Stopping Distance

Stopping distance definition

Total distance a vehicle travels from seeing a hazard to stopping

Stopping distance components

Thinking distance + braking distance

Thinking distance definition

Distance travelled while driver reacts

Braking distance definition

Distance travelled while brakes slow the car to a stop

Thinking distance depends on

Reaction time and speed

Factors increasing reaction time

Tiredness, alcohol, drugs, distractions

Factors increasing thinking distance

Higher speed, slower reactions

Braking distance depends on

Speed, mass, brake condition, tyre condition, road surface

Factors increasing braking distance

Wet roads, icy roads, worn tyres, worn brakes, greater mass

Speed effect on braking distance

Braking distance increases with the square of speed

Doubling speed effect

Braking distance becomes four times larger

Stopping distance increases with

Higher speed, poor conditions, impaired driver

Good road conditions

Dry, good tyres, good brakes → shorter braking distance

Poor road conditions

Wet or icy → much longer braking distance

Vehicle condition

Heavy load increases braking distance

Reaction time typical value

About 0.2–0.9 seconds

Key idea

Stopping distance is the sum of thinking and braking distance, both affected by speed and conditions