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 Driver reaction time

Faced with an obstacle that unexpectedly appears in front of the vehicle, no driver, no matter how quickly their reflexes, can react instantly to avoid an accident.

Seeing, understanding and acting, although very fast operations, take approximately 1 second to complete (REACTION TIME) and during this time the vehicle continues to move forward.

Reaction time is therefore the amount of time that elapses between the perception of a new action and the exact moment when you act. 

Most drivers take approximately one second to react to dangerous situations, although there are some factors that can greatly increase this reaction time, such as:

Having little driving experience.

Being older.

Being sleepy or fatigued.

Being physically or mentally unwell.

Being under the influence of certain medications.

Being under the influence of alcohol or drugs.

Please note Reaction time never decreases, it can only increase due to the factors mentioned.

This is not to be confused with the reaction distance, which can decrease, for example if the speed is lower. Whenever the reaction time increases, the reaction distance also increases.

Reaction, braking and stopping distances.

Reaction distance: 

During the reaction time, the vehicle continues to move (at the same speed), covering a certain distance, measured in metres. This is longer the higher the speed at which the vehicle is travelling.

Reaction Distance is the distance travelled during the reaction time and depends on the speed of the vehicle and the reaction time.

 

Braking Distance: 

Vehicle won't suddenly stop when we hit the break. It will travel some distance. This distance varies not only with the speed of the vehicle but also with the condition of the tires, the effectiveness of the brakes and the condition of the road surface (wet, slippery or sandy).

Braking Distance is the Distance travelled between the moment the driver starts to brake and the moment the vehicle stops, and depends on grip, road slope, vehicle load, brake effectiveness and speed. For Calculating Purpose it is the square of the tens digit of speed. Generally called multiplying the tens digit by itself. For example Suppose we have a speed of 47 kilometres per hour.

Identifying the digit in the tens place: The tens digit in 47 is 4.

Multiply the tens digit by itself: 4 times 4 or the square of 4 is equal to 16.

So, in this example, the digit in the tens place is 4, and multiplying it by itself gives us 16. Means if We have a vehicle having speed of 47 kilometre per hour then the braking distance will be 16 metre,

Another Example: Let's take the speed of a vehicle 92 kilometres per hour.

Identifying the digit in the tens place: The tens digit in 92 is 9.

Multiply the tens digit by itself: 9 times 9 or the square of 9 is equal to 81.

then braking distance will be 81 metre. 

Stopping Distance: 

Stopping Distance is the Total distance travelled between the moment the driver sees the obstacle and the moment the vehicle stops.

The stopping distance is obtained by adding the reaction distance to the braking distance.

That is Stopping Distance is equal to reaction distance plus braking distance.

 

Calculating a vehicle's stopping distances at various speeds. Lets see the table. For the calculation we assume the reaction time is 1 second. And Breaking Distance= square of the digit of the tens of the speed. If the Instantaneous Speed of a vehicle is 40 kilometre per hour, the reaction distance will be 11 metre, calculating braking distance 16 metre total stopping distance will be 27 metre. Similarly If the Instantaneous Speed of a vehicle is 80 kilometre per hour, the reaction distance will be 22 metre, calculating braking distance 64 metre total stopping distance will be 86 metre approximately. Again If the Instantaneous Speed of a vehicle is 120 kilometre per hour, the reaction distance will be 33.5 metre, calculating braking distance 144 metre total stopping distance will be approximately 177.5 metre.

Kinetic Energy and Tyre Grip

Any vehicle in motion accumulates a certain amount of kinetic energy which is reflected in the resistance offered to the braking effect.

This accumulated kinetic energy (inertia) will be higher the faster the vehicle is travelling and the greater its total weight (mass).

When the vehicle is travelling downhill, the difficulty of braking is further exacerbated by the force of gravity, the effect of which increases with the slope of the road.

The effectiveness of braking depends fundamentally on

The vehicle's speed.

Its total weight (mass).

The slope of the road.

