The distance required to stop a vehicle depends on its speed and weight, in addition to the factors of energy, heat and friction. The brake power required to stop a vehicle varies directly with its weight and the ‘square’ of its speed. For example, if the weight is doubled, the stopping power must be doubled to be able to stop in the same distance. If the speed is doubled, the stopping power must be increased four times to be able to stop in the same distance. And, when weight and speed are both doubled, the stopping power must be increased eight times to be able to stop in the same distance.

For example, a vehicle carrying a load of 14,000 kgs down a steep grade at 16 km/h is brought to a stop in a distance of 30 meters by normal application of the brakes. If this same vehicle carried 28,000 kgs down the same grade at 32 km/h, it would require eight times the braking power to stop the vehicle in 30 meters. This would be more braking power than the brakes could provide. No vehicle has enough braking power when it exceeds its limitations.