Many accidents are caused by late braking and/or braking with insufficient force. A driver may brake too late for several reasons: he is distracted or inattentive; visibility is poor, for instance when driving towards a low sun; or a situation may be very difficult to predict because the driver ahead is braking unexpectedly. Most people are not used to dealing with such critical situations and do not apply enough braking force to avoid a crash.
Several manufacturers have developed technologies which can help the driver to avoid these kinds of accidents or, at least, to reduce their severity. The systems they have developed can be grouped under the title:
Autonomous: the system acts independently of the driver to avoid or mitigate the accident.
Emergency: the system will intervene only in a critical situation.
Braking: the system tries to avoid the accident by applying the brakes.
AEB systems improve safety in two ways: firstly, they help to avoid accidents by identifying critical situations early and warning the driver; and secondly they reduce the severity of crashes which cannot be avoided by lowering the speed of collision and, in some cases, by preparing the vehicle and restraint systems for impact.
Most AEB systems use radar or lidar-based technology to identify potential obstacles ahead of the car. This information is combined with what the car knows of its own travel speed and trajectory to determine whether or not a critical situation is developing. If a potential collision is detected, AEB systems generally (though not exclusively) first try to avoid the impact by warning the driver that action is needed. If no action is taken and a collision is still expected, the system will then apply the brakes. Some systems apply full braking force, others an elevated level. Either way, the intention is to reduce the speed with which the collision takes place. Some systems deactivate as soon as they detect avoidance action being taken by the driver.