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Rained Out: Vehicle Safety Systems Struggle to "See" in Bad Weather

AAA finds automatic emergency braking and lane keeping assistance performance is impeded by rain

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TAMPA, Fla. (Oct. 14, 2021) – New research from AAA finds that moderate to heavy rain affects a vehicle safety system's ability to "see", which may result in performance issues.

During closed course testing, AAA simulated rainfall and other environmental conditions (bugs and dirt) to measure impact on the performance of ADAS like 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% of test runs
  • In aggregate, testing conducted at 35 mph resulted in a collision for 33% of test runs

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

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

During testing with a simulated dirty windshield (stamped with a concentration of bugs, dirt and water), minor differences were noted, however, performance was not negatively impacted.

These vehicle safety systems, also known as advanced driver assistance systems (ADAS), rely on sensors and cameras to see road markings, other cars, pedestrians and roadway obstacles. This makes them more vulnerable to environmental factors like rain.

"These systems are normally evaluated in ideal operating conditions. The problem with that is people don't always drive in perfect, sunny weather," said Mark Jenkins, spokesman, AAA – The Auto Club Group. "While these systems can be helpful for drivers, they are not perfect. So it's important that drivers be aware of their vehicle's limitations and remain fully engaged while behind the wheel, regardless of the weather."

AAA's Wet Weather Tips

Wet conditions present challenges to drivers regardless of whether their vehicles are equipped with safety systems. AAA recommends using extra caution in slick conditions by doing the following:

  • Keep windshield clean and ensure that wipers are not streaking the windshield.
  • Slow down and avoid hard braking and sharp turning. If possible, follow in the tracks of other vehicles.
  • Increase following distance to 5-6 seconds behind the vehicle ahead.
  • Do not use cruise control in order to stay alert and to respond quickly if the car's tires lose traction with the road.
  • If the car begins to hydroplane, ease off the accelerator to gradually decrease speed until the tires regain traction, and continue to look and steer where you want to go. Don't jam on the brakes—this can cause further traction loss.

Previous AAA studies on ADAS Technology

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 Jenkins. "Fine-tuning their performance and providing drivers with a more consistent experience will go a long way in unlocking their true potential."

Optimizing Use of Vehicle Safety Systems

It's essential for drivers to be familiar with how their system operates. AAA urges drivers to take time to read the vehicle owner's manual to learn when, where and how to use them.

  • Vehicles with ADAS cameras located behind the windshield, like those used in this research, "see" the same things a driver does.
  • If the windshield wipers are worn and streak across the window, this could interfere with the system's performance.
  • Drivers should regularly inspect their wipers and replace at the first sign of streaking, chattering or if the blades appear hard and brittle.
  • A good rule of thumb is to replace each year, especially in hot, sunny climates or if a vehicle sits outside all day.