate, veered outside of the lane markers 69 percent of the time

During testing with a simulated dirty windshield (stamped with a concentration of bugs, dirt and water), minor differences were noted, but performance was not negatively impacted. While AAA’s testing found that overall system performance was not affected, ADAS cameras can still be influenced by a dirty windshield. It is important drivers keep their windshields clean for their own visibility and to ensure their ADAS system camera is not obstructed.

Also, some systems may provide an alert or deactivate in extreme situations, however, the conditions AAA tested under provided no such alert or warning.

To simulate rainfall, AAA engineers designed a system using a reservoir to hold water, a high-pressure pump for a consistent flow of water and a precision injector nozzle to spray the windshield. This system was secured in the cargo area of the test vehicle and was connected to a nozzle positioned above the windshield so that the spray pattern covered the entire windshield. It should be noted that water sprayed by this system did not reach the pavement or interact with the test vehicle’s tires.

A Helpful Aid but not a replacement for an engaged driver

Previous AAA testing of vehicle safety systems in both closed-course and real-world settings show that performance is greatly impacted by driving scenarios, road conditions and vehicle design, finding issues like the following:

AAA’s research continues to show that vehicle safety system performance varies widely, reinforcing that they are not a replacement for a fully engaged driver.

“AAA recognizes these systems have the ability to lessen the chance of a crash and improve the overall safety of driving,” continued Brannon. “Fine-tuning their performance and providing drivers with a more consistent experience will go a long way in unlocking their true potential.”

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