Advanced driver assistance systems (ADAS) have become a staple in modern vehicles, providing features like automatic emergency braking and lane‑keeping assistance to help drivers stay safe.

These systems are designed to assist with visibility, react quickly in emergencies, and make driving easier. But, as AAA’s recent tests show, these high‑tech features may not work as well in bad weather.

If the road is slick or visibility is poor, how well do these systems perform? Can they keep you safe if the weather makes it hard to see?

How ADAS Works in Normal Conditions

Most new vehicles are equipped with a combination of radar sensors and cameras. Radar is excellent at detecting obstacles, even in poor weather, and is mounted behind plastic bumpers so bugs and debris don’t interfere with it. Radar can track objects at a distance but has difficulty with details like lane markings. Cameras, however, are better at identifying objects in more detail, such as lane markers and pedestrians. But their effectiveness diminishes in bad weather: in rain, snow, or fog, a camera’s ability to “see” and identify these features is significantly reduced.

AAA's Testing: How Weather Affects ADAS

To investigate how weather impacts the performance of ADAS, AAA worked with the Automobile Club of Southern California’s Automotive Research Center. They tested a range of SUVs using radar and cameras, simulating moderate to heavy rainfall. While the radar sensors were mostly unaffected by the rain, the cameras’ visibility was significantly reduced when water was sprayed across the windshield.

Here's what they found in the tests:

1. Automatic Emergency Braking:

When vehicles were tested at 25 mph, about 17% of the test runs resulted in collisions. At 35 mph, the collision rate increased to about 33%. Even though radar still functioned, the cameras’ inability to see clearly in the rain limited the system’s effectiveness.

2. Lane-Keeping Assistance:

The lane‑keeping assistance systems performed poorly under rainy conditions. Test vehicles veered out of their lanes about 69% of the time. Since radar can’t detect lane markings, and cameras struggle to see through heavy rain, these systems were often unable to keep the vehicle properly centered on the road.

Other Factors That Impact ADAS Performance

AAA also tested how dirty windshields affected the performance of cameras by applying a solution of bugs and dirt to simulate debris buildup. This did not significantly impact camera function in AAA’s controlled testing — but, as anyone who’s driven with a dirty windshield knows, driver visibility is reduced, which can indirectly affect ADAS performance in real‑world conditions.

It’s also worth noting that previous AAA research has shown that ADAS struggles with other obstacles too: for example, curved lanes, heavy traffic, and reduced lighting conditions can all affect the system’s ability to track lane markings and detect pedestrians at night.

Why You Shouldn't Rely Fully on ADAS

While ADAS can help improve safety, it is not a replacement for attentive driving. These systems work best in ideal conditions, but during challenging weather, their limitations become clear. Your own attention and reaction time remain essential.

As advanced as these systems are, they cannot predict every danger. Weather, road conditions, and other drivers all play a part in how safe your trip will be. ADAS is there to assist you, but it is not foolproof.

Technology Isn't Perfect Yet

As we move toward fully automated driving, we still rely heavily on human attention. Advanced driver assistance systems are valuable tools, but they have limitations — especially in bad weather. Understanding these limitations can help you stay safer when visibility is reduced.

Always stay vigilant when driving in challenging weather, even if your car is equipped with the latest safety technology. As AAA’s tests show, sometimes it’s up to you to make the right decisions behind the wheel.