Automotive Research

AAA study finds automatic emergency braking struggles at higher speeds & intersections

Touted as lifesaving, crash-preventing tech, automatic emergency braking (AEB) is standard equipment in most new cars sold in the United States.

Over the years, AEB has successfully stemmed rear-end crashes, which often result in injuries, property damage, and even fatalities. A study by the Partnership for Analytics Research in Traffic Safety, for example, found that rear-end crashes dropped 49% when the approaching vehicle had AEB, and the number of collisions with injuries was reduced by 53%.

But AAA wanted to know if the latest generation of AEB could handle higher speeds and detect moving vehicles in its path at intersections. It struggled with the former and failed with the latter.

How automatic emergency braking works

AEB uses forward-facing cameras and other sensors to tell the car to automatically apply the brakes when a crash is imminent. AEB is common in vehicles, regardless of price. Starting September 1, 2022, 20 automakers representing more than 99% of the U.S. market pledged to make AEB standard equipment on all their new vehicles. It has reduced rear-end crashes at slower speeds, and the technology has been refined over the years with upgraded hardware and software. 

But 2 of the most common deadly crashes at intersections are T-bones and left turns in front of oncoming vehicles. From 2016 to 2020, these 2 types of crashes accounted for 39.2% of all fatalities in collisions involving 2 passenger vehicles during which the striking vehicle did not lose traction or leave the roadway before the collision.

A test vehicle approaches a collapsible dummy car, known as a "guided soft target," while assessing AEB performance in the 40 mph rear-end test.

What AAA tested

AAA looked at 2 scenarios, using 4 different models of SUVs equipped with AEB in each test:

  • AEB rear-end crash performance when approaching a stopped vehicle at 30 mph and again at 40 mph. (Currently, manufacturers are mandated to test AEB at 12 and 25 mph.)
  • AEB performance when approaching a moving vehicle at an intersection, either approaching the side of a moving car in a T-bone configuration, or to make an unprotected left turn in front of an oncoming car.

A test vehicle collides with the guided soft target while testing AEB in the left-turn scenario.

What AAA found

  • At 30 mph, AEB prevented a rear-end collision 85% of the time (17 out of 20 test runs). For the test runs that resulted in a crash, the impact speed was reduced by 86%.
  • But at 40 mph, AEB only prevented a rear-end crash 30% of the time (6 out of 20 test runs). Test runs that ended in a crash saw impact speeds reduced by 62%.
  • In both the T-bone and left turn tests, crashes occurred 100% of the time. AEB failed to alert the driver, slow the vehicle's speed, or avoid the crash every time.

What it means for automakers & drivers

AAA strongly urges automakers and regulatory agencies to focus on designing systems and tests that better handle the types of crashes where injuries and fatalities commonly occur. Automakers must improve AEB systems to assist drivers in intersection-based crash scenarios. Automakers should include AEB systems as standard equipment on all their makes and models.

Drivers must recognize the limitations of AEB systems and remain engaged behind the wheel. As seen in testing, AEB systems primarily help prevent rear-end collisions at lower speeds. Drivers should not expect or rely on current AEB systems to prevent collisions in other situations.

 Cover of the PDF report with the title "Automatic Emergency Braking Performance in the Context of Common Crash Scenarios"

See the full report

Get all the details with the full 34-page report, including individual vehicle results.

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