Reaction time and braking distance
Reaction time and braking distance determine how long it takes to stop. They underpin safe following distance, speed choice and risk assessment.
What is reaction time?
Time from hazard detection to starting to brake. Typical for an alert driver is 1–1.5 s.
Reaction distance
Distance covered during reaction time: Reaction distance = (Speed ÷ 10) × 3
Braking distance and stopping distance
Factors that increase stopping distance
- Speed, mass and gradient
- Road surface and tyres
- Load, trailer and brakes
- Attention, fatigue, alcohol and medicines
Practical driving
Leave at least 3 seconds in dry, more in wet/ice. Increase margins at night and in complex traffic.
Use firm, straight braking; steer around only if you have space and stability.