In an emergency, a driver must bring their vehicle to a stop in the shortest distance possible:
This is when:
Reaction times vary from person to person but are typically 0.2 to 0.9 seconds (s). A driver's reaction time can be affected by:
Longer reaction times increase the thinking distance when stopping from a given speed.
There are different ways to measure reaction times. One simple method involves dropping a ruler between someone's open thumb and forefinger. The higher the reaction time needed to grasp the falling ruler, the further the ruler falls before being stopped. The ruler can be adjusted to measure in seconds rather than in millimetres.
The braking distance of a vehicle can be increased by:
When a force is applied to the brakes of a vehicle, there is work done by the friction between the brakes and the wheel. This reduces the kinetic energy of the vehicle, slowing it down and causing the temperature of the brakes to increase.
The faster a vehicle travels, the greater the braking force needed to stop it in a certain distance. A greater braking force produces a greater deceleration. Large decelerations may cause the brakes to overheat, and the driver may also lose control of the vehicle.