If you’re learning about Autonomous Emergency Braking (AEB) and want to know how it works, our full explainer on AEB will help you understand it.

PICTURE THIS: you’re cruising down the road, lost in thought, when suddenly, the car ahead comes to an unexpected halt. Before panic sets in, AEB springs into action. It’s like having an extra set of eyes and reflexes, detecting potential collisions and applying the brakes if you’re unable to react in time.

Australia, particularly Victoria, has been at the forefront of automotive safety technology. Victoria led the charge by becoming the first state to mandate electronic stability control (ESC), a computer-controlled system that selectively applies brakes to individual wheels, ensuring the car maintains its intended direction.

Following ESC, the next essential safety feature on the list was AEB, or Autonomous Emergency Braking. Simply put, AEB anticipates potential collisions and intervenes if the driver fails to react promptly. AEB comes in various forms, including city systems designed for low-speed crash avoidance, cruise systems tailored for higher speeds, and specialised pedestrian detection systems.

Australia mandated car-to-car AEB on new car models in March 2023 and requires car-to-car AEB on all light commercial vehicles by 2025. Pedestrian detection is coming for cars by August 2024 for new models, and August 2026 for light commercial.

What is AEB and How Does it Work?

Cars with AEB sense potential collision objects using systems such as radar or stereo cameras. Once the object is detected, the car determines the distance to the object and the car’s speed. As the car approaches the object it warns the driver of a potential impact with beeps and dash flashes, and it pre-charges the brakes, which means applying a little braking pressure; basically taking up the slack in the system. If the driver ignores the warning the system applies the brakes without driver intervention, hence the name of ‘autonomous emergency braking’. The driver can still steer, accelerate and do whatever else they want, taking instant control as you would in the case of cruise control for example. There is very little time between the warning and the start of automatic braking, perhaps only a second or two.

That is the theory, and in practice it works, but only some of the time, so let’s be clear on one point – you absolutely cannot rely on AEB to do your braking for you. Consider it an extra, just-in-case, backup to your own driving, but it’s valuable because that one time it works it could save a life.

The reason you can’t fully trust AEB (some are much better than others) is that the technology suffers from two big problems. Firstly, it doesn’t take enough factors in to account to determine stopping distances, and secondly, it isn’t all that great at recognising a problem.

AEB systems often operate optimally under ideal conditions, such as dry roads and well-maintained vehicles, yet real-world scenarios can pose challenges. Factors like wet or uneven surfaces, improper tyre inflation, heavy loads, or unconventional spare tires can compromise AEB’s effectiveness by increasing stopping distances. Additionally, AEB’s reliance on radar, lidar, or camera technology for danger recognition presents its own set of limitations.

Cameras may struggle in low light conditions or glare, while radar and lidar may have difficulty detecting narrow or small objects. Furthermore, AEB’s response time to potential dangers varies, leading to instances where fast-moving obstacles might not be recognised in time.

Is brake assist the same as AEB?

It’s crucial to note that AEB is distinct from Emergency Brake Assist (EBA), which aids drivers in panic braking situations by applying maximum braking force. Another related technology, adaptive cruise control (ACC), enhances driving comfort and safety by maintaining a set distance from the vehicle ahead.

Why is my AEB warning light on?

The AEB warning light can come on if there’s an issue with the Autonomous Emergency Braking system. Common reasons for the AEB warning light to come on include a dity sensors cover on the exterior of the car (muck on the windscreen or grill where the sensor is), a system malfunction, or low brake fluid levels. If the AEB warning light is on, try cleaning where the sensor is and if it doesn’t fix itself when restarting the car, you might need to book into to have it checked over.

Can I drive with my AEB light on?

In most instances, you should be able to drive with the AEB warning light on, but it’s important to address the underlying issue. Driving with the AEB light on could indicate a safety risk, as the Autonomous Emergency Braking system may not work correctly.

How do I turn off AEB?

You might not be able to, although it can be done in easily enough in most four-wheel drives. This is because AEB can be a bit trigger happy when off-roading. If possible, check the manual for your car as the procedure for turning off AEB varies. Typically, AEB can be changed through the vehicle’s settings or by pressing button such as a traction mode that will disable AEB.

What speed does AEB activate at?

AEB does no always work at any speed. It will be vehicle specific, but generally, AEB is designed to operate from low speeds around 10-20km/h up to highway speeds of 130km/h. This means that at a slow speed in the city you could hit something without AEB engaging.

It’s quite possible that drivers may begin to rely on AEB in the wrong way and succumb to the (illegal) temptation of playing with smartphones as they drive through suburbia or crawl through city traffic, falsely safe in the knowledge that if anything did happen, the car will take car of it.

AEB’s proven effectiveness in reducing accident rates, particularly in rear-end collisions, highlights its significance to reduce incidents on our roads. And the fact it has been mandated as a requirement to sell new cars in Australia underpins just how important it is to help reduce road toll – but like any new safety system available right now, there is no room to be complacent.

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Practical Motoring

The team of journalists at Practical Motoring bring decades of automotive and machinery industry experience. From car and motorbike journalists to mechanical expertise, we like to use tools of the trade both behind the computer and in the workshop.


  1. My ACC loses the car in front in heavy rain combined with heavy traffic causing a lot of road spray. I’d assume that AEB wouldn’t “see” either. Under those circumstances, the ACC will accelerate, assuming there is no car in front – then as it gets closer and closer again sees it and backs off again – but I take manual control instead.

    My AEB has operated a few times, most of which I’ve been glad, several times when someone has cut into the gap which didn’t actually exist in front of me.

    But Semis and (worse) B-Doubles need to understand they need to sit back much further than they do at present – and stop telling my AEB off with his air-horns – sorry, mate, it wasn’t me that did it, and GET OFF MY TAIL next time.

  2. Hi Wayne, what bad things happen in the wet? The ’email’ referenced in your NRMA link was an Australianised American chain email that circulates on the dangers of cruise control in the wet… I think it might be time for some myth busting. Thanks Isaac

    1. disregard the “email”… take note of the last paragraph on the linked page. it should also be remembered that while ACC is very good, it is not perfect. for example: if you have your cruise set to 100kph in the wet and then hit a patch of stationary water, your driving wheels may loose some grip and compensate by speeding up… then in that possibly split second when full grip is obtained, maybe on a bend, or close to a following vehicle, you find yourself travelling a heck of a lot quicker… panic, hit the brakes and loose control. now, you might want to take the risk of using your ACC in the wet, however having had the experience of the above happening (driving a MY14 Subaru Liberty), I make sure my ACC is in the “off” position when driving in the wet. cheers

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