Tech’splaining: What is Automatic Emergency Braking and How Does It Work?

  • Christian Wardlaw has 25 years of experience serving in automotive editorial leadership roles with Autobytel, Edmunds, J.D. Power, and Tribune Publishing. A married father of four, Chris is based in the Los Angeles suburbs and believes fuel cell electric vehicles will power the future.

can be reached at christianwardlaw@gmail.com
  • Christian Wardlaw has 25 years of experience serving in automotive editorial leadership roles with Autobytel, Edmunds, J.D. Power, and Tribune Publishing. A married father of four, Chris is based in the Los Angeles suburbs and believes fuel cell electric vehicles will power the future.

can be reached at christianwardlaw@gmail.com
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Automatic emergency braking (AEB) has been available for more than 15 years. It was first offered in luxury cars, but is now available as standard equipment on entry-level models as inexpensive as the Toyota Yaris. It is typically bundled with forward collision warning, and data from the Insurance Institute for Highway Safety (IIHS) shows that it can reduce collisions like the one I described above by 50%. AEB is also effective, in combination with a pedestrian detection system, when some fool crossing the street is paying more attention to a smartphone than traffic.

This technology has a self-explanatory name. Nevertheless, you might be wondering what it is, what it does, and how it works. Let’s get into the details.

What is automatic emergency braking? How does it work?

Dual cameras power Subaru's EyeSight system
Subaru’s EyeSight system uses dual cameras mounted at the top of the windshield to monitor conditions ahead and determine if a threat exists. (Photo: Subaru)

AEB is designed to stop or slow a vehicle before it hits an object in its path. When sensors or cameras detect an object ahead, determine that the vehicle is closing on it at too fast a rate of speed, and establish that the driver is taking no action to slow or stop the vehicle, it automatically activates the brakes.

Some AEB systems work only at lower speeds, helping to prevent fender benders in traffic. Others work at higher speeds, slowing a vehicle before an impact in order to reduce injuries and prevent deaths. Some react to pedestrians, cyclists, and animals, while others don’t. Increasingly, AEB is available when reversing, too.

Depending on the design of the system, AEB relies on cameras, radar, or sensors. When these technologies identify an object in the car’s path and the potential for a collision with that object, they automatically activate the braking system.

These systems do not guarantee that you’ll avoid a collision. Rather, under normal situations, they will try to stop your vehicle in time. At a minimum, they slow your vehicle to reduce the severity of the impact.

It is also important to remember that AEB works only when the camera, radar, or sensors can identify objects ahead. Bright sunlight, heavy rain, caked-on snow, darkness, and other variables affect AEB operation. Therefore, it is not a replacement for attentive driving. Rather, it is a safety net.

Automatic emergency braking is sometimes inaccurate

Overhead view of automatic emergency braking
Radar can sense when traffic ahead comes to a stop. If the red car’s driver fails to brake, AEB will activate to reduce the impact speed or to avoid a collision. (Image: Nissan)

Sometimes, AEB technology will activate when perceived threats are not real. In such cases, sudden braking is usually momentary. However, when this happens it can rattle a driver’s nerves. Occasionally, the system will falsely identify a vehicle in an adjoining lane in a curve as an obstacle, and trigger full braking power. Dappled sunlight and reflections from signs can also momentarily trigger activations. These false positives are usually harmless — but underline the importance of remaining alert behind the wheel.

While imperfect, AEB is nevertheless an important safety feature. The IIHS data proves it.


About the Author

  • Christian Wardlaw has 25 years of experience serving in automotive editorial leadership roles with Autobytel, Edmunds, J.D. Power, and Tribune Publishing. A married father of four, Chris is based in the Los Angeles suburbs and believes fuel cell electric vehicles will power the future.

can be reached at christianwardlaw@gmail.com
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