An Autonomous Emergency Brake (AEB) system is an emergency brake system that intervenes autonomously when (after several warnings) the driver does not apply the brakes. Maximum brake delay is applied, which means more braking force is used than the driver usually applies. In this way, crashes may be prevented or injury severity may be mitigated on account of a lower collision speed. Two types of AEB systems may be distinguished: a system that merely responds to the presence of other cars and a system that also responds to the presence of cyclists and pedestrians. The first uses radar for example, the second uses (smart) cameras.
Both the effectiveness of an AEB system  , and the cost-benefit ratio  are assessed positively. A study into the effectiveness, based on crashes in several European countries, showed a 38% reduction of rear-end collisions .The European Commission has included AEB systems in its proposals for revised type approval .
AEB systems do not always work flawlessly, for instance because the software has trouble recognizing an image or because a sensor (radar, camera) simply cannot see everything. When a system alerts the driver or intervenes, the chances of unjustly alerting or intervening (false positive) or unjustly not alerting or intervening (false negative) should be balanced against each other. In the case of alerts, occasional unnecessary warnings are less serious, as long as the system remains credible. Better one too many than one too few warnings; it is, after all, the driver who remains in control. In case of an intervening system, groundless abrupt braking is objectionable; it may lead to dangerous situations, especially in the presence of following traffic. This will more likely result in the choice not to intervene when intervention was called for. Moreover, if a system regularly makes mistakes, drivers will switch it off. Sensors and software continuously improve however, which will decrease the number of mistakes and increase the effectiveness of autonomous (intervening) systems in particular. To enable fully self-driving cars, such systems should comply with very strict requirements, which means they are only expected to arrive in a few decades . Meanwhile, the improvement of existing ADAS, such as AEB systems, may greatly increase safety.