Decoding Blind Spot Detection and Warning Systems

What do blind spots have to do with driving?

A blind spot detection warning indicator on a car mirror.


Blind spots are areas outside of a vehicle that the driver is unable to see. Window pillars, headrests, passengers, and other obstructions can all block a driver's view, creating blind spots.

Special mirrors can help reduce or eliminate blind spots, and blind-spot detection systems use technology to provide a warning whenever a vehicle, pedestrian, or other object enters a blind spot.

What Causes Blind Spots in Cars?

Every part of a car that isn't glass can create a blind spot. That means vehicles with larger window pillars have larger blind spots, and vehicles with smaller rearview windows have larger blind spots. Both cargo and passengers themselves can also create blind spots.

Blind spots expand as they move further from the vehicle. At even moderate distances, a blind spot caused by an A-pillar can obscure large objects such as cars and people.

Another type of blind spot exists in the space between the driver’s peripheral vision and the area reflected by the side and rear-view mirrors. This type of blind spot can swallow up entire vehicles, which is why it's dangerous to change lanes without looking to the left or right.

How Can Technology Help Remove Blind Spots?

Mirrors can help remove blind spots behind a driver, but they still leave hidden areas along the sides of the vehicle. The addition of a convex blind spot mirror can allow a driver to see objects that fall within those spaces, but because the mirrors are distorted they make it difficult to judge distances. In some jurisdictions it is even illegal to install a blind spot mirror.

blind spot mirror
A blind spot mirror is a low tech solution to the problem, but they don't always eliminate enough of the blind spot to make a difference. Robert Couse-Baker

Blind spot detection systems use a variety of sensors and cameras to provide a driver with information about objects that are outside the field of view. Cameras can provide views from either side of a vehicle, allowing drivers to verify that a blind spot is clear. Rear-view cameras can be useful when backing up or parallel parking.

A diagram showing how blind spot detection works.

Other systems use sensors to detect the presence of objects like cars and people, and that information can be presented to the driver in a number of ways.

Some blind spot detection systems are able to tell the difference between a large object like a car and smaller objects like a person. They simply alert the driver that there is a car or pedestrian located in a blind spot. Some systems use an audible alert, and others display a simple warning in the corner of the rear-view or side mirror.

What Cars Have Blind Spot Detection?

Due to a growing focus on advanced driver assistance systems (ADAS), there are a number of different automakers that offer some type of blind-spot detection.

Volvo and Ford both use a sensor-based system that provides the driver with a warning if a vehicle enters a blind spot. Mercedes, Nissan, Chrysler, and many other automakers also offer their own blind-spot warning, monitoring, or alert systems.

blind spot detection and warning button
Marin Tomas / Getty

Some vehicles have a blind spot intervention system, such as the one found in the Infiniti M-Series. In addition to alerting the driver when there is a vehicle in a blind spot, the intervention system delivers resistance to the steering wheel if the driver attempts to veer or turn into the blind spot.

There are also numerous aftermarket products that can add blind spot detection to virtually any vehicle. These systems can be camera or sensor-based, and they vary in complexity from one product to the next.

Does Blind Spot Detection Really Work?

There are important questions about whether blind spot detection systems result in fewer accidents. A study from the NHTSA found that some blind spot detection systems were unable to detect traffic moving slowly in the same direction as the test vehicle.

Common sense indicates that blind spot detection technology can help drivers avoid accidents, but real-life data does not always line up with expectations. In a study performed by the HDLI, lane departure warning systems correlated with a higher number of insurance claims. With that in mind, if you have one of these systems, it's important to remember that while they can help alert you to things you otherwise would not see, there is no substitute for good situational and spatial awareness.

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