1.13 - Stopping Distances

Stopping distance = thinking + braking distance

The stopping distance is the total distance a car travels from the moment a driver spots a hazard to when the car comes to a complete stop:

• Thinking distance - The distance the car travels during the driver's reaction time, between noticing the hazard and applying the brakes.
• Braking distance - The distance the car travels once the brakes are applied, while slowing to a stop.

In an emergency stop, the driver applies the maximum braking force to stop in the shortest possible distance.

What increases thinking distance

• Higher speed - The faster the car travels, the further it goes during the reaction time.
• Longer reaction time - Increased by tiredness, alcohol, drugs and distractions.

What increases braking distance

• Higher speed - A faster car travels further before the braking force brings it to a stop.
• Greater mass - A heavier car takes longer to stop under the same braking force.
• Worn or faulty brakes - These can't apply as much braking force.
• Poor road or tyre conditions - Wet or icy roads, dirt, or worn tyres reduce friction, making skidding more likely.

Typical stopping distances for a family car

• Braking distance increases much faster than thinking distance as speed increases, so total stopping distance more than quadruples between 30 mph and 70 mph.
• To avoid collisions, drivers must leave a gap of at least the stopping distance behind the vehicle in front.