Road Safety: Stopping Distance

Fast driving causes many road collisions. Collisions occur when a vehicle is unable to come to a complete stop before hitting another vehicle or object. When a driver wishes to stop a vehicle he applies the brakes. With the brakes applied, the car slows down and will eventually stop. The distance that the car moves once the brakes are applied is called the braking distance. The stopping distance for a vehicle includes the distance travelled by the vehicle while the driver reacts and applies the brakes and the braking distance.

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The stopping time depends on the driver’s reaction time and the speed at which the car was travelling. Other factors which affect this distance are the condition of the road (wet or dry), the slope of the road, that is if the car is headed up or down a hill, the condition of the tyres and the brake system of the car. All of these factors affect the distance a car travels before stopping once a driver has decide to stop the vehicle. The faster a car is going the greater the distance required to come to a complete stop. A wet surface will increase the stopping time as will a downward slope because the slope will encourage the car to keep rolling down.

Drivers are advised to keep at least a ‘three-second gap’ between cars, for safety. This means counting three seconds from the time the back bumper of the car in front passes a point to when the front bumper of the following vehicle passes the same point. For example counting three seconds from the time the car in front passes a tree until your vehicle reaches the same tree. This gap should be increased in wet road conditions. This distance is critical as it allows time for a driver to react to a sudden stop by the vehicle it is following. It is also important to keep in mind that heavier vehicles, such as trucks, require even more stopping distance, so when driving behind a heavier vehicle, distance should be increased.

The following table shows approximate stopping distances for a car travelling at different speeds under wet and dry conditions.

Written: March 2009