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How Do Blind Spot Monitors Work?

how do blind spot monitoring systems work
Pixabay.com / CC0 1.0.

Blind spots are an unfortunate and unwanted feature of almost every vehicle; as the name suggests, they are areas in the immediate vicinity of the vehicle that obscure the driver’s vision. Blind spots can be caused by a number of obstacles, including vehicle pillars, headrests, passengers, cargo, pets, and lighting glare. Luckily, car manufacturers are actively working on new types of blind spot technology that will make cars safer.


Blind Spot Dangers in Numbers

Blind spots represent an extreme danger for motorists, especially at highway speeds; each year, thousands of accidents happen when drivers change lanes and collide with other vehicles that were in their blind spots. According to the National Highway Traffic Safety Administration, blind spot-related accidents are responsible for more than 800,000 accidents and more than 300 fatalities each year. These accidents are especially difficult to avoid because even practicing defensive driving is not always enough to prevent them; you cannot react to a vehicle that you cannot see.

Why Blind Spots Are Such a Problem

Close to your vehicle, each individual blind spot may not be large, but even a 6-inch obstruction in your cabin can be enough to hide a vehicle in the next lane. For example, the blind spot created by an A-pillar can conceal a small car or a person. Other blind spots exist in the gaps between your side view mirrors, your peripheral vision and your rear view mirrors. If your mirrors are not set right, it is possible for a vehicle to hide just behind the driver’s side. Because of this, blind spot awareness is an important element of driving lessons; drivers are taught to crane their necks to spot vehicles in their blind spots before changing lanes. This habit has its own problems, however; turning around to look behind you forces you to take your eyes off the road in front of you, reducing your ability to react to traffic in front of you for a few crucial moments.

Automakers are Developing New Blind Spot Technology

Blind spots are a major flaw of automobile design, but automakers have not been content to simply accept blind spots as a fact of life and ignore the danger they pose. Rear and side mirrors are some of the oldest solutions that manufacturers have used to help drivers avoid the dangers of blind spots. As new technologies arise, automakers have quickly taken advantage of the new solutions and features that help reduce the impact of blind spots. Today’s drivers enjoy a number of new blind spot monitoring technologies, including cameras, radar systems, vehicle sensors and more. By playing a proactive role in eliminating blind spots through new features and technologies, blind-spot related accidents might soon become a thing of the past. Let us see what new (and old) technologies help eliminate the issue of blind spots.


Blind Spot Monitors: What Are They and How Do They Help?

Blind spot monitors are a broad category of safety devices that reduce the impact of blind spots on driver awareness and safety. Drivers can take advantage of both complex high-tech monitors and simple low-tech devices to give themselves improved awareness of the immediate vicinity of their vehicles. Regardless of the form that these devices take, however, they all serve to fill in the visibility gaps left by the vehicle’s mirrors.

passive blind spot monitoring
Photo by Nimish Gogri on Flickr / CC BY 2.0

Mirrors serve an important function in effectively giving the driver vision of the back and sides of their vehicle, but there are limits inherent to mirrors that are impossible to work around; no matter how effectively the mirrors are positioned, most vehicles will always have some type of blind spot. Part of the problem is that light travels in straight lines, making it impossible to see everything in mirrors. Objects that cannot find a direct line from your mirrors to your eyes will be out of sight; if an unfortunate vehicle can position itself in the perfect spot, you won’t even see it until your vehicles are trading paint.

Automakers have developed a number of different systems to eliminate this vulnerability. For most vehicles, these systems are optional upgrades, but many experts predict that some of these systems will become standard features of most or all vehicles in the future. There are quite a few different blind spot monitoring systems available, of varying degrees of sophistication, but they can generally be divided into two distinct categories: active systems and passive systems.

Active systems actively scan your vehicle’s blind spots using cameras, radar, sonic waves, or other sensing technologies; when these systems detect an obstacle, such as a cyclist, in your blind spot, they pass along a message to warn you. Passive systems are typically additions to your mirrors; for example, many trucks include a convex mirror with the side view mirror to give a more comprehensive view of your immediate surroundings. The view from a convex mirror is often more difficult to interpret, but simply seeing a vehicle in the mirror gives the driver awareness of a possible obstacle in their blind spot.


