When is it recommended to use a retarding device?

Using a retarding device is particularly recommended when descending steep grades because it helps to manage vehicle speed and maintain control. Steep descents can lead to excessive acceleration due to gravity, and if a driver solely relies on brakes to control speed, there is a risk of brake overheating, which can compromise braking efficiency and safety. Retarding devices, such as engine brakes or exhaust brakes, function by using the engine's power to slow the vehicle down, thus reducing the reliance on the traditional braking system.

In these situations, employing a retarding device enhances safety by ensuring the vehicle remains within a safe speed range without overheating the brakes. The other choices do not reflect ideal scenarios for using such devices, as driving on flat roads does not generally pose a speed control problem, a vehicle at a complete stop does not require additional braking force, and turning at intersections typically involves maneuvering and maintaining control rather than the need for speed reduction through a retarding device.