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Driver Reaction Time

Driver reaction time may be defined as the time that passes from the moment a driver feels the need for an action to be taken to the moment he takes that action.

Action of Reaction Time

The action may be applied to the steering, accelerating or braking or may be a combination of steering and acceleration or braking. Reaction time is of major importance when applied to braking. A driver should be capable of reacting to an emergency stop by braking in two third of a second or under normal travel within 30 feet before any braking movement actually commences. This distance is sometimes called the “Thinking Distance” and is reoffered to as such in the Highway Code. Under normal conditions the reaction time for alert driver is 3/4 second.

Thinking Distance

The distance traveling by the vehicle or car in reaction time is shown as the thinking distance. It is the time in between the driver think he needs to brake and when he actually make brake, the distance is covered by the vehicle or car in this time is thinking distance.

Thinking distance may vary with the following conditions:

  • With the speed of vehicle or car.
  • With the physical and mental condition of the driver.
  • With the degree of concentration which he is applying to the driving.
Braking Distance

The distance traveling by the vehicle or car from the time the brakes are applied to the time the vehicle or car stops. To find the braking distance the following formula may be used:

Speed × Thinking Distance = Braking Distance.

Stopping Distance

Basically, stopping distance is the sum of thinking distance and braking distance.

Thinking distance + Braking distance = Total stopping distance.

Table of Total Stopping Distance:

Speed in MPH    Thinking Distance      Braking Distance      Total Stopping Distance

10 MPH                10 Feet                          5 Feet                           15 Feet

20  „                      20  „                               20  „                              40  „

30  „                      30  „                               45  „                              75  „

40  „                      40  „                               80  „                              120  „

So stopping distance will be:

20 @@@@ **** = 40 feet stopping distance.

30 @@@@@@ ********* = 75 feet stopping distance.

Legend: One @ = 5 feet thinking distance.

One * = 5 feet braking distance.

The following facts must be noted by a driver:

  • A good driver – A vehicle in perfect condition – Good weather – Good daylight – Good dry road – under these conditions a vehicle can not stop in a distance less then those shown above.
  • Vehicle other then private cars or small vans may need twice these distances to stop on dry roads.
  • On wet roads; for all vehicles, allow twice the normal margin of safety.