Why does Radar outwit ultrasonic and other sensing technologies for blind spot detection?

Date: January 2, 2019

Author: Akshay Srinivasa

Statistics from the National Highway Traffic Safety Administration show that blind spots cause nearly 840,000 accidents and 300 fatalities each year in the United States. Blind spots are areas in the surrounding of the vehicle which are not captured by rear-view mirrors. While there is no ideal position of the mirror or driver seat which would eliminate this blind spot, a lot of these accidents can be attributed to manual error. 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.

While there are several mechanisms designed to detect objects in blind-spots, there are typically three sensors used

  • Ultrasonic sensors
  • Optical sensors
  • Radar sensors

1. Ultrasonic sensors for blind spot detection

Ultrasonic sensors emit sound waves. Their reflection is analysed for any shift in reflected waves based on which object is detected in the blind spot. Ultrasonic sensors are cost effective and are reliable for applications like park assist. This may seem like a perfect solution for blind spot detection, however there are a lot of disadvantages that hinder the use of ultrasonic sensor for this application.

  • Detection range of ultrasonic sensors is really small to be used in moving vehicles
  • Accuracy of ultrasonic sensors varies considerably with changes in operating temperature
  • Reflections from curved and smooth surfaces are difficult to read
  • Rain and other harsh climate conditions like snow affect accuracy
  • Field of view of ultrasonic sensors are quite good but the response rate for detection of objects present in those regions is low
  • It is difficult to detect heterogeneous objects like humans and road signs

2. Optical sensors for blind spot detection

Optical sensors are costlier to implement compared to ultrasonic sensors but can be scaled in automotive industry easily. Optical sensors analyse the actual flow of traffic to identify any objects in the blind spot of the vehicle. Even though these are cost effective they come with numerous disadvantages which cannot be ignored just because it is a cost-effective option.

  • Requires high computational power to work in real time
  • Detection range is small at 4 meters (Max)
  • Dust and water affect the system
  • Snow and other extreme weather limits the use of this sensor
  • Measuring range is small

3. Radar based solution for blind spot monitoring

Radio waves reflect back when they hit a surface and are easily transmitted through the atmosphere. As a result, Radar is widely used in various object detection applications. where the above-mentioned sensors fail to perform. Millimetre wave radar is generally used in automotive blind spot monitoring. Regulations are already in place for this use in passenger cars. Radar based systems use radio waves to detect any object in the operating range and notify the driver. A simple radar-based system consists of- Transmitter, Waveguides, Antenna, Receiver, and a Processing unit. Automotive radar can be broadly classified into: -

  • Short range radar (SRR) – 0.5 to 20 meters
  • Medium range radar (MRR) – 1 to 60 meters
  • Long range radar (LRR) – 10 to 250 meters
Advantages of using radar-based systems for blind spot monitoring:

Radar based systems are known for their advantages in object detection and are predominantly used in aviation industry for their versatility. Advantages of radar-based systems over other sensors are listed below and we can observe how they outperform other sensors.

  • Radar is an all-weather solution. Real world working conditions such as temperature, humidity, rainfall, snowfall, etc. do not affect the functioning of radar-based systems. One of the key advantages of radar is that it works seamlessly under varying light conditions – night or day.
  • Long range radar systems can see as far as 250meters.
  • Materials that are generally considered as insulators such as rubber do not affect radar-based systems. The surface of the reflecting object does not affect the system.
  • It is relatively easier to accurately measure velocity, distance, and exact position of the object using radio waves, in turn identifying an object in the blind spot.
  • Radar can easily differentiate between stationery and moving objects. This is one of the major shortcomings of other sensor-based systems.
  • Existing radar-based blind spot monitoring work well in closed environments such as tunnels where other sensors usually go into standby mode

Even though radar-based systems have the upper hand over proximity-based systems there are quite a few shortcomings of these systems: -

  • Detection of small objects at close range. This is not a problem in blind spot monitoring.
  • Other stationery objects in the blind spot like tress side walls of the bridge are also detected. As a result, a proprietary algorithm for filtering is required.
  • Radar-based systems have their limitations when it comes to recognizing and classifying objects.
  • Interference from other radar systems, which causes accuracy problem
  • Time taken in actual detection and delivering a warning sign to the driver is on the higher side. This requires serious intervention in reducing processing time so that warnings and other precautionary measures are taken as quickly as possible.


Radar is not only economical compared to other technology, but it also provides a wider range of applications. It is a proven technology, and with advances in customized software algorithms, it fast becoming one of the most viable options for car manufacturer and OEMs who are implementing blind spot monitoring in their offering.

Further reading

Here is our radar series of blogs explaining Automotive Radar

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