Active and Passive Safety Systems in Cars

Date: July 12, 2019

Author: Akshay Srinivasa

As vehicle density increases year by year, so do the accidents caused due to poor driving habits, environmental factors or factors beyond one’s control. This has led manufacturers to pack their offerings with safety features, making it more compelling for users to buy these passenger and commercial vehicles. These safety features in general are classified as active and passive safety features. With autonomous cars making headway, these features are treated as mandatory rather than as optional extras in the cost-sensitive automotive market.

Active Safety System

  • Always on the look-out for driver and aides in driving
  • Sensors used are always on lookout mode
  • Example-Adaptive cruise control, Lane departure warning, Night vision, Blind spot detection, vulnerable road user detection, Driver Monitoring system and more

Passive Safety System

  • Comes into play only after a certain event outcome like a crash or roll-over
  • Sensors are active only in case of a crash
  • Example- Occupancy detection, Airbag, Seat belts, Fuel pump shutoff system

Active Safety Features in Cars

As the name suggests, these systems are always in a vehicle to mitigate any accidents and mishaps. These systems use- Ultrasonic, Radar, Lidar and cameras to monitor the surrounding. Various active safety systems are listed below.

Adaptive Cruise Control (ACC)

ACC is the higher version or next stage of cruise control where in the vehicle adjusts its speed depending upon the speed of the vehicle in front.

Type of sensor- Radar, Ultrasonic and Lidar

Lane Departure Warning (LDW)

On motorways it is necessary to stick on to a single lane making way for faster traffic. However, prolonged driving which leads to stress and lack of concentration, may result in drivers not following this. A lane departure warning system uses any of the following sensors to clearly identify the path and takes necessary preventive measures, adhering to lane change discipline and practise.

Type of sensor- Radar, Ultrasonic and Lidar

Night Vision

Even with innovations in automotive lighting it is still difficult for users to have a clear view of the road ahead. With assistance from a night vision camera or lidar, users will be assisted with object avoidance in their path in the dark.

Type of sensor- Radar, Ultrasonic and Lidar

Blind Spot Detection (BSD)

Blind spots are areas surrounding the vehicle that are not captured by rear-view mirrors and side view mirrors. There is no ideal position of the mirror or driver seat that can eliminate this blind spot. A lot of accidents can be attributed to changing lanes when other vehicles are in blind spot. As a result, an automatic warning sign/ indicator to alert the driver about any object or other vehicle in the blind spot becomes a major requirement to enhance safety.

Type of sensor- Radar, Ultrasonic, Camera and Lidar

Driver Monitoring Solutions-

Driver Monitoring solutions or systems in general use a single camera to track various facial features of the driver. Upon tracking facial features, CNN models or traditional machine vision algorithms are used to predict any distraction or sleep deprivation. A sophisticated DMS can do more than just distraction alerts, like cabin personalization to specific user and emotion estimations.

Type of sensor- Camera

Road Sign or Vulnerable Road User Detection-

As vehicles become semi-autonomous, they should be able to identify various traffic signs, traffic lights and other objects and pedestrians on the road. Identifying all these will make sure the cars take necessary precautions as well as obey various traffic rules.

Type of sensor- Camera

Passive Safety Features in Cars

In the previous section, we discussed various features that assist drivers to take preventive measures and make the roads a lot safer. However, some cases may end in not-so-safe results. Hence, cars are equipped with various passive safety features that help in overcoming post-incident hurdles.

Occupancy Sensing

People are no longer shocked when they hear news of a living being left behind in the back seat of a car which can turn out to be fatal. To address this, manufacturers are using technology similar to ADAS for cabin sensing, wherein the device scans the car’s interior for any actual living being after the user/driver locks and moves away from the car. The device alerts the user if anything or anyone is left behind.

Type of sensor- Camera and Radar


This is a feature initially introduced by a Swedish car maker and later made available to all for the greater good. Sensors are placed across the vehicle to sense impact and within a set time frame, airbags are deployed inside the cars to protect passengers. The same car maker recently announced airbags for pedestrians which are placed outside the vehicle - thus making their impact in case of an accident less harmful.


This is one of the first passive safety feature to ever be made available to users. This system reduces the chances of facial impact of the users on the front dashboard or front seat (for rear seat passengers). There are numerous types of seatbelts depending on the number of harnesses that secures the users.

In Conclusion

Early 21st century manufacturers started to equip cars with a host of both active and passive safety systems, making their products not only safer on roads but also more of a USP for differentiating among competition. The next decade will see more innovation in active and passive systems such as ADAS, which houses a variety of sensors to make the journey safer for users as well as pedestrians.

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