Automatic Emergency Braking, or AEB, is a vehicle safety system that can slow or stop a car when a collision is likely. It matters because drivers may be distracted, tired, or unable to react quickly enough in sudden traffic situations. AEB uses sensors and computer decisions to reduce stopping distance and crash speed.
Even when it cannot avoid a crash completely, it can make the impact much less severe.
A typical AEB system uses radar, cameras, lidar, or ultrasonic sensors to detect vehicles, pedestrians, cyclists, and obstacles ahead. The control computer estimates distance, relative speed, and time to collision, then warns the driver or applies the brakes automatically. The braking command is sent through electronic brake control, which increases hydraulic pressure or uses electric braking hardware.
Good AEB design must balance quick action with avoiding false braking when there is no real danger.
Key Facts
- Stopping distance = reaction distance + braking distance.
- Time to collision = distance to obstacle / closing speed.
- Braking distance is approximately d = v^2 / (2a), where v is speed and a is braking deceleration.
- AEB often uses sensor fusion, combining radar distance data with camera object recognition.
- If a car slows from 20 m/s to 0 m/s at 8 m/s^2, the braking time is t = v / a = 2.5 s.
- AEB is a driver assistance system, not a replacement for safe following distance and attention.
Vocabulary
- Automatic Emergency Braking
- A safety system that automatically applies the brakes when the vehicle predicts an imminent collision.
- Radar
- A sensor system that sends radio waves outward and measures their reflections to estimate distance and speed.
- Sensor Fusion
- The process of combining information from multiple sensors to make a more reliable decision.
- Time to Collision
- The estimated time before impact if the current closing speed continues unchanged.
- Electronic Brake Control
- A computer controlled braking system that can adjust brake force without the driver pressing the pedal.
Common Mistakes to Avoid
- Assuming AEB can stop any crash is wrong because braking depends on speed, road friction, tires, sensor view, and available distance.
- Ignoring relative speed is wrong because a stopped obstacle and a slower moving vehicle create different closing speeds and time to collision.
- Using braking distance as the total stopping distance is wrong because human reaction time and system detection time can add extra distance before strong braking begins.
- Thinking one sensor does everything is wrong because many AEB systems combine radar and camera data to reduce missed detections and false alarms.
Practice Questions
- 1 A car travels at 18 m/s toward a stopped vehicle 45 m ahead. If the AEB system begins braking immediately with a deceleration of 6 m/s^2, what braking distance is required, and does the car stop before the obstacle?
- 2 A vehicle is moving at 25 m/s behind a truck moving at 15 m/s. If the gap is 30 m, what is the time to collision if neither vehicle changes speed?
- 3 Explain why an AEB system might use both radar and a camera instead of only one sensor when deciding whether to brake.