The characteristics of the brakes.

The type and state of repair of the tyres.

The quality and condition of the road surface.

During rainy periods, the number of road accidents increases considerably because the water accumulated on the road reduces the grip of the tyres, increasing the braking distance by around 40%.

When it starts to rain, after a long dry spell, the pavement is covered in a thin and dangerous layer of mud that dangerously reduces tyre grip, making braking very difficult.

In these cases, when the tires lose their grip on the road, a slipping effect (skidding) begins which, despite the braked wheels no longer turning, keeps the vehicle moving out of control.

Drivers who are distracted or less aware of their tyres, lack of grip can already be involved in serious accidents.

To avoid skidding, instead of braking intensively and continuously, it is preferable for the driver to apply a series of brief, repeated brakes.

Safety Distance

Safety Distance is The distance that the driver must maintain between their vehicle and the vehicle travelling in front of them. In order to avoid accidents, It must be the distance travelled in 2 seconds of instantaneous speed. Normally to have a reasonable margin of safety it should be double the reaction distance  to avoid an accident in the event of a sudden stop or sudden reduction in speed. It varies according to speed.

In addition, a sufficient lateral distance of 1.5 metres must be maintained between the vehicle and the cyclist.

Example of the application of the safety distance standard. Lets see in the given table.

When the Speed of a vehicle is 90 Kilometres per hour the assuming reaction time is 1 second, Reaction distance will be approximately 25 metres.  Safety distance must be double that is 50 metres. Similarly when the speed is 100 Kilometres per hour Reaction distance approximately will be 28 metres, according to this the Safety distance is needed approximately 56 metres. Now you can see when the Speed of a vehicle is 120 Kilometres per hour,Reaction distance will be approximately 33 metres and Safety distance must be double that is 65 metres approximately. 

Lateral Safety Distance

When two vehicles are travelling on the same carriageway, in the same direction or in opposite directions, each driver must keep a sufficient lateral distance to avoid an accident.

To correctly judge this safety distance, each driver must take into account the width of the carriageway, the speed at which they are travelling, the characteristics of the vehicles, the type of load they may be carrying and the possible effect of crosswinds.

Lets do some questions related to Safety Distance.

Example 1

If the driver in front of me slows down, the safety distance: 

A: Increase.

B : Decrease.

C: Maintain.

In this type of question, the IMT wants to see what happens when speeds change. Imagine two vehicles travelling at a speed of 50 km/h, vehicle A is in front and vehicle B is behind A:

When vehicle B increases its speed to 60 km/h, vehicle B's safety distance decreases because, as it is travelling at a higher speed than the vehicle in front, it gets progressively closer to that vehicle until the distance between these two vehicles is 0 metres. The same happens if vehicle A slows down.

When vehicle B slows down to 40 kilometres per hour, vehicle B's safety distance increases because it is travelling at a slower speed than the vehicle in front and the distance between the two vehicles increases gradually. The same happens if vehicle A increases its speed.

If both vehicles are travelling at the same speed, if they both increase or decrease their speed at the same time, the safety distance will remain the same, as their speeds are equal.

So the answer to this question is "B Decreases".

Example 2

In this situation, if you can increase the speed, the safety distance must:

A: Increase.

B: Decrease.

C: Be Maintained.

In this question, the IMT wants to assess what should happen when vehicles change speed. Using the same example as in the previous case:

If vehicle A decreases its speed, vehicle B must also decrease its speed for the safety distance to be maintained because, as we saw earlier, if vehicle A decreases its speed and vehicle B maintains its speed, the distance between the two vehicles decreases and consequently the safety distance decreases as well.

If vehicle B increases its speed, the safety distance must increase. If vehicle A doesn't increase its speed, then vehicle B must overtake or reduce its speed again to that of vehicle A.

Whenever the speed increases, the safety distance must also increase to compensate for the stopping distance, and the stopping distance increases whenever the speed also increases.

So the answer to this question is " A Increase".