Active Blind Spot Monitors Alert You of the Presence of Obstacles

There are many different technologies behind active blind spot monitors, but they all serve the same purpose. All active systems, whether they use lasers, radars, or cameras, constantly monitor the spaces around your vehicle. If they detect a vehicle in the car’s blind spot, they pass a message to the driver, usually in the form of an indicator light on either the dashboard or the side view mirrors. Some systems also give the driver an audio warning if the turn signal is activated when the blind spot monitor has been triggered. The most sophisticated systems have some ability to intervene and prevent the driver from merging into another lane when another vehicle is detected in the blind spot.

Photo by Michael Sheehan / Flickr / CC BY 2.0
Photo by Michael Sheehan / Flickr / CC BY 2.0

Automakers have developed a number of different systems to keep drivers aware of their blind spots. In the most common active monitoring systems, an emitter sends out an electromagnetic wave, such as a radio wave, into the vehicle’s blind spot. If there is a vehicle there, the wave will bounce off the vehicle and return to the sensor. The time the wave’s echo takes to return to the car’s sensor allows the control system to calculate the distance of the vehicle in the blind spot; if it falls within a certain threshold, the blind spot monitoring system is triggered. Systems that are more expensive also use a camera system to supplement the electromagnetic detectors.

Active Blind Spot Monitors Are Most Often Included in Driver Assistance Packages

Many automakers include blind spot monitoring systems with their driver assistance packages. Honda’s Sensing technology suite, for example, includes blind spot monitoring to go along with lane departure warnings, lane keeping systems, and other systems; the suite even has the ability to take limited control of the vehicle to prevent you from leaving the road or colliding with another vehicle. Acura’s Blind Spot Information system, which is included as part of its technology package, includes visible indicators. The system also plays audible warnings when the driver flashes their turn signal and there is an obstacle in the blind spot. Subaru’s EyeSight system, like Honda’s system, features a number of different driver assistance technologies and includes blind spot monitoring as part of its lane keeping system. Audi’s SideAssist technology actively monitors the key approach zones around the vehicle, including blind spots, and warns the driver whenever he tries to change lanes with another vehicle in an approach zone. These features are popular with many drivers, but none of them are standard features yet; these are all optional features that may set a car buyer back several hundred or thousand dollars to add to a new vehicle.


Blind Spot Detection Systems

Blind spot detection systems, the simplest type of active blind spot monitors, are solely focused on watching the spots around your car that you cannot see with your mirrors. These systems are especially important on vehicles with larger A-pillars and B-pillars, which can obscure your vision even if you turn to look at the side of your vehicle. With a blind spot detection system, drivers can enjoy complete awareness of all 360 degrees around their vehicles. Although most blind spot monitoring systems can be added as standalone packages, these systems pair well with more advanced driver assistance technologies, including adaptive cruise control, lane keeping systems, parking sensors, rear traffic alerts and parking assistance systems.

active blind spot monitoring
Photo by tommy japan on Flickr / CC BY 2.0

Most systems use either ultrasonic pulses or radar sensors. These sensors are valued for both their fast response time and their wide effective range. Unlike a laser, which can only cover a narrow beam without complicated machinery to direct the laser, both of these technologies emit a 360-degree wave. This omnidirectional coverage gives drivers the confidence to know whether objects are currently in their blind spots. Systems that are more sophisticated include cameras to the blind spot monitoring system; these cameras are often paired with image recognition software so that the system can tell the difference between a person, a vehicle, and a guardrail.

