Automatic Emergency Braking
Automatic emergency braking detects a likely collision and applies the brakes to avoid impact or reduce collision speed. AEB is a momentary safety intervention, not sustained driving automation, and therefore remains SAE Level 0.
Sensors used
Automatic emergency braking commonly uses forward Cameras, Radar or both. Some systems add Lidar. Cameras contribute classification and path context; radar contributes direct range and radial velocity; lidar can contribute detailed geometry. Wheel speed and vehicle motion come from Positioning and Vehicle Motion.
Detection alone is insufficient: the system must determine path relevance, time to collision and a safe braking response. Sensor Fusion covers combined evidence, while Calibration, Cleaning and Sensor Health covers contamination, alignment and degraded operation.
Warning, brake support and automatic braking
A typical sequence begins with forward collision warning. Some systems prefill the brake circuit or increase braking force when the driver reacts but does not brake hard enough. Automatic braking begins when the system determines that a collision is likely and the available response time is short.
The sequence and timing vary. A vehicle may brake without a preceding warning when the threat develops too quickly, and the driver can normally override or supplement the intervention.
The scenario determines the capability
“AEB fitted” does not describe a complete performance envelope. Relevant distinctions include:
- moving, slowing or stationary vehicles;
- pedestrians, cyclists and motorcyclists;
- vehicles crossing at a junction;
- an oncoming vehicle during a turn across its path;
- daylight, darkness and reduced visibility;
- straight roads, curves and road crests; and
- forward driving versus reversing.
A system approved or rated for one target and speed range should not be assumed to cover another. UN Regulation No. 152 establishes requirements for advanced emergency braking on passenger cars and light commercial vehicles, while the EU General Safety Regulation phases in detection requirements for vehicles and vulnerable road users.
How the vehicle decides to brake
Cameras classify road users and lane geometry. Radar measures range and relative velocity. Some vehicles add lidar or other sensing. The software estimates predicted paths, time to collision and the likelihood that the driver is already taking effective action.
Braking too late reduces the safety benefit. Braking unnecessarily can create a new hazard. Development and testing must therefore address missed detections, false positives, sensor blockage and unusual objects as well as successful demonstrations.
EV-specific control
An EV may use regenerative braking during the early part of an intervention, but friction brakes must deliver predictable deceleration when regeneration is limited by battery charge, temperature, motor capability or tyre grip. Stability control and anti-lock braking remain active during hard braking.
Limits and buyer checks
Dirty sensors, glare, darkness, precipitation, poor contrast and unusual approach angles can reduce performance. The driver must continue to watch the road and brake or steer when required.
Check the exact vehicle’s target coverage, speed range, nighttime performance, junction capability and rear AEB availability. Consumer-test results identify the tested scenarios; they do not prove that every real collision can be avoided.