Stopping distance depends on several factors, and each one affects the thinking distance, the braking distance, or both.
- Mass: a vehicle with more mass has more momentum and more kinetic energy at the same speed. With the same braking force it takes longer to slow down, so the braking distance is greater. Mass does not change the thinking distance.
- Speed: thinking distance is directly proportional to speed, so doubling the speed doubles the thinking distance. Kinetic energy depends on speed squared, so doubling the speed makes the braking distance four times as great for the same braking force. Increasing speed increases both parts of the stopping distance.
- Reaction time: a longer reaction time means the vehicle travels further before the brakes are applied, so the thinking distance increases. The braking distance is not changed.
Other factors such as worn brakes, worn tyres and wet or icy roads reduce the braking force or the friction between tyre and road, which also increases the braking distance.