The greater your speed, the more distance is covered while you make decisions and take action to avoid a collision.Also, the faster you are going, the longer it takes for the vehicle to stop when you do brake.
The higher the speed, the more kinetic or movement energy the vehicle and you (the driver or passengers) are carrying. Therefore more energy is released when colliding into another vehicle or stationary object, such as a tree or wall. Part of the energy released will be absorbed by the objects involved in the crash and part will be absorbed by the human body, causing injuries. Our human body is vulnerable and there is only so much energy it can handle without being seriously damaged. The more energy, the greater the damage.
Pedestrians, cyclists, and persons in lighter vehicles will have more severe injuries if hit by a speeding vehicle. An adult pedestrian has less than a 20% chance of dying if struck by a car at less than 50 km/h but almost a 60% risk of dying if hit at 80 km/h.
While other factors likely to influence speed include alcohol, road layout, traffic density and weather conditions. A 5% cut in average speed can result in 30% reduction in the number of fatal crashes.