Emergency braking system (Autonomous Emergency Braking, AEB) is one of the key safety technologies of modern cars, which can prevent accidents or significantly reduce the severity of the consequences. According to Euro NCAP, cars with AEB are 38% less likely to be involved in rear-end collisions and 27% less likely to be involved in collisions with pedestrians. But how exactly does this system detect danger, make a decision and stop the car faster than the driver can react?

In this article we will analyze in detail working principle of AEB, from sensors and algorithms to the physical impact on the braking system. You will learn what types of systems exist (for city traffic, intercity speeds or pedestrian protection), how they interact with other assistants like adaptive cruise control or traffic sign recognition, and why sometimes AEB can false alarm or, conversely, “sleep through” the accident. We will pay special attention critical limitations of first generation systems (until 2018), which are still found on budget models.

What is an emergency braking system and why is it needed?

Emergency braking system (AEB) is a complex of hardware and software that automatically activates the brakes, if the driver does not have time to react to the obstacle. Its main task is to prevent or mitigate the consequences:

  • 🚗 Rear collisions (the most common scenario is 40% of all accidents according to NIIAT)
  • 🚶 Pedestrian collisions (especially in urban environments)
  • 🚲 Accidents involving cyclists and motorcyclists (in systems with advanced recognition)
  • 🦌 Animal collisions (in premium versions, for example, Volvo City Safety)

According to IIS (US Insurance Information Institute), AEB reduces the number of insurance claims for road accidents by 14-23%, depending on the manufacturer. However, it is important to understand that the system does not replace the driver, but only complements his reaction. For example, at a speed of 60 km/h, a car travels 16.7 meters per second - if the driver is distracted by a smartphone, AEB can operate 0.5-1 seconds before the collision, but physics will not allow the car to completely stop at such a distance.

📊 Does your car have Assisted Emergency Braking (AEB)?
Yes, factory
Yes, additionally installed
No, but I plan to install it
No and not needed
I don't know

System design: what sensors and modules are involved

The AEB system consists of several key components that work in unison. Main elements:

Component Type Function Examples of manufacturers
Radar Millimeter (77 GHz) Measures the distance to objects and their speed (effective at high speeds) Bosch MRR, Continental ARS 408
Lidar Laser scanner Creates a 3D map of the environment (more precisely a radar in urban environments) Velodyne, Ibeo
Camera Monocular or stereo Recognizes objects (pedestrians, signs, markings) and classifies them Mobileye EyeQ, Nvidia Drive
Control unit ECU (electronic unit) Processes sensor data and makes decisions about braking Delphi, ZF TRW
Actuator Hydraulic or electric Activates the brake system (injects pressure into the circuit) Bosch iBooster, Continental MK C1

Most production cars use radar and camera combination — this allows you to level out the shortcomings of each sensor. For example, the radar does not recognize static objects (parked cars) well, and the camera can be “blinded” by the bright sun. Modern systems (eg Tesla Autopilot or Mercedes Drive Pilot) use sensory fusion — merging data from multiple sources to improve accuracy.

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If you have an AEB camera installed on your car's windshield, never apply tint or film to it - this may block the infrared sensors and lead to system failure.

How the algorithm works: from danger detection to braking

The AEB actuation process can be divided into 4 Key Stages, each of which takes a fraction of a second:

  1. Object detection — sensors scan the space in front of the car (usually in a range of up to 200 meters). The radar records distance and speed, the camera records the shape and type of object (for example, it distinguishes a pedestrian from a pole).
  2. Threat classification — the system determines whether the object poses a danger. For example, if there is a car ahead at the same speed, AEB will not work. But if she brakes suddenly or a pedestrian appears, the algorithm will regard this as a risk.
  3. Advance warning - a signal (usually a red triangle) lights up on the dashboard, a beep sounds, and in some systems (Toyota Safety Sense) The brake pedal also twitches.
  4. Brake activation — if the driver does not react, the system itself builds up pressure in the brake system. Depending on the speed, this can be either a complete stop or simply slowing down before a collision.

