Understanding Vision Limits as a driver/rider to reduce risks on roads

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.

BHPian chaitanyakrish recently shared this with other enthusiasts:

Introduction

I have seen a 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 into details, let's see the crash videos and dig deeper into the concept.

• A biker and a car are approaching an intersection and crashing into each other - Video

• A biker changes multiple lanes and crashes with a car - Video
• A driver can see a merging car but fails to plan ahead and develops a road rage situation - Video
• A car driver and a biker crashed near a gap in the median - Video

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

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 the navy where it's essential to find out if the ships or aircraft are about to crash.

Video

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

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.

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.

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.

• Video 1
• Video 2

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.

• Video 1
• Video 2
• Video 3

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

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.

Video

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.

Video

How to avoid getting into a 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 manoeuvres, if there is no safe exit route to go back to your 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 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.

Continue reading chaitanyakrish's thread for BHPian comments, insights and more information.