Drivers Receive a Warning When There is a Vehicle in Their Blind Spot

Automakers use a variety of different signals to let drivers know when there is something in their blind spot, but in most cases, the presence of another vehicle in your blind spot is indicated with a yellow warning light. Common locations for the warning light are the side view mirrors or the A-pillar of the vehicle. Some also display warning information on the face of the rear view mirror. These lights are designed to give the driver the information they need without distracting them. If the driver attempts to change lanes while the warning light is illuminated, the warning light often begins flashing to draw the driver’s attention. Some systems may also sound a warning beep or vibrate the steering wheel slightly to make sure that the driver is aware of the obstruction in his or her blind spot. Blind spot monitors often track vehicles that are behind the driver in addition to tracking those that are in the driver’s blind spots. Once the system has started tracking a vehicle, the warning light will typically remain illuminated until the vehicle is no longer in your blind spot.


Rear View Cameras

Rear view cameras, often part of parking assistance systems or parking guidance systems, are an indirect type of blind spot monitoring system. Typically, these systems send a video feed of the rear of the vehicle to a display in the center console of the vehicle, giving the driver a sharp, unobstructed view of the rear of their vehicle and all of the potential obstacles and vehicles behind them. Their primary use is to aid the driver in parking safely without the guesswork required when parking without a camera guide.

Photo by Nozilla / Wikimedia Commons / CC BY-SA 3.0
Photo by Nozilla / Wikimedia Commons / CC BY-SA 3.0

Parking assistance systems use both sensors and cameras to help drivers park successfully in both parallel and traditional parking situations. The cameras give the driver a clear view of their surroundings, and the sensors give them feedback on distances to obstructions; without the benefit of sensors, it can sometimes be difficult to judge distances on the display accurately. In addition to the benefits of these parking assistance systems in avoiding blind spot accidents, many of the more advanced systems can actually take control of the steering wheel during parking; the driver only has to control the speed of the vehicle as it parks itself.

Rear-view Cameras to Become Mandatory from 2018

The improvement that rear view cameras offer over rear view mirrors recently inspired Congress to pass legislation mandating that all new vehicles come equipped with a rear view camera. By 2018, all new vehicles will carry a rear view camera as a piece of standard equipment.


Lane Departure Warning Systems

Lane departure warning systems are an evolution from regular blind spot monitoring systems. As the name suggests, these systems are designed to protect drivers from inadvertently leaving their lanes. Lane departure accidents can be especially devastating at freeway speeds; the higher speeds of these situations also makes these accidents tougher to prevent, especially for the tired or distracted drivers that typically cause most of these accidents. Lane departure warning systems use one or more cameras to monitor the roadway; using the onboard computer, the system identifies the lane markings on the road and the vehicle’s position within those markings. When the vehicle veers too close to the lane markings without the turn signal engaged, the lane departure warning system switches from its monitoring state to an active state; the system’s actions after it’s been activated depend on which type of system is installed in the vehicle.

Various Levels of Sophistication

There are two main types of lane departure warning systems. In the most basic type of system, the system is limited to warning the driver about his or her lane status. When the vehicle veers too close to the markings, it sounds an audible warning to help the driver correct his vehicle’s positioning. Systems that are more advanced, also called lane keeping systems or lane keeping assists, allow the vehicle to take a more proactive approach when the driver starts to drift from the lane. In these systems, if the driver ignores the warning from the system, the lane keeping assist can intervene and maneuver the vehicle back into a safer position without the driver’s input.

Early systems typically used a single video camera to monitor lane markings, but modern systems use multiple cameras for increased accuracy. Some systems also use laser or radar sensors in addition to, or sometimes in place of, video cameras. When lane keeping systems were first introduced, they took advantage of the vehicle’s electronic stability control system to keep vehicles in their lanes. These earlier systems applied selective braking pressure to individual wheels to give the vehicle a gentle tug back into the correct position. Modern systems with more advanced computer control systems can actually tap into the steering system itself, directly and gently steering the vehicle back into position without changing the speed of the vehicle.

Lane Keeping Assist Stays Alert When you Might not be

Having a lane keeping system installed on your vehicle gives you an extra layer of protection when driving. A moment of distraction is more than enough to drift out of your lane; if another vehicle is next to you when you drift from your lane, you can easily cause an accident. A lane departure warning system keeps you safe, as you’ll receive an immediate warning to help you correct your positioning. A more advanced lane keeping system will actively intervene to keep you safe if you cannot respond to the warning. Even with one of these systems installed in your vehicle, however, it is still vitally important to remain aware of your surroundings at all times while driving. When changing lanes, always exercise caution and check all of your mirrors and sensors. Before completing your lane change, make sure that you turn around for a moment to check your blind spot in case there is something that your sensors cannot detect.