The critical parameter is system response time. In modern AEB (for example, in Volvo XC90 or BMW 5 Series) it amounts to 0.2–0.5 seconds, while a person has an average reaction - 1–1.5 seconds. However on systems before 2018 (for example, in early versions Honda Sensing) reaction time could reach 0.8 seconds, which is critical at speeds above 80 km/h.

Why might AEB work on an empty road?

Sometimes the system triggers falsely due to:

- Dirt or snow on the sensors (the radar perceives this as an obstacle),

- Low sun (the camera “sees” the highlights as an object),

- Metal bridges or tunnels (radar reflected from structures),

- Interference from other radars (for example, in a traffic jam with many cars with AEB).

In such cases, it is enough to restart the system (turn off/on the ignition) or clean the sensors.

Types of emergency braking systems: how they differ

Not all AEBs are the same - their functionality depends on target scenario and car class. There are three main types:

  • 🏙️ City systems (City AEB) - operate at speeds up to 50–60 km/h, optimized for pedestrians and cyclists. Examples: Ford Pre-Collision Assist, Hyundai SmartSense.
  • 🛣️ Intercity systems (Highway AEB) - designed for speeds up to 120–160 km/h, focus on other cars. Examples: Mercedes PRE-SAFE Brake, Audi Pre Sense Front.
  • 🚶➡️🚗 Universal systems — combine both modes and add recognition of animals, motorcycles, and sometimes road signs. Examples: Tesla Collision Avoidance, Volvo City Safety.

In addition, systems differ in level of autonomy:

  • 🔴 Level 1 — driver warning only (sound + visual signal).
  • 🟡 Level 2 — partial braking (reduces speed, but does not stop the car completely).
  • 🟢 Level 3 — full stop (if speed allows).

For example, Nissan ProPilot belongs to level 2, and Subaru EyeSight — to level 3. When choosing a car, it is important to check what type of AEB is installed, as this directly affects effectiveness in real conditions.

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Level 3 (full stop) systems require regular calibration of sensors - after replacing the windshield, bumper or even wheels. Ignoring this may result in AEB failure at a critical time.

Limitations and blind spots of AEB systems

Despite its high efficiency, the emergency braking system has physical and algorithmic limitations, which are important to know:

⚠️ Attention: Most AEB do not work when driving in reverse (exception - premium models like BMW 7 Series with option Reversing Assistant). Also, systems often “do not see” objects moving across the trajectory at a speed higher than 30 km/h (for example, a car leaving a parking lot).

Main blind spots:

  • 🌧️ Weather conditions — rain, snow or fog reduce the accuracy of the radar and camera. For example, during heavy rain, the detection range may drop from 150 to 50 meters.
  • 🌅 Lighting — direct sunlight or darkness impairs the performance of the cameras. Night systems (for example, in Lexus Safety System+) compensate for this with infrared sensors.
  • 🚧 Difficult road conditions — AEB can “lose” objects in traffic jams, at intersections or during frequent lane changes.
  • 🛠️ Technical problems — dirty sensors, damaged cables or uncalibrated cameras lead to false alarms or failures.

Another critical point - interaction with other systems. For example, if simultaneously with AEB the electronic differential lock (EDL), the braking distance may increase due to the distribution of braking forces. In some vehicles (eg VW Golf) this can be solved programmatically, but in budget models such a conflict can lead to insufficient braking.

Why AEB may not work: real cases and statistics

Even the most advanced systems do not guarantee 100% protection. Analysis of accidents involving vehicles equipped with AEB shows typical causes of failures:

  1. Exceeding the system speed limit. For example, Toyota Safety Sense in the basic version it works up to 80 km/h — at higher speeds it only warns the driver, but does not brake.
  2. Unexpected obstacle. If an object appears in the system's field of view later than 0.7 seconds Before a collision (for example, an animal jumping out onto the road), AEB physically does not have time to react.
  3. Disabled system. Some drivers deliberately deactivate AEB due to false alarms (especially in urban environments). B Ford Focus 2019 this can be done through the menu Settings → Driving assistants.
  4. Incompatible with vehicle modifications. Installing non-standard bumpers, headlights or suspension may block the sensors. For example, in Skoda Octavia The radar is mounted behind the bumper - if you replace it with a non-original one, the viewing angle will change.

