How does Autonomous Emergency Braking work?

Assistance systems help prevent accidents. In a new series on VisionZeroWorld we explain how ABS, ESP & Co. work. This time it’s the turn of Autonomous Emergency Braking.

You’re driving home after a long and stressful day at work. The traffic on the freeway is slow-moving, and testing everyone’s patience. To make matters worse, you’re both tired and hungry. The setting sun is providing a little diversion, however, turning the evening sky a fiery red. And just to add to this breathtaking panorama a hot-air balloon is drifting across the sky. What a spectacle! In a moment you’ll be able to see the balloon through the sun roof. You look up just for a second and – there’s a  sickening crunch as you hit the car in front. The moment you looked away, the slow-moving traffic came to a stop. And when you’re not paying attention, there’s no such thing as a safe following distance. Any distraction cuts vital meters from your braking distance. At 50 km/h, you lose approximately 15 meters for every second you take your eyes off the traffic. Unless, of course, your car is equipped with Autonomous Emergency Braking.

Because Autonomous Emergency Braking (AEB) never gets distracted. Like an ever-attentive co-driver, it is always ready to intervene when it detects a critical situation. Automatic braking technology is evolving all the time, and with every new generation manufacturers like Continental are helping to make the roads an ever-safer place. So how does AEB actually work? AEB is a proactive and predictive driver assistance system that provides emergency braking assistance – or can even brake autonomously – if an accident risk is detected. This intelligent system aims to avoid collisions with all types of obstacle. Alternatively, if an accident is unavoidable, the system targets maximum reduction of the impact speed. AEB systems use a network of sensors to continuously monitor and evaluate basic operating and driving conditions such as speed, acceleration and proximity to obstacles, along with pedal positions and steering angle. The sensors can detect, say, if the vehicle is starting to close up on a vehicle in front. The detected speed and proximity data is used by an onboard computer to calculate when the driver would need to react in order to prevent a collision. If the driver has not responded appropriately by that time, for example by lifting off the gas or braking, the system takes appropriate action automatically. Experts estimate that fitting vehicles with state-of-the-art AEB systems could cut road accident injuries by approximately 35 percent.

Autonomous Emergency Braking systems come in three different types, distinguished by their applications: “pedestrian”, “city” and “inter-urban” (for out-of-town highway driving). The algorithms of city AEB systems are adapted to dense traffic conditions, frequent braking and acceleration, and roundabouts, while inter-urban systems are adapted to the higher speeds and longer safety margins on highways. Pedestrian AEB systems meanwhile feature special sensors designed to detect pedestrians in the immediate vicinity of the vehicle, who could potentially step out suddenly into its path. Ideally, the AEB technology will be complemented by appropriate occupant protection systems. If an impact with an obstacle is unavoidable, these systems can respond by instantly tightening the seatbelts, adjusting the backrests to an upright position and raising lowered head restraints. Finally, AEB retains its ability to intervene even after a collision has taken place. For example if the system is integrated with the airbag control unit, the onboard computer can use the ESC system to automatically stabilize and brake the vehicle following airbag deployment in order to minimize the risk of secondary collisions.

In Germany, AEB was first fitted in 2006, in the Mercedes CL Class, and in the meantime this “intelligent co-driver” technology has trickled down to become a standard feature on many mid-range models too. But the experts also sound a warning note: Responsibility for making the correct driving decisions always rests with the driver, and Autonomous Emergency Braking was developed only to assist in emergencies. It is not a substitute for normal braking.