What is autonomous emergency braking?

Autonomous or auto emergency braking (AEB) is a technology already at the very forefront of active safety on our roads.

Utilising radar or cameras, AEB prevents or minimises potential crashes by braking the vehicle if the system detects that a collision is imminent and the driver fails to take appropriate action.

Experts claim that AEB is perhaps the biggest advance in road safety since the widespread introduction of electronic stability control (ESC).

Early systems like Volvo’s City Safety were designed to work at relatively low speeds, seemingly aimed at reducing the cost of urban nose-to-tail accidents as much as reducing road trauma.

The initial focus on low-speed crashes was understandable, given that even today the most common type of two-vehicle crash at an intersection is a rear-end collision; light vehicles (cars and utes) impacting the rear of another vehicle account for almost 15 per cent of all Australian light vehicle trauma.

Today, there are essentially four types of AEB in use by car-makers. They are:

City AEB

Typically working at speeds below the built-up area speed limit, these systems have the potential to eliminate or reduce whiplash-style injuries. Although they aim to protect car occupants, a significant focus appears to be on the minimisation of vehicle damage. They are slowly being rendered obsolete as newer systems incorporate higher-speed operating ranges.

Vulnerable road users

These systems use radar and cameras to detect pedestrians, motorcyclists and cyclists via shape recognition. After calculating differential movement and speed, if there’s a danger of impact the system brakes the car.

High-speed AEB

Now becoming increasingly prevalent, high-speed AEB can operate at speeds well in excess of Australian speed limits and uses radar scanning further ahead of the vehicle to detect the risk of a possible collision. In the absence of timely action by the driver, high-speed AEB then auto-brakes the car to avoid or at least mitigate the severity of a collision.

Reverse AEB

Relatively new on the scene, reverse AEB, as the name suggests, will bring the car to an immediate halt when it is reversing. Such systems can detect stationery objects or brake the vehicle if a child or vehicle is detected crossing the path of the reversing vehicle.

Dr David Young, Manager for Vehicle Safety, Innovation and Technology at Victoria’s Transport Accident Commission (TAC), says that AEB “can definitely progress” in future, with new systems being developed all the time.

“A lot of these [systems] are starting to be tested as a part of the Australasian New Car Assessment Program [ANCAP], and in turn we hope for them to be regulated as well,” he says.

“Some of the latest systems are motorcycle AEB – AEB that works to avoid a crash with a motorcyclist – [and] junction AEB, which functions when you are approaching an intersection or a junction. The latter are systems that can work at very low speeds and look at vehicles that are coming in all different directions and ensure that you do not creep out into the intersection when it’s not safe to do so.

“The other which could be a gamechanger is high-speed/head-on impact AEB. There are some really exciting new systems that are coming.

“We’ve got a good basis to build from,” Dr Young commented.

The basic requirement for high-speed AEB to work effectively is the ability to scan a considerable distance ahead of the vehicle so the system has time to react if an unfolding hazardous situation is detected.

Typically, though not exclusively, this is achieved through the use of long-range radar and in many ways is an extension of the adaptive cruise control function seen in increasing numbers on new cars.

This type of system can be effective from highway speeds right through to a full stop, and usually operates in a staged manner to warn the driver first of an impending accident, before applying the brakes progressively, with full emergency braking exerted just before impact.

If the driver does hit the brakes, the system will ensure sufficient force is applied to bring the car to a timely stop.

The majority of AEB systems work via sensors located right at the front of the car where they are able to send out radar signals, lidar or laser beams to scan the road ahead. One exception is Subaru’s camera-exclusive EyeSight system, which scopes out the road ahead via stereoscopic cameras mounted at the top of the windscreen. Tesla also uses a camera-based system.

The biggest hurdle to overcome with AEB is that drivers can become complacent, depending heavily on the system. One example is a US-based Tesla driver who died after his Model S failed to register a semi-trailer crossing in front of the car, due to sun glare.

Dr Young is firmly of the opinion that car manufacturers need to ensure their customers aren’t buying into any mythology about their cars’ respective capabilities.

“That’s the most important thing; there are situations where AEB works very well, and is tested and proven, and there are areas where AEB is less effective, or not yet capable, in the case of some systems,” Dr Young explained.

“You might be driving a car with an older system of AEB as well. It’s about understanding what [the] vehicle can do, and making the driver aware that the system is a back-up. It’s not all-encompassing, it’s not all-capable yet. Drivers need to be aware and in control.”

Because not every AEB system is the same, the effectiveness can vary according to circumstances. For example, all systems can be affected by prevailing weather. Neither camera-only systems nor radar-based systems function at their optimum in heavy rain or extremely heavy fog — and Subaru’s camera system has been known to switch off temporarily if it is effectively blinded when facing directly into the sun.

Other scenarios, such as slick, icy, or gravel road surfaces, or if a heavy caravan is being towed, may not impact on the AEB’s workings, but they will influence the car’s ability to stop as and when the system determines it should.

Many systems use a mix of technologies to produce an effective result, particularly in terms of pedestrian protection where cameras are better able to recognise specific shapes than radar or other technologies.

Whenever a new active safety system is introduced to the market, there will always be someone to boast that they can react faster and more safely than the electronic system. But fatigue and distraction can affect even the best of drivers, slowing reaction times. AEB, on the other hand, has metronome-like consistency on its side. It doesn’t get tired or distracted.

“Obviously there are scenarios where a fully alert driver is monitoring their periphery,” says Dr Young.

“[They] may detect something before an AEB system, particularly if it’s an AEB system that was maybe an early-stage system. However, as we know, the job for a driver is a very tricky one, and a driver may not always be able to be as fully alert and attentive as a system in a vehicle.

“There is potential for both scenarios — and AEB is really good as a fail-safe, as something that backs up driver.

“It’s not there in place of the competent driver. It’s there to be sure that we back up that competent driver as much as we can — so that when they’re distracted or unable to perform at their absolute peak, they’ve got that safety net there to help protect them and others.”

Research released in December 2022 by Monash University Accident Research Centre suggests the fitment of AEB to light passenger vehicles has the potential to impact the outcome and to potentially avoid or mitigate up to 67 per cent of trauma incidents occurring in light vehicle crashes.

But although AEB will be mandated by Australian Design Rules for new vehicles this year, we’re still perhaps a decade away from registering the full effect of AEB on road trauma, says Dr Young.

Technology like AEB needs time to trickle down through our national fleet.

“We know here in Australia we typically have an older fleet – with the average [vehicle] age in Australia now ticking over the 10 years mark,” Young says.

“The Commonwealth Government estimates over a 15-year period, following regulation, the Australian Design Rule for AEB will save 582 lives, over 20,000 serious injuries – in terms of hospital admissions – and over 70,000 minor injuries,” Dr Young stated.

The message is clear — AEB saves lives. And it will save even more if we all commit to buying cars with this important safety feature now – and in the future.

Here is a full list of vehicles currently available with AEB