According to insurance company Allianz, in 2023, 18% of accidents with cars equipped with AEB occurred precisely because the system was disabled. Moreover, in 60% of cases, drivers did not even remember that they had deactivated it earlier. To avoid this, newer models (e.g. Peugeot 308) is provided automatic activation of AEB every time the engine is started.

🔹 Look at the on-board computer menu (Security or Driver Assistants section)

🔹 Look for the AEB icon on the dashboard (usually the car with an exclamation mark)

🔹 Carry out a test in an empty parking lot: drive slowly up to an obstacle (for example, a cardboard box) - the system should work at a distance of 1-2 meters

🔹 Check the sensors for cleanliness (the radar is usually hidden behind the bumper, the camera is on the windshield)

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How to check and maintain the AEB system

For the emergency braking system to work correctly, it must be regularly diagnose. Here are the key points:

  1. Visual inspection of sensors - check once a month:
    • 🔦 Cleanliness of the radar (usually located behind the front bumper, under the emblem)
    • 📷 Keep the camera clean (on the windshield near the rear view mirror)
    • 🔌 Wiring integrity (especially after an accident or repair)
  2. Software diagnostics - using a scanner (for example, Launch X431 or Autel MaxiCOM) check errors in the AEB control unit. Fault codes usually start with:
    • C1A - problems with radar
    • B13 - camera errors
    • U01 — loss of communication between modules
  • Calibration - required after:
    • 🔧 Windshield replacement (camera moves)
    • 🚗 Front body repair
    • 🔄 ECU firmware updates

    The cost of calibration in the service varies from 3,000 to 10,000 rubles depending on the car brand. For example, for Kia Ceed it will cost 4,500 rubles, and for Mercedes E-Class - up to 15,000 rubles due to the complexity of the equipment. Some dealers (eg. Hyundai or Toyota) offer free calibration within the framework of warranty service.

    ⚠️ Attention: If you ignore calibration after repairing or replacing glass, the system may incorrectly estimate the distance to objects. For example, in Renault Arkana with an uncalibrated camera, AEB triggered 2–3 meters later than normal, which is critical at a speed of 60 km/h.

    FAQ: Frequently asked questions about the emergency braking system

    Can AEB completely stop a car at high speed?

    No, the physics of braking is limited by the adhesion of the wheels to the road. For example, at speed 100 km/h even an ideal system will be able to reduce the speed to a maximum of 30–40 km/h due to emergency braking (on dry asphalt). However, this will significantly reduce the severity of the accident. A complete stop is guaranteed only at speeds up to 50–60 km/h (depending on model).

    Does AEB work on animals?

    Only in premium systems (for example, Volvo City Safety or Mercedes PRE-SAFE). Most budget AEBs (like Lada Vesta with LADA Pilot) only recognize cars and pedestrians. Even in advanced systems, the efficiency of recognizing animals does not exceed 60% due to their unpredictable trajectory.

    Can I disable AEB myself?

    Yes, but the methods differ depending on the brand:

    • Toyota: Settings → Security → Pre-Collision System → Off
    • Volkswagen: Assist → Front Assist → Deactivate
    • Hyundai/Kia: Hold button DRIVE MODE 3 seconds.
    Important: In most cars, the system automatically turns on the next time you start the engine.
    Is it true that AEB damages brake pads?

    Partially yes. Systems with aggressive braking (for example, Tesla or BMW) can reduce the life of the pads by 10–15% due to frequent emergency operations. However, this is compensated prevented road accidents, which would cost more. In some models (for example, Audi) is used regenerative brakingto reduce wear.

    How does AEB behave in traffic?

    Modern systems (eg Bosch AEB City) are adapted for traffic jams and can:

    • Automatically brake to a stop at speeds up to 30 km/h.
    • Maintain a distance from the car in front (in conjunction with adaptive cruise control).
    • Resume movement after a short stop (if the pause is less than 3 seconds).

    However, in dense traffic it is possible false positives due to the frequent appearance/disappearance of objects (for example, motorcycles “slipping” between rows).