Autonomous emergency braking is one of the most significant road safety advances of recent decades. AEB detects potential collisions and automatically applies the brakes if the driver does not react, potentially preventing accidents or substantially reducing their severity. ## How AEB Works AEB systems use a combination of cameras, radar, and sometimes lidar sensors to detect vehicles, pedestrians, cyclists, and other road users ahead. Sensor fusion algorithms combine data from multiple sources to build a comprehensive picture of the road ahead. The system operates in stages. First, forward collision warning provides an audible and visual alert when a collision appears imminent. If the driver does not react, partial autonomous braking applies moderate brake pressure to slow the vehicle. If the driver still does not react, full autonomous braking applies maximum brake pressure. AEB operates across different speed ranges. Low-speed AEB, typically functional up to approximately 30mph, addresses urban accidents at roundabouts and junctions. High-speed AEB extends to motorway speeds, addressing rear-end collisions at motorway cruising speeds. The system calculates time-to-collision based on the relative speed and distance of objects ahead. When time-to-collision drops below a threshold, the warning activates. If it drops further, braking intervention begins. ## Pedestrian and Cyclist Detection Modern AEB systems detect pedestrians and cyclists, not just vehicles. This required significant algorithm development because pedestrians and cyclists move differently from vehicles and require separate detection models. Pedestrian detection uses pattern recognition trained on thousands of images of people walking, running, and crossing roads. The system must distinguish pedestrians from roadside furniture, shadows, and other objects that could be mistaken for people. Cyclist detection is particularly challenging because cyclists travel faster than pedestrians and may approach from behind at junctions. The system must detect bicycles from multiple angles and in varying postures. Night-time pedestrian and cyclist detection relies on both camera recognition and infrared capabilities. Some systems use dedicated infrared cameras for night-time pedestrian detection, extending AEB benefits to low-light conditions. ## AEB Effectiveness Thatcham Research estimates that AEB reduces rear-end collisions by approximately 38% and reduces associated injuries by similar proportions. The systems are most effective in urban conditions where collisions typically occur at lower speeds. AEB does not prevent all accidents. The system cannot detect objects outside its field of view, and in some scenarios the collision is simply unavoidable regardless of braking force. AEB reduces the severity of most detectable collision scenarios. The effectiveness of AEB varies significantly between manufacturers and systems. Euro NCAP rates AEB systems on their ability to prevent collisions at different speeds and scenarios. Check Euro NCAP ratings for your vehicle's AEB performance. ## Limitations and Maintenance AEB sensors, particularly cameras mounted behind the windscreen, must remain clean and unobstructed. A dirty windscreen, snow accumulation, or damaged camera cover can reduce or disable AEB functionality. Keep the windscreen clean and inspect camera covers regularly. Aftermarket windscreen replacement may not include recalibration of the AEB camera, causing the system to malfunction. Always use qualified windscreen replacement services that include ADAS recalibration. Sensor misalignment from minor bumper damage or panel gaps can affect AEB accuracy. After any front-end impact, even minor ones, have the sensor alignment checked. ## Frequently Asked Questions **Can I turn off AEB?** Most vehicles allow AEB to be temporarily disabled through the infotainment system. Some allow permanent disabling, but this is not recommended. The system re-enables automatically after the ignition is cycled on most vehicles. **Does AEB work in heavy rain?** Heavy rain can reduce camera effectiveness significantly, potentially limiting AEB functionality. Radar is less affected by rain. In severe weather, AEB performance may be reduced, and the driver must remain alert regardless. **Is AEB mandatory in the UK?** AEB has been mandatory on all new cars sold in the EU and UK since 2022. Used cars may not have AEB. Check for AEB when purchasing used vehicles and consider its absence in safety assessment.