4.2.3. Reaction time

The road user is subjected to a series of stimuli both expected and unexpected. The time taken to perform an action according to the stimulus involves a series of stages like:

• Perception: Perception is the process of perceiving the sensations received through the sense organs, nerves and brains. It is actually the recognition that a stimulus on which a reaction is to happen exists.
• Intellection: Intellection involves the identification and understanding of stimuli.
• Emotion: This stage involves the judgment of the appropriate response to be made on the stimuli like to stop, pass, move laterally etc.
• Volition: Volition is the execution of the decision which is the result of a physical action of the driver.

This chunk describes the different stages of reaction time when a road user encounters various stimuli. During

• Perception, the person recognizes that a stimulus, such as a traffic signal changing, is present.
• In Intellection, they understand what the stimulus means, for example, recognizing a red light indicates 'stop.'
• The Emotion stage involves deciding how to respond—deciding whether to stop or move. Finally, in Volition, the individual acts on their decision by executing a physical action, like stepping on the brake pedal to stop the car. All these stages happen quickly, impacting the overall reaction time significantly.

Think of a game of catch. When someone throws a ball, you first see the ball coming (perception), then you think about how to catch it (intellection), decide to move your hands to catch it (emotion), and finally, you make the motion to catch it (volition). Just like catching a ball, driving requires processing information in these stages to respond appropriately to road signals or hazards.

Fore.g., if a driver approaches an intersection where the signal is red, the driver first sees the signal (perception), he recognizes that it is a red/STOP signal, he decides to stop and finally applies the brake (volition). This sequence is called the PIEV time or perception-reaction time. But apart from the above time, the vehicle itself traveling at an initial speed would require some more time to stop.

This chunk introduces the PIEV time, which stands for Perception, Intellection, Emotion, and Volition, a term used to describe the total time it takes for a driver to react to a stimulus. For example, when a driver sees a red light, they first perceive it, understand its meaning, decide to stop, and then apply the brakes. However, it’s crucial to remember that the vehicle also takes time to stop after the brakes are applied, especially if it's moving at a fast speed, which must be factored into the total reaction time to accurately assess stopping distance.

Imagine you're at a stoplight on your bicycle. You notice the light turning yellow (perception), realize you should stop (intellection), decide to apply the brakes (emotion), and then actually squeeze the brake handles (volition). However, if you're going fast, the bike will still roll forward a bit even after you start braking, like how a car takes longer to stop based on its speed.

That is, the vehicle traveling with initial speed u will travel for a distance, d=vt where, t is the above said PIEV time. Again, the vehicle would travel some distance after the brake is applied.

This chunk discusses how far a vehicle travels while the driver is reacting to a stimulus. The distance (d) covered is calculated using the formula d = vt, where 'v' is the speed of the vehicle and 't' is the PIEV time. After the brakes are applied, the car will continue to move a certain distance before coming to a complete stop due to inertia, which is significant for understanding how far a vehicle will travel before it comes to rest.

Consider a speeding train approaching a station. Before it can come to a stop, even after the engineer decides to stop, the train won’t stop immediately because of its high speed and momentum. It continues to travel a certain distance on the tracks before halting. Similarly, with cars, the faster they go, the more distance they cover during the reaction period and while braking.

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