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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


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. View the full report.

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.”

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 them 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.


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