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Autonomous Emergency Braking explained

By David Bonnici, 24 Mar 2017 Car Advice

Autonomous Emergency Braking explained

Not all AEB systems are created equal so if buying a new car with the equipment it’s important to know what you’re getting and how it works

AUTONOMOUS Emergency Braking (AEB) is a form of automatic braking which stops your car automatically if it senses you’re about to hit an object such as a vehicle stopped in front or in some cases people on the road.

AEB is becoming more common across manufacturers as standard, or optional equipment as part of a wider safety package.

While it’s an excellent idea to buy a car with AEB it’s important to know that there are different kinds of systems with various capabilities.

For example some systems will only slow the car to reduce the impact of a crash – look for words like ‘collision mitigation’ which only lessen the severity of an unavoidable accident rather than avoid an impact outright. Others are only effective up to lower speeds and often referred to as low speed or city braking.

There are three main categories of braking systems.

Low Speed systems

These target city driving where crashes often occur at low speeds but can cause debilitating injury such as whiplash. Typically, these systems look for the reflectivity of other vehicles and are not as sensitive to pedestrians or roadside objects.

Such systems use a laser sensor (usually mounted in the top of the windscreen) to detect obstacles. Because the laser’s range is limited there is less warning meaning it’s only effective at lower speeds and in some cases will lessen impact rather than come to compete stop. Depending on the system the maximum effective speed can be anywhere between 40 and 80km/h.

A disadvantage of laser sensors is they can be hindered by atmospheric conditions such as rain or fog.


Higher Speed systems

These typically utilise long range radar to scan further ahead of the vehicle (up to 200 metres) which allows for higher closing speeds. Another advantage of radar is it’s less susceptible to interference from atmospheric conditions that can interfere with lasers.

Other systems, such as Subaru EyeSight, use a pair of stereoscopic cameras at the top of the windscreen and some sophisticated software to generate a three-dimensional picture of what’s on the road ahead of the car. The cameras can also detect smaller objects like people or when the car is straying out of its lane.

However, the cameras can be adversely affected by harsh weather or light conditions (such as when driving directly into the sun), wet roads or even a dirty windscreen in front of the lenses.


Pedestrian detection systems

These versions use a camera(s) combined with radar to detect vulnerable road users through their shape and characteristics. The way in which pedestrians move relative to the path of the vehicle is calculated to determine whether they are in danger of being struck. Some high end systems can work at speeds up to 210km/h and bring the car to a complete stop.

Even with the most advanced AEB systems nothing prevents a collision more than the Mk1 Eyeball so it’s important to treat the technology as a system of last resort rather than a substitute for being alert.