The American Automobile Association (AAA) conducted a study that found that Automatic Emergency Braking (AEB) systems are reasonably good at preventing low-speed rear-end collisions, but often fail when vehicles are traveling at medium speeds, reports The Verge.

Starting in September 2022, all new cars sold in the U.S. must be equipped with AEB, which uses forward-facing cameras and other sensors to automatically apply the brakes when a crash is imminent. The Insurance Institute for Highway Safety estimates that AEB could help prevent 28,000 crashes and 12,000 injuries by 2025.

Using four conventional vehicles, AAA wanted to test AEB to see how far it has progressed since it was first implemented on production cars nearly 20 years ago. The results were not so great.

“Automatic emergency braking performs well in the limited task for which it was designed,” Greg Brannon, AAA’s director of automotive engineering and industry relations, said in a statement. “Unfortunately, this task was drawn up years ago and the regulator’s standards for low-speed crashes have not evolved.”

The group selected four vehicles for testing, all of which were equipped with driver assistance systems that include AEB: the 2022 Chevrolet Equinox LT; 2022 Ford Explorer XLT; 2022 Honda CR-V Touring; and the 2022 Toyota RAV4 LE.

Automatic emergency braking is not very good at preventing collisions at medium speeds

Over the years, AEB has proven its usefulness in reducing low-speed rear-end collisions, but AAA wanted to see how well it works in two more common, and more deadly, crash scenarios: T-collisions and left turns in front of oncoming vehicles. From 2016 to 2020, these two types of crashes accounted for nearly 40% of all deaths in two-car crashes in the United States.

The results were quite disappointing. In both the T-intersection and left-turn tests in front of an oncoming vehicle, AEB failed to prevent 100% of AAA-staged crashes. The system also failed to warn the driver and reduce the vehicle’s speed.

In rear-end collision tests, AEB performed slightly better provided the speed was low. At 30 mph (48 km/h), the system avoided 17 out of 20 collisions, or 85%. For test runs that resulted in a crash, the crash rate was reduced by 86%. But at 40 mph (64 km/h), AEB prevented just six out of 20 rear-end collisions or 30%. In test trials that ended in a crash, impact speed was reduced by 62%.

This is not the first time AAA has highlighted the shortcomings of automatic braking and other driver assistance features. A 2019 study by the group found that AEB did a pretty poor job of preventing cars from hitting pedestrian dummies at 20 mph (32 km/h).