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 weight is doubled, stopping power must be doubled to stop in the same distance. If speed is doubled, stopping power must be increased four times to stop in the same distance. When weight and speed are both doubled, stopping power must be increased eight times to stop in the same distance.

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