Road safety – car stopping distances
Stopping safely
When a car has to stop, the The total distance needed by a car to stop. Stopping distance = thinking distance + braking distance. total is made up of two distances – the Distance travelled between reacting to a danger or a reason to stop the vehicle and braking., and the Distance travelled while braking..
The thinking distance is the distance travelled by the car while the driver is reacting.
The braking distance is the distance travelled by the car once the driver has put their foot on the brakes.
What factors affect thinking and braking distance?
Thinking distance:
- speed
- distractions, eg mobile phones
- alcohol
- drugs
- tiredness
- visibility
Braking distance:
- speed
- worn brakes
- wet road
- mass of the car
- worn tyres
- icy road
The thinking distance depends on the Time taken between seeing an event and reacting to it. of the driver which could be affected by drugs, alcohol, distractions and tiredness. This distance will also be affected by the car’s speed. The braking distance also depends on the speed of the car, the mass of the car, how worn the brakes and tyres are, and the road surface. A fast, heavy car with worn tyres and brakes, on a wet or icy road will have a large braking distance.
You might be asked to look for patterns in car stopping distances, and how they change with the speed of a car. Look at the diagram and answer the question.
Question
A car doubles its speed from 30 mph to 60 mph. How does this affect:
A) The thinking distance
B) The braking distance
C) The total stopping distance
a) The thinking distance doubles from 9 m to 18 m.
b) The braking distance quadruples from 14 m to 56 m.
c) The total stopping distance increases from 23 m to 74 m.
The kinetic energy of a car goes up by a factor of four if the speed doubles. This increased kinetic energy and increased stopping distance can increase the risk of collisions and death. That’s why there are speed restrictions in urban areas and particularly near schools.