What is unlawful when going downhill with a heavy vehicle?

Coasting, or allowing the vehicle to roll down a hill without using any power or brake assistance, is considered unlawful and unsafe for heavy vehicles. When a driver coasts, they lose the ability to control the vehicle's speed effectively, which can lead to dangerous situations. Heavy vehicles, due to their weight and momentum, require careful handling to manage speed when going downhill.

Using the engine brake is a legitimate method to help control speed while descending, as it allows the driver to utilize the vehicle's engine to slow down without overheating the brakes. Shifting into neutral is also unsafe, as it disengages the engine from the wheels, leading to a complete loss of control over the vehicle’s speed and power. Therefore, coasting is not only against the law but also compromises safety when driving downhill with a heavy vehicle.