What does a steep hill sign warning of a 15% downgrade for 3km signify?

A steep hill sign warning of a 15% downgrade indicates that drivers should prepare to slow down and gear down. This warning is crucial because a steep decline can significantly increase the vehicle's speed due to gravity. When descending such a slope, it is essential for drivers to reduce speed to maintain control of the vehicle and prevent brake overheating or failure, which can occur if brakes are used excessively over a long period.

Going down a 15% grade for 3km can create hazardous conditions if not approached correctly; therefore, gearing down helps utilize engine braking, which reduces reliance on the brake pedal. This technique not only enhances safety but also ensures that the vehicle remains stable and controllable during the descent.