Passive Blind Spot Monitors

Passive blind spot monitors are simultaneously one of the cheapest and most used blind spot monitoring features. A passive blind spot monitor is a fancy phrase for a simple item: Passive blind spot monitors are mirrors. Unlike your regular mirrors, however, passive monitors are specially designed convex mirrors that give you a wider viewing angle than a standard flat mirror. The view from one of these mirrors might remind you of a funhouse mirror, but precision is not the purpose of these mirrors. Instead, these mirrors are carefully positioned and designed to give you a complete unobstructed view of your entire blind spot. You will not want to rely on these mirrors to guide you if you need to be accurate to the inch, but they are invaluable for being able to tell you when you should not change lanes. Typically, these mirrors are mounted on the outside edge of your side view mirrors to give you the widest possible field of vision without having to turn around in your seat.

Passive Blind Spot Monitors are More Popular. Why?

Many drivers actually prefer this simple, low-tech version of blind spot monitoring over more sophisticated and expensive systems. Once you have become accustomed to the mirror, it is every bit as effective as the more technologically advanced systems. Additionally, a passive monitor is favored among some drivers, as they feel it is not such a distraction because there are no blinking lights or loud beeps.

Photo by State Farm / Flickr / CC BY 2.0
Photo by State Farm / Flickr / CC BY 2.0

Passive systems are much cheaper than active blind spot monitoring systems; the only necessary components are the mirror and its housing. Even if blind spot monitoring is included as a standard feature on your car, you will likely be paying more for the type of premium luxury car that would include it as a standard feature. If your car did not come with a passive monitor, any car can be retrofitted with one of these convex mirrors. You can pick one up at most auto parts stores for just a few dollars; however, most experts advise against installing it yourself. These mirrors require precise placement for maximum effectiveness, and this precision can be difficult if you are working by yourself. It is worth it to spend a few extra dollars to have a professional install your mirror so that you can be sure it is installed correctly.


Can Blind Spot Monitors be Turned Off?

Many drivers doubt the effectiveness or usefulness of an advanced blind spot monitoring system. Some advocates even believe that these systems can be dangerous in certain situations. In a busy morning commute, for example, the lights on a blind spot monitoring system can blink on and off repeatedly, distracting the driver for no good reason. Even worse are systems that sound a beep when there is a vehicle in your blind spot, which is virtually guaranteed during traffic jam situations. Hearing a jarring beep every time you begin making preparations for a lane change is not a good way to stay calm during a stressful commute. In addition, some obstacles might set off a false alarm. For example, many systems have difficulty telling the difference between a tunnel wall or a guardrail and an actual car in your blind spot; driving near one of these obstacles will often set off your blind spot monitoring system.

Thankfully, blind spot systems do not take control over the vehicle, and these systems can usually be turned off with the push of a single button. If the system drives you mad during your morning commute, you can simply disengage it until you are in more wide-open driving conditions where the system is more useful. Most of the time, however, turning off the system will turn on a separate indicator light on your dashboard while the system is disengaged. Some drivers might find this light annoying, but it does have its benefits. If the driver accidentally turns off the system in a situation where he might want it to be active, for example, the indicator light will let him know that the system is currently disengaged.


Are Blind Spot Monitors Worth the Investment?

Blind spot monitors are most often an integral part of a robust safety package. Such safety packages reduce both the number and severity of collisions and other accidents on our roads. According to the IIHS, if all vehicles came standard with blind spot monitoring and similar technologies, the number of fatality accidents could be reduced by as much as 33 percent and injury collisions could be reduced by 20 percent. Widespread adoption of these technologies could therefore annually save thousands of lives. Additionally, preventing those accidents could save time as well; without the traffic jams caused by accidents and accident investigations, drivers could spend more time at home instead of trapped in traffic.

