AEB

Automatic emergency braking is a vehicle safety system that detects an imminent collision and applies the brakes without driver input. The system uses radar, lidar, or camera sensors mounted in the front bumper or behind the windshield to monitor the road ahead. When the sensors detect an obstacle or another vehicle within a closing distance that the system calculates will result in a crash, it triggers the brake actuators. The time window is measured in fractions of a second; most systems operate between 0.3 and 0.8 seconds from detection to full braking pressure.

AEB systems operate in stages. The first stage is a warning to the driver, usually a visual or audible alert, giving them a chance to brake manually. If the driver does not respond, or responds too slowly, the system enters intervention mode and applies braking force. Some systems apply partial braking first, allowing the driver to take over; others go directly to maximum pressure. The strength of deceleration depends on the system design and the detected threat, ranging from 0.5g to 1.0g (5 to 10 meters per second squared). Vehicles equipped with advanced systems can achieve full braking in under one second.

The technology varies significantly between manufacturers and price points. Basic systems detect only other vehicles directly ahead; advanced versions track pedestrians, cyclists, and stationary objects. Some systems only function at low speeds, below 50 kilometers per hour, while premium systems operate across the full speed range. Integration with vehicle stability control and electronic braking systems allows AEB to modulate brake pressure across individual wheels, preventing skids during emergency stopping.

Common failure modes and limitations

AEB is not foolproof. Sensor fouling from dirt, snow, or heavy rain can blind the system entirely. Dark-colored objects at night, particularly unlit vehicles or animals, may not register until too late. The system cannot compensate for extreme closing speeds; a vehicle traveling at 120 kilometers per hour approaching a stationary object may not stop in time even with maximum intervention. False positives occur, particularly with bridge structures, overhead signs, or stationary debris that the sensors misidentify as obstacles.

The term "autonomous emergency braking" emerged as the technology matured and became more reliable; both phrasings are now used interchangeably in the industry, though "automatic" is more common in regulation and testing standards. AEB is now mandatory or strongly encouraged in new vehicle homologation across Europe, North America, and other regions, typically tested against fixed barriers and moving target vehicles in standardized crash test protocols.