Stopping distance

The stopping distance or technical stop is the distance a vehicle travels from the moment the driver perceives an obstacle until the vehicle comes to a complete stop.

Likewise, the stopping time is the time it takes the driver to completely stop the vehicle from the moment a stimulus or danger appears. In other words, the stopping distance is the distance traveled by the vehicle during this time.

The technical stop time is the sum of the reaction time plus the braking time:

• The reaction time is since the danger appears until the driver reacts (foot the brake pedal).
• The braking time is the time that from the start of the brake pedal until the vehicle stops completely.

Braking time varies with speed, vehicle load, brake effectiveness, tire condition, aerodynamics, suspension, road condition, and overall vehicle condition and of the driver. The reaction time varies due to the factors of the psycho-physical state of the driver, such as fatigue, sleep, concentration, alcohol level, drugs, illnesses and medicines.

To improve the reaction time, some systems have been tested. At Saab they developed a mono-pedal prototype that combined the accelerator and brake in the same pedal. This cut the reaction time in half, because it avoided moving from the accelerator to the brake.
Some vehicles have a radar system, which, in the event of encountering an obstacle with which it is going to impact imminently, brakes the vehicle without driver intervention.