Blind Spot Monitoring Technologies Will Slowly Become Standard Features

Government agencies have already seen the wisdom in mandating some of these technologies for all vehicles; beginning in 2018, the NHTSA will require all new vehicles to come equipped with rear view cameras. The agency expects that the inclusion of rear view cameras will have as much positive effect on accident rates as the widespread adoption of blind spot monitoring systems would, greatly reducing the incidence of accidents related to backing up.

Because blind spot monitoring systems are not standard features just yet, they typically represent an extra expense for most car buyers.

Some vehicles do include these systems as standard features. Many drivers wonder whether the extra expense of these systems is a worthwhile investment. It is a decision that drivers have to make for themselves, but in simple terms, a blind spot monitoring system is usually cheaper than the bodywork necessary to repair your car after an accident that could have been prevented by the system. Not only will these systems save you from the direct financial cost of an accident, they will also save you the time and headache that accompanies negotiating a settlement after an accident. Having one of these systems installed can also reduce your insurance premiums.

Most Common Complaints About Blind Spot Monitoring Systems Are Their Tech Limitations 

Many drivers do have complaints with these systems, but most of the complaints can be chalked up to the current limitations of technology. For example, most blind spot systems do not understand double turn lanes. Some systems seem to be calibrated poorly and might give too many false alarms. Bad weather can reduce the effectiveness of the monitoring system. Some drivers may decide that they are better off without the system and turn it off in frustration, completely negating any benefits that the system might offer. However, just like any new technology, there is a learning curve associated with getting the most out of these systems. Learning the strengths and limitations of a monitoring system is an important step that all drivers who have these systems must take. Before deciding to install a monitoring system on your new car, test drive a vehicle that already has the system installed so that you can get a feel for how it works in real-world conditions.

Key Points to Consider Before Buying a Blind Spot Monitoring System

When deciding whether to have blind spot monitors installed on your next car, you should consider several factors before finalizing your decision:

  • Consider the type of vehicle that you will be purchasing. Blind spot monitors are most effective for larger vehicles with correspondingly large blind spots. SUVs and pickup trucks, for example, often have large blind spots that can be difficult to see into even when you look over your shoulder.
  • If you typically drive with children or pets, blind spot monitors might be a worthwhile investment. Blind spot monitors can help keep you aware of your surroundings even while your passengers are distracting you with conversation.
  • Think about the visibility from your vehicle. If your new vehicle has huge windows and slim pillars that don’t impede your visibility much, then you may not need blind spot monitors. If your vehicle’s windows are relatively small, or if visibility is especially poor on one part of your vehicle, then blind spot monitors are more likely to be a good investment.
  • The type of driving that you do also matters when considering blind spot monitors. These systems are somewhat unnecessary if you spend most of your time on one-lane roads or stuck in traffic jams; in both situations, lane changes are either unnecessary or undertaken at very slow speeds, giving you plenty of time to change lanes safely. Blind spot monitors can be quite useful if you spend a lot of time on multilane roads at higher speeds.

Blind spot monitors give drivers an extra layer of safety, and government data indicates that they are effective at preventing lane change collisions. However, blind spot monitors should be used as a supplement to your usual driving behavior, not as a replacement. Even with blind spot monitors, you will still want to check your mirrors and check over your shoulder when you get ready to change lanes. Experts expect that these systems will eventually become legally mandated standard features, so the time will come that you find yourself thanking your monitors after they save you from a collision.


Blind Spot Monitors Increase Safety and Decrease the Number of Accidents

Blind spot monitors, whether active or passive, help drivers to remain safe while on the road. In combination with good driving habits, these systems do an excellent job of preventing collisions from changing lanes. Both active and passive systems do an excellent job at keeping their drivers aware of the conditions around their vehicles, helping their drivers to make good decisions when it comes time to change lanes. Although the ideal type of system will depend on the driver’s personal preferences, both systems do an excellent job of reducing the impact of blind spots on driver safety.