Many drivers have a false belief that if the car in front starts braking they can react, brake and come to a stop, still leaving the same distance between the two vehicles.
The total stopping distance of your vehicle depends on four things:
• your perception time,
• your reaction time,
• your vehicle reaction time, and
• your vehicle braking capability.
Your perception time is how long you take to see a hazard and your brain realising it is a hazard requiring you to take immediate action. This can be as long as 1/4 to 1/2 of a second.
Your reaction time is how long you take to move your foot from the accelerator to the brake pedal once your brain understands you are in danger. Your reaction time can vary from 1/4 to 3/4 of a second.
These first 2 components of stopping distance are down to you and can be affected by alcohol, drugs, tiredness, fatigue or lack of concentration. A perception and reaction time of 4 seconds at 100 km/h means the car travels 110 metres before the brakes are applied (this is more than the length of a football pitch).
Once you apply the brake pedal it will take time for your vehicle to react. This depends on the condition your vehicle is in and, in particular, the condition of the braking system.