[chaitanyakrish]

Introduction :

I have seen few crashes recently where there's a clear pattern in the way the vehicles crashed and thought of writing about it. There might be many more similar crashes in the past but unfortunately I did not find much written about it in India.

The article is divided into 3 parts where we discuss the risks and strategies to minimize the risks.

1. Constant Bearing Decreasing Range
2. Motion Camouflage
3. Saccadic Masking

Before going to details, let's see the crash videos and dig deeper into the concept.

1. A biker and a car are approaching an intersection and crashes into each other.

https://www.youtube.com/watch?v=JraPJ67TQOQ

2. A biker changes multiple lanes and crashes with a car

https://youtube.com/watch?v=oa36Op4D1X8?feature=share

3. A driver can see a merging car but fails to plan ahead and develops a road rage situation

https://youtu.be/56H6GB67a-o

4. A car driver and a biker crashed near a gap in median

https://youtube.com/watch?v=ila2IZerX8I?feature=share

These videos and many such clips are avoidable, if the driver recognizes the hazardous situation.

[chaitanyakrish]

Constant Bearing Decreasing Range :

Constant Bearing, Decreasing Range (CBDR) is a concept used to describe a situation where two objects (such as vehicles, ships, or aircraft) are on a collision course. The key idea is that if the bearing (the angle or direction from one object to the other) remains constant while the distance between the two objects decreases, a collision is likely unless corrective action is taken.

CBDR is very popular in aviation or navy where its very essential to find out, if the ships or aircrafts are on about to crash.

https://www.youtube.com/watch?v=WCoDMUBXKQY

As shown in the image below, if two cars are approaching an intersection/highway merging at the same speed, theoretically the angle between them remains constant and there's a crash risk.





Key Concepts of CBDR:

1. Constant Bearing:
   • The bearing is the angle from one object to another, typically measured in degrees from a fixed reference point (like true north or the front of a vehicle).
   • Constant bearing means that this angle does not change over time. If you’re moving in a straight line and another object’s position relative to you stays at the same angle, this indicates a constant bearing.
2. Decreasing Range:
   • The range refers to the distance between the two objects.
   • Decreasing range means that the distance between the two objects is getting smaller over time. This indicates that the two objects are moving closer to each other.

If the bearing is constant and the range is decreasing, it means that the two objects are on a collision course. In simpler terms, they are headed toward the same point at the same time.

How to identify a CBDR situation ?

If you observe another vehicle and it doesn’t appear to move left or right relative to you (i.e., it stays in the same position in your field of view on the windshield or the car windows), but it is getting closer, this indicates a high risk CBDR situation and a chance for a collision.

As an example, check out the position of the red car as visible through the windshield of the dashcam car. The position remains unchanged and the size keeps increasing, indicating a CBDR situation.












Situations Where CBDR situation is more likely

1. Intersections

While approaching an intersection, if another vehicle from a side road appears in your field of vision and stays in the same spot while getting closer, you are likely to collide unless one of you adjusts speed or direction.

https://youtu.be/RVaNiuDLWgo

https://youtu.be/JDfhlmwyoWU

2. Merging on to the highway

When merging onto a highway or joining traffic from an on-ramp, if a vehicle in the lane you're merging into appears stationary relative to you but is getting closer, you are at risk of a collision unless you adjust your speed or timing.

https://youtu.be/NtzcJG5BPl4

https://youtu.be/maYX-6IpqHA

https://youtu.be/7pajne8Cob8

A clip from my dashcam where we can see the biker in a CBDR situation with me but reduced crash risk by slowing down.

https://www.youtube.com/watch?v=GAwqzF3Al3A

3. Roundabouts

In a roundabout, if another vehicle appears to remain in the same relative position as you both enter the circle, and the distance decreases, this indicates a potential collision as both vehicles are headed for the same point.

https://www.youtube.com/watch?v=y6gdPkbVPZ4

4. Overtaking on single lane roads

On single lane roads, if the overtaking vehicle from the opposite side or when we are overtaking a slow moving vehicle on our side, did not get an exit route to go back to the respective lanes, a head-on crash is imminent. In such cases, a CBDR situation arises as well as we both are headed to the same point and crash.

https://www.youtube.com/watch?v=8l7DQQzR9UI

How to avoid getting into CBDR situation :

1. Check mirrors, windshield and windows - Check your mirrors, windshield and windows to see if any vehicle is maintaining a constant position as it closes the gap. If the vehicle is always in the same spot in your mirror but getting closer, you're in a CBDR situation. If you can see a vehicle approaching and the distance between you is decreasing rapidly without any change in its relative angle (bearing), it’s a clear sign that you’re headed toward the same spot at the same time. This is very critical near intersections, highway merging,roundabouts etc.

