The stopping distance of a vehicle is affected by many different factors whether that be the applied braking force, or the driver of the vehicle and their reaction time.

The higher the stopping distance, the more space you should leave between your vehicle and the vehicle in front of you.

Say a car is driving along, and suddenly sees an obstacle ahead. The driver applies the brakes, and the car comes to a stop. This is an emergency stop. The stopping distance is the total distance the car travels between the driver seeing the hazard and the car coming to a stop.

So the stopping distance is: $Stopping Distance=Thinking Distance+Braking distance$