How Does the Automatic Emergency Braking System Work in Cars?

How Does the Automatic Emergency Braking System Work in Cars?

The safest way of driving is to have your eyes constantly on the road and drive carefully. However, with technology rapidly opening new doors, there are now driver-assist features in cars that can make your ride safer and take some weight off your shoulders.

These features work on the basis of fixing your slip-ups. One major issue drivers commit is not braking when there’s an obstacle in your way. That’s where automatic emergency braking or AEB comes in.

So, what is AEB, and how does it work?

What Is Automatic Emergency Braking?

Disc brakes on a ferrari.

AEB or automatic emergency braking system is an active driver assistance and safety feature. This feature was first introduced by Volvo in 2008 and serves to prevent crashes and collisions by automatically activating the brakes.

This system constantly receives and monitors information from the environment, such as your distance from other vehicles, their speed, and your speed.

If the AEB system detects the sudden stop of a vehicle in front of you or really anything that would cause a collision, it will first give you a warning. If you still refuse to hit the brakes, AEB will intervene and bring the car to a stop to avoid a potential collision or reduce the impact of an inevitable crash.

How Does Automatic Emergency Braking System Work?

Driver inside a car on a road.

Most new cars already come equipped with sensors such as radars. These radars are used in other driver-assist features such as active cruise control or ACC. AEB can use these radars and other sensors such as lidars and cameras to get a good image and calculation of the surrounding environment and objects.


AEB also has access to the information on your car through the ECU or the electronic control unit. By taking in your car’s speed and calculating the distance to an object in front of you, AEB can calculate and determine if your current speed has the potential to cause a collision.

If AEB detects a potential collision, AEB will check the braking systems. If you’ve already engaged the brakes and are decelerating enough to avoid the collision, AEB won’t intervene. However, if you haven’t hit the brakes despite the upcoming obstacle or haven’t put enough force on the brakes, AEB will take over and brake with enough force to avoid the collision.

AEB systems can detect vehicles and big obstacles. However, more advanced models can even detect two-wheeler vehicles and pedestrians.

Some cars take AEB to the next level and come equipped with reverse automatic braking. Reverse automatic braking works the same as AEB but is designed to keep low-speed collisions, especially parking collisions where you rear into someone else’s car, from happening.

Reverse automatic braking receives information from the radars and rear cameras to observe and monitor the rear end of the car. If a pedestrian walks in as you’re rearing, or if you get too close to someone else’s car, the reverse automatic braking system will engage and save you from a collision.

Related: Standalone vs. Integrated Car Navigation Systems: What’s the Best Option?

Is Automatic Emergency Braking System Reliable?

City traffic from bird's view.

Institutes such as Euro NCAP are constantly pushing to have AEB become a requirement on new cars. This has happened with ABS in the past. Anti-locking brake systems were at first introduced as an extra fitment on cars but then became a requirement on every production car.

Despite AEB’s growing reputation, it’s important to note that although these systems are tested in environments simulating real-life scenarios and have proven to have high accuracy, they are still prone to fail. Sensors such as lidars and cameras lose accuracy in bad weather, and if the car’s AEB system relies on these sensors, it will fail as well.

Related: RADAR vs. LiDAR: What’s the Difference?

This is a contradictory disadvantage, as automatic emergency brakes would be most useful in poor weather conditions that reduce your eyesight, such as fog and snowstorms. Yet, the chances of them failing in these conditions are higher.

Less developed AEB systems also tend to become hyperactive in city traffic. An instance is when you’re driving to a redlight where other vehicles have stopped. There’s a chance that the AEB might see your approach to the stationary vehicles as a threat and engage full brakes.

Reverse automatic brake systems can also get very bothersome if not properly calibrated. The system can get too sensitive and fully stop the car even though you have more than enough space to park the car.

Is It Worth Getting a Car with Automatic Emergency Brakes?

A crashed car.

AEB is a precious and advanced feature to have on your car. AEB requires multiple parts and sensors to work, but the good thing is that none of those sensors are exclusive to AEB.

A car with AEB is likely also to have active cruise control or even 360-degree cameras. AEB uses the same sensors as these features (radars, lidars, cameras, etc.), so it doesn’t require any parts exclusive to itself.

AEB might sound like something superfluous and an extra cost, but it’s definitely much cheaper than a car crash. According to Euro NCAP research [PDF], AEB can reduce real word rear-end crashes by 31% and save many lives in the coming years.

Related: How Does the 360 Degree Camera in a Car Work?

Automatic Emergency Brakes Can Save Lives and Money

AEB was once limited to high-trim luxury cars, but now it’s available on plenty of cars as a standard feature. AEB is not perfect. It can sometimes act when not needed or not act when needed. Regardless, AEB greatly reduces the chances of a rear-end crash or collision and can save many lives.

Though still an optional feature, AEB can become a requirement for new production cars. For example, the Australian government has announced that it will require all new cars to have AEB from 2023.

Cars on a highway at night.
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