2. Change road position or speed - adjust road position or speed to avoid getting into a CBDR scenario

3. Abort overtaking maneuvers, if there is no safe exit route to go back to our lane

Summary of Visual Indicators of CBDR situation:

• Vehicle remains at a fixed point in your field of view (constant bearing).
• Distance between you and the other vehicle is decreasing.
• The other vehicle appears to get larger without changing position in your view.

By being aware of these visual cues and adjusting your driving when you detect a CBDR situation, you can avoid potential collisions on the road.
And by following Stop, Look and Proceed, we can reduce risk, but if the other car also does the same, then we need to above observation to prevent a crash.

[chaitanyakrish]

Now, we had read and understood about CBDR, there is another derivative of this situation where motorcycles are involved and is called Motion Camouflage.

Introduction :

Before going to motion camouflage, human eye detects motion by the change in contrast or size or position with respect to the background. Animals use stealth techniques like blending with the color of the surroundings like a chameleon to reduce contrast or walking slowly like a cat etc to reduce the chances of detection.

Lateral movement only helps human eyes to detect objects at a distance as we cannot detect movement, if the object is far away.

For example, everyone who had looked through the window of a train or a car can recognize this phenomenon where the buildings that are very far do not appear to move but the buildings that are close appear to move.



Until the vehicles comes so close, we tend to underestimate the speed as the motion is camouflaged due to lack of lateral movement. This is one of the main reason for crashes.

This type of camouflage which is used widely by dragon flies, cheetahs, expert hunters etc is called motion camouflage. Motion camouflage is a strategy used by dragon flies,cheetahs and sometimes in robotics or military applications, where an object moves in a way that makes it appear stationary or less detectable to an observer. Instead of following a direct approach toward a target, the object moves in such a way that it maintains a constant relative position in the observer's field of vision, making it harder to perceive the approach.

In the animal kingdom, in addition to speed and strength, stealth is also essential for hunting as it helps to hunt easily without making the prey alert.

https://www.youtube.com/watch?v=Ul5zvzCKxVo

Key Concepts of Motion Camouflage:

1. Constant Visual Angle:
   • The approaching object, like a predator or another vehicle, moves in a way that its position relative to the observer doesn’t seem to change.
   • To the observer, the object appears to remain in the same spot, even though it’s moving closer.
2. Decreasing Range Without Notice:
   • Even though the distance between the observer and the moving object is decreasing, the lack of lateral movement (side-to-side shift) makes it hard for the observer to notice the motion until the object is very close.
   • The object appears "camouflaged" against the background because it blends into its previous visual position.

Let's take an example of a tiger trying to hunt a goat or a deer. If it moves laterally across the background, there's more chance of detection. However, if the tiger moves towards the deer by keeping the background constant, there's less lateral movement and less chance for deer to detect the tiger.



From the point of view of the deer,it would see the tiger as below. If the tiger was moving towards the deer without any lateral movement, the deer might not detect its presence, until its so close.



If the deer stays at the same place and the tiger takes a path keeping the background constant, the deer might not be able to detect the motion until the tiger becomes big enough in its view.

Birds, dragon flies, vultures also use the same technique to catch the prey by giving them a surprise.



So, how does it apply to driving and especially while riding a bike ?

Watch the below clip shared by Czech Police to demonstrate the motion camouflage concept.

https://youtu.be/UyPg8b61rBk

Bikers approaching towards cars or other heavy vehicles without any lateral movement relative to a background, creates a motion camouflage situation where the drivers might not notice the bikers at all. The only evidence for the car drivers is the increase in size, which sometimes becomes too late to react as well.

This creates a crash risk at the following scenarios for bikers, cyclists etc :

1. Near intersections where the car drivers turn across the path of the bikers, only to realize that, they hadn't seen them at all.

