Section 1 of 4Parts of the Stopping Distance
The total distance needed to stop a vehicle is made of two separate parts.
Thinking distance
- The distance the vehicle travels during the driver's reaction time, before the brakes are applied.
Braking distance
- The distance the vehicle travels while the brakes are applied and it slows to a stop.
Stopping distance
- The sum of thinking distance and braking distance for a given speed.
Reaction time
- The time taken for the driver to notice a hazard and react by pressing the brake pedal.
Typical reaction time
- A typical reaction time is about 0.2 to 0.5 s, which is a significant distance at speed.
Section 2 of 4Sequence of Events
Each stage of stopping adds to the total distance.
1
The driver sees a hazard and the reaction time begins.
2
During the reaction time the car keeps moving at its original speed.
3
The driver presses the brake, and the car starts to decelerate.
4
The car continues slowing down until it comes to a complete stop.
Section 3 of 4Factors That Change Stopping Distance
Factors That Change Stopping Distance
Speed
- A higher speed increases thinking distance proportionally and braking distance by a much larger amount.
Driver condition
- Tiredness, alcohol, drugs and distraction all increase the reaction time and thinking distance.
Road condition
- A wet or icy road reduces friction, which increases the braking distance.
Vehicle condition
- Worn brakes or tyres reduce braking force, which increases the braking distance.
Section 4 of 4Exam Checklist & Tips
1.2.6 – Key Points for the Exam
- Thinking distance The distance travelled during the driver's reaction time.
- Braking distance The distance travelled while the vehicle slows down after the brakes are applied.
- Stopping distance Thinking distance plus braking distance.
- Reaction time The time between noticing a hazard and applying the brakes.
- Friction The force between tyres and the road that slows the vehicle when braking.
Common Mistakes
- Saying speed only affects thinking distance; speed also strongly increases braking distance.
- Confusing thinking distance with braking distance, which occur at different stages.
- Assuming braking distance depends only on the driver; road and vehicle condition matter too.
- Stating that braking distance roughly doubles when speed doubles;
- it roughly quadruples for the same braking force.