2. A biker approaching an intersection perpendicularly and is blinded by the A pillar of the car in a CBDR situation. Here, the movement of the biker is undetected until the biker reaches so close and a crash is inevitable.



3. A biker approaching head-on and without any lateral movement, his movement is undetected.

https://www.youtube.com/watch?v=lvAJz3hGgJo

Without any lateral movement, bikers remain undetected on highways where the bikers occupy a small portion of the huge landscape. Only when the bike is so close, car drivers start detecting them and by that time, it might be too late as well. Lack of lateral movement gives the bikers an illusion of staying still and it gets difficult to judge the speed as well,until they are so close where a CBDR situation becomes unavoidable.

https://www.youtube.com/watch?v=BR9UZaCQuLE

It is very important for bikers to understand this phenomenon and also very useful for car drivers to know about what could possibly go wrong.

This is the reason for many intersection crashes where car drivers suddenly change lanes across the bikers either coming from the front or behind only to find a speeding biker crashing against the car or on the sides.

How do bikers reduce the risk of being camouflaged?


1. Change lane position slight as you ride, instead of riding on a straight line
2. Make subtle movements of the upper body to make yourself visible
3. Slowdown near intersections where car drivers are more vulnerable

https://youtube.com/watch?v=flGzG8ihc0w?feature=share

https://youtube.com/watch?v=ROuHgnVC3W4?feature=share

https://youtube.com/watch?v=ErpTzMbknTo?feature=share

To conclude, As a responsible bikers, bikers must try to make them more visible instead of getting camouflaged. Bikers can wear high visible jackets etc but if they're getting themselves camouflaged, they invite crash risk.

Also, at the same time, car drivers must try to understand the vulnerability of the human perception and stay alert at areas of high crash risk.

[chaitanyakrish]

Now as we are aware of CBDR and Motion Camouflage, we will check another phenomenon or a visual limitation

Introduction:

Before delving into detail, let's try a small game. Stand in front of a mirror and move your eyes left and right.

Can you see your eye balls moving left to right? No. But, others can see our eye balls moving. Why is it so ?



Let's try another game. Look at the seconds hands of your clock and quickly turn your head towards something else and again look at the clock. The seconds hand appear as if its motion is frozen.



This is due to a phenomenon called "Saccadic Masking". We assume that are our eyes are like a camera. However, when we move our head left and right,our brain captures snapshots of information to prevent blur and fills the gaps with some information which it considers not risky. The brain selectively blocks visual processing during eye movements to suppress motion blur. Without this suppression, the blur would become a frequent source of distraction, nausea rather. These rapid eye movements are formally known as saccades. And the absence of their perception or the inability to perceive your saccades is called saccadic masking or suppression.

Saccadic masking is a phenomenon that occurs when the brain blocks out visual information during rapid eye movements, in order to prevent motion blur. This can make it difficult to see objects that are in the process of moving, or to track objects that are moving quickly.

A good video by BBC to demonstrate saccadic masking.

https://www.youtube.com/watch?v=qIF3FRwbG6Y

How does it apply to road safety near intersections?

When we approach an intersection, if we move our head fast from left to the right to scan for hazards, there's a chance of missing a biker or a pedestrian or a cyclist near intersections, if they fall in those saccades, where our brain suppresses the information to prevent blur.

Did it ever happen to you that, when you are making a right turn across the road, you had noticed a pedestrian in your path at the last moment?

https://youtu.be/0Nn6WXIlc8I

https://www.youtube.com/watch?v=JraPJ67TQOQ

How to avoid saccadic masking?

As we approach junctions, scan slowly by pausing briefly as we scan our left, center and right instead of a continuous sweeping motion. This gives our brain enough time to process the information and spot hazards.

https://www.youtube.com/watch?v=XL_NvUHGgi8

Conclusion:

Finally, to conclude, in India, everyone takes risks on the road. But, we never know if the person who's driving, took the risk with awareness of what can go wrong or completely unaware of the limitations of our vision. However, as learned road users, we should improve our skill set to reduce known risks.

[Aditya]

Thread moved out from the Assembly Line. Thanks for sharing!

[electric_eel]

As usual a great post. If the other posts were gems, this is a whole treasure. Bookmarked this as I will be visiting this post multiple times.

[krackr]

Such a nicely structured post, with clear explanations and examples. Unhurriedness (if that's a word) and observation is key.

This one needs to be pinned somewhere on this forum. Definitely needs a re-read over and over. Thanks so much!

[tofudriver]

This post felt like a proper workshop, adequate information for CBDR, Motion Camouflage and Saccadic Masking. It got captivating with 2D images and real life visuals/experience. Interesting mix of decision making, observation, alertness and geometry. Thank you for rain of knowledge OP.

[Sidd_Kan]

Very Very informative post! I watch a lot of accident videos online, from a learning perspective, how I would have handled that situation on road and how to drive responsibly. It really makes a lot of difference in your driving and thinking. Since, I own both a bike and a car, I'm now able to understand both drivers perspective, their driving patterns and how to avoid them. I religiously follow lane discipline, slow down on intersections, allow vehicles to pass, maintain patience and have no ego on roads. Try to do my best in following traffic rules as much as possible. And posts like these are literally eye openers. Thanks a lot @chaitanyakrish!

[Entsurgeon]

It will be pertinent to mention that all the above phenomena in cases of cars have A-pillars of modern car design as villain. This phenomena didn't happen in older designs eg Ambassadors, Padminis etc. where the A-pillars were closer and much upright relative to the drivers eyes. Both the thickness of modern A-pillars as well as their slant angle and distance from drivers head position creates a major blind spot. Unfortunately, nothing can be done of those pillars under modern safety norms. However educating the two wheeler riders may help them understand the perspective of a car driver.

[AutoGalaxy]

@chaitanyakrish, Thank you for this very structured post. This thread provides insights that every road user must be well aware of. I request Moderators to include this in the https://www.team-bhp.com/safety section.

I was in a situation where I totally missed to "see" a cow even after looking carefully at intersection. Thankfully I was warned by others in my car and avoided mishap. I can now really use pointers in the thread to improve driving skill.

Many thanks!

[deepaksekar]

Fantabulous post. I have witnessed some seniors / experienced drivers exhibiting these concepts while driving and I used to question them when I was a kid as to why they are slowing down at certain points despite there is enough room and they simply used to say "you will know". During certain such instances, I used to think how they could predict such scenarios a little earlier. In fact, they were able to subconsciously factor in and act wisely well ahead though they do not / might not know these concepts. Slowly, I also realized that subconsciously, my senses also got tamed to such scenarios.

A simple example of Saccadic masking is when you blink frequently by starring at a fan when it is in motion, you can spot it's individual blades (This is not perception that your brain fills with since when you do this with a four blade fan, you can spot four blades as against three blades). But if you blink too fast, you experience nausea. Another example is during night driving, you feel more comfortable when you turn off your headlights at spots where there is light flooding from your opposite direction from oncoming vehicles and your environment is also flooded with lights (like banner lights etc.). This is because there is overlapping of light everywhere and your brain is unable to interpret visibility where it is supposed to.

[Mystic]

Very informative post. Thanks. In the event of an unfortunate accident, there are 3 variables namely man, machine and road. In our civil engineering curriculum, we studied transportation engineering / highway engineering. Typically, one can predict an accident in countries where is a lot of importance given to roads design, machine capabilities and road sense by drivers. For example, I see a lot of people going beyond 300 kmph on autobahn which is ok as the man, machine and road are in perfect sync without any surprises and work the way they are designed to work which is correct most of the time. One doesn't except to see other drivers around you doing crazy things as the reaction time for you is a split second to life and death at speeds in excess of 300 kmph.

When it comes to India, a lot of safety aspects are thrown out of window and hence one needs to be double cautious when foreigners start driving immediately rental cars in India after they land. To add to the problems, we have corrupt contractors bypassing the design of roads construction resulting in dangerous situations. In fact, we were discussing during a condolence meeting of our professor who passed away recently. As students 4 decades back, we used to wonder on why he takes a large factor of safety in his designs specifically for India even though he was educated abroad where a lot of optimisation in design is given importance. In India, the reality is that contractors take liberty to cut the design by half and hence this is taken care in the original design itself in desi juggad style.

[RGK]

Great technical post, Chaitanya.

Has subconsciously prompted me to pay more attention to the concept of "Constant Bearing" during merges. Hope this awareness remains ingrained in my mind at all times, helping